A high-precision intra-pulse motion compensation method for inverse synthetic aperture imaging of high-speed relative motion targets
By using time-frequency ridge line extraction and instantaneous frequency tracking, the problem of insufficient accuracy and robustness of intrapulse motion compensation in ISAR imaging of long-distance, high-speed, relatively moving targets was solved, achieving high-resolution image focusing and reducing computational complexity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-03-27
- Publication Date
- 2026-06-12
Smart Images
Figure CN122194076A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for intra-pulse motion compensation in moving target imaging, belonging to the field of civilian microwave remote sensing technology. Background Technology
[0002] With the rapid development of civil aerospace technology, the demand for detailed imaging of extremely high-speed moving targets is becoming increasingly urgent. Inverse Synthetic Aperture Radar (ISAR), as an important active observation method, has become one of the core detection devices in commercial aerospace telemetry and control, as well as space debris monitoring, due to its all-weather, all-day imaging capabilities and ability to perform high-resolution two-dimensional imaging of high-speed moving targets. ISAR can obtain detailed structural images of targets by imaging their motion; its imaging effect largely depends on signal processing algorithms.
[0003] However, when performing ISAR imaging on distant, high-speed, relatively moving targets, the radial velocity of the target relative to the radar can reach several kilometers per second due to the great distance between the radar platform and the observed target, both being in high-speed motion. This renders the traditional "stop-go-stop" model assumptions invalid. This results in a non-negligible relative motion between the radar and the target during the transmission and reception of a single radar pulse; this phenomenon is called intra-pulse walk. Intra-pulse walk introduces significant range-direction matched filtering errors, causing ISAR image defocusing, significantly reducing image quality, and consequently affecting the accurate assessment of the target's structural integrity. Existing intra-pulse walk compensation methods generally estimate motion parameters by constructing cost functions such as image entropy, or by calculating the phase difference of the echo signal.
[0004] For intrapulse movement compensation algorithms, the existing technical solutions mainly have the following defects and shortcomings: (1) insufficient parameter estimation accuracy and robustness; (2) failure to consider the spatial variation of intrapulse movement error; (3) high computational complexity.
[0005] Patent CN106872974A, filed on January 23, 2017, discloses a high-precision moving target imaging method based on a dual-channel hypersonic platform radar. Addressing the problem of low accuracy in moving target parameter estimation and poor focusing performance caused by the high-speed movement of the platform in hypersonic platform radar systems, the method first obtains the pulse-compressed echo signals from the two receiving channels. Through channel compensation and clutter suppression, an azimuth descrambling filter is constructed for azimuth compression. Then, Radon transform is used to estimate the radial velocity and correct for range travel. Finally, a fractional Fourier transform is used for tangential velocity estimation and compensation to obtain a precisely focused image of the moving target. This method effectