A method for positioning rotating radar targets

Abstract

The present invention discloses a method for positioning a rotating radar target, which belongs to the field of radar target detection technology and solves the technical problem that the prior art cannot detect and position micro-moving targets. The positioning method includes: step 1, using a radar to receive the echo signal of a point target in the observation scene to obtain a matched filtered signal; step 2, obtaining a baseband signal after distance compression based on the matched filtered signal of step 1; step 3, designing an imaging grid on an imaging plane; step 4, obtaining an imaging result; step 5, interpolating and aligning any two imaging results to obtain a compensated imaging result to compensate for the phase error caused by the azimuth position deviation of the receiving aperture; step 6, obtaining the micro-moving target energy based on the obtained compensated imaging result, and determining the target position based on the micro-moving target energy. The present invention can extract a moving target on a SAR image and obtain the motion parameter information of the moving target.

Description

Technical Field

[0001] The present invention relates to the technical field of radar target detection, and in particular to a method for positioning a rotating radar target. Background Art

[0002] Traditional SAR is only suitable for target detection and imaging in static scenes. However, in actual reconnaissance areas,

[0003] High-value targets often exhibit unusual movements, such as the rotation of radar antennas and the pitch and roll of ships. These micro-movements also induce the Doppler effect, modulating the phase of radar echoes. This causes a time-varying Doppler modulation frequency and broadens the signal spectrum, manifesting as ghosting or defocusing at the locations of these targets in SAR images. This type of movement distorts the phase history of the target echo, appearing as an out-of-focus signal in SAR images. Consequently, existing detection methods are unable to detect and locate micro-moving targets.

[0004] When a radar target or target component moves, it is often accompanied by micro-motions (micro-dynamics) such as vibration, rotation, and acceleration in addition to the translational motion of the center of mass [2]. Target micro-motion modulates the phase of the radar echo, thereby generating corresponding frequency modulation, and introducing additional modulation sidebands near the radar echo Doppler frequency shift signal generated by the translational motion of the target body. This additional modulation signal is called a micro-Doppler signal, and this modulation phenomenon caused by micro-motion is called the micro-Doppler effect. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a method for locating rotating radar targets to solve the technical problem in the prior art that micro-moving targets cannot be detected and located.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] A method for positioning a rotating radar target of the present invention comprises the following steps:

[0008] Step 1: Use the radar to receive the echo signal of the observation scene point target and obtain the matched filtered signal;

[0009] Step 2: Obtain a range-compressed baseband signal based on the matched filtered signal obtained in step 1;

[0010] Step 3: Design an imaging grid on the imaging plane;

[0011] Step 4: Reconstruct the pixel points. According to the distance from the antenna phase center APC to the point target, the contribution of the current pulse to the point target is obtained. The contribution of the pulse to the point target at each azimuth moment is coherently accumulated to obtain the reconstruction result of the point target. Reconstruct each pixel point within the beam illumination range to obtain multiple imaging results.

[0012] Step 5: interpolate and register any two of the imaging results to obtain compensated imaging results to compensate for the phase error caused by the azimuth position deviation of the receiving aperture;

[0013] Step 6: Based on the compensated imaging result, obtain the micro-motion target energy, and determine the target position based on the micro-motion target energy.

[0014] Furthermore, in step 1, the echo signal of the observation scene point target received by the radar is:

[0015]

[0016] in For fast time, t m is the slow time, γ is the signal modulation frequency; c is the speed of light, R(t m ) is the instantaneous slant distance from the antenna phase center APC to the target point, j is an imaginary number, T p is the pulse width, r is the modulation frequency, f c is the signal center frequency.

[0017] Furthermore, in step 1, equation (1) is transformed into the range frequency domain, and the signal after matched filtering is:

[0018]

[0019] where f r is the distance frequency, B r is the transmission signal bandwidth, R(t m ) is the instantaneous slant range from the antenna phase center APC to the target point, k r =4π(f c +f r ) / c is the wave number, and j is an imaginary number.

[0020] Furthermore, in step 2, the process of performing inverse Fourier transform on equation (2) to obtain the baseband signal after range compression is:

[0021]

[0022] in k rc =4πf c / c is the wave number center, and the influence of propagation attenuation factor on signal amplitude is ignored.

[0023] Further, in step 3, the imaging grid includes a polar coordinate grid or a rectangular coordinate grid.

