Modern methods and technologies of laser ranging. Optical location

The method includes scanning space with a sequence of laser signals generated by a laser locator, registering laser signals scattered and/or reflected by an object, determining the distance to the object and the angular position of the object. The distance to the object is determined by the delay time between the emitted and received signals. The angular position of the object is determined by the direction of the corresponding emitted signal. A train of at least two pulses with a variable time interval between pulses and/or the ratio of pulse amplitudes in each train is used as a signal generated by a laser locator. The technical result is an increase in laser ranging performance.

The claimed technical solution relates to methods for determining the location of objects, more precisely to methods of laser ranging, and is of interest for laser ranging of space objects, the Earth's surface, laser geodesy, and can also be used to determine the speed of a moving object.

There is a known method for determining the distance to a distant object, including irradiating it with a laser signal, receiving the signal reflected or scattered by the object and determining the delay time ΔT between the moments of emission of the probing signal and the reception of the signal reflected or scattered by the object, while the distance to the object L is determined by the simple formula L=cΔT/ 2, where c is the speed of light.

The advantage of the known method is the ability to determine the distance to distant objects, including cosmic distances, with high accuracy, which is actually determined by the speed of the receiving system and the ability of the radar to generate short light pulses (primarily with a short leading edge). With a performance level of ~0.1 ns achieved long ago, the distance can be determined with an accuracy of several centimeters; this is precisely the accuracy achieved, for example, with laser ranging of the Moon.

The disadvantage of this known method is the impossibility of determining with sufficient accuracy the direction to the located object; usually this direction is known in advance (as in the case, for example, of laser ranging of the Moon, the position of the corner reflectors that returned the locator signal was precisely known). In another embodiment of the known method, a powerful laser pulse is generated, which immediately “illuminates” a significant area of ​​space (a significant solid angle), in which the location object is known to be located, that is, the divergence of the laser radiation used is quite large. This allows you to determine the distance to the object, but not its position in space. The need to use high-energy laser locators is a significant disadvantage of the known method, since this requires a fairly powerful and relatively bulky laser installation. Obviously, if the probing radiation can have a divergence 10 times smaller, then the energy of the laser pulse can be reduced by at least 100 times (if the distance to the object is large enough).

The closest technical solution (prototype) is a laser ranging method, which includes scanning space with a sequence of laser signals generated by a laser locator, registering a laser signal scattered and/or reflected by an object and determining the distance to the object by the delay time between the emitted and received signals, and the angular position of the object in the direction of the emitted signal. In the known method, the scanning device performs a programmable rotation in space of the probing laser beam with a relatively low divergence. Using a known method allows you to determine not only the distance to an object, but also its angular position in space, and applying the corresponding procedure twice (that is, determining the position of an object at two different moments in time) allows you to find the speed of the object.

The main disadvantage of the known method is its relatively low performance in determining the position of an object with sufficiently high accuracy. In fact, the next laser signal is emitted after the previous signal “returned by the object” is detected or when it can be guaranteed that there is no desired object in the probed region of space (otherwise it is possible to “confuse” which emitted signal the recorded signal corresponds to). The formulated condition limits the repetition rate of laser signals f at the limiting level fmax=c/2L, and, accordingly, the time for determining the position (search) of an object can be long. For example, if an object can be located at a distance of up to 300 km, then the maximum operating frequency of the laser locator will be 500 Hz. If an object is known to be located in an area with a transverse dimension of 10×10 km, and its position is required to be determined with an accuracy of 100×100 meters (the required divergence of laser radiation is only ~0.3 mrad and corresponds to a telescope aperture of less than 1 cm for diffraction quality radiation and the wavelength of the probing radiation is ~1 μm, the angular accuracy of the scanning device can be an order of magnitude higher), then a total of 10,000 laser pulses and, accordingly, about 20 seconds may be required. Note that during this time the object can go beyond the study area (for this, a transverse velocity of ~500 m/s is sufficient).

This reason limits, among other things, the operating frequency and productivity of laser locators used for laser probing of the earth's surface, since each subsequent probing pulse can be emitted only after the previous “reflected” pulse has been registered. As a result, the cost of, for example, laser geodesy and high-resolution topography is quite high.

The technical result of the invention is to increase the productivity of laser ranging.

The technical result is achieved in that in the laser ranging method, which includes scanning space with a sequence of laser signals generated by a laser locator, recording scattered and/or reflected laser signals by an object, determining the distance to the object by the delay time between the emitted and received signals, and the angular position of the object - in the direction of the corresponding emitted signal, a train of at least two pulses with variable time intervals between pulses and/or the ratio of pulse amplitudes in each train is used as a signal generated by the laser locator.

By pulse amplitude, depending on the relationship between the duration of an individual pulse τti and the time resolution of the recording system τp, we mean the pulse energy (if τti<τр) или его мощность (если τи>τр).

The application of the proposed technical solution makes it possible to actually “mark” the signals emitted by a laser locator and establish a one-to-one correspondence between the emitted and received signals. As a result, even at a significantly higher repetition rate of laser signals generated by the locator than in the prototype, it is possible to determine which emitted signal the received signal corresponds to, and, accordingly, using only a high-speed photodetector, simultaneously determine the distance to the object (based on the delay time) and the angular position of the object (in the direction in which the signal that was subsequently received was emitted).

The implementation of the proposed technical solution for the example described above of localizing an object located at a distance of ~300 km in an area with a transverse dimension of 100×100 meters can, for example, be as follows. A laser locator at a frequency of 100 kHz generates a sequence of trains of paired (“double”) short (~1 ns) pulses with a variable time interval between them, for example: in the first pair, the second pulse follows 20 ns after the first, in the second pair - after 40 ns, in the hundredth pulse train the interval between pulses will be 2 μs, etc.; after generating 200 double pulses (the time interval between the last pulses in the pair will be 4 μs), the sequence of trains described above is repeated. Here, a frequency of 100 kHz means that the time interval between the first laser pulses in successively generated trains is 10 μs. Thus, from the time interval between pulses in a train (with sufficient resolution of the recording system), it is possible to determine the “number” and moment of generation of this particular train. The same time interval between two pulses in a train is repeated every 2 ms (10 μs × 200), which exactly corresponds to the maximum distance to the object of 300 km. That is, when registering a signal returned by an object, it is possible to “confuse” only the distance L and L+300 (L is the distance to the object in kilometers), which, obviously, will not happen at L≤300 km, since the amplitude of the received signal will differ many times over.

With the same radiation divergence as in the prototype of 0.3 mrad (spatial “resolution” of 100 meters), the time for viewing a region of space 10×10 km from a distance of ~300 km will be 0.1 s and will decrease by 200 times compared to the prototype . Note that the angular speed of beam rotation, ~30 rad/s, required for operation at the specified frequency of 100 kHz, is provided with a multiple margin with modern scanning devices. In addition, with preliminary localization of an object in an area, for example, 1×1 km, the time of fixing the object can be further reduced by 10 times (or spatial resolution improved).

If the object is supposedly located at a greater distance or a higher scanning frequency is required (shorter viewing time of space), then the period of the generated sequence of trains can, for example, be tripled as follows: first, the sequence of trains described above is generated with the same amplitude of both pulses in each train, then a sequence of 200 trains is generated with a similarly variable time interval between pulses in the train, but with the amplitude of the first pulse, for example, three times greater than the amplitude of the second pulse, then a sequence of 200 trains is generated with an inverse relationship between the amplitudes of the generated pulses in the train. When trains consisting, for example, of three pulses are used to “mark” signals emitted by a laser locator, the generated sequence of non-repeatable trains can be even much longer.

The claimed technical solution makes significant use of the fact that in each specific train the time interval between the pulses entering the train is small and does not exceed several microseconds. This means that at any real speed of the located object, if one pulse from a train hits it, then all other pulses from this train will also hit it. Indeed, with a maximum time interval between pulses in one train of 4 μs and a transverse velocity of the object of 8 km/s (first cosmic velocity), the movement of the object (and signal receiver) between pulses will be only ~3 cm. This also means that all pulses from one the trains propagate virtually along the same trajectory and the losses when light passes through this trajectory are identical with good accuracy for all pulses that make up a separate train; therefore, the ratio of the amplitudes of the received pulses in a train will correspond to the ratio of the amplitudes of the emitted pulses in this train.

Similarly, a multiple increase in productivity is possible during laser sensing of the Earth not only from “cosmic” distances (from satellites), but also during aerial photography (from airplanes). Thus, at a shooting altitude (aircraft flight altitude) of 1.5 km, the repetition rate of sounding signals does not exceed 100 kHz and can be increased to 500-700 kHz (and higher) using the proposed method. In this case, the mutual movement of the object and the signal receiver within one pulse train will not exceed ~0.2 mm (the maximum time interval between pulses in one train is no more than 1 μs, and the relative speed of the object and receiver is ≤200 m/s).

Generation of a sequence of pulse trains by a laser locator according to the claimed technical solution can be realized by various means, for example, a generator-amplifier system, when the generator emits short pulses at the maximum required frequency (in the above example at a frequency of 50 MHz, corresponding to a time interval of 20 ns), and the system control “cuts” the pulses required for amplification, or when using two (or more) suitably synchronized lasers. Likewise, spatial scanning can be implemented by various methods, however, the specific implementation of the proposed laser ranging method is not the subject of this patent application.

