CN104898107B - A kind of MIMO Synthetic Aperture Laser Radar signal processing method - Google Patents

Abstract

The present invention provides a kind of MIMO Synthetic Aperture Laser Radar signal processing method, can effectively solve orientation high-resolution with distance to the contradiction of wide swath, realizes that high resolution wide swath SAL is imaged.The method comprises the following steps：N number of array element receives target echo signal respectively, and each array element does Residual video phase compensation deals and form simplification treatment to target echo signal；Target echo signal after each array element is processed the form simplification does fourier transform of azimuth；Observation vector to being made up of the target echo Doppler signal after the aliasing of N number of array element does ambiguity solution treatment；Each element without fuzzy target echo Doppler signal vector is arranged according to the numerical values recited of obscuring component, the fuzzy target echo Doppler signal of complete nothing is obtained using Doppler frequency spectrum splicing, so as to obtain Synthetic Aperture Laser Radar image.

Description

Multiple-sending multiple-receiving synthetic aperture laser radar signal processing method

Technical Field

The invention belongs to the technical field of communication, and particularly relates to a multiple-sending and multiple-receiving synthetic aperture laser radar signal processing method. The invention can be used for high-resolution wide-swath synthetic aperture laser radar imaging.

Background

The high resolution is higher for earth observation, the observation distance is longer, the mapping bandwidth is larger, and the Synthetic Aperture laser radar (SAL) and the microwave Synthetic Aperture Radar (SAR) have good complementary advantages in the direction of mutual cooperative work of various sensors. The SAR can be adopted for general survey in a large-range region, and then SAL can be adopted for higher-resolution observation of interested target facilities, wherein SAL is a necessary supplementary means for the current high-resolution earth observation means.

High-resolution observation with resolution improved by at least one order of magnitude compared with that of the current SAR can be realized at a long distance by adopting SAL technology. The synthetic aperture imaging lidar has a shorter operating wavelength than conventional synthetic aperture radars, which can yield images with much higher resolution (resolution of tens of microns to millimeters) than synthetic aperture radars.

The research of the SAL technology has been put into the development planning of national high-resolution earth observation, and the central laboratory of the science and technology of the radar signal processing defense of the university of the west ampere electronic technology finds that the mapping bandwidth of the SAL which is transmitted and received in a single transmission and single receiving mode is greatly limited in the research. The research of the SAL technology in foreign countries has carried out the airborne flight test of the single-transmitting single-receiving SAL, and the mapping bandwidth is only 2 meters when the distance is operated within one kilometer, so the property of the narrow mapping bandwidth of the single-transmitting single-receiving SAL severely restricts the practicability of the SAL technology.

How to solve the contradiction between the distance direction mapping band and the azimuth direction resolution and realize the high-resolution wide mapping band SAL imaging is the core problem of SAL research in the future.

Disclosure of Invention

In view of the above disadvantages, the present invention provides a method for processing signals of a multiple-transmit multiple-receive synthetic aperture laser radar, which performs a deblurring process on a multiple-transmit multiple-receive echo doppler signal to obtain a blur-free doppler spectrum for a later imaging.

The invention can effectively solve the contradiction between the azimuth direction high resolution and the distance direction wide swath, and realize the high resolution wide swath SAL imaging.

In order to achieve the purpose, the invention is realized by adopting the following technical scheme.

A method of multiple-transmit multiple-receive synthetic aperture lidar signal processing, the multiple-transmit multiple-receive synthetic aperture lidar having N array elements, the method comprising the steps of:

step 1, N array elements respectively receive target echo signals, and each array element performs residual video phase compensation processing and form simplification processing on the target echo signals to obtain the target echo signals after the form simplification processing; wherein, the array element is a multiple-sending multiple-receiving array element;

step 2, each array element performs azimuth Fourier transform on the target echo signal subjected to the form simplification processing to obtain a target echo Doppler signal subjected to aliasing;

step 3, forming an observation vector by the target echo Doppler signals of N array elements after mixing and overlapping, and performing ambiguity resolution processing on the observation vector to obtain an unambiguous target echo Doppler signal vector;

step 4, arranging all elements of the target echo Doppler signal vector without ambiguity according to the numerical value of the ambiguity component, and splicing by adopting Doppler frequency spectrum to obtain a complete target echo Doppler signal without ambiguity;

and 5, imaging the complete target echo Doppler signal without blurring to obtain a synthetic aperture laser radar image.

The invention has the following characteristics and further improvements:

(1) the step 1 specifically comprises the following substeps:

(1a) determining a target echo signal S received by the ith array element_i(t,τ)，

Where i is 1,2, …, N is the number of array elements, t is the fast time, τ is the slow time, R_refAs a central action distance, G_i,kRepresents the gain of the target echo transmitted by the kth array element and received by the ith array element, R_ipIndicating the distance from the ith array element to the target, R_kpThe distance between the kth array element and a target is shown, and gamma is the modulation frequency;

(1b) for the target echo signal S received by the ith array element_i(t, tau) performing residual video phase compensation processing to obtain a target echo signal S received by the ith array element after residual video phase compensation processing_i′(t,τ)，

Where c is the speed of light, f_cIs the carrier frequency;

(1c) the target echo signal S received by the ith array element after the phase compensation processing of the residual video_i' (t, tau) performing simplified form processing to obtain a target echo signal S received by the ith array element after the simplified form processing_i″(t,τ)，

Wherein,v is the azimuth velocity of the platform operation, a is the interval between two adjacent array elements, x_pIs the range position of the target, r_pA center offset distance;

(1d) sequentially taking 1,2, … and N, repeating the steps (1b) and (1c) to obtain target echo signals S of N array elements with simplified forms₁″(t,τ)，…,S_N″(t,τ)。

Further, in the above-mentioned case,

in sub-step (1a), the distance R from the ith array element to the target_ipThe method specifically comprises the following steps:

wherein i is more than or equal to 1, N is the number of the receiving and transmitting array elements, and v is the azimuth speed of the platform operation.

In sub-step (1a), the distance R from the kth array element to the target_kpThe method specifically comprises the following steps:

and k is less than or equal to N, N is the number of the transmitting and receiving array elements, and v is the azimuth speed of the platform in operation.

(2) The step 2 specifically comprises the following substeps:

(2a) the target echo signal S of the ith array element after form simplification processing_iPerforming azimuth Fourier transform to obtain target echo Doppler signal S of ith array element_i(t,f_a)，

Wherein i is 1,2, …, N, f_aIs the frequency of the doppler frequency and is,PRF is pulse repetition frequency;

(2b) the target echo Doppler signal S of the ith array element_i(t,f_a) Expressed as:

S_i(t,f_a)＝A_i(f_a)S₀(t,f_a)

wherein,

(2c) for the target echo Doppler signal S of the ith array element_i(t,f_a) Generating aliasing to obtain the target echo Doppler signal S after the aliasing of the ith array element_i′(t,f_a)，

Wherein, the fuzzy component q has a value range of q ═ M, -M +1, …, M-1, M;

(2d) sequentially taking i as 1,2, … and N to obtain a target echo Doppler signal S after N array elements are mixed and overlapped₁′(t,f_a)，…，S_N′(t,f_a)。

(3) The step 3 specifically comprises the following substeps:

(3a) the target echo Doppler signal S after the aliasing of the N array elements₁′(t,f_a)，…，S_N′(t,f_a) Constructing an observation vector X (t)_l,f_a)，

Wherein, t_lIs a certain moment in the fast time t, L ═ 1,2, …, L is the length of the fast time discrete sequence (·)^TRepresentation matrix transformationPlacing and operating;

(3b) determining the Doppler frequency f of the target echo signal according to the Capon beam forming principle_aAn adaptive optimal weight vector w of_opt(f_a(q))，

Wherein R (f)_a) Is the Doppler frequency f_aA statistical covariance matrix of the target echo signals of (f), v (f)_a(q)) is the Doppler frequency f_aThe guide vector of the q-th blur component of (1)^-1Representation matrix inversion operation, (-)^HRepresenting a matrix conjugate transpose operation;

(3c) according to the self-adaptive optimal weight vector w_opt(f_a(q)) to the observation vector X (t)_l,f_a) Weighting to obtain Doppler frequency f_aTarget echo Doppler signal vector S without ambiguity_DBF(t,f_a)。

Further, in the above-mentioned case,

the Doppler frequency f_aTarget echo Doppler signal vector S without ambiguity_DBF(t,f_a) Comprises the following steps:

S_DBF(t,f_a)＝[S₀(t,-M·PRF+f_a),......S₀(t,-M·PRF+f_a)]^T

wherein,

the multi-transmitting and multi-receiving SAL system provided by the invention can effectively solve the contradiction problem of distance direction wide swath and azimuth direction high resolution in the traditional single-transmitting and single-receiving SAL system, and realizes high resolution wide swath SAL imaging.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a basic process flow provided by an embodiment of the present invention;

FIG. 2 is a schematic diagram of an azimuth multiple-input multiple-output synthetic aperture laser radar system;

FIG. 3 is a diagram of a Doppler spectrum for a multiple transmit multiple receive SAL regime, with Doppler frequency on the abscissa in Hertz (Hz) and amplitude on the ordinate;

FIG. 4 is a schematic contour line diagram of 9-point target imaging in a single-shot SAL system, with the abscissa being a position unit and the ordinate being a distance unit;

FIG. 5 is a schematic diagram of an azimuthal pulse pressure profile of 9-point target imaging in a single-shot single-receive SAL system, with the abscissa being the azimuthal distance in meters (m) and the ordinate being the normalized amplitude in decibels (dB);

FIG. 6 is a schematic contour line diagram of imaging of 9 point targets in a multiple-shot SAL system, with the abscissa being a position unit and the ordinate being a distance unit;

FIG. 7 is a schematic diagram of an azimuthal pulse pressure profile of 9-point target imaging in an azimuthal multiple-shot SAL system, with the abscissa being the azimuthal distance in meters (m) and the ordinate being the normalized amplitude in decibels (dB);

FIG. 8 is a schematic diagram of the point target at the intermediate position in FIG. 6 after imaging and magnification, with the abscissa being the azimuth unit and the ordinate being the distance unit;

FIG. 9 is a schematic diagram of a cross-sectional view of the pulse pressure at the target location at the middle position in FIG. 6, with the abscissa being the azimuthal distance in meters (m) and the ordinate being the normalized amplitude in decibels (dB);

FIG. 10 is a schematic diagram of a cross-sectional view of target range pulse pressure at a mid-point in FIG. 6, with the abscissa being the azimuthal distance in meters (m) and the ordinate being the normalized amplitude in decibels (dB).

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, a specific implementation of the present invention includes the following steps:

and 1, respectively receiving target echo signals by N array elements, and performing residual video phase compensation processing and form simplification processing on the target echo signals by each array element to obtain the target echo signals subjected to the form simplification processing.

Wherein, the array element is a multiple-sending and multiple-receiving array element.

N array elements are array elements which are uniformly distributed in the azimuth direction, the N array elements transmit laser linear frequency modulation signals, a target echo signal is received in a dechirping (dechirping) mode, residual video phase compensation processing is firstly carried out on the target echo signal, then form simplification processing is carried out on the target echo signal which is subjected to the residual video phase compensation processing, and a target echo signal S of the N array elements after the form simplification processing is obtained₁″(t,τ)，…,S_N″(t,τ)。

The specific substeps of step 1 are:

(1a) determining a target echo signal S received by the ith array element_i(t, τ) is:

where c is the speed of light, f_cI is carrier frequency, i is 1,2, …, N is array element number, t is fast time, tau is slow time, R is_refAs a central action distance, G_i,kRepresenting the gain of the echo transmitted by the kth transmitting array element and received by the ith receiving array element, R_ipIndicating the distance, R, from the ith receiving array element to the point target_kpThe distance from the kth transmitting unit to the point target is shown, and gamma is the tuning frequency.

Referring to fig. 2, the focal length of the convex lens is f, N array elements are arranged along the track direction (only 3 array elements are drawn in the figure for simplicity of illustration) in the focal plane of the convex lens, the interval between two adjacent array elements is a, and the middle array element is placed at the coordinate (0, 0). The array element emits laser linear frequency modulation signals, the modulation frequency is gamma, and the target position of a point on the ground is p (x)_p,R_ref+r_p) Wherein x is_pIs the distance to the target location of the point, r_pAs the center deviates from the distance, a dechirping receiving mode is adopted to receive the echo signal, and then the target echo signal S received by the ith array element_i(t, τ) is:

in the above formula (1), c is the speed of light, f_cIs the carrier frequency, t is the fast time, τ is the slow time, R_refAs a central action distance, G_i,kRepresents the gain of the target echo transmitted by the kth array element and received by the ith array element, R_ipRepresents the ithDistance of array element to target, R_kpIndicating the distance of the kth array element to the target,

wherein,

in the above formula (2), i is more than or equal to 1, k is less than or equal to N, N is the number of array elements, v is the azimuth velocity of the platform in operation, and a is the interval between two adjacent array elements.

Target echo signal S received by ith array element_iThere are 3 exponential terms in (t, τ), the first exponential termDistance information representing the echo signal of the target, second exponential termAzimuth-doppler information representing the echo signal of the target, third exponential termAnd the residual video phase received by the target echo signal in a dechirping mode is shown.

(1b) For the target echo signal S received by the ith array element_i(t, tau) performing residual video phase compensation processing to obtain a target echo signal S received by the ith array element after residual video phase compensation processing_i' (t, τ) is:

where c is the speed of light, f_cIs the carrier frequency;

(1c) a target echo signal S received by the ith array element after the phase compensation processing of the residual video_i' (t, τ) for form simplificationThen, a target echo signal S received by the ith array element with a simplified form is obtained_i"(t, τ) is:

wherein,v is the azimuth velocity of the platform operation, a is the interval between two adjacent array elements, x_pIs the range position of the target, r_pIs the center offset distance.

The operating distance of the multi-transmitting and multi-receiving SAL is far greater than the length of the transmitting and receiving aperture, namely, the following requirements are met:

therefore, the range of the multiple-transmit multiple-receive SAL satisfies the following relationship:

in the above formula (5):

therefore, the form simplification processing is carried out on the formula (3) to obtain the target echo signal S received by the ith multi-transmitting and multi-receiving array element after the form simplification processing_i″(t,τ)：

(1d) The traversal is performed for i and the traversal is performed,repeating the steps (1b) and (1c) to obtain N target echo signals S of the multiple transmitting and receiving array elements after form simplification processing₁″(t,τ)，…,S_N″(t,τ)。

And 2, performing azimuth Fourier transform on the target echo signal subjected to the form simplification processing by each array element to obtain a target echo Doppler signal subjected to aliasing.

The step 2 specifically comprises the following substeps:

(2a) and performing azimuth Fourier transform on the target echo signal of the ith array element after the form simplification processing to obtain the target echo Doppler signal of the ith array element.

Simplifying the form of the processed target echo signal S of the ith array element by using stationary phase theorem_iPerforming azimuth Fourier transform to obtain target echo Doppler signal S of ith array element_i(t,f_a) Comprises the following steps:

wherein i is 1,2, …, N, f_aIs the frequency of the doppler frequency and is,PRF is the pulse repetition frequency.

(2b) The target echo Doppler signal S of the ith array element_i(t,f_a) Expressed as:

S_i(t,f_a)＝A_i(f_a)S₀(t,f_a) (9)

wherein,

(2c) for the target echo Doppler signal S of the ith array element_i(t,f_a) Generating aliasing to obtain the target echo Doppler signal S after the aliasing of the ith array element_i′(t,f_a) Comprises the following steps:

the fuzzy component q has a value range q of-M, -M +1, …, M-1, M, and the number of fuzzy components is 2 × M + 1.

A doppler spectrum diagram of a multiple transmit and multiple receive SAL is given with reference to fig. 3. As can be seen from fig. 2, the multiple-transmit and multiple-receive array elements are not strictly operated in the front side view mode, wherein the multiple-transmit and multiple-receive array element at the middle position is operated in the front side view mode, the multiple-transmit and multiple-receive array element at the front side is operated in the back squint mode, and the multiple-transmit and multiple-receive array element at the back side is operated in the front squint mode, so that the echo doppler frequency band of the multiple-transmit and multiple-receive SAL is wider than that of the single-transmit and single-receive system. We use a smaller pulse repetition frequency to ensure that a larger mapping bandwidth is obtained and therefore, undersampled for the entire doppler bandwidth, which can be aliased. Target echo Doppler signal S of ith array element_i(t,f_a) After aliasing is generated, obtaining a target echo Doppler signal after aliasing of the ith array element as follows:

the fuzzy component q has a value range q of-M, -M +1, …, M-1, M, and the number of fuzzy components is 2 × M + 1.

(2d) Traversing the i to obtain a target echo Doppler signal S after N array elements are mixed and overlapped₁′(t,f_a)，…，S_N′(t,f_a)。

And 3, forming observation vectors by the overlapped target echo Doppler signals of each array element, and performing deblurring processing on the observation vectors to obtain target echo Doppler signal vectors without blurring.

The specific substeps of step 3 are:

(3a) for the target echo Doppler signal S after N array elements are mixed and overlapped₁′(t,f_a)，…，S_N′(t,f_a) Constructing an observation vector X (t)_l,f_a)：

Obtaining the target echo Doppler signal S after all array elements are mixed and overlapped according to the step 2₁′(t,f_a)，…，S_N′(t,f_a) An observation vector X (t) is constructed_l,f_a)：

Wherein, t_lIs a certain time in the fast time t, L is 1,2, …, L is the length of the fast time discrete sequence. (.)^TRepresenting a matrix transpose operation.

(3b) Determining the Doppler frequency f of the target echo signal according to the Capon beam forming principle_aAn adaptive optimal weight vector w of_opt(f_a(q)) is:

doppler frequency f according to Capon beamforming principle_aAn adaptive optimal weight vector w of(f_a) The following conditions are satisfied:

v (f) in the above formula (14)_a(q)) is the Doppler frequency f_aThe steering vector of the q-th blur component.

R(f_a) Is the Doppler frequency f_aThe statistical covariance matrix of the echo signals, which can be estimated using the sample covariance matrix because the noise is not known,

the above type middle (·)^HRepresenting a matrix conjugate transpose operation, (-)^*Indicating that the signal takes the conjugate operation.

Obtaining the Doppler frequency f from equation (15)_aAn adaptive optimal weight vector w of_opt(f_a(q)) is:

the above type middle (·)^-1Representing a matrix inversion operation.

(3c) According to the self-adaptive optimal weight vector w_opt(f_a(q)) to the observation vector X (t)_l,f_a) Weighting to obtain Doppler frequency f_aTarget echo signal vector S without ambiguity_DBF(t,f_a) Comprises the following steps:

S_DBF(t,f_a)＝[S₀(t,-M·PRF+f_a),......S₀(t,-M·PRF+f_a)]^T

utilizing the self-adaptive optimal weight vector w obtained in the step (3b)_opt(f_a(q)) to the observation vector X (t)_l,f_a) Weighting to obtain Doppler frequency f_aIs a non-fuzzy signal vector S_DBF(t,f_a)：

S_DBF(t,f_a)＝[S₀(t,-M·PRF+f_a),......S₀(t,-M·PRF+f_a)]^T(18)

In the above formula, the first and second carbon atoms are,

the fuzzy component q has a value range q of-M, -M +1, …, M-1, M, and the number of fuzzy components is 2 × M + 1.

Step 4, arranging all elements of the target echo Doppler signal vector without ambiguity according to the numerical value of the ambiguity component, and obtaining the complete target echo Doppler signal without ambiguity by adopting Doppler frequency spectrum splicing

For target echo Doppler signal vector S without ambiguity_DBF(t,f_a) Of (5) each element S₀(t,p·PRF+f_a) Arranging according to the numerical value of the fuzzy component q, and performing Doppler frequency spectrum splicing to obtain a complete target echo Doppler signal S without fuzzy_UnAmb(t,f_a′)。

Referring to fig. 3, the target echo doppler signals without ambiguity are arranged according to the azimuth frequency sequence and spliced into a complete signal without ambiguity S_UnAmb(t,f_a') is:

wherein,

and 5, imaging the complete target echo Doppler signal without blurring to obtain a synthetic aperture laser radar SAL image.

The method comprises the following specific substeps:

(5a) introducing an azimuth matching function:

target echo Doppler signal S after azimuth matching_match(t_l,f_a') is:

(5b) order toA(f_a) At f_aThe taylor series expansion at 0 is approximated as:

equation (23) can thus be approximated as:

(5c) matching the direction of the approximate target echo Doppler signal S_match′(t_l,f_a') performing an inverse Fourier transform of azimuth and distance to obtain SAL image S_SAL(f_rτ) is:

in the above formula, A is an envelope, f_rIn order to be the distance-wise frequency,f_sfor sampling frequency, T_pIs the pulse width, B_aIs the doppler bandwidth.

So far, the imaging of the multiple-sending multiple-receiving synthetic aperture laser radar is completed.

The effectiveness of the invention in achieving synthetic aperture lidar imaging is further illustrated by simulations as follows.

1. Simulation conditions

For convenience, we use a three-transmit-three-receive mode, with simulation parameters as shown in table 1.

TABLE 1 SAL System simulation parameters for three-Transmit three-receive

If an azimuth 1.5mm resolution SAL image is to be achieved, the minimum pulse repetition frequency is required to be:

and the PRF of the actual transmitting signal is 10kHz, the data of three transmitting and receiving units are coherently combined into a full-resolution SAL image.

2. Emulated content

Three transmitting and receiving array elements are adopted for three transmitting and three receiving, and the positions of the three array elements are as follows: (-a,0), (0,0), (a,0), a is the transmit-receive element interval, and simulates 9 point targets on the ground. Fig. 4 is a contour diagram of 9-point target imaging in the single-shot single-receive SAL system, with the abscissa as the azimuth unit and the ordinate as the distance unit. Fig. 5 is an azimuthal pulse pressure profile of 9-point target imaging in single-shot single-receive SAL regime, with the abscissa being the azimuthal distance in meters (m) and the ordinate being the normalized amplitude in decibels (dB). Fig. 6 is a contour diagram of an image of a 9-point target in the multi-shot and multi-shot SAL regime, with the abscissa as the azimuth unit and the ordinate as the distance unit. Fig. 7 is an azimuthal pulse pressure profile of 9-point target imaging in an azimuthal SAL regime, with azimuthal distance in meters (m) on the abscissa and normalized amplitude in decibels (dB) on the ordinate. FIG. 8 is an enlarged view of the point target at the intermediate position in FIG. 6, with the abscissa being the azimuth unit and the ordinate being the distance unit. FIG. 9 is a plot of the azimuthal pulse pressure profile of the point target at the intermediate position in FIG. 6, with the abscissa being the azimuthal distance in meters (m) and the ordinate being the normalized amplitude in decibels (dB). FIG. 10 is a plot of the range-target pulse pressure profile at the mid-position in FIG. 6, with the abscissa being the azimuthal distance in meters (m) and the ordinate being the normalized amplitude in decibels (dB).

3. Analysis of simulation results

The pulse repetition frequency PRF of the single-transmit single-receive SAL system is about one third of the doppler bandwidth, and the azimuth doppler is overlapped three times, and it can be seen from fig. 4 and 5 that the doppler blur appears in the two-dimensional imaging image as dispersing a target point into three points, and besides the target appearing at the correct azimuth position, a false target appears on each of the left and right sides of the azimuth position. The azimuth multiple-transmitting multiple-receiving SAL system synthesizes large-bandwidth unambiguous data imaging by using echo data of 3 transmitting and receiving units in the azimuth direction, Doppler ambiguity can be eliminated, images after frequency band synthesis can be clearly seen through the images in fig. 6 and 7, a target point only appears at a correct azimuth position, and false targets are eliminated.

And selecting a middle point target of the 9 points to analyze the azimuth resolution and the compression effect of the single target image. From fig. 8 it can be seen that a single object is imaged resulting in a better cross-image. In the three-transmission three-receiving SAL system, three receiving and transmitting units in the azimuth direction are used for expanding the width of azimuth beams by three times, large-bandwidth non-fuzzy data are obtained through frequency band synthesis, and the azimuth resolution is improved by about three times. It can be seen from fig. 9 and 10 that the peak side lobe ratios of the azimuthal pulse pressure and the range pulse pressure are-13.24 dB and-13.27 dB, respectively, and the range compression effect and the azimuthal compression effect are good. The azimuth resolution of the single-transmitting single-receiving SAL system isThe azimuth resolution obtained by three-transmission three-receiving SAL system demodulation blurring and frequency band synthesis is about rho_am0.0012m, an improvement of about 3 times over single-shot single-receive SAL systems.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims (6)

1. A method for processing multiple-transmit multiple-receive synthetic aperture laser radar signals, the multiple-transmit multiple-receive synthetic aperture laser radar having N array elements, the method comprising:

step 1, N array elements respectively receive target echo signals, and each array element performs residual video phase compensation processing and form simplification processing on the target echo signals to obtain the target echo signals after the form simplification processing; wherein, the array element is a multiple-sending multiple-receiving array element;

the step 1 specifically comprises the following substeps:

(1a) determining a target echo signal S received by the ith array element_i(t,τ)，

$\begin{array}{c}{S}_i(t,\mathrm{\τ})=\underset{k=1}{\overset{N}{\Σ}}{G}_{i,k}\exp (-j\frac{2\mathrm{\π}}{c}\mathrm{\γ}(t-\frac{2R_{ref}}{c}\left)\right(R_{ip}+R_{kp}-2R_{ref}\left)\right)\\ \×\exp (-j\frac{2\mathrm{\π}}{c}{f}_c(R_{ip}+R_{kp}-2R_{ref}\left)\right)\exp \left(j\frac{4\mathrm{\π}\mathrm{\γ}}{c^2}{\left(\frac{R_{ip}+R_{kp}}{2}-R_{ref}\right)}^2\right)\end{array}$

