RU2422853C1 - Instrument for statistical analysis of power distribution in glare re-reflections of continuous laser radar radiation from sea surface - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: proposed instrument comprises single-frequency CO2-continuous laser, matrix photo receiver, transceiver lens and laser beam drive. Matrix photo receiver is built around "cadmium-mercury-tellurium" elements cooled by liquid nitrogen. Transceiver lens generated CO2-continuous laser radiation, receives glare re-reflections and record them in matrix photo receiver. Matrix photo receiver elements are connected via low-noise amplifiers with integrators. Outputs of the latter are connected with analogue memory devices. Cloak pulse generator is connected in series with binary counter with digit outputs connected with analogue decoder. Decoder data inputs are connected with analogue memory outputs. Binary counter overflow signal output is connected to reset device of all integrators and analogue memories. Output of analogue decoder is connected via serial receiving bus with ADC. ADC code output, digit outputs and those of binary counter overflow signal are connected to personal computer with monitor to memorise and display images of glare re-reflections. ^ EFFECT: provision of important data on glare signal power and statistics of distribution of illuminated sea surface. ^ 1 dwg

Description

The invention relates to the field of instrumentation and can be used in the laser location of low-flying sea-based missiles, for example, the Harpoon type, used by Argentina against a British ship in a military conflict in the 80s of the last century due to the identification of the Malvinas (Falkland) Islands in waters of South America, as well as the result of the alleged use against Russian ships in the Georgian-Abkhaz military confrontation in the Black Sea in August 2008.

Missiles flying low above sea level are a formidable weapon, because their radar detection and auto tracking along angular coordinates is significantly complicated due to their very small effective scattering surface. By means of laser Doppler location, this problem is basically solvable, but requires the use of single-frequency continuous-wave lasers, for example, CO ₂ lasers, increased radiation power (of the order of 1 kW or more) with a sufficient width of the Doppler contour and high short-term frequency stability, which is practically quite difficult [1-4]. Such locators use channels for processing received signals based on dispersion delay lines as optimal filters, which significantly increases the energy signal-to-noise ratio [5-14].

As is known, the signal-to-noise ratio µ at the input of the optimal photodetector is determined by the expression (S / N) _ВХ = µ _ВХ = (2E _C / G _Ш ) ^1/2 , where Е _С = P _C τ _И is the energy [J] of the received signal (optical radiation at the photodetector), G _Ш - spectral noise density reduced to the input of the photodetector [W / Hz], P _C and τ _И - power [W] and duration [sec] of radiation at the photodetector input. Using optimal filtering of the received signals using dispersion delay lines (DLS), it is possible to increase the signal-to-noise ratio at the output of the filter μ _{OUT by} (V) ^1/2 times, where B = ΔF _LZ τ _LZ is the base of the DLZ, and ΔF _LZ and τ _LZ - respectively, the working bandwidth and the duration of the impulse response of the DLZ. Thus, the probability of the correct detection of p _OBN signals at a given probability of false alarms p _LT is determined from the well-known expression:

_OPL = F p (μ _OUT -α _n), where F (x) = (1 / 2π) ∫exp (-t ^2/2) dt - integral probabilities. α _П = Ф ^-1 (1-р _ЛТ ) is the relative level of the threshold limit of the signal compressed in the DLS, Ф (х) ^-l is the inverse operator of the integral Ф (х). Therefore, the value of p _OBN is determined by the energy E _{C of the} received signals at the input of the photodetector.

The resolution of the contradictions between the increase in the energy potential of the locator (the limiting detection range of a small target) and the simplification of the procedure for measuring the main characteristics of the located objects - their flight altitude, slant range and velocity vector (including the radial velocity parameter) is achieved using the location method known from the RF patent No. 2296350 (published in Bulletin No. 9 of 03/27/2007) by the same author [15]. The known method is based on the use of a combination of the Doppler principle of location with the triangulation method of target determination. The latter is achieved through the use of glare reflected from the target at different angles of radiation from the sea surface, the radiation from which comes to the locator at different measured angles and with Doppler frequency shifts as a function of the reflection angles of the incident radiation from the target surface of the target. By measuring the angles of arrival of radiation from the glare of the sea surface by a photosensitive receiving matrix and by measuring the values of Doppler frequency shifts in a multichannel optimal filtering unit based on heterodyne reception methods using multichannel DLS, it is possible to reconstruct the current target location and its velocity vector by statistical averaging methods.