Thus, the use of the proposed technical solution makes it possible to repeatedly increase the productivity of laser ranging and determine not only the distance to an object, but also the direction towards it (that is, the angular position of the object) using highly sensitive and high-speed photodetectors without the use of radiation detectors with spatial resolution of the CCD type at all. matrices - as a rule, noticeably less sensitive and with a high noise level, as well as having relatively low performance. The inventive laser ranging method makes it possible to use compact low-power laser locators and record a signal against a daytime background. This allows us to conclude that the proposed technical solution satisfies the criteria of “novelty” and “significant differences”.

Literature

1. Smirnov V.A. Introduction to optical radio electronics. M.: Soviet radio, 1973. - 189 p.

2. Matveev I.N., Protopopov V.V. and others. Laser location. M.: Mechanical Engineering, 1984. - 272 p. (prototype).

3. Danilin I.M., Medvedev E.M., Melnikov S.R. Laser location of the Earth and forests: a tutorial. - Krasnoyarsk: Forest Institute named after. V.N.Sukacheva SB RAS, 2005. - 182 p.

4. Patent RU 2352959, IPC: G01S 17/06, 04/20/2009.

A method of laser ranging, including scanning space with a sequence of laser signals generated by a laser locator, recording scattered and/or reflected laser signals by an object, determining the distance to the object by the delay time between the emitted and received signals, and the angular position of the object - in the direction of the corresponding emitted signal, different in that a train of at least two pulses with a variable time interval between pulses and/or the ratio of pulse amplitudes in each train is used as a signal generated by the laser locator.

Similar patents:

The invention relates to distance measuring equipment and can be used, for example, to determine the distance from a measuring device to the surface of a wall, the ceiling of a room, or to an object (object) inside or outside the room.

The invention relates to optical-electronic instrument making. The surrounding space is scanned in a horizontal plane and a video frame with an object to which you want to measure the distance is selected. The vertical and horizontal coordinates of the object image are measured relative to the coordinates of the beginning of the video frame, while the horizontal coordinate of the object is calculated by summing the coordinates of the beginning of the selected video frame with the value of the horizontal coordinate in the video frame. The sighting axis of the laser rangefinder is set according to the measured vertical coordinate of the object. During the next scanning cycle, the distance to the object is measured at the moment the sighting axis of the laser rangefinder passes along the horizontal coordinate of the object calculated during the previous scanning cycle. The device implementing the method includes an optical-electronic module on a scanning platform with rotation around a vertical axis, equipped with a drive and an angular position sensor. The laser rangefinder is placed on its uniaxial platform with the possibility of its rotation in a vertical plane and equipped with a drive and an angular position sensor. The technical result is to provide the ability to measure the distance to an object with a laser range finder during continuous scanning of the surrounding space, including circular space, at high speeds. 2 n.p. f-ly, 2 ill.

A method for increasing the information content and productivity of laser ranging includes scanning space with a sequence of laser signals generated by a laser locator, registering laser signals scattered and/or reflected by an object, and determining the distance to an object based on the delay time between emitted and received signals. The angular position of the object is determined by the direction of the corresponding emitted signal. In this case, a sequence of laser pulses, differing in wavelength, arriving at the scanning device is used as scanning laser radiation. The laser pulses are separated by wavelength using a wavelength selector. The technical result is to increase the productivity and information content of the laser radar. 7 salary f-ly, 3 ill.

Laser ranging method

Annotation

Introduction

Chapter 1. Study of the characteristics of the rangefinder-altimeter analogue DL-5

1.1 Rangefinder range. Energy calculation

1.1.1 Calculation methodology

1.1.2 Calculation results in monopulse mode

1.1.3 Energy calculation in storage mode

1.2 Calculation of range measurement accuracy

1.2.1 Range measurement accuracy in monopulse mode

1.2.2 Range measurement accuracy in accumulation mode

Chapter 2. Processing of location information

2.1 Methods for processing location information

2.1.1 Methods for increasing the accuracy of time fixation of the received signal

2.1.2 Incoherent accumulation method

2.1.3 Optimal method for determining speed in terms of accuracy and noise immunity

2.2 Working in the near field and methods for reducing the minimum measurable range

3.1 Radiation divergence corrector using a cylindrical lens

3.2 Optical combiner based on birefringent elements

Chapter 4. Experimental testing of technical proposals for upgrading the DL-5 altimeter

4.1 Experimental results

4.1.1 Transmission channel energy measurement results

4.1.2 Result of visualization of the shape of light spots

4.1.3 Results of using an optical design with a birefringent crystal

4.1.4 Transmission channel layout results

4.1.5 Results of measuring the power at the output of the optical unit

4.2 Design and technological part

4.2.1 Description of the design of the DL-5 laser altimeter

4.2.2 Technological features of the construction of the DL-5 laser altimeter

Chapter 5. Life safety

5.1. Dangerous and harmful factors when operating laser systems

5.2 Laser hazard classes

5.3 Methods and means of protection against laser radiation

5.4 Calculation of laser safety of laser altimeter DL-5

Chapter 6. Ecological part

6.1 Electromagnetic pollution of the environment

6.2 Impact of low power EMF on biological objects

6.3 Foreign and Russian experience in standardizing electromagnetic fields

Chapter 7. Economic part

7.1 Calculation of the cost of a prototype of the DL-5M altimeter

7.2 Calculation of the cost of the DL-5M altimeter in mass production

Conclusion

References

Annotation

Laser altimeters have become an integral part of the on-board equipment of unmanned aerial vehicles. Their widespread implementation is due to a range of tasks to support flights using satellite images, determining the coordinates of observed objects, monitoring the underlying surface, and measuring the rate of descent when landing an unmanned aerial vehicle.

The thesis presents theoretical and experimental studies of the best domestic laser altimeter DL-5 based on a semiconductor laser, proposes methods and techniques for increasing range measurement ranges, increasing measurement accuracy, as well as measuring speed when landing a UAV.

The scientific and experimental results obtained became the basis for the creation of a new generation laser altimeter.

Introduction

Modern methods and technologies for laser ranging of underlying surface objects.

The development of pulsed laser ranging at the present stage is marked by a wide functional diversity: rangefinders, altimeters, lidars, 3D registration systems, etc. This diversity depends on the consumer market and on the solid-state and semiconductor lasers used.

Laser ranging is the field of optoelectronics that deals with determining the location of various objects using electromagnetic waves in the optical range emitted by lasers. Objects of laser ranging can be: military and civilian equipment, industrial and military structures, components of the underlying surface - ravines, forests, reservoirs, etc. Laser sensing is an integral part of the latest methods and technologies of geoinformatics and digital photogrammetry.

The first local pulse solid-state rangefinders were based on neodymium garnet (YAG Nd3+,) and neodymium potassium gadolinium tungstate (KGV Nd 3+, - safe for vision). They have large dimensions and weight, so portable rangefinders are made using semiconductor lasers

Review of the use of pulsed rangefinders based on semiconductor lasers for sensing ground objects.

The requirements for a laser diode with (radiation hazardous to vision) or with 0 differ significantly from the requirements for a solid-state laser of a monopulse rangefinder for the following reasons:

1) a semiconductor pulsed laser emits into a corner; behaves like a diffuse emitter with dimensions (dimensions of p-n junction) at and; due to the optics of the transmitting channel, the divergence of the probing radiation is obtained (for solid-state ones 0.5 mrad), providing 50% of the power emitted by the laser;

2) a fundamental difference - a semiconductor pulsed laser has several orders of magnitude lower radiation energy and coherence length. With an output radiation energy of 10-2 J, a solid-state pulse laser provides measurement to a large-sized target at a distance of 10,000 m, and a semiconductor laser with an energy of 10-6 J allows measurement of a range only up to 100 m.

Therefore, to increase the measured range in rangefinders with semiconductor lasers, it is necessary to use the incoherent accumulation method - multiple target probing. Incoherent accumulation allows you to “increase” the equivalent signal energy by a factor. N is the number of soundings in a series (accumulation volume). The accumulation method will be discussed in detail in Chapter 2.

Let us give, for example, the use of a DL-1 pulse rangefinder based on a semiconductor laser with a radiation wavelength of 905 nm for a ground-based environmental reconnaissance complex.

The DL-1 rangefinder is used as part of a ground-based environmental reconnaissance complex designed to monitor the state of the environment in the area of ​​industrial facilities (Fig. 1B). The environmental reconnaissance complex includes a passive spectroradiometer IR-FSR “Climate”, which provides measurements of parameters from the location of the complex to the controlled object.

The IR-FSR receiving channel is aimed at the area of ​​the polluting emission, and the DL-1 is aimed directly at the wall of the building.

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Figure 1. Ground-based environmental reconnaissance complex

A complex of environmental control similar in composition (Fig. 2B) can be deployed as part of a customs post at a port terminal to provide remote monitoring of ships moving in the direction of the port: determining the degree of danger of the cargo they transport and making a decision to stop the vessel at a safe distance, in the event detection of potential danger from the cargo it transports for the port complex. The environmental control complex can be located permanently at the entrance to the port. The DL-1 rangefinder provides measurement of the distance to the vessel and the speed of its approach. In addition, as in the previous version, the complex can be deployed on a mobile carrier (vehicle), this will make it possible to quickly analyze the potential danger from the cargo of ships carrying out loading and unloading operations at the berth wall along the entire port water area.

The IR-FSR receiving channel is aimed at the area of ​​space above the deck of the ship, while the DL-1 is aimed directly at the hull or superstructure of the ship.

The stationary location of the environmental control complex is shown in Figure 2.

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Figure 2. Complex for monitoring surface objects

Figure 3B shows the LIND-27 laser altimeter (Developed by Polyus Research Institute), which was installed on the MI-8 helicopter and was intended to work as part of a radiation monitoring measuring complex when assessing the background radiation above the Chernobyl nuclear power plant.