Where i is 1,2, …, N is the number of array elements, t is the fast time, τ is the slow time, R_refAs a central action distance, G_i,kRepresents the gain of the target echo transmitted by the kth array element and received by the ith array element, R_ipIndicating the distance from the ith array element to the target, R_kpThe distance between the kth array element and a target is shown, and gamma is the modulation frequency;

(1b) for the target echo signal S received by the ith array element_i(t, tau) performing residual video phase compensation processing to obtain a target echo signal S received by the ith array element after residual video phase compensation processing_i′(t,τ)，

$\begin{array}{c}{S_i}^{\′}(t,\mathrm{\τ})=\underset{k=1}{\overset{N}{\Σ}}{G}_{i,k}\exp (-j\frac{2\mathrm{\π}}{c}\mathrm{\γ}(t-\frac{2R_{ref}}{c}\left)\right(R_{ip}+R_{kp}-2R_{ref}\left)\right)\\ \×\exp (-j\frac{2\mathrm{\π}}{c}{f}_c(R_{ip}+R_{kp}-2R_{ref}\left)\right)\end{array}$

Where c is the speed of light, f_cIs the carrier frequency;

(1c) the target echo signal S received by the ith array element after the phase compensation processing of the residual video_i' (t, tau) performing simplified form processing to obtain a target echo signal S received by the ith array element after the simplified form processing_i″(t,τ)，

$\begin{array}{c}{S_i}^{\′\′}(t,\mathrm{\τ})\≈\underset{k=1}{\overset{N}{\Σ}}{G}_{i,k}\exp (-j\frac{4\mathrm{\π}}{c}\mathrm{\γ}(t-\frac{2R_{ref}}{c}\left)\right(R_{\frac{i+k}{2}p}-R_{ref}\left)\right)\\ \×\exp (-j\frac{4\mathrm{\π}}{c}{f}_c(R_{\frac{i+k}{2},p}-R_{ref}\left)\right)\end{array}$

Wherein,v is the azimuth velocity of the platform operation, a is the interval between two adjacent array elements, x_pIs the range position of the target, r_pA center offset distance;

(1d) sequentially taking 1,2, … and N, repeating the steps (1b) and (1c) to obtain target echo signals S of N array elements with simplified forms₁″(t,τ)，…,S_N″(t,τ)；

Step 2, each array element performs azimuth Fourier transform on the target echo signal subjected to the form simplification processing to obtain a target echo Doppler signal subjected to aliasing;

step 3, forming an observation vector by the target echo Doppler signals of N array elements after mixing and overlapping, and performing ambiguity resolution processing on the observation vector to obtain an unambiguous target echo Doppler signal vector;

step 4, arranging all elements of the target echo Doppler signal vector without ambiguity according to the numerical value of the ambiguity component, and splicing by adopting Doppler frequency spectrum to obtain a complete target echo Doppler signal without ambiguity;

and 5, imaging the complete target echo Doppler signal without blurring to obtain a synthetic aperture laser radar image.

2. The multiple-shot multiple-receive synthetic aperture lidar signal processing method of claim 1, wherein in sub-step (1a), the distance R from the ith array element to the target_ipThe method specifically comprises the following steps:

$R_{ip}=\sqrt{{(R_{ref}+r_p)}^2+(v\mathrm{\τ}-x_p+(i-\left(\frac{N+1}{2}\right)\left)a\right)}$

wherein i is more than or equal to 1, N is the number of the receiving and transmitting array elements, and v is the azimuth speed of the platform operation.

3. The multiple-shot multiple-receive synthetic aperture lidar signal processing method of claim 1, wherein in sub-step (1a), the kth array element is directed to a targetDistance R of_kpThe method specifically comprises the following steps:

$R_{kp}=\sqrt{{(R_{ref}+r_p)}^2+(v\mathrm{\τ}-x_p+(k-\left(\frac{N+1}{2}\right)\left)a\right)}$

and k is less than or equal to N, N is the number of the transmitting and receiving array elements, and v is the azimuth speed of the platform in operation.

