A method for monopulse forward-looking scanning imaging focus compensation

Abstract

The application relates to a single-pulse forward-looking scanning imaging focus compensation method, and aims to solve the problem of imaging defocus caused by the angle measurement deviation of a nonlinear angle discrimination curve in the single-pulse angle measurement process of an existing single-pulse forward-looking scanning imaging result. The process comprises the following steps: 1, obtaining the pulse compression echo results of sum and difference channels, namely one-dimensional range images; 2, taking N pulse compression echoes of the center scanning angle of the sum channel, calculating the normalized amplitude variance, selecting a distance unit with the maximum amplitude of the one-dimensional range image and a normalized amplitude variance less than 0.12; 3, obtaining a time-frequency diagram, calculating an azimuth angle and recording the corresponding scanning angle; 4, in the distance unit, selecting each scanning angle respectively, repeating step 3 to obtain a curve, and fitting the curve with a polynomial; 5, obtaining a focused compensated image by using the corrected angle single-pulse projection. The application is used in the field of radar imaging.

Description

Technical Field

[0001] This invention relates to a focusing compensation method for single-pulse forward-looking scanning imaging results. Background Technology

[0002] Imaging of the forward-looking area is of paramount importance in military applications such as missile-borne seekers and civilian applications such as civil aviation takeoffs and landings. Monopulse forward-looking scanning imaging is a technique that transmits and receives radar signals through sum and difference channels, and performs range pulse compression processing, azimuth Doppler processing, and monopulse angle measurement followed by projection imaging on the echo signals. During transmission and reception, the antenna continuously scans. Monopulse angle measurement technology obtains the target's angle information from the sum and difference channels using a specific algorithm. However, due to the nonlinearity of the angle discrimination curve, the angle obtained for the same target at different scanning positions will have a certain deviation. When the distance between the target radars is large, this deviation will cause a significant position measurement error, manifesting as "defocus" in the imaging result, greatly reducing image quality. Since the quality of forward-looking imaging is crucial for subsequent judgment and response, focus compensation is extremely important. Summary of the Invention

[0003] The purpose of this invention is to solve the problem of defocusing in existing single-pulse forward-looking scanning imaging due to angle measurement deviation caused by nonlinearity of the angle discrimination curve during single-pulse angle measurement. Therefore, a focusing compensation method for single-pulse forward-looking scanning imaging results is proposed.

[0004] The specific process of a single-pulse forward-looking scanning imaging focus compensation method is as follows:

[0005] Step 1: Perform range processing and range migration correction on the sum and difference channel echo data of the single-pulse forward-looking imaging radar to obtain the pulse compression echo results of the sum and difference channels, i.e., the one-dimensional range image.

[0006] Step 2: Obtain the center scanning angle θ of the summation channel. scan0 Calculate the normalized amplitude variance from N pulse compression echoes. Selecting normalized amplitude variance And the distance unit t with the largest one-dimensional distance image amplitude c ;

[0007] Step 3: For the sum and difference channel distance units t respectively c The pulse compression data are processed by performing a short-time Fourier transform in the azimuth direction to obtain a time-frequency diagram. The maximum amplitude at the midpoint of the sum channel time-frequency diagram is selected, and the azimuth angle θ is calculated by combining it with the amplitude at the corresponding position in the difference channel time-frequency diagram. The corresponding scanning angle θ is then recorded. scan0 ;

[0008] Step 4: At distance cell t c In the middle, select each scanning angle θ respectivelyscan Repeat step three to obtain θ ~ θ + θ scan curve;

[0009] Using the polynomial f(θ) = a0 + a1θ + a2θ 2 +a3θ 3 +a4θ 4 +a5θ 5 Fit the curve;

[0010] Where a i , i = 1…5 are the polynomial coefficients;

[0011] Step 5: Use the formula θ′=θ-f0(θ) to correct the angle measurement values ​​of each scattering point in all range cells;

[0012] The new curve obtained by translating the curve vertically to the origin is f0(θ) = f(θ) - f(0);

[0013] The image with focus compensation is obtained by projecting the corrected angle using a single pulse.