Problems of laser altimetry. Altimeters

Laser altimeters have become an integral part of the on-board equipment of aircraft, helicopters and unmanned aerial vehicles (UAVs). Their widespread introduction is due to a range of problems, the solution of which became possible thanks to laser ranging technology. These tasks can be divided into the following main groups:

Laser navigation means for an aircraft measuring slant range (altitude) and speed as a relative increment of range per unit time;

Optical-electronic means of special aircraft for viewing space, detecting targets, identifying them, determining coordinates and target designation for targeting ground or airborne weapons;

Complexes for geophysical research, etc.

This range of applications determines the differences in the design and characteristics of laser altimeters.

In terms of composition and principle of operation, laser altimeters do not differ significantly from laser rangefinders designed for operation on ground-based horizontal routes. However, laser altimeters have differences and features associated with their installation on board an aircraft.

Laser altimeters:

They do not have their own sight, guidance is carried out according to information from special vision systems or according to the flight program of the course processor;

They do not have working control bodies; their operation is controlled from the central console;

They do not include a display, which is located on the central console;

They have a developed interface for two-way communication with the central processor.

The working field of the altimeter moves in the picture plane relative to the underlying surface at an aircraft speed of 30-400, which imposes a requirement on the speed of the altimeter. Figure 3 shows the block diagram of the rangefinder-altimeter.

The rangefinder-altimeter works on the principle of measuring the travel time of a probing laser pulse to a reflecting object and back.

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Figure 3. Block diagram of the rangefinder-altimeter

where is the distance to the object, is the speed of light (Fig. 4).

Figure 4. The principle of measuring distance with a laser pulse rangefinder: 1- rangefinder; 2- pulse of transmitter radiation; 3- pulse of reflected radiation; 4- goal; 5-starting light pulse; 6- stop pulse; 7- pulses of the reference (clock) frequency generator; R - measured range, m; R=cT/2=nc/2f; c - speed of light, m/s; T is the time of propagation of laser radiation to the object and back, s; T=nt=n/f; n is the number of pulses of the reference frequency generator of the time interval meter (TIM); t - period of oscillations of the IVI reference frequency, s

The probing pulse triggers the time interval meter (TIM), implemented as part of the decision device, and, with the help of optics that forms a given radiation pattern, arrives at the object. The radiation reflected by the object is focused using receiving optics onto the photosensitive element of the photodetector device (PDE). A standard electrical pulse is generated at the output of the FPU, stopping the IVI counting circuit. Information about the measured range is taken from the IVI output. The operation of the rangefinder-altimeter units is ensured by a power supply and control unit that generates the necessary voltages and synchronizing signals.

Information processing is carried out in the decision device. The launch of the IVI (start) in our case is carried out according to a combined scheme - part of the radiation energy is allocated to the FPU receiver. Launching the IVI (start) according to a separate scheme requires the addition of a start-pulse generation circuit with a separate receiver to the rangefinder-altimeter.

With a combined scheme, the probing pulse and the pulse reflected by the target (object) pass through one channel. Thanks to this, some systematic errors are compensated and maximum measurement accuracy is ensured.

3. Review of the use of pulsed rangefinders-altimeters (analogues) based on semiconductor lasers for monitoring objects on the underlying surface

At the Polyus Research Institute, among the developed, implemented and mass-produced pulse rangefinders-altimeters for monitoring objects on the underlying surface, LD-1 and LD-5 can be distinguished.

The main comparative technical characteristics of the DL-1 and DL-5 rangefinder-altimeters are given in Table 1.

Table 1. Comparative technical characteristics of rangefinders-altimeters DL-1 and DL-5

The complex consists of a laser analyzer, an autonomous navigation system, an altimeter, a television camera, a system for transmitting video images and measured data to a ground point.

In terms of purpose and principle of operation, the DL-5 rangefinder is similar to the DL-1 device, but thanks to the transition to a more modern element base and information processing principles, it surpasses its analogue in the main parameters (Table 1) - maximum measurable range, dimensions and weight. This allowed the DL-5 to be used in the navigation systems of an unmanned aerial vehicle.

The use of the DL-5 altimeter when installed on the Rakurs UAV (Fig. 8B), take-off weight 27 kg, developed by OJSC NIITP, made it possible to measure the topography of the underlying surface to ensure that the resulting images from the on-board television camera are linked to satellite images of the flight mission and additionally provide information to the navigation complex about the glide path in the automatic landing mode of the UAV.

Laser altimeter DL-5 provides:

Determining the distance to the underlying surface;

Linking the moment of height measurement to the center of the television frame with the image of the underlying surface;

Automatic transfer of measured distances to an external device.

The disadvantages of the DL-5, based on the requirements for unmanned aerial vehicles, include:

Inability to measure vertical speed with the required accuracy when landing a UAV;

A fairly large value of the lower controlled height (2 m) and low accuracy of its measurement when landing a UAV (0.5 m);

Limited value of the maximum measured range (1000 m) and accuracy (2 m) when probing remote objects on the underlying surface.

Thus, the modernization of the studied rangefinder-altimeter DL-5, aimed at eliminating the above shortcomings, is very relevant.

Therefore, it is possible to formulate the purpose of the thesis and research objectives.

Purpose of the work

Conducting complex theoretical and experimental studies, as well as performing calculations, circuitry and design solutions aimed at improving the basic technical characteristics of rangefinders-altimeters: expanding the range of the measured range and increasing the accuracy of measurements; ensuring vertical velocity measurement with high accuracy as part of an unmanned aerial vehicle for monitoring objects on the underlying surface.

Research objectives

1. Comparative studies of existing pulse rangefinders-altimeters based on semiconductor lasers to improve their technical characteristics and the need to measure speed when landing an aircraft.

2. Analysis of methods for processing location information.

3. Research on ways to optimally construct a pulse rangefinder-altimeter with improved basic technical characteristics.

4. Experimental studies of a rangefinder-altimeter with improved technical characteristics.

Thus, for the effective use of pulsed rangefinders-altimeters based on semiconductor lasers (in systems of unmanned aerial vehicles for monitoring objects on the underlying surface), their modification is necessary, namely:

Increased maximum measuring range (> 1000 m) and accuracy (< 2 м);

Reducing the minimum measurable range (< 2 м) при повышении точности измерения (< 0,5 м) для обеспечения посадки БПЛА.

Possibility of measuring the vertical component of speed with the accuracy of its measurement.

altimeter semiconductor laser signal

Chapter 1. Study of the characteristics of the rangefinder-altimeter analogue DL-5

The optical design of the DL-5 laser altimeter is shown in Figure 1.1.

Figure 1.1 Schematic optical diagram of the rangefinder-altimeter DL-5

1. Laser diode SPL PL90-3 from OSRAM

2. Lens

3. Light filter

Assessing the energy level of the DL-5 pulse laser rangefinder-altimeter necessary to ensure maximum range measurement (Table 1.B) is the first step in studying its characteristics and finding methods for their possible improvement: expanding the range measurement range (increasing max range and decreasing min range); increasing accuracy when measuring range, measuring vertical speed when landing a UAV.

Improving the characteristics of the DL-5 must be carried out without changing the weight and dimensions and without reducing the requirements for external interfering factors.

1.1 Rangefinder range. Energy calculation

The range of measured ranges is the main characteristic of a rangefinder (altimeter), which determines the possibilities of its use. The range of measured ranges is provided by: 1) hardware limitations (shadow zone, capacity of the time interval meter, probing frequency, etc.) 2) energy potential of the rangefinder, determined by the energy characteristics of the optical-electronic elements of the receiving-transmitting path, the design characteristics of the optical system. The actual range measured by the device to a given target under certain conditions and with known probabilistic detection characteristics is called the range.

1.1.1 Calculation methodology

The range of 1000 m specified for the analogue is ensured subject to the inequality determined by the laser ranging equation, provided that the fields of the emitter and receiver are matched:

Emin< Eпр = EoКD2прао/4R2, (1.1)

where Emin is the minimum signal energy received with a given probability, provided by the sensitivity of the photodetector (real sensitivity);

Epr is the energy of the signal arriving at the working platform of the sensing element of the FPU;

Eo is the energy of the probing signal;

K = - coefficient of energy overlap of the probing beam by the target (radiation utilization coefficient);

(x,y) - spatial distribution of the target brightness coefficient;

(x,y) - radiation pattern of the output probing beam;

Dpr - diameter of the receiving lens;

a = e-2R - atmospheric transmittance along the path;

Attenuation index;

o is the transmittance of the optics of the rangefinder receiving channel;

R - range to target.

The attenuation index is related to the meteorological visibility range V, km, by the well-known empirical expression:

where is the working wavelength, µm;

The initial data for calculating Epr are given in Table 1.1

Table 1.1 Initial data for calculating the range of an analogue laser rangefinder (DL-5)

1.1. 2 Calculation results in monopulse mode

Calculation the range of the ranging system was carried out for the received initial data (optical ranging equation 1.1 and table 1.1) are given in tables 1.2 and 1.3.

Table 1.2. Energy calculation results for a height of 1000 m

As can be seen from the above calculation results, at the maximum range to the target, even a large-sized target is not able to create a signal on the photodetector sufficient for its operation, and there is a deficit of received energy = Epr/Emin. For a given target with a diameter of 5 m at a distance to it R = 1000 m, the energy deficit is = 20.

Table 1.3. Energy calculation results for a height of 200 m

According to the data presented, at an intermediate height of 200 m, under favorable conditions, measurements in a monopulse mode are possible.

1.1. 3 Energy calculation in storage mode

The rangefinder range is determined by its energy potential, determined mainly by the energy of the probing signal, the sensitivity of the receiver and the diameter of the receiving lens. For a given energy potential of the rangefinder, the magnitude of the Epr signal on the sensitive area of ​​the photodetector is determined, as follows from location equation 1.1, by the parameters Eo and D2, which have a limit due to restrictions on the weight and size characteristics of the rangefinder. The sensitivity of the receiving channel Emin is limited by the noise of the receiver and the input stage of the amplifier, which are determined by the physical nature of signal conversion in the photoreceiving path and also have a theoretical limit, below which it is impossible to reduce Emin in principle. The ratio Epr/Emin, called the signal-to-noise ratio, determines the range of the rangefinder and, as shown above, with a monopulse measurement mode and given design limitations, it does not provide the ability to measure a range of 1000 m for a given target under given meteorological conditions.

There is a method for increasing the range of a rangefinder without increasing its energy potential. The essence of this method lies in N-fold repetition of measurements and statistical processing of the results obtained, which makes it possible, with optimal implementation of this method, to increase the effective value of the signal-to-noise ratio up to times.

The energy deficit indicated in Table 1.2 can be compensated by a similar method, so that the condition / = 1 is satisfied, from which the accumulation volume N required to measure a range of 1000 m with the same energy potential of the rangefinder is determined by the relation N = 2 = 202 = 400.

With a sounding frequency of 8000 1/s, the range measurement time will be 400/8000 = 0.05 s, which allows measurements to be carried out with a specified information update period of 0.1 s.

To compensate for the energy deficit when working on targets with a smaller reflective surface, the measurement time can be increased to 0.1 s, while the accumulation volume is N = 800, and the maximum possible energy deficit = ~ 28, which allows measurements to be carried out on the specified targets.

Consequently, the energy assessment of the DL-5 rangefinder showed:

The energy potential of the rangefinder in monopulse mode provides range measurement in a range of up to 200 m, and in accumulation mode it provides measurement of a maximum range of up to 1000 m;

To increase the maximum range measurement beyond 1000 m, additional methods to increase the energy potential of the rangefinder must be explored.

1.2 Calculation of range measurement accuracy

1.2.1 Range measurement accuracy in monopulse mode

In the considered ranging system, a combined launch scheme is used, in which most of the error components are compensated. Of the uncompensated sources of error, the following have the greatest impact.

Discreteness of the RIVI time interval meter.

To ensure standard tasks, it is usually sufficient that the data sampling error does not exceed 5 m. Most laser rangefinders are built with such discretization. However, there are a number of tasks that require significantly greater accuracy. These primarily include:

The need to measure target speed;

Using rangefinder data to determine the absolute coordinates of objects using information from satellite coordinate determination systems.

Determination of the target profile (underlying surface) along the flight path of the aircraft;

Determination of the spatial extent of the target;

Ensuring the safe landing of the aircraft.

In this regard, the discreteness of RIVI in modern monopulse ranging systems usually does not exceed 1 m. In systems with accumulation, the necessary accuracy can be ensured by averaging data during the accumulation process. The DL-5 rangefinder uses a clock frequency of 25 MHz, which corresponds to a resolution of 6 m in each individual measurement.

The probability density distribution w(r) of the random error r caused by this component has a rectangular shape with a synchronized start and a triangular shape when the IVI clock pulses are not tied to the start moment (Fig. 1.2).

Figure 1.2 Probability density distribution of the range measurement error component r due to the discreteness of the IVI during asynchronous start

In this case:

w (r) = 1/(R)2r + 1/R at r< 0,

1/(R)2r - 1/R for r > 0. (1.2)

The variance of this error

DIVI = r2w (r) dr = R2/6,

And its mean square value

IVI = = 0.408 R = 2.448 (1.3)

Instability of the threshold device operation when recording received pulses at the leading edge.

Figure 1.3 Instability of threshold device operation

The mechanism of instability of the temporary fixation of the received signal is clear from Figure 1.3, where R1 is the response delay of the threshold device at the maximum signal amplitude S(r), and R2 at the minimum signal.

The minimum excess of the signal over the threshold is set by the required signal/threshold ratio, determined by the required probability of a reliable measurement. The maximum excess of the signal over the threshold is determined by the dynamic range of the received signals.

When the leading edge has a sine-square shape, it is described by the expression.

S(r) = Sin2 (r/4rmax)

where rmax = ctmax/2;

c is the speed of light;

tmax - duration of the front at levels 0-1.

From this expression it is possible to determine R1 and R2 with a known rise time tmax and the above-mentioned limit values ​​of the signal/threshold ratio.

So, with a front duration of 100 ns, which corresponds to rmax = 15 m, R1 = 0.1 m, and R2 = 8.4 m, i.e. the maximum response delay spread is 8.4 - 0.1 = 8.3 m.

At short and medium ranges, the minimum excess of the signal amplitude above the threshold is usually 100 times or more.

Then R2< 4 rmax arcSin()/, что для приведенного примера составляет 1 м. Угол arcSin(х) измеряется в радианах.

Obviously, this value depends on the range of measured ranges and is determined by the energy potential of the rangefinder in this range.

The value of the root mean square error fr can be related to the maximum spread of the response delay by the known relation

fr = (R2 - R1)/6 = m (1.4)

1.2.2 Range measurement accuracy in accumulation mode

WITH The statistical spread of measurement results during averaging decreases with increasing volume of statistical data. Average variance

where D is the variance of the result of one measurement, and N is the number of measurements in the series. Accordingly, the standard deviation of the averaged measurement

Thus, to increase the accuracy in the accumulation mode with N measurements, it is necessary to form an estimate of the measured range

Ri is the result of the i-th measurement;

i is the serial number of the measurement.

The root mean square error of such an estimate, due to the discreteness of the time interval meter, with the above accumulation volume N = 800, will be

N = 0.408 R/ = 0.408 6/ = 0.08 m.

The specified measurement accuracy at the specified clock frequency of the time interval meter is ensured. Thus, the resulting root mean square measurement error of 0.08 m allows us to consider that in the accumulation mode the DL-5 has a significant margin in range measurement accuracy (see Table 1B).

Thus, the energy potential of the rangefinder in monopulse mode provides measurement of an intermediate height of 200 m. At a distance to the target of 1000 m, the energy deficit is 20 times.

Operating the rangefinder in accumulation mode compensates for the energy deficit, which allows you to measure a maximum range of up to 1000 m.

Calculation of the accuracy of range measurement in the accumulation mode showed that its energy potential provides a root-mean-square measurement error of 0.08 m, which is significantly lower than the norm specified in the technical specifications agreed with the customer DL-5: 0.5 m for measurements in the range 2-200 m and 2 m for the range 200-1000 m.

Chapter 2. Processing of location information

2.1 Methods for processing location information

Selection of targets and interference

The most important task of the rangefinder is to determine the range to the selected target in conditions of the interfering influence of internal noise and foreign objects located in the target range. Such objects are atmospheric inhomogeneities, which are most pronounced at ranges of 20-200 m (backscatter interference), vegetation, terrain folds, structural elements, etc.

Figure 2.1 shows a diagram of the location path with the most common interference and the corresponding signals at the input and output of the threshold device. When vertically probing the underlying surface from an aircraft, the target interference environment remains fundamentally the same, although the nature of the interference and their relative influence may differ somewhat.

To combat these interferences, various selection schemes are used. The most commonly used:

Limitation of the minimum measured range (gating);

Selecting a target by its ordinal position (first, second, last target);

Selection of signals by their shape; this method is most effective for combating extended interference, mainly backscatter interference;

amplitude selection (temporary automatic gain or threshold adjustment).

Figure 2.1 Locating route, locating signals and their selection. Targets selected in selection modes are marked: first, second and last target

Accumulation method

The accumulation method assumes:

Multiple repetition of measurements;

Accumulation and storage of location information in range channels corresponding to the serial number and duration of the clock pulse;

Correlation or other processing of an array of accumulated data in order to isolate the signal reflected by the target;

Time reference of the selected signal to the clock sequence of timing pulses.

2.1.1 Methods for increasing the accuracy of time fixation of the received signal

Chapter 1 of this work discusses a method for fixing the temporary position of a pulse reflected by a target along its front. As shown in the considered example, with a pulse duration of 100 ns, the spread of the moment of temporary fixation in the entire amplitude dynamic range can be ~ 8 m. Unlike the sampling error of the measured interval, this error component does not reset during accumulation, since signals in one series arrive approximately equal amplitudes, and the timing error is systematic rather than random for a given measurement.

This drawback is eliminated by binding to the maximum signal. and fixing the derivative at zero.

Figure 2.2 Method of fixing the maximum signal: S1(t) - signal; t1 - time reference point corresponding to the signal maximum

Figure 2.3 Method of fixing the derivative at zero: a) S1(t) - signal at the input of the fixation circuit; S1? (t) - signal at the input of the NK null comparator; t1 - result of timing; b) a differentiating link in the structure of the receiving path with a timing device - DZ. In this case, the time constant of the DZ, and 0 is much less than the duration S1(t).

Figure 2.4 Zero crossing method: a) S1(t) - signal at the DS input; S1?(t) - signal at the input of the NK null comparator; tm - maximum position. t1 is the result of the timing. b) timing device with a differentiating link DS and a null comparator

The method of fixing the maximum (Fig. 2.2) represents an ideal solution; the maximum represents a limit in the region of infinitesimal approximations that are practically impracticable. This remark is also true with respect to the derivative method (Fig. 2.3), in which the maximum of the signal is noted at the time instant corresponding to the zero of its derivative. In practice, the zero crossing method is widely used (Fig. 2.4), which is a “deviation” from the zero derivative method in that the “differentiation” of the signal is carried out by passing it through a differentiating link (differential chain) with a non-zero time constant, and also by the fact that the differentiated the signal is compared in the general case with a non-zero threshold of the comparator.

This results in a maximum fix error.
tm = t1 - tm. Usually this error does not exceed 2-5 ns, however, with significant overloads of the receiving path, the signal shape is greatly distorted and this error can increase significantly. To eliminate this drawback, automatic gain control of the received signal is introduced.

Methods for increasing the accuracy of temporary fixation of an array of accumulated information

The accumulation method provides not only energy gains, but also increased measurement accuracy. Thanks to this, it is possible and desirable to set the duration of the probing pulse several times longer than the duration of the IVI sampling period. According to a well-known technical solution, the time reference of the accumulated data array is carried out as a projection onto the time axis of the intersection point of the tangents to the front and rear “fronts” of the accumulated array (Fig. 2.5).

The analysis showed the insufficient efficiency of such methods for processing accumulation results. Firstly, as can be seen from Figure 2.5, the “fronts” of the array cannot be accurately interpreted and the position of the tangents to them is ambiguously established. Secondly, the shape of the array envelope depends significantly on the signal magnitude. As a result, the timing using this method has a significant scatter.

Figure 2.5 Method of timing the accumulated array using the tangent method with signal-to-noise ratio = 1

These shortcomings are eliminated by the method of timing the data array by determining the position of its first initial moment (center of gravity), calculated by the expression:

Tз = ((j-p) + ) T , (2.1)

Where j is the number of the time discrete in which the accumulated amount is maximum;

K(a) - accumulated amount in the (a)th discrete;

k(a) - weight coefficient of the (a)th discrete; if the position of the signal is unknown a priori, we can take k(a) = 1;

m = tfr/T - number of discretes corresponding to the duration of the leading edge of the laser pulse;

tfr is the duration of the leading edge of the laser pulse;

q = ti/T - number of discretes corresponding to the pulse duration;

ti is the duration of the laser pulse;

p - correction number characterizing the signal timing point;

T is the duration of the discrete.

This method maintains high timing accuracy not only in the linear range of the input signal, but also under significant overloads.

2.1.2 Incoherent accumulation method

The accumulation problem is formulated as follows: d The range of measured ranges DR is divided into m equal intervals Dr = DR/m; all intervals are considered statistically independent and are considered as range channels where the processing (accumulation) of location information is carried out; it is believed that the measured signal is in one of these channels (j-th channel). To obtain the measurement result, N range soundings are carried out. At the receiver output there is a mixture of signal with amplitude S and noise with effective value y. During i-th sensing, analog information from the receiver output is converted into digital information by single-level threshold quantization (STC) or multi-level threshold quantization (MLT) of the signal.

The OPK is called binary: the i-th signal of the j-th range channel is assigned the value kij=0 if

where Uj0 is the analog quantization threshold, or kij=1 if Sij>Uj0. These values ​​are summed (accumulated) in each j-th channel during each of the N soundings, forming the sums

Kj= kji (i=1…N)

If Kj>Kj0 is the threshold level, then it is decided that the range to the target is determined by the j-th range channel and is equal to:

where R0 is the beginning of the range of measured ranges.

Computer modeling of the receiving path with accumulation

A computer model of the receiving path with accumulation was developed. The model uses the Monte Carlo method and is based on MATLAB 7.0 software. At the output of the linear path there is a random process representing the sum of the signal and noise. One such implementation is shown in Figure 2.6. The signal is characterized by a relative amplitude S, specified in effective noise levels y and representing the signal-to-noise ratio. The program parameter A is related to S by the ratio A = 1.85 S. In the figure, S = 1. Figures 2.7 and 2.8 show the results of computer simulation of a two-threshold storage device under the above conditions and the number of accumulation cycles (accumulation volume) N = 200. The index below shows the position the center of gravity of the resulting arrays.

Figure 2.6 Implementation of a random signal + noise process at the input of a two-level threshold device. Threshold levels +0.5 and -0.5 are shown as dotted lines. Signal to noise ratio S = 1

Drive simulation results

Figure 2.7 Realization of accumulation results with accumulation volume N = 200 and signal-to-noise ratio at input S = 1. Calculated range R = 205 m. Measurement result R* = 204.8 m.

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Figure 2.8 Implementation of accumulation results with an accumulation volume N = 200 and signal-to-noise ratio at the input S = 10. Calculated range R = 5 m. Measurement result R* = 5.0 m

The data in Figure 2.7 were obtained for the signal-to-noise ratio at the drive input S/N = 1, and the results in Figure 2.8 were obtained for S/N =10. With a further increase in S/N, the estimate of the time position of the signal shifts slightly to the left towards the original value. As can be seen, with such a construction of the storage device and an algorithm for estimating the temporal position of the signal at the center of gravity of the accumulated array, the spread of range measurement results in the unlimited amplitude range of signals does not exceed 20% of the value of the IVI sample. For the example considered, this corresponds to 0.2 m, which is a systematic error that can be eliminated at short distances by introducing a correction.

Despite such a small spread in range estimates during accumulation, there are ways to further reduce it. This is possible due to the introduction of a correction depending on the number of overflowed storage cells or the sum of accumulated amounts in cells adjacent to the center of gravity of the accumulated array. Then the error in range estimation can be reduced to 10% of the discrete value or less.

2.1.3 Optimal method for determining speed in terms of accuracy and noise immunity

Optimal speed measurement algorithm

If a number of range measurements are available, a procedure for measuring the target's speed can be proposed by determining the coefficient xy of the regression line y = xy x + b (Fig. 2.9).

Figure 2.9 Determination of speed as a regression coefficient pxy of a series of measurements y(x)

In this case, the dispersion of the estimate pxy is minimal if it is optimized using the least squares method. In the general case, for arbitrary moments of time of measuring ranges and the volume of a series of measurements n, the velocity estimate, optimal in the sense of least squares, is determined by the expression valid for values ​​of V* from 0 to 5 m/s and above.

In particular, for equally spaced samples Ri with a period DT:

or, after simplifications,

In this case, the root-mean-square error of speed estimation is:

where is the root-mean-square error of range measurement in each of the measurements.

In particular:

Table 2.1 shows the calculation results for several accumulation modes.

Table 2.1 Calculation results of the velocity measurement error V at R ~ 0.41 R=2.4 m

Note Calculations of V were carried out using formula (2.7)

The choice of the optimal accumulation mode depends on the aircraft’s flight mission, altitude and piloting mode.

It must be noted that in speed determination procedures, all measurements must be reliable. Any false range reading or missed measurement (= 0) will result in a gross distortion of the speed measurement result. Therefore, when developing a calculation algorithm, measures must be taken to eliminate unreliable range measurements, for example, by eliminating measurements that differ from the average speed estimate for each range by an amount greater than 3.

Consequently, the speed measurement algorithm that is optimal in terms of standard deviation provides the ability to measure speed within specified limits from 0 m/s to 5 m/s and above. The speed measurement error can be reduced to acceptable values ​​by increasing the accumulation time to 0.5-1 s; in this case, the frequency of updating speed data can be the same as in the height measurement mode - for this, the speed calculation algorithm must provide for a shift in the accumulation interval with each specified update period, a given error of 0.2 m/s is ensured with an accumulation time T = 1 With.

2. 2 Near-field work and methods for reducing the minimum measurable range

Hardware function and shadow zone

With increased requirements for the minimum measurable range of a laser rangefinder, the problem arises of forming its hardware function (geometric factor) in such a way that the length of the shadow zone does not exceed the specified minimum range. The diagram for the formation of a typical hardware function of a laser rangefinder with separated transmitting and receiving channels is shown in Figure 2.10.

The hardware function A(R) characterizes the degree of overlap of the fields of the transmitting and receiving channels and varies in the near zone of the range from 0 to 1.

In the shadow zone, A(R) = 0, so range measurements in this zone are impossible. Typically, when constructing a rangefinder according to the above scheme, the shadow zone of the rangefinder R0 is 2-20 m, depending on the mutual configuration and optical characteristics of the emitting and receiving channels.

The value of R1 has virtually no effect on the characteristics of the rangefinder in the near zone, and R0 determines the minimum measured range, which cannot be less than this value. To reduce the minimum measured distance with a DL-5 altimeter to 0.5 m, it is enough to glue a plate of MC21 type milk glass measuring 7x3x0.3 mm onto the outer surface of the transmitting channel lens from the mandrel side.

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Figure 2.10 Scheme of formation of the hardware function: Di - diameter of the exit pupil of the emitting channel; Dп - diameter of the entrance pupil of the receiving channel; B is the distance between the axes of the emitting and receiving channels (base); R0 is the far boundary of the near (shadow) zone, where the fields of view of the emitting and receiving channels begin to combine; R1 is the near boundary of the far zone, in which there is complete overlap of the fields of view of the emitting and receiving channels; - angle of the receiving channel field of view; - angular divergence of the output beam of the emitting channel

Features of the rangefinder in the near zone

Requirements for the minimum measurable range and measurement accuracy are contradictory. The first of these requirements forces us to reduce the shadow zone of the rangefinder, and the second forces us to reduce the level of overload of the receiving path with reflected signals, which places opposite demands on the hardware function.