In this location method, based on sensing a diffractively limited object moving above the surface of the sea (ocean), unmodulated emissions from a single-frequency continuous laser and multichannel coherent processing of received radiation by a matrix photodetector with the determination of Doppler frequency shifts in the reflected radiation and subsequent multichannel parallel matched filtering radio signals, distinctive operations are as follows. The coherent reception and processing is additionally and simultaneously subjected to radiation reflected from several glare of the sea surface, arriving at the photodetector array from different randomly distributed angular directions, and the Doppler frequency shifts in the received radiation for reflections reflected from the glare of the sea surface are determined in the corresponding channels associated with the photodetector array signals and the corresponding angular coordinates for these sea glare, calculate the current coordinates of the location of the object and that the true velocity, and the results are averaged statistically computing the totality of joint measurements of the above parameters. Thus, laser radiation is received by the photodetector array from flare reflections from the sea surface onto which the laser radiation scattered by a low-flying cruise missile (or invisible aircraft) is incident upon its illumination by the probe radiation of the locator.

For the practical implementation of this method and the corresponding location devices and their individual components proposed by the author [16-22], first of all, it is necessary to conduct a statistical study of the flashing re-reflections of laser radiation from the sea surface, for which it should be irradiated in a limited space and accumulate information about the distribution of reflections working for the reflections and the energy of these reflections. Such studies must be carried out in various zones of the sea surface and with various unrests of the sea surface - from calm to storm. In addition, these studies must be carried out by simulating the movement of a cruise missile above the sea surface by moving the illuminating spot of laser radiation at a speed corresponding to the speed of movement of the cruise missile.

The closest analogues of the claimed technical solution by the author were not found.

The purpose of the invention is determined by its name.

The claimed technical solution is a device for a statistical study of the energy distribution of glare of reflections of laser radiation from the sea surface - includes a single-frequency continuous-wave CO ₂ laser and an array photodetector based on cadmium-mercury-tellurium elements cooled by liquid nitrogen, as well as a transceiver lens, forming CO ₂ laser radiation in the form of spots illuminating the sea surface, sea of multipath receiving reflections of this spot area and focusing them on the photodetector arrays k, as well as a device for moving the illuminating laser spot along the sea surface, the elements of the photodetector matrix through low-noise amplifiers are connected to integrators, the outputs of which are connected to analog storage devices, in addition, the device includes a series-connected clock pulse generator, a binary counter, the discharge outputs of which are connected to analog decoder, the information inputs of which are connected to the outputs of analog storage devices, the output of the signal overflow binary counter it is connected to the reset device of all integrators and analog storage devices, and the output of the analog decoder is connected via a serial receiving bus to an analog-to-digital converter, the code output of which, as well as the outputs of the bits and the overflow signal of the binary counter, are connected to a personal computer (special processor) with a monitor for storing and displaying on the monitor screen patterns of glare reflections with a frame-by-frame tabular indication of the energy distribution of the corresponding glare reflections grain radiation in the considered area of the sea surface.

The device is clear from the attached drawing and contains the following nodes and blocks.

1. A single-frequency CO ₂ laser of continuous action;

2. Matrix photodetector (on the elements "cadmium-mercury-tellurium");

3. Transceiver lens;

4. Reflector homodyne channel mixing;

5. Translucent reflector (low transmittance);

6. A moving device illuminating the sea surface spots;

7. Multichannel block of low noise amplifiers;

8. Multichannel unit of integrators;

9. Multichannel block of analog storage devices;

10. The clock generator;

11. Binary counter;

12. Analog decoder;

13. The reset device (information signals in the blocks of integrators 8 and analog storage devices 9);

14. An analog-to-digital converter;

15. Personal computer (special processor);

16. Monitor (information display);

17. The area of the sea surface illuminated by laser radiation is a spot (circled by a dashed curve).

Consider the action of the claimed device.

The radiation of a single-frequency continuous-wave CO ₂ laser 1 through a focusing transceiver lens 3 is directed using a moving device illuminating the sea surface of the spot 6 into the zone of interest of the sea surface 17, which is reflected by the glare of the latter back to the transceiver lens 3 and focuses on the corresponding elements array photodetector 2, containing mn elements from the ternary compound "cadmium-mercury-tellurium", cooled with liquid nitrogen. These elements have the best threshold sensitivity to radiation with a wavelength of λ = 10.6 μm (of the order of 2 · 10 ^-20 W / Hz in the mode of homodyne (or heterodyne, as in Doppler locators) reception. The latter is provided by irradiating the matrix photodetector with laser radiation using a translucent reflector 5 with low transmittance and a forming reflector 4 with the required curvature of the reflecting surface.The matrix photodetector 2 has m rows and n columns - total mn elements, each of which has a size commensurate with angles m with the resolution of the used transceiver lens 3. Using mn elements of the matrix, the photodetector “sees” the spot of the illuminated zone of the sea surface. Within this spot, taking into account the dynamics of the sea surface and the speed of movement of the illuminating spot, randomly following on time and in space of the illuminated spot appear on it sea surface specular reflections, each of which has on the photodetector elements S _jk certain power value P _C (S _jk) and the lifetime τ _and (S _jk), where the indices j and k indicate by dix this element in the matrix (j = 1, 2, 3, ... m and k = 1, 2, 3, ... n). Each of the elements of the matrix photodetector has a certain value of the volt-watt characteristic and converts the absorbed power of the optical signal P _C (S _jk ) into the value of the corresponding voltage u _jk (t), which is a function of time. This voltage is then amplified in the low-noise amplifier of the jk-th channel of the multi-channel block of low-noise amplifiers 7 to the value U (t) _jk = Кu _jk (t), where К is the gain. The amplified signals are then acted upon by integrators as part of a multi-channel unit of integrators 8, which makes it possible to estimate the ENERGY of laser reflection, acting on the S _jk element of the matrix photodetector, according to the formula:

где α - вольт-ваттная чувствительность элемента [В/Вт], τ - постоянная интегрирования [сек]. Напряжение U_И(jk) на выходе интегратора, однозначно определяющее энергию E_C(jk), задается в виде:

where α is the volt-watt sensitivity of the element [V / W], τ is the integration constant [sec]. The voltage U _AND (jk) at the output of the integrator, which uniquely determines the energy E _C (jk), is set in the form:

The voltages from the outputs of jk-integrators are stored in the corresponding analog memory cells of the multichannel block of analog memory devices 9 within the time cycle T of accumulating information on all working elements of the matrix photodetector 2. The duration of this cycle is T = mn / F, where F is the pulse repetition rate, generated in the clock generator 10. Clock pulses are fed to the binary counter 11, which has r = log ₂ (mn) binary bits (and r is an integer). For example, if m = n = 128, then r = 14 bits. The binary counter 11 sets the addresses of the elements of the matrix photodetector 2, as well as the addresses of the analog memory devices in the multi-channel block 9. The binary address code from the output of the binary counter 11 is fed to the address input of the analog decoder 12, the information inputs of which are connected to the outputs of the analog memory devices of the multi-channel block 9 . At the same time, at the output of the analog decoder 12, a sequence of analog signals arises from all mn elements of the matrix with a clock frequency F, and the interrogation in the cycle continues time interval T. At the end of the cycle, the signal from the reset output of the binary counter 11 resets information from all integrators and analog storage devices of multi-channel blocks 8 and 9 using the reset device 13. The signals from the output of the analog decoder are fed to the input of a high-speed analog-to-digital converter 14, so for each address specified by the code from the output of the binary counter 11, there corresponds a code information signal equivalent to the energy E _C (jk) for the corresponding elements S _{jk of the} matrix receiver 2. Address and information code sequences are then fed to the inputs of a personal computer (special processor) 15 together with a reset signal to synchronize measurement cycles. The information obtained is processed according to the appropriate program and can be displayed for any of the cycles received in the memory of the personal computer 15 on the monitor 16 both in the form of tables and in the form of images of the distribution of glare on the sea surface with the display of energy from these glare (for example, by the brightness of glare ) Information on the elevation angle β of the illumination spot spot on the sea surface is fed to the personal computer, and a control signal for the device for moving the spot light illuminating the sea surface 6 is generated in the personal computer, that is, the rate of change of elevation angle dβ / dt at a given height h of the location of the device above sea level to simulate the movement of a cruise missile. So, with an inclined range to the center of the spot illuminating the sea surface D >> h (which is always true), we have the relation for angle β in the form sin β = h / D (angle β is counted from the horizontal plane). If we assume the case when the rocket moves toward the locator with a speed V, then the current value of the range in time will be expressed by the formula D (t) = DV t. Then we obtain sinβ (t) = h / (D-Vt), whence β (t) = arcsin [h / (D-Vt)].