[0024] Furthermore, in step 4, the contribution of the pulses at each azimuth moment to the point target is coherently accumulated, and the reconstruction result of the point target is obtained as follows:

[0025]

[0026] where R p is the distance from the APC to the target point, and each pixel point within the beam illumination range is reconstructed to obtain the imaging result; j is an imaginary number, R p (t m ) is the distance from the antenna phase center APC to the point P, t m For slow time.

[0027] Furthermore, in step 5, the two complex images are interpolated and registered to compensate for the phase error caused by the azimuth position deviation of the receiving aperture. The compensation function is:

[0028]

[0029] Where j is the imaginary unit, γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; t m For slow time; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X-axis.

[0030] Furthermore, in step 6, the two complex image data are conjugate multiplied to extract the phase, and the interference phase is detected by setting a certain threshold phase to cancel the stationary target, and then the cancellation result is modulo-measured to obtain the energy of the micro-motion target.

[0031] Furthermore, in step 6, the stationary target is cancelled, and the result after cancellation is:

[0032]

[0033] Where j is the imaginary unit; γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; t m For slow time; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X-axis.

[0034] Furthermore, in step 6, the square of the modulus value of the cancellation result is taken to obtain the micro-motion target energy:

[0035]

[0036] Among them, A3(t r ,t a ) is the additional modulation term; λ is the wavelength of the radar transmission signal; γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; r is the target rotation radius; r<<R o ;ω is the rotation speed; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X axis; B is the signal bandwidth; c is the speed of light; t^ is the fast time; t m For slow time, J m (2γr) is the first kind of m-order Bessel function, m is the order, B d is the Doppler bandwidth of the echo signal.

[0037] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0038] (1) The present invention can utilize the relationship between the phase difference between two SAR images and the interferometric SAR system parameters and target motion parameters to derive target motion parameter information. The method of the present invention is simple and highly operable, combining SAR high-resolution imaging of ground targets with micro-motion target detection. In subsequent engineering transformation and practical applications, it can detect, locate, and track high-value targets, providing useful information for battlefield situation assessment, command, and control, and is of great significance to reconnaissance and battlefield perception.

[0039] (2) Dual-channel image interference cancellation is performed by the method provided by the present invention, and micro-motion target detection is performed based on the detection threshold, and the micro-motion target results are extracted as follows: Figure 4 According to the relationship between the dual-channel interferometric phase and the rotation parameters, the relocation of the rotating radar target is realized, and the results are shown in Figure 5 As shown in the figure, when the SNR is better than 15dB, the corresponding target positioning accuracy can reach 1 / 15 of the beam width, and is better than 0.5° when the beam width is less than 7°.

[0040] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages will become apparent from the description or be understood through practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the embodiments of the description and the contents particularly pointed out in the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0042] Figure 1 Schematic diagram of the flow of the positioning method of the present invention;

[0043] Figure 2 is a schematic diagram of a dual-channel SAR system of the present invention;

[0044] Figure 3 This is a schematic diagram of the imaging results of a ship and a micro-moving target according to the present invention;

[0045] Figure 4 Schematic diagram of the micro-motion target interference detection result of the present invention;

[0046] Figure 5 Schematic diagram of the repositioning result of the micro-movement target of the present invention. DETAILED DESCRIPTION

[0047] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0048] A method for positioning a rotating radar target of the present invention comprises the following steps:

[0049] Step 1: Use the radar to receive the echo signal of the observation scene point target and obtain the matched filtered signal;

[0050] Step 2: Obtain a range-compressed baseband signal based on the matched filtered signal obtained in step 1;

[0051] Step 3: Design an imaging grid on the imaging plane;

[0052] Step 4: Reconstruct the pixel points. According to the distance from the APC to the point target, the contribution of the current pulse to the point target is obtained. The contribution of the pulse to the point target at each azimuth moment is coherently accumulated to obtain the reconstruction result of the point target. Reconstruct each pixel point within the beam illumination range to obtain the imaging result.

[0053] Step 5: interpolate and register any two of the imaging results to obtain compensated imaging results to compensate for the phase error caused by the azimuth position deviation of the receiving aperture;

[0054] Step 6: Based on the obtained compensated imaging result, obtain the micro-motion target energy, and determine the target position based on the micro-motion target energy.

[0055] Specifically, in step 1 above, the echo signal of the observation scene point target received by the radar is:

[0056]

[0057] in For fast time, t m is the slow time, c is the speed of light, R(t m ) is the instantaneous slant distance from the antenna phase center APC to the target point, j is an imaginary number, T p is the pulse width, γ is the signal modulation frequency, f c is the signal center frequency.