An additional factor that negatively affects near-field accuracy is the different mode structure of laser radiation in the near and far zones. These differences are aggravated by the influence of partial overlap of the fields of the emitting and receiving channels in the near zone. As a result, in the near zone the hardware function selects some modes and suppresses others. The difference in the temporal position of the radiation components corresponding to these modes can reach 0.1-1 ns, which corresponds to a range measurement error of 0.01 - 0.2 m.

Thus, to reduce the minimum measurable range< 2 м необходимо принять меры по сокращению теневой зоны аппаратной функции и устранению влияния модовой структуры излучения лазера.

Chapter 3. Proposals for the optimal construction of a pulse altimeter using a semiconductor laser

Methods for increasing the energy of the probing signal

Currently, several directions have been outlined for increasing the energy of the probing radiation of rangefinders through the use of a radiation divergence corrector made using a cylindrical lens and by combining radiation beams from several lasers using special optical combiners. Thanks to this and with the simultaneous use of highly sensitive receivers, effective accumulation methods, interference selection means and signal timing algorithms, it was possible to increase the range of rangefinders to 2-3, and in some cases up to 10 km.

3.1 Radiation divergence corrector using cylindrical lens

In the sample of the DL-5 altimeter under study, a laser diode SPLPL90-3 is used, the size of the luminescent body is 200x10 µm. Three emitting junctions fit into a size of 10 µm.

The far-field characteristics of the laser diode used are shown in Figure 3.1.

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Figure 3.1. Radiation divergence of pulsed diode SPL PL90-3

Only part of the laser diode power is transmitted to the underlying surface, lying inside the cone with an angle at the apex AND equal to:

And = 2arctg(D/2Fob)

Where: D=18mm - Lens luminous diameter.

Fob =65mm - Focal length of the lens.

For our case AND? 160

From Figure 3.1A it is clear that in the plane parallel to the p-n junction almost all the energy is taken, and in the plane perpendicular (Figure 3.1B) approximately at a level of 0.8. The measured relative energy in this corner is approximately 30% of the total radiant energy. At the same time, the size of the glow body in the plane perpendicular to the p-n junction is h+=10 µm and the geometric divergence of the rangefinder radiation in this plane is equal to:

2g = h+/Fob = 0.15x10-3rad

The size of the luminous body in a parallel plane is h = 200 µm and, accordingly, the divergence of radiation in this plane is equal to:

2g =h///Fob = 3x10-3rad

It can be seen from this that an increase in the radiation power can be obtained by increasing the divergence of the radiation in the plane perpendicular to the plane of the pH transition.

The radiation correction scheme with a cylindrical lens is illustrated in Figure 3.2.

Figure 3.2 Correction of radiation from a pulsed diode with a cylindrical microlens: n0 = 1 - refractive index of air; n > 1 - refractive index of the lens material; r is the radius of curvature of the microlens; D - distance from the glow body to the center of curvature

Parameter D is determined by the design of the laser diode and is equal to the distance from the glow body to the output end of the diode body. The average statistical value of this parameter for the SPL PL90-3 laser is 0.285mm within a batch of 50 pcs.

H is the reduced size of the glow body in the plane perpendicular to the p-n junction;

h is the size of the glow body;

In the plane perpendicular to the p-n junction, the image is shifted by the amount L, and in the parallel plane by the amount L1. As a result of this setting for the output lens, the light source becomes astigmatic.

The value S = L1+L is the astigmatism of the light source.

And+ is the angle at which light energy is absorbed in a plane perpendicular to the pn junction.

For given values:

A cylindrical lens has the following parameters:

n=1.62, r=0.5 (lens radius)

The calculation gave the following values:

S = L1+L=0.62mm. Astigmatism of the light source.

The divergence in the perpendicular plane of the p-n junction is determined by the expression 2g+? H/Fob + S*D/(Fob)2

For the obtained value of astigmatism of the light source, the divergence in the perpendicular plane of the p-n junction will be I+ = 410.

Correction of radiation by a cylindrical microlens allows you to absorb energy in a plane perpendicular to the plane of the p-n junction at approximately a level of 0.2 versus a level of 0.8 without correction.

3.2 Optical th adder on birefringent elements

The radiation beams of two semiconductor lasers are polarized and combined using an optical combiner, the optical combiner is made in the form of a birefringent plane-parallel plate, the laser emitters are located on the side of one of its faces so that their optical axes are parallel, and the polarization planes of the laser radiation are mutually perpendicular. The thickness h of the birefringent plate is determined by the formula:

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The principle of laser ranging (LL) is based on the fact that light propagates in a vacuum rectilinearly and at a constant speed. A short laser pulse is emitted and the time is detected, the laser beam is reflected from the target object and returns back, where it is caught using a telescope and sensitive photodetectors and the time between the emission of the pulse and its return is determined. Knowing the speed of light, you can calculate the distance to an object. If the pulse is short and the time between the emission and reception of the reflected signal is measured accurately, then the distance to the object can be calculated with appropriate accuracy. The influence of the atmosphere, which bends the beam (refraction) and introduces a delay, is taken into account separately, but these are subtle details.

Ideas about the location of the Moon have been expressed for a long time, back in the 20s. 20th century, when there were no lasers. As soon as the laser was invented, the idea immediately arose to use the unique properties of laser radiation for lunar laser ranging (LLR). The first experiments on LLL were carried out in 1962-63. in the USA and USSR. At that time there was no talk of any measurements; the very possibility of implementing such a location was being tested. The experiments turned out to be quite successful, the reflected signal was reliably recorded, although the pulse duration of 1 ms did not allow measuring a distance more accurately than 150 km. In 1965-66, experiments were carried out with shorter pulses - an accuracy of about 180 m was achieved. Moreover, the accuracy was limited not so much by the pulse duration as by the terrain.

Then the idea was put forward to deliver corner reflectors (CR) to the Moon to improve location accuracy. Corner reflectors are notable for the fact that they always return the signal strictly in the opposite direction, and in addition, the signal does not have time smearing due to the terrain.

It is alleged that 5 corner reflectors were delivered to the Moon - two on Soviet lunar rovers and three by American astronauts - Apollo 11, Apollo 14 and Apollo 15.

This is where the tedious banality ends, and then magical fairy tales with incredible miracles and detective mysteries begin!

Let's start with the fact that the control device installed on Lunokhod-1 was suddenly “lost”! Moreover, there are two opinions on this matter. Leading researcher, head. Postgraduate student at the Pulkovo Observatory, Ph.D. E.Yu.Alyoshkina

in his article he claims that his control device is out of order.

This happened while moving in very difficult conditions inside one of the craters. On the wall of this crater there is another, secondary, small one. This is the meanest thing on the moon. To get out of this lousy crater, the operator-driver and the crew decided to turn the lunar rover back. And the solar panel was folded back. And it turned out that with the cover of the solar panel he drove into the wall of this invisible crater, because the cameras looked only forward. He scooped some lunar soil onto the solar panel. And after we got out, we decided to close this panel. But the moon dust is so nasty that you can’t shake it off so easily. Due to dust on the solar battery, the charging current has dropped. and due to the fact that dust hit the radiator, the thermal regime was disrupted. As a result, Lunokhod 2 remained in this ill-fated crater. All attempts to save the device ended in nothing.

The second story turned out to be stupid. He had already been on the Earth's satellite for four months. On May 9 I took the helm. We landed in a crater, the navigation system failed.

How to get out? We have found ourselves in similar situations more than once. Then they simply covered the solar panels and got out. And here there are new people in the management group. They ordered not to close it and to get out. They say, we close it, and there will be no pumping of heat from the lunar rover, the instruments will overheat.

We didn’t listen and tried to leave like that. We hit the lunar soil. And moon dust is so sticky. And then they order to close the solar panel - they say, the dust will fall off on its own. It crumbled - onto the internal panel, the lunar rover stopped receiving recharging with solar energy in the required volume and gradually lost power. On May 11, there was no longer a signal from the Lunokhod.

This information is confirmed by... LRO! Here is an image of Lunokhod 2 with the lid open, facing east:

In general, it is useless to locate the second lunar rover now.

The operating range of angles for the corner reflector installed on lunar rovers is ±10 degrees. In order to be able to locate the UO installed on the Lunokhod, taking into account the lunar libration of approximately 7 degrees,

The lunar rover must be properly oriented towards the Earth in azimuth (to a subterral point) and elevation with an accuracy of 2-3 degrees.

UPD from 03.11.2013. I called V.P. Dolgopolov and clarified the placement of the corner reflectors on the body of the lunar rover - they are located with an inclination strictly forward along the course, exactly as shown in photographs of museum models.

And now we remember Dovgan’s words that Lunokhod 2 is looking east, and we look closely at the map:


Green arrows show the actual orientation of the lunar rovers, yellow arrows show the orientation necessary for successful location of the control devices installed on the lunar rovers. The subterral point, which is located in the center of the image, and to which Lunokhod-2 should be oriented in azimuth, is located to the southwest of Lunokhod-2, and Lunokhod-2 is turned to the east (in my opinion, the azimuth is approximately 100-110 degrees) - in this position, the angle of incidence of the locating beam on the device is approximately 70 degrees, an angle that is completely prohibitive for a quartz device, i.e. The corner reflector of Lunokhod-2 is absolutely non-functional. And astronomers have been successfully locating it for almost 40 years??? I close my eyes and imagine how photons with a dashing pirouette dive into the corner reflector of the Lunokhod-2 turned backwards, to be reflected there and, after doing a reverse pirouette, head towards the Earth... Scheherazade nervously smokes on the sidelines! She only had enough fairy tales for 1001 nights.

A natural question arises - what did they (the astronomers) locate then?