The size H (t) of the cross-section of the area illuminated by the laser radiation (the cross-section of the spot) is determined by the number n of lowercase elements of the photodetector array 2, the maximum resolution of the transceiver lens is the radius of the Airy disk r _E = 1.22λf / d _OB , where d _OB and f is the diameter and focal length of the transceiver lens 3, respectively. Moreover, the size is H (t) = 2nr _E D (t) / f, and it is understood that the radius of the photodetector array element is comparable with the radius of the Airy disk r _E.

Using the inventive device, it is possible to carry out a statistical analysis of reflections of laser radiation from sea glare for both the static problem (at V = 0) and the dynamic (at V ≠ 0), that is, obtain important information to substantiate a fundamentally new way of locating low-flying winged animals proposed by the author sea-based missiles.

The repetition rate of clock pulses F in the clock generator 10 can be adjusted depending on the results of a statistical study and the speed of movement along the sea surface of the illuminating spot. One of the options for choosing the frequency F is matching the longitudinal size L (t) with the cycle duration T = mn / F, the number m of the column elements of the photodetector array 2 and the speed V of moving the spot towards the device. For example, a link L (t) = VT (t ) = 2mr _E D (t) ctgβ (t) / f≈2mr _E D (t) / f [h / (D-Vt)] ( as the small angles β (t), we have the approximate equality tgβ (t) ≈sinβ (t) .In this embodiment, the clock frequency of the clock 10 must change according to the law:

F (t) = mn / T (t) = nVhd _OB / 2,44λD (t) ² ,

and the change in the frequency F (t) as a function of time can be carried out under the control of a personal computer 15 (this connection is shown in the drawing, since another option for choosing the repetition rate of clock pulses can be used).

A corresponding study can be carried out at the Federal State Research Center “GOI named after S. I. Vavilova ”(St. Petersburg) using the waters of the Gulf of Finland, and the development of a matrix photodetector was carried out at the Istok NPO (Fryazino, Moscow Region). It is advisable to develop VLSI from elements of the matrix photodetector and elements of blocks 7, 8, and 9 in their integral design, and such a VLSI can be cooled with liquid nitrogen, which will additionally reduce the noise factor during the operation of low-noise amplifiers of the multi-channel block 7.

Information on photodetectors is contained in [23-29].

Literature

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Claims (1)

Device for statistical studies of the energy distribution of the laser radiation specular reflections from the sea surface comprises a CO ₂ laser single-frequency continuous matrix, and a photodetector based on a liquid nitrogen-cooled elements "mercury-cadmium-tellurium", and transceiving lens forming CO ₂ laser radiation in the shape of a spot illuminating the sea surface, receiving reflections from sea glare from the area of this spot and focusing them on a matrix photodetector, as well as a device for moving of a broadcasting laser spot on the sea surface, the elements of the photodetector matrix through low-noise amplifiers are connected to integrators, the outputs of which are connected to analog storage devices, in addition, the device includes a series-connected clock pulse generator, a binary counter, the discharge outputs of which are connected to an analog decoder, the information inputs of which connected to the outputs of the analog storage devices, the output of the binary counter overflow signal is connected to the reset device ex integrators and analog storage devices, and the output of the analog decoder is connected via a serial receiving bus to an analog-to-digital converter, the code output of which, as well as the outputs of the bits and the overflow signal of the binary counter, are connected to a personal computer (special processor) with a monitor for storing and displaying on the screen monitor of the pattern of flare reflections with a frame-by-frame tabular indication of the energy distribution of the corresponding flare reflections of the laser radiation in the considered sea surface area.