[0058] In step 1 above, transform equation (1) to the range frequency domain, and the signal after matched filtering is:

[0059]

[0060] where f r is the distance frequency, B r is the transmission signal bandwidth, R(t m ) is the instantaneous slant range from the antenna phase center APC to the target point, k r =4π(f c +f r ) / c is the wave number.

[0061] In step 2 above, the process of performing inverse Fourier transform on equation (2) to obtain the baseband signal after range compression is as follows:

[0062]

[0063] in k rc =4πf c / c is the wave number center, and the influence of propagation attenuation factor on signal amplitude is ignored.

[0064] In the above step 3, the imaging grid includes a polar coordinate grid or a rectangular coordinate grid.

[0065] In step 4 above, the contribution of the pulses at each azimuth moment to the point target is coherently accumulated, and the reconstruction result of the point target is obtained as follows:

[0066]

[0067] where R p is the distance from APC to the point, and each pixel point within the beam illumination range is reconstructed to obtain the imaging result; j is an imaginary number, R p (t m ) is the distance from the antenna phase center APC to the point P, tm For slow time.

[0068] In step 5 above, the two images are interpolated and registered using the following compensation function to compensate for the phase error caused by the azimuth position deviation of the receiving aperture. After imaging processing, the azimuth position deviation of the receiving aperture exists, so before performing ground clutter cancellation, the phase error caused by this position deviation needs to be compensated. The compensation function is shown below:

[0069]

[0070] Where, The term actually corresponds to the compensation function Compensation C1(t m ) is because the time domain linear term corresponds to the frequency domain shift, so compensation is performed to align the center. However, after imaging, a dual time domain image is obtained. Therefore, the phase before compensation corresponds to the phase error caused by the antenna aperture, which can be seen to be independent of the starting position x0 of the target point; where j is the imaginary unit, γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; t m For slow time; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X-axis.

[0071] In step 6 above, the two complex image data are conjugate multiplied to extract the phase. By setting a certain threshold phase, the interference phase is detected and the stationary target is canceled. That is, the two images are subtracted and canceled, and then the cancellation result is modulo (see the following formula) to obtain the energy of the micro-motion target.

[0072] Cancel the stationary target, and the result after cancellation is:

[0073]

[0074] Where j is the imaginary unit; γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; t a For slow time; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X-axis.

[0075] In step 6, the cancellation result is squared with the modulus value to obtain the slightly moving target energy. After obtaining the slightly moving target energy, the maximum value of the slightly moving target energy is obtained, and the position of the maximum value is the position of the slightly moving target in the SAR image.

[0076]

[0077] Among them, A3(t^,t m ) is the additional modulation term; λ is the wavelength of the radar transmission signal; γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; r is the target rotation radius; r<<R o ;ω is the rotation speed; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X axis; B is the signal bandwidth; c is the speed of light; t^ is the fast time; t m For slow time, J m (2γr) is the first kind of m-order Bessel function, m is the order, B d is the Doppler bandwidth of the echo signal.

[0078] In one embodiment, through digital simulation, a ship is selected as an imaging target, wherein the ship warning radar has micro-motion target characteristics, and the simulation parameters used are shown in Table 1.

[0079] Table 1 Simulation parameters of micro-motion target

[0080]

[0081] According to the above simulation parameters, the ship target imaging results are as follows: Figure 3 As shown in Figure 2, we can see that the ship target can be well imaged and the outline of the ship is clear. At the same time, during the accumulation time, the radar rotation causes obvious Doppler stripes, such as Figure 3 As shown in the white circle.

[0082] The method provided by the present invention is used to perform dual-channel image interference cancellation, and to detect micro-movement targets based on the detection threshold, and to extract micro-movement target results such as Figure 4 According to the relationship between the dual-channel interferometric phase and the rotation parameters, the relocation of the rotating radar target is realized, and the results are shown in Figure 5 As shown in the figure, when the SNR is better than 15dB, the corresponding target positioning accuracy can reach 1 / 15 of the beam width, and is better than 0.5° when the beam width is less than 7°.

[0083] In summary, the method of the present invention can utilize the changes in the Doppler frequency of echoes from different antennas to offset stationary targets and extract moving targets. Target motion parameter information is derived by utilizing the relationship between the phase difference between two SAR images, the interferometric SAR system parameters, and the target motion parameters. The method of the present invention is simple and highly operational, combining SAR's high-resolution imaging of ground targets with its micro-motion target detection capabilities. In subsequent engineering transformation and practical applications, it can detect, locate, and track high-value targets, providing useful information for on-site situation assessment, command, and control, and is of great significance for reconnaissance and on-site perception.

[0084] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for positioning a rotating radar target, characterized in that: The following steps are involved: Step 1: Use the radar to receive the echo signal of the observation scene point target and obtain the matched filtered signal; Step 2: Obtain a range-compressed baseband signal based on the matched filtered signal obtained in step 1; Step 3: Design an imaging grid on the imaging plane; Step 4: Reconstruct the pixel points. According to the distance from the antenna phase center APC to the point target, the contribution of the current pulse to the point target is obtained. The contribution of the pulse to the point target at each azimuth moment is coherently accumulated to obtain the reconstruction result of the point target. Reconstruct each pixel point within the beam illumination range to obtain multiple imaging results. Step 5: interpolate and register any two of the imaging results to obtain compensated imaging results to compensate for the phase error caused by the azimuth position deviation of the receiving aperture; In step 5, the two complex images are interpolated and registered to compensate for the phase error caused by the azimuth position deviation of the receiving aperture. The compensation function is: Where j is the imaginary unit, γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; t m For slow time; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X-axis; Step 6: Based on the obtained compensated imaging result, obtain the micro-motion target energy, and determine the target position based on the micro-motion target energy.

2. The method for locating a rotating radar target according to claim 1, wherein: In step 1, the echo signal of the observation scene point target received by the radar is: in, For fast time, t m is the slow time, c is the speed of light, R(t m ) is the instantaneous slant distance from the antenna phase center APC to the target point, j is an imaginary number, T p is the pulse width, γ is the signal modulation frequency; f c is the signal center frequency.

3. The method for locating a rotating radar target according to claim 2, wherein: In step 1, formula (1) is transformed into the range frequency domain, and the signal after matched filtering is: where f r is the distance frequency, B r is the transmission signal bandwidth, R(t m ) is the instantaneous slant range from the antenna phase center APC to the target point, k r =4π(f c +f r ) / c is the wave number, and j is an imaginary number.

4. The method for locating a rotating radar target according to claim 3, wherein: In step 2, the process of performing inverse Fourier transform on equation (2) to obtain the baseband signal after range compression is as follows: in k rc =4πf c / c is the wave number center, and the influence of propagation attenuation factor on signal amplitude is ignored.

5. The method for locating a rotating radar target according to claim 1, wherein: In step 3, the imaging grid includes a polar coordinate grid or a rectangular coordinate grid.

6. The method for locating a rotating radar target according to claim 5, wherein: In step 4, the contribution of the pulses at each azimuth moment to the point target is coherently accumulated, and the reconstruction result of the point target is obtained as follows: where R p is the distance from the APC to the target point, and each pixel point within the beam illumination range is reconstructed to obtain the imaging result; j is an imaginary number, R p (t m ) is the distance from the antenna phase center APC to the point P, t m For slow time.

7. The method for locating a rotating radar target according to claim 6, wherein: In step 6, the two complex image data are conjugate multiplied to extract the phase, and the interference phase is detected by setting a certain threshold phase to cancel the stationary target. Then, the cancellation result is modulo-measured to obtain the energy of the slightly moving target.

8. The method for locating a rotating radar target according to claim 7, wherein: In step 6, the stationary target is cancelled, and the result after cancellation is: Where j is the imaginary unit; γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; t m For slow time; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X-axis.

9. The method for locating a rotating radar target according to claim 8, wherein: In step 6, the square of the modulus value of the cancellation result is taken to obtain the micro-motion target energy: Among them, A3(t r ,t a ) is the additional modulation term; λ is the wavelength of the radar transmission signal; γ is the signal modulation frequency; R0 is the distance from the phase center of antenna 1 to the target; r is the target rotation radius; r<<R o ;ω is the rotation speed; D a is the phase center distance between the two antennas of the dual-channel SAR system; V a is the flight speed of the SAR carrier along the positive direction of the X axis; B is the signal bandwidth; c is the speed of light; t^ is the fast time; t m For slow time, J m (2γr) is the first kind of m-order Bessel function, m is the order, B d is the Doppler bandwidth of the echo signal.

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