The details of the American experiment are described in more or less detail in the document Apollo 11 Preliminary Science Report. Details of Soviet experiments on laser ranging of the Moon, conducted at the Crimean Astrophysical Observatory (CrAO) are given in the second volume of the collection “Mobile Laboratory on the Moon LUNOKHOD-1”. There is also a formula for calculating the magnitude of the response signal

and the result of the calculation is indicated - 0.5 photoelectrons from one pulse, i.e. approximately 1 photoelectron should be recorded from two laser pulses.

The number of photons that will reach the Moon is equal to the number released from the laser multiplied by this transparency coefficient N M = K λ N t . For example, for KrAO it is indicated on average as 0.73. For higher altitude observatories, the atmosphere is more transparent. An obstacle in the form of the atmosphere will meet on the path of the photons again when the reflected photons return to Earth - the result will have to be multiplied once again by the transparency coefficient of the atmosphere K λ.

The beam fired from the laser diverges. There are two fundamental reasons for this. The first is diffraction beam expansion. It is defined as the ratio of the wavelength of light to the diameter of the beam. Therefore, in order to reduce it, it is necessary to increase the diameter of the beam. To do this, the laser beam is expanded and passed through the same telescope, which will then catch the response photons. The switching is carried out by a reversible mirror - given that the response photons will arrive only after 2.5 seconds, this is not at all difficult to ensure. For a telescope with an output diameter of 3 meters, the diffraction expansion of the beam is only 0.05" (arcsecond). The second reason is much stronger - turbulence in the atmosphere. It ensures the beam divergence at a level of approximately 1". This reason is fundamentally irremovable. The only way to combat it is to take the telescope outside the atmosphere.

So, the beam at the exit from the atmosphere has a divergence θ. For small angles θ, one can use the approximation θ = tan(θ) = sin(θ). Consequently, the beam will illuminate a spot with a diameter of D = Rθ, where R is the distance to the Moon (average 384,000 km, maximum 405,696 km, minimum 363,104 km). A beam with a divergence of 1" will illuminate a spot on the Moon with a diameter of approximately 1.9 km. The area of ​​the spot, as is known from the geometry course, is equal to .

The amount of light entering the telescope as a result of reflection from the EO or lunar soil is proportional to the area of ​​the telescope. For a telescope with diameter d, the area is .

In the case of reflection from the CR, not all photons that hit the Moon will hit the CR and be reflected. The number of photons reflected from the device is proportional to the area of ​​the reflector S 0 and its reflection coefficient K 0 . (This is provided that you have touched the device with at least the edge of the spot.) For French-made reflectors, the total area is 640 cm 2 with a reflection coefficient of 0.9, but we must remember that for prisms with a triangular front face, the working area is 2/3 of the total. The American ones were made of non-metalized quartz prisms and had a reflection coefficient three times less, but a larger area - the IR allegedly delivered by the Apollo 11 and Apollo 14 expeditions is 0.1134 m 2, Apollo 15 - 0.34 m 2 ( NASA-CR-113609). As a result, the number of photons that will be reflected from the CR will be .

In fact, the distribution of photons over the spot area is significantly uneven:

However, when summing up the results over several laser “shots” in order to isolate the useful signal from the background noise, this unevenness will be smoothed out.

Not all photons reflected from the EO will end up in the telescope. The reflected beam has a divergence θ" and will illuminate a spot on Earth with a diameter of L=Rθ". The area of ​​the spot on the Earth over which the reflected beam will be distributed is equal to . From this spot, the number of photons will fall into the telescope (if it does, which also needs to be checked). For French IOs installed on lunar rovers, the divergence of the reflected beam is indicated as 6" (for the wavelength of a ruby ​​laser 694.3 nm), which gives the diameter of the reflected spot on Earth 11 km; the American ones were made of smaller triple prisms, and therefore had a slightly a large divergence of 8.6" (also for the ruby ​​laser wavelength of 694.3 nm), the diameter of the spot on Earth will be about 16 km. In fact, the divergence of the reflected beam is determined by diffraction, i.e. the ratio of the laser wavelength to the aperture of one element UO θ" = 2.44 λ/D RR. Therefore, the use of a green laser with a wavelength of 532 nm may well be justified - despite the greater absorption and scattering of green light in the earth's atmosphere compared to red and infrared.

As we can see, we obtained practically the same formula that was indicated in the work of Kokurin et al., only in that work the transmission coefficients in the transmitting and receiving paths and the efficiency of quantum conversion of the photodetector were added (how many photons from the number that hit the telescope will be recorded in the form electrical signal). What is still missing is the dependence of the effective reflection area on the angle of incidence, i.e. the formulas are derived from the assumption that the angle of incidence of the locating beam on the target is close to normal. In fact, the dependence is like this:

In the case of reflection from the ground, most of the light will be absorbed, and the remaining will be scattered according to a law close to Lambertian (uniformly in all directions), in a solid angle of 2π steradians. In fact, the reflection from the Moon is somewhat trickier - the lunar soil has pronounced backscattering and oppositional effects, which lead to the fact that the lunar soil reflects 2-3 times more strictly in the opposite direction than a conventional Lambertian (matte) surface. Roughly speaking, the entire surface of the Moon acts as a corner reflector, although not a very good one.

The average albedo of the Moon is considered to be 0.07, although in different places on the visible surface of the Moon the albedo ranges from 0.05 to 0.16. (UPD: According to the latest data obtained by the LOLA laser altimeter, when reflected strictly back, the albedo can reach as much as 0.33, and in some permanently dark craters at the south pole even 0.35!)

We check which part of the illuminated spot will fall into the telescope. The field of view of a telescope is determined by its maximum magnification, which is determined by its diameter. The calculation for the CrAO telescope with a diameter of 2.64 m gives a field of view of 22", the work gives a value of 15" - the values ​​are close. The size of the illuminated spot is usually smaller, so that the entire spot appears in the field of view of the telescope.

The number of photons reflected from the lunar soil and entering the telescope is equal to .

From here we derive a formula for assessing the effectiveness of using a corner reflector as the ratio of the brightness of the target to the brightness of the lunar soil. A quick glance at this formula is enough to see that in order to increase the level of the response signal from the device compared to reflection from the ground, it is necessary to reduce the divergence angle of the locating laser beam - the dependence is quadratic.

(UPD: “Lunokhod-1”, although it is positioned poorly, is still visible. The calculated angle of incidence at its EO is 31.5 degrees from the normal (without taking into account libration), at this angle the EPR decreases by an order of magnitude and the spread of the impulse response from -due to the non-perpendicularity of the target beam to the locating beam. But for Lunokhod-2, the calculated angle of incidence is approximately 70 degrees from the normal - the angle is completely prohibitive even for a quartz target beam. No libration will help.)

One and a half hundred photons should fall into the telescope from the device, about 5 from the ground, and Aleshkina writes about “1 photon per 10-20 shots.” What does this mean? Even fewer photons are recorded than should have been from the ground!

And that's how it should be! We recall that when located away from the subterral point, the surface of the Moon is significantly non-perpendicular to the beam, therefore, the reflected signal is smeared in time,

and the temporal filter cuts out from it only those photons that correspond to the expected result.


If we remember that the surface of the Moon is not perfectly smooth, and there are mountains and craters on it, then the presence of a crater wall or mountain slope facing the Earth, onto which the laser locating beam falls perpendicularly, will give exactly the same time-compact signal as and reflected from the US, but of lower intensity.

If we weaken the calculated signal from the ground as the ratio of the area of ​​the lunar surface perpendicular to the locating beam to the cross-sectional area of ​​the locating beam, we will obtain full agreement of the experimental results with the calculation for the hypothesis with reflection from the ground. Considering that the diameter of the locating beam on the Moon is 2-7 km, then mountains or crater walls 2-3 km high are already enough, and there are plenty of such mountains and craters on the Moon. Moreover, a perfectly flat surface is not even required. As follows from the calculation, with an albedo of 0.16 (and the mountains on the Moon are lighter than the seas), the calculated number of photons from the ground exceeds the experimental values ​​by approximately 3 times, i.e. To coincide with the calculation, it is enough that only a third of the illuminated spot falls on a surface lying on the expected plane. The remaining 2/3 can have any relief.


The red line marks a conditional surface, the reflected signal from which will pass through the time filter. Ideally, this would be a fragment of a sphere with a radius of 380,000 km and centered approximately at the center of the Earth. Such a fragment of a sphere differs little from a plane.

The hypothesis with the reflection of the signal from the control device is not confirmed by published experimental data - the error is not by percentages, not even by times, but by orders of magnitude.

In general, everything is clear to me with our applied astronomy -

Laser ranging is the field of optoelectronics that deals with detecting and determining the location of various objects using electromagnetic waves in the optical range emitted by lasers. Objects of laser ranging can be tanks, ships, missiles, satellites, industrial and military structures. In principle, laser ranging is carried out using the active method. We already know that laser radiation differs from temperature radiation in that it is narrowly directed, monochromatic, has high pulse power and high spectral brightness. All this makes optical location competitive in comparison with radar, especially when used in space (where there is no absorbing influence of the atmosphere) and under water (where there are windows of transparency at a number of waves in the optical range).

Laser ranging, like radar, is based on three main properties of electromagnetic waves:

1. The ability to be reflected from objects. The target and the background on which it is located reflect the radiation falling on them differently. Laser radiation is reflected from all objects: metallic and non-metallic, from forests, arable land, and water. Moreover, it is reflected from any objects whose dimensions are smaller than the wavelength, better than radio waves. This is well known from the basic principle of reflection, which states that the shorter the wavelength, the better it is reflected. The power of the reflected radiation in this case is inversely proportional to the wavelength to the fourth power. A laser locator fundamentally has a greater detection ability than a radar - the shorter the wavelength, the higher it is. That is why, as radar developed, there was a tendency to move from long waves to shorter ones. However, the manufacture of radio frequency generators emitting ultra-short radio waves became increasingly difficult, and then reached a dead end.

The creation of lasers opened up new perspectives in location technology.

2. Ability to spread in a straight line. The use of a narrowly directed laser beam, which scans the space, allows you to determine the direction to the object (target bearing).

This direction is found by the location of the axis of the optical system that generates the laser radiation (in radar - in the direction of the antenna). The narrower the beam, the more accurately the bearing can be determined. Let us determine the directivity coefficient and the diameter of the antenna using the following simple formula,

G= 4p*S

where G is the directivity coefficient, S is the antenna area, m2, / is the radiation wavelength μm.

Simple calculations show that in order to obtain a directivity coefficient of about 1.5 when using radio waves in the centimeter range, you need to have an antenna with a diameter of about 10 m. It is difficult to install such an antenna on a tank, much less on an aircraft. It is bulky and non-transportable. You need to use shorter waves.

The angular angle of a laser beam made using a solid-state active substance is known to be only 1.0 - 1.5 degrees and without additional optical focusing systems (antennas). Consequently, the dimensions of a laser locator can be significantly smaller than a similar radar. The use of small-sized optical systems will make it possible to narrow the laser beam to several arc minutes, if the need arises.

3. The ability of laser radiation to propagate at a constant speed makes it possible to determine the distance to an object. So. The pulse ranging method uses the following ratio:

L= ctAnd

Where L - distance to the object, km, C - radiation propagation speed km/s, t and - time of passage of the pulse to the target and back, s.

Consideration of this relationship shows that the potential accuracy of range measurement is determined by the accuracy of measuring the time it takes for the energy pulse to travel to the object and back. It is absolutely clear that the shorter the pulse, the better (if there is a good bandwidth, as radio operators say). But we already know that the physics of laser radiation itself provides the possibility of obtaining pulses with a duration of 10-7 - 10-8 s. And this provides good data to the laser locator.

What parameters are used to characterize a locator? What are his passport details? Let's look at some of them, see Fig.

First of all, the zone. It is understood as the region of space in which observation is carried out. Its boundaries are determined by the maximum and minimum range and viewing limits in elevation and azimuth. These dimensions are determined by the purpose of the military laser locator.

Another locator parameter is the viewing time. It refers to the time during which the laser beam provides a single overview of a given volume of space.

The next parameter of the locator is the determined coordinates. they depend on the purpose of the locator. If it is intended to determine the location of ground and surface objects, then it is enough to measure two coordinates: range and azimuth. When observing aerial objects, three coordinates are needed. These coordinates should be determined with a given accuracy, which depends on systematic and random errors. Their consideration is beyond the scope of this book. However, we will use such a concept as resolving power. Resolution means the ability to separately determine the coordinates of closely located targets. Each coordinate has its own resolution. In addition, such a characteristic as interference immunity is used. This is the ability of a laser locator to operate in conditions of natural (Sun, Moon) and artificial interference.

And a very important characteristic of a locator is reliability. This is the property of a locator to maintain its characteristics within established limits under given operating conditions.

For a diagram of a laser locator designed to measure four main parameters of an object (range, azimuth, elevation and speed), see Fig. on page 17. It is clearly seen that structurally such a locator consists of three blocks: transmitting, receiving and indicator. The main purpose of the transmitting locator is to generate laser radiation, its formation in space, time and direction to the object area. The transmitting unit consists of a laser with an excitation source, a Q-switch, a scanning device that ensures the sending of energy in a given area according to a given scanning law, as well as a transmitting optical system.

The main purpose of the receiving unit is to receive radiation reflected by an object, convert it into an electrical signal and process it to extract information about the object. It consists of a receiving optical system, an interference filter, a radiation receiver, as well as units for measuring range, speed and angular coordinates.

The indicator block is used to indicate in digital form information about the target parameters.

Depending on the purpose for which the locator serves, there are: rangefinders, speed meters (Doppler locators), locators themselves (range, azimuth, and elevation).

LASER LOCATOR DIAGRAM

receiver radiation

optical filter

receiving optical system

INDICATOR BLOCK

RECEIVING BLOCK

range measurement unit

speed measurement unit

angular coordinate measurement unit

Elevation angle

Speed

power unit

Laser location in foreign press refers to the field of optoelectronics, which deals with the detection and location of various objects using electromagnetic waves of the optical range emitted by lasers. Objects of laser ranging can be tanks, ships, missiles, satellites, industrial and military structures. Fundamentally Laser ranging is carried out using the active method. We already know that laser radiation differs from temperature radiation in that it is narrowly directed, monochromatic, has high pulse power and high spectral brightness. All this makes optical ranging competitive with radar, especially when used in space (where there is no absorbing influence of the atmosphere) and under water (where there are transparency windows for a number of waves in the optical range). Laser ranging, like radar, is based on three main properties of electromagnetic waves: 1. The ability to be reflected from objects. The target and the background on which it is located reflect the radiation incident on them differently. Laser radiation is reflected from all objects: metallic and non-metallic, from forests, arable land, and water. Moreover, it is reflected from any objects whose dimensions are smaller than the wavelength, better than radio waves. This is well known from the basic principle of reflection, which states that the shorter the wavelength, the better it is reflected. The power of the reflected radiation in this case is inversely proportional to the wavelength to the fourth power. A laser locator fundamentally has a greater detection ability than a radar - the shorter the wave, the higher it is. That is why, as radar developed, a tendency to move from long waves to shorter ones appeared. However, the manufacture of radio frequency generators emitting ultrashort radio waves became increasingly difficult, and then came to a standstill. The creation of lasers opened up new perspectives in location technology. 2. Ability to spread in a straight line. The use of a narrowly directed laser beam, which scans the space, allows you to determine the direction to the object (target bearing) (Fig. 40). This direction is found by the location of the axis of the optical system that generates the laser radiation (in radar - in the direction of the antenna). The narrower the beam, the more accurately the bearing can be determined. Let us determine the directivity coefficient and antenna diameter using the following simple formula Rice. 40. Object coordinates: a - bearing or azimuth; elevation angle where the directivity coefficient, antenna area, is the radiation wavelength, microns. Simple calculations show that in order to obtain a directivity coefficient of about 1.5° when using radio waves in the centimeter range, you need to have an antenna with a diameter of about 10 m. Such an antenna is difficult to install on a tank, much less on an aircraft. It is bulky and non-transportable. You need to use shorter waves. The angular angle of a laser beam made using a solid-state active substance is known to be only this, and without additional optical focusing systems (antennas). Consequently, the dimensions of a laser locator can be significantly smaller than a similar radar. The use of small-sized optical systems will make it possible to narrow the laser beam to several arc minutes, if the need arises. 3. The ability of laser radiation to propagate at a constant speed makes it possible to determine the distance to an object. Thus, with the pulse ranging method, the following relationship is used: where the distance to the object is the speed of radiation propagation, the time it takes for the pulse to travel to the target and back, s. Consideration of this relationship shows that the potential accuracy of range measurement is determined by the accuracy of measuring the time it takes for the energy pulse to travel to the object and back. It is absolutely clear that the shorter the pulse, the better (if there is a good bandwidth, as radio operators say). But we already know that the physics of laser radiation itself provides the possibility of obtaining pulses with a duration of . And this provides good data to the laser locator. What parameters are used to characterize a locator? What are his passport details? Let's look at some of them. First of all, the coverage area. It is understood as the region of space in which observation is carried out. Its boundaries are determined by the maximum and minimum operating ranges and viewing limits in elevation and azimuth. These dimensions are determined by the purpose of the military laser locator. Another locator parameter is review time. It refers to the time during which the laser beam produces a single survey of a given volume of space. The next locator parameter is the determined coordinates. They depend on the purpose of the locator. If it is intended to determine the location of ground and surface objects, then it is enough to measure two coordinates: range and azimuth. When observing aerial objects, three coordinates are needed. These coordinates should be determined with a given accuracy, which depends on systematic and random errors. Their consideration is beyond the scope of this book. However, we will use such a concept as resolution. Resolution means the ability to separately determine the coordinates of closely located targets. Each coordinate has its own resolution. In addition, such a characteristic as noise immunity is used. This is the ability of a laser locator to operate in conditions of natural (Sun, Moon) and artificial interference. (click to view scan) And a very important characteristic of a locator is reliability. This is the property of a locator to maintain its characteristics within established limits under given operating conditions. A diagram of a laser locator designed to measure four main parameters of an object (range, azimuth, elevation and speed) is shown in Fig. 41. It can be clearly seen that such a locator consists of three blocks: transmitting, receiving and indicator. The main purpose of the transmitting unit is to generate laser radiation, its formation in space, time and direction to the object area. The transmitting unit consists of a laser with an excitation source, a Q-switch, a scanning device that ensures the sending of energy in a given area according to a given scanning law, as well as a transmitting optical system. The main purpose of the receiving unit is to receive radiation reflected by an object, convert it into an electrical signal and process it to extract information about the object. It consists of a receiving optical system, an interference filter, a radiation receiver, as well as units for measuring range, speed and angular coordinates. The indicator block is used to indicate in digital form information about the target parameters. Depending on the purpose for which the locator serves, there are: rangefinders, speed meters (Doppler locators), locators themselves (range, azimuth and elevation). Did you like the article? Share with your friends! Share on Facebook Read also The photograph shows a view of the Earth from lunar orbit. 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