[0014] The beneficial effects of this invention are as follows:

[0015] This invention further improves the focusing ability of the original single-pulse forward-looking scanning imaging, significantly enhancing the imaging quality. Under conditions of a signal-to-noise ratio of 15 dB, a target radar distance of 6 km, and low target density, the focusing ability of the imaging result is improved by approximately 10 times. Simultaneously, it greatly suppresses the broadening of the imaging result, thereby improving the imaging resolution. By using characteristic points selected using normalized amplitude variance to replace isolated scattering points, the application range of this method is expanded. Furthermore, this invention exhibits good robustness, still providing a certain degree of imaging quality improvement even in low signal-to-noise ratio, dense imaging scenarios. Attached Figure Description

[0016] Figure 1 This is a flowchart of the present invention;

[0017] Figure 2 Example of normalized magnitude variance calculation results for each distance cell;

[0018] Figure 3 The result image shows the one-dimensional distance image of scene 2 and the channel.

[0019] Figure 4 The time-frequency diagrams for scene 2 and channel 1025 distance unit are shown.

[0020] Figure 5 The relationship between the azimuth angles and sumA angle in scenarios 1, 2, and 3, and the fitted curve;

[0021] Figure 6a This is a traditional imaging result for Scene 1;

[0022] Figure 6b The focus compensation imaging result after adding this invention to Scene 1;

[0023] Figure 6c This is a traditional imaging result image for Scene 2;

[0024] Figure 6d The image shows the focus compensation imaging result after adding this invention to scene 2;

[0025] Figure 6e This is a traditional imaging result image for Scene 3;

[0026] Figure 6f The focus compensation imaging result after adding this invention to scene 3;

[0027] Figure 6g This is a traditional imaging result for Scene 4;

[0028] Figure 6h The focus compensation imaging result after adding this invention to scene 4;

[0029] Figure 7 This is a simulation diagram of the scattering point distribution in scenario 5.

[0030] Figure 8 This is a simulation diagram of the scattering point distribution in scenario 6.

[0031] Figure 9a The image shows the traditional imaging result for scene 5 with a signal-to-noise ratio of 30dB.

[0032] Figure 9b The focus compensation imaging result after adding this invention to scene 5 with a signal-to-noise ratio of 30dB;

[0033] Figure 9c The image shows the traditional imaging result for scene 5 with a signal-to-noise ratio of 15dB.

[0034] Figure 9d The image shows the focus compensation imaging result after adding this invention to scene 5 with a signal-to-noise ratio of 15dB.

[0035] Figure 10a The image shows the traditional imaging result for scene 6 with a signal-to-noise ratio of 30dB.

[0036] Figure 10b The focus compensation imaging result after adding this invention to scene 6 with a signal-to-noise ratio of 30dB;

[0037] Figure 10c The image shows the traditional imaging result for scene 6 with a signal-to-noise ratio of 15dB.

[0038] Figure 10d The image shows the focus compensation imaging result after adding this invention to scene 6 with a signal-to-noise ratio of 15dB. Detailed Implementation

[0039] Specific implementation method one: Combining Figure 1 , 2 This embodiment describes a single-pulse forward-looking scanning imaging focus compensation method as follows:

[0040] Step 1: Perform range processing and range migration correction on the sum and difference channel echo data of the single-pulse forward-looking imaging radar to obtain the pulse compression echo results of the sum and difference channels, i.e., the one-dimensional range image.

[0041] Step 2: Obtain the center scanning angle θ of the summation channel. scan0 Calculate the normalized amplitude variance from N pulse compression echoes. Selecting normalized amplitude variance And the distance unit t with the largest one-dimensional distance image amplitude c (Here, the sum channel is used to find the distance cell number that meets the criteria; this number also applies to the difference channel);

[0042] Step 3: For the sum and difference channel distance units t respectively c The pulse compression data are processed by performing a short-time Fourier transform in the azimuth direction to obtain a time-frequency diagram. The maximum amplitude at the midpoint of the sum channel time-frequency diagram is selected, and the azimuth angle θ is calculated by combining it with the amplitude at the corresponding position in the difference channel time-frequency diagram. The corresponding scanning angle θ is then recorded. scan0 ;