4. The multiple-shot multiple-reception synthetic aperture laser radar signal processing method according to claim 1, wherein the step 2 specifically includes the following sub-steps;

(2a) the target echo signal S of the ith array element after form simplification processing_iPerforming azimuth Fourier transform to obtain target echo Doppler signal S of ith array element_i(t,f_a)，

$S_i(t,f_a)=\underset{k=1}{\overset{N}{\Σ}}\begin{array}{c}{G}_{i,k}\exp (-j4\mathrm{\π}(R_{ref}+r_p)\sqrt{({\left(\frac{f_c+\mathrm{\γ}t}{c}\right)}^2-{\left(\frac{f_a}{2v}\right)}^2)}-\frac{2{\mathrm{\πf}}_a}{v}{x}_p)\\ \×\exp \left(j\frac{2{\mathrm{\πf}}_a}{v}\right(\frac{i+k}{2}-\frac{N+1}{2}\left)a\right)\end{array}$

Wherein i is 1,2, …, N, f_aIs the frequency of the doppler frequency and is,PRF is pulse repetition frequency;

(2b) the target echo Doppler signal S of the ith array element_i(t,f_a) Expressed as:

S_i(t,f_a)＝A_i(f_a)S₀(t,f_a)

wherein,

$\begin{array}{c}{S}_0(t,f_a)=\exp (-j4\mathrm{\π}(R_{ref}+r_p\left)\sqrt{({\left(\frac{f_c+\mathrm{\γ}t}{c}-\frac{2{\mathrm{\γR}}_{ref}}{c^2}\right)}^2-{\left(\frac{f_a}{2v}\right)}^2)}\right)\\ \×\exp (-j\frac{2{\mathrm{\πf}}_a}{v}{x}_p)\×\exp \left(j\frac{4\mathrm{\π}}{c}\mathrm{\γ}\right(t+\frac{f_c}{\mathrm{\γ}}-\frac{2R_{ref}}{c}\left)R_{ref}\right)\end{array};$

(2c) for the target echo Doppler signal S of the ith array element_i(t,f_a) Generating aliasing to obtain the target echo Doppler signal S after the aliasing of the ith array element_i′(t,f_a)，

${S_i}^{\′}(t,f_a)=\underset{q=-M}{\overset{M}{\Σ}}{A}_i(q\·PRF+f_a)S_0(t,q\·PRF+f_a)$

Wherein, the fuzzy component q has a value range of q ═ M, -M +1, …, M-1, M;

(2d) sequentially taking i as 1,2, … and N to obtain a target echo Doppler signal S after N array elements are mixed and overlapped₁′(t,f_a)，…，S_N′(t,f_a)。

5. The multiple-shot multiple-receiver synthetic aperture lidar signal processing method of claim 1, wherein step 3 comprises the following sub-steps:

(3a) the target echo Doppler signal S after the aliasing of the N array elements₁′(t,f_a)，…，S_N′(t,f_a) Constructing an observation vector X (t)_l,f_a)，

$X(t_l,f_a)\stackrel{\mathrm{\Δ}}{=}{\[{S_1}^{\′}(t_l,f_a),......{S_N}^{\′}(t_l,f_a)\]}^T$

Wherein, t_lIs a certain moment in the fast time t, L ═ 1,2, …, L is the length of the fast time discrete sequence (·)^TRepresenting a matrix transpose operation;

(3b) determining the Doppler frequency f of the target echo signal according to the Capon beam forming principle_aAdaptive optimal weight vector of (2)w_opt(f_a(q))，

$w_{opt}\left(f_a\right(q\left)\right)=\frac{R^{-1}\left(f_a\right)v\left(f_a\right(q\left)\right)}{v^H\left(f_a\right(q\left)\right)R^{-1}\left(f_a\right)v\left(f_a\right(q\left)\right)}$

Wherein R (f)_a) Is the Doppler frequency f_aA statistical covariance matrix of the target echo signals of (f), v (f)_a(q)) is the Doppler frequencyRate f_aThe guide vector of the q-th blur component of (1)^-1Representation matrix inversion operation, (-)^HRepresenting a matrix conjugate transpose operation;

(3c) according to the self-adaptive optimal weight vector w_opt(f_a(q)) to the observation vector X (t)_l,f_a) Weighting to obtain Doppler frequency f_aTarget echo Doppler signal vector S without ambiguity_DBF(t,f_a)。

6. The method of claim 5, wherein the Doppler frequency f is a frequency of multiple-shot synthetic aperture laser radar (MLSS)_aTarget echo Doppler signal vector S without ambiguity_DBF(t,f_a) Comprises the following steps:

S_DBF(t,f_a)＝[S₀(t,-M·PRF+f_a),......S₀(t,M·PRF+f_a)]^T

wherein,