[0043] Step 4: At distance cell t c In the middle, select each scanning angle θ respectively scan Repeat step three to obtain θ ~ θ + θ scan curve;

[0044] Using the polynomial f(θ) = a0 + a1θ + a2θ 2 +a3θ 3 +a4θ 4 +a5θ 5 Fit the curve;

[0045] Where a i , i = 1…5 are the polynomial coefficients;

[0046] Step 5: Use the formula θ′=θ-f0(θ) to correct the angle measurement values ​​of each scattering point in all range cells;

[0047] The new curve obtained by translating the curve vertically to the origin is f0(θ) = f(θ) - f(0);

[0048] The image with focus compensation is obtained by projecting the corrected angle using a single pulse.

[0049] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that, in step one, the range direction processing and range migration correction are performed on the sum and difference channel echo data of the single-pulse forward-looking imaging radar to obtain the pulse compression echo results of the sum and difference channels, i.e., a one-dimensional range image.

[0050] The specific process is as follows:

[0051] Step 11: The sum and difference channel radar (i.e., monopulse radar) transmits N linear frequency modulated pulse signals at each scanning angle. After being reflected by the target, the linear frequency modulated pulse signals are received by the radar's sum and difference channels, and the received signals are echo signals.

[0052] Steps 1 and 2: Perform range-direction matched filtering on the received echo signals of the sum and difference channels respectively, and then perform range migration correction to obtain the pulse compression echo result, i.e., a one-dimensional range image.

[0053] The other steps and parameters are the same as in Specific Implementation Method 1.

[0054] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that, in step two, the center scanning angle θ of the summation channel is taken. scan0 Calculate the normalized amplitude variance from N pulse compression echoes. Selecting normalized amplitude variance And the distance unit t with the largest one-dimensional distance image amplitude c The specific process is as follows:

[0055] Step 1) Assume the scanning angle θ of the radar antenna scan If the range is (α, β), then the center scanning angle Select the center scanning angle θ scan0 For the corresponding N pulse pressure echoes, calculate the normalized amplitude variance of the pulse pressure echoes from the channel. like Figure 2 Example results of normalized magnitude variance calculation;

[0056] in It is the first The average of the echo amplitude of each distance cell. For the first The mean of the squared echo amplitude of each distance cell;

[0057] Step 2) Select And the distance cell with the largest amplitude is the distance cell t. c .

[0058] Here, we need to take into account both of the above two parameters. We need to minimize the normalized amplitude variance and maximize its corresponding amplitude. Generally, we find a group of distance cells with the smallest variance, compare their amplitudes, and select the distance cell with the largest amplitude.

[0059] This indicates that the echo power at the prominent point of the distance cell is more than 4 dB greater than the sum of clutter and noise.

[0060] The other steps and parameters are the same as those in one of the specific implementation methods one or two.

[0061] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that step three involves adjusting the distance units t of the sum and difference channels respectively. c (The sum and difference channel distance units are in one-to-one correspondence, resulting in the sum channel distance unit t) c This indicates the distance unit t c To meet the requirement of "containing isolated scattering points," the pulse compression echo data of the difference channel is directly used. A short-time Fourier transform is performed on the azimuth direction to obtain the time-frequency diagram. The maximum amplitude at the midpoint of the sum channel time-frequency diagram is selected, and the azimuth angle θ is calculated by combining it with the amplitude at the corresponding position in the difference channel time-frequency diagram. The corresponding scanning angle θ is then recorded. scan0 The specific process is as follows:

[0062] Step 1) For the sum channel and difference channel distance units t respectively c Perform a short-time Fourier transform on the N pulse compression echo data to obtain a time-frequency graph with the horizontal axis representing time and the vertical axis representing frequency.

[0063] Step 2) Find the position with the largest numerical amplitude in the column of data corresponding to the center of the horizontal axis (i.e., the center time) of the channel time-frequency plot, and denote it as (t). m ,f n Let A be the value corresponding to a given point, where 1 ≤ m, n ≤ N. Σ (plural);

[0064] Step 3) Find the position with the largest numerical amplitude in the column of data corresponding to the center of the horizontal axis (i.e., the center time) of the difference channel time-frequency plot, and denote it as (t). m ,f n Let A be the value corresponding to a given point, where 1 ≤ m, n ≤ N. Δ (plural);

[0065] Step 4) Assume the slope of the single-pulse angle detection curve is k. ae Using the single-pulse angle measurement formula The azimuth angle θ can be calculated (the azimuth angle is unknown and is usually calculated based on echo data. When the beam is at a certain scanning angle, the angle of the target relative to the beam center is the azimuth angle; the azimuth angle will change with the scanning angle).

[0066] Where real(·) is the real part operation;

[0067] Step 5) Record θ and the corresponding scanning angle θ scan0 (The scanning angle is known, such as in airborne radar. The beam needs to illuminate a certain direction, and the corresponding beam angle is the scanning angle.)

[0068] The other steps and parameters are the same as those in one of the specific implementation methods one to three.

[0069] Specific Implementation Method Five: This implementation method differs from one of Specific Implementation Methods One to Four in that step four involves distance unit t. c In the middle, select each scanning angle θ respectively scan Repeat step three to obtain θ ~ θ + θ scan Curve; using the polynomial f0(θ) = a0 + a1θ + a2θ 2 +a3θ 3 +a4θ 4 +a5θ 5 Fit the curve; where a i , i = 1…5 are the polynomial coefficients; the specific process is as follows:

[0070] Step 1) Assume the radar antenna's half-power beamwidth is θ 0.5 Then select the scanning angle θ scan ∈(θ scan0 -θ 0.5 ,θ scan0 +θ 0.5 Repeat step three to obtain a series of (θ, θ) scan angles and corresponding N pulse compression echo results within the range. scan );

[0071] Step 2) Plot a scatter plot of (θ, sumA). Under the least squares criterion, use the 5th degree polynomial f(θ) = a0 + a1θ + a2θ 2 +a3θ 3 +a4θ 4 +a5θ 5 Fit the scatter plot to obtain the relationship curve between θ and sumA;

[0072] Where, sumA=θ+θ scan θ is the absolute azimuth deflection; θ is the azimuth angle, also known as the relative azimuth deflection relative to the antenna beam center; a i , i = 1…5 are the polynomial coefficients.

[0073] The other steps and parameters are the same as those in one of the specific implementation methods one to four.

[0074] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that step five uses the formula θ′=θ-f0(θ) to correct the angular measurement values ​​of each scattering point in all range units; wherein the new curve f0(θ)=f(θ)-f(0) is obtained by shifting the curve up and down to the origin; the image with focus compensation is obtained by single-pulse projection of the corrected angle; the specific process is as follows:

[0075] Step 1) According to the single-pulse angle measurement formula Calculate the azimuth angle θ and elevation angle of each scattering point in all range cells. The azimuth angle θ′ after focusing compensation at this point is obtained using the formula θ′=θ-f0(θ);

[0076] Since this invention does not involve pitch angle, the pitch angle is obtained by processing according to traditional algorithms.

[0077] Step 2) Utilize the azimuth angle θ′ and elevation angle of each scattering point The position of the scattering point is calculated using the specific radar target geometry relationship with the slant range R. (Once the azimuth, elevation, and slant range of the scattering point are determined, its position can be determined in three-dimensional coordinates in space; the amplitude of the point at this position is the amplitude of the scattering point in the channel). Energy projection is then performed (energy projection means determining the position and amplitude of the point in the three-dimensional coordinate system) to obtain the imaging result after focus compensation.

[0078] The slant distance R is calculated from the distance unit.

[0079] The other steps and parameters are the same as those in any of the specific implementation methods one to five.

[0080] The following examples demonstrate the beneficial effects of the present invention:

[0081] Example 1:

[0082] This embodiment of a single-pulse forward-looking scanning imaging focus compensation method is prepared according to the following steps:

[0083] A spatial coordinate system xyz is established, with the positive x-axis pointing in the direction of radar platform motion, the positive y-axis pointing vertically upwards, and the z-axis derived from the x and y axes using the right-hand rule. The antenna has a half-power beamwidth of 3 degrees, and the antenna beam center is aligned with the scene center at the midpoint of the scan. The antenna azimuth angle scan range is (-4°, 4°) with an interval of 0.1°, transmitting 32 pulses at each angle. The linear frequency modulated pulse signal has a carrier frequency of 33 GHz, a pulse repetition rate of 4000 Hz, a pulse width of 10 μs, a bandwidth of 160 MHz, a sampling frequency of 200 MHz, and is noise-free.

[0084] The imaging scene center is set at the origin, and four imaging scenes are set: {Scene 1: Single target coordinates [0,0,-15]}, {Scene 2: Single target coordinates [0,0,0]}, {Scene 3: Single target coordinates [0,0,20]}, {Scene 4: Multi-target coordinates [0,0,20], [-20,0,0], [20,0,0]}; the radar initial position is [-5000,4000,-400], all in meters, and the radar velocity is V = 100 m / s.

[0085] Taking {Scenario 2: Single point target coordinates [0,0,0]} as an example, as follows Figure 3 For scene 2 and the one-dimensional range image results of the channel, the amplitude is the highest in the 1025th range cell (since there is no noise and it is a single-point target scene, the normalized amplitude variance is 0), therefore t c =1025; Take 32 echoes from the sum and difference channels with a scanning angle of 0°, take the 1025th distance cell of their one-dimensional range image, and perform a short-time Fourier transform to obtain the time-frequency map; the result of the sum channel time-frequency map is as follows Figure 4 As shown, in the intermediate time 16, the frequency unit with the highest amplitude is the 17th frequency unit. Therefore, the position of the time-frequency diagram (t) is... m ,f n = (16, 17), calculate the time-frequency plot (t) for each scanning angle. m ,f n The azimuth angle at (16, 17) is calculated and fitted to obtain the focusing compensation result image after incorporating this invention. Figure 6d ).

[0086] For a single target, such as in scenarios 1, 2, and 3, the prominent point in the echo is the target at that point; the corresponding θ~sumA scatter plot and the fitted f(θ) are as follows: Figure 5 As shown, the point targets f(θ) at different locations differ by a constant f(0). Therefore, the f0(θ) obtained by subtracting f(0) is exactly the same, indicating that the defocusing law is the same for different points.

[0087] Imaging was performed using the uncompensated azimuth angle θ. The imaging results for the four scenes are as follows: Figure 6a , Figure 6c , Figure 6e , Figure 6g ;

[0088] After applying the formula θ′=θ-f0(θ), imaging was performed. The imaging results for the four scenes after incorporating this invention are as follows: Figure 6b , Figure 6d , Figure 6f , Figure 6hAs can be seen, compared with the traditional imaging results, the defocusing is greatly improved after adding the present invention, from the original single-point result of 40m defocusing to within 1m, and the focusing is improved by about 40 times.

[0089] Therefore, for single-point target scenarios (Scene 1, Scene 2, Scene 3) and sparse point scenarios (Scene 4), the focusing performance is improved by about 40 times in the absence of noise.

[0090] Example 2:

[0091] To simulate a real-world environment, signal-to-noise ratios were set to 30dB and 15dB, with the scenes being a relatively dense point scene and a dense point scene, respectively. Figure 7 , Figure 8 The simulation results show the distribution of scattering points in scenario 5 and scenario 6, respectively.

[0092] A spatial coordinate system xyz is established, where the positive x-axis represents the radar platform's motion direction, the positive y-axis points vertically upwards, and the z-axis is obtained from the x and y axes using the right-hand rule. The antenna's half-power beamwidth is 3 degrees, and the antenna beam center is aligned with the scene center at the midpoint of the scan. The antenna's azimuth angle scan range is (-2°, 2°), with an interval of 0.2°, transmitting 32 pulses at each angle. The linear frequency modulated pulse signal carrier frequency is 33GHz, the pulse repetition rate is 4000Hz, the pulse width is 10µs, the bandwidth is 160MHz, and the sampling frequency is 200MHz.

[0093] The imaging scene center is set at the origin of the coordinate system. Two imaging scenes are set: {Scene 5: a sparse imaging scene, distributed as shown in the figure}, and {Scene 6: a denser imaging scene, distributed as shown in the figure}. The initial radar position is [-5000, 4000, -400], all in meters. The target radar distance is 6.5 km. The radar velocity is V = 100 m / s.

[0094] Figure 9a , Figure 9c , Figure 10a , Figure 10c The images show the conventional imaging results for scene 5 (30dB signal-to-noise ratio), scene 5 (15dB signal-to-noise ratio), scene 6 (30dB signal-to-noise ratio), and scene 6 (15dB signal-to-noise ratio) without the present invention.

[0095] Figure 9b , Figure 9d , Figure 10b , Figure 10d The images show the focus compensation imaging results for scene 5 (30dB signal-to-noise ratio), scene 5 (15dB signal-to-noise ratio), scene 6 (30dB signal-to-noise ratio), and scene 6 (15dB signal-to-noise ratio) incorporating the present invention.

[0096] As can be seen, when the signal-to-noise ratio is high (30dB), the imaging results after adding the present invention have significantly improved focusing, and the focusing is improved by about 40 times; when the signal-to-noise ratio is low (15dB), the focusing is improved by about 10 times due to noise interference.

[0097] Furthermore, compared to denser imaging scenarios, where there is stronger mutual interference between echoes from different points, the focusing performance is still improved by about 5 times after incorporating this invention. Therefore, this invention has good robustness and still provides a certain degree of image quality improvement for low signal-to-noise ratio, dense imaging scenarios.

[0098] This invention may have other embodiments. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A single-pulse forward-looking scanning imaging focus compensation method, characterized in that: The specific process of the method is as follows: Step 1: Perform range processing and range migration correction on the sum and difference channel echo data of the single-pulse forward-looking imaging radar to obtain the pulse compression echo results of the sum and difference channels, i.e., the one-dimensional range image. Step 2: Obtain the center scanning angle θ of the summation channel. scan0 Calculate the normalized amplitude variance from N pulse compression echoes. Selecting normalized amplitude variance And the distance unit t with the largest one-dimensional distance image amplitude c ; Step 3: For the sum and difference channel distance units t respectively c The pulse compression data are processed by short-time Fourier transform in the azimuth direction to obtain a time-frequency map; the maximum amplitude at the midpoint of the sum channel time-frequency map is selected, and the azimuth angle θ is calculated by combining the amplitude at the corresponding position in the difference channel time-frequency map, and the corresponding center scan angle θ is recorded. scan0 ; Step 4: At distance cell t c In the middle, select each scanning angle θ respectively scan Repeat step three to obtain θ ~ θ + θ scan curve; Using the polynomial f(θ) = a0 + a1θ + a2θ 2 +a3θ 3 +a4θ 4 +a5θ 5 Fit the curve; Where a i , i = 1…5 are the polynomial coefficients; Step 5: Use the formula θ′=θ-f0(θ) to correct the angle measurement values ​​of each scattering point in all range cells; The new curve obtained by translating the curve vertically to the origin is f0(θ) = f(θ) - f(0); The image with focus compensation is obtained by projecting the corrected angle using a single pulse.

2. The single-pulse forward-looking scanning imaging focus compensation method according to claim 1, characterized in that: In step one, the range direction processing and range migration correction are performed on the sum and difference channel echo data of the monopulse forward-looking imaging radar to obtain the pulse compression echo results of the sum and difference channels, i.e., a one-dimensional range image. The specific process is as follows: Step 11: The sum and difference channel radar transmits N linear frequency modulated pulse signals at each scanning angle. After being reflected by the target, the linear frequency modulated pulse signals are received by the radar's sum and difference channels, and the received signals are echo signals. Steps 1 and 2: Perform range-direction matched filtering on the received echo signals of the sum and difference channels respectively, and then perform range migration correction to obtain the pulse compression echo result, i.e., a one-dimensional range image.

3. The single-pulse forward-looking scanning imaging focus compensation method according to claim 2, characterized in that: In step two, the center scanning angle θ of the channel is taken. scan0 Calculate the normalized amplitude variance from N pulse compression echoes. Selecting normalized amplitude variance And the distance unit t with the largest one-dimensional distance image amplitude c The specific process is as follows: Step 1) Assume the scanning angle θ of the radar antenna scan If the range is (α, β), then the center scanning angle Select the center scanning angle θ scan0 For the corresponding N pulse pressure echoes, calculate the normalized amplitude variance of the pulse pressure echoes from the channel. in It is the first The average of the echo amplitude of each distance cell. For the first The mean of the squared echo amplitude of each distance cell; Step 2) Select And the distance unit with the largest amplitude is distance unit t. c .

4. The single-pulse forward-looking scanning imaging focus compensation method according to claim 3, characterized in that: Step three involves processing the sum and difference channel distance units t respectively. c The pulse compression echo data is processed by short-time Fourier transform in the azimuth direction to obtain a time-frequency diagram. The maximum amplitude at the midpoint of the sum channel time-frequency diagram is selected, and the azimuth angle θ is calculated by combining it with the amplitude at the corresponding position in the difference channel time-frequency diagram. The corresponding center scanning angle θ is also recorded. scan0 The specific process is as follows: Step 1) For the sum channel and difference channel distance units t respectively c Perform a short-time Fourier transform on the N pulse compression echo data to obtain a time-frequency graph with the horizontal axis representing time and the vertical axis representing frequency. Step 2) Find the position with the largest numerical amplitude in the column of data corresponding to the center of the horizontal axis of the channel time-frequency plot, and denote it as (t). m ,f n Let A be the value corresponding to a given point, where 1 ≤ m, n ≤ N. ∑ ; Step 3) Find the position with the largest numerical amplitude in the column of data corresponding to the center of the horizontal axis of the difference channel time-frequency plot, and denot it as (t). m ,f n Let A be the value corresponding to a given point, where 1 ≤ m, n ≤ N. Δ ; Step 4) Assume the slope of the single-pulse angle detection curve is k. ae Using the single-pulse angle measurement formula The azimuth angle θ can be calculated. Where real(·) is the real part operation; Step 5) Record θ and the corresponding center scanning angle θ scan0 .

5. The single-pulse forward-looking scanning imaging focus compensation method according to claim 4, characterized in that: The fourth step is in the distance unit t c In the middle, select each scanning angle θ respectively scan Repeat step three to obtain θ ~ θ + θ scan Curve; using the polynomial f0(θ) = a0 + a1θ + a2θ 2 +a3θ 3 +a4θ 4 +a5θ 5 Fit the curve; where a i , i = 1…5 are the polynomial coefficients; the specific process is as follows: Step 1) Assume the radar antenna's half-power beamwidth is θ 0.5 Then select the scanning angle θ scan ∈(θ scan0 -θ 0.5 ,θ scan0 +θ 0.5 Repeat step three to obtain a series of (θ, θ) scan angles and corresponding N pulse compression echo results within the range. scan ); Step 2) Plot a scatter plot of (θ, sumA). Under the least squares criterion, use the 5th degree polynomial f(θ) = a0 + a1θ + a2θ 2 +a3θ 3 +a4θ 4 +a5θ 5 Fit the scatter plot to obtain the relationship curve between θ and sumA; Where, sumA=θ+θ scan θ is the absolute azimuth deflection; θ is the azimuth angle, also known as the relative azimuth deflection relative to the antenna beam center; a i , i = 1…5 are the polynomial coefficients.

6. The single-pulse forward-looking scanning imaging focus compensation method according to claim 5, characterized in that: Step five uses the formula θ′=θ-f0(θ) to correct the angular measurement values ​​of each scattering point in all range cells; The new curve obtained by translating the curve vertically to the origin is f0(θ) = f(θ) - f(0); The image with focus compensation is obtained by single-pulse projection of the corrected angle; the specific process is as follows: Step 1) According to the single-pulse angle measurement formula Calculate the azimuth angle θ and elevation angle of each scattering point in all range cells globally. The azimuth angle θ′ after focusing compensation at this point is obtained using the formula θ′=θ-f0(θ); Step 2) Utilize the azimuth angle θ′ and elevation angle of each scattering point By finding the slant range R, the position of the scattering point is obtained, and energy projection is performed to obtain the imaging result after focus compensation. The slant distance R is calculated from the distance unit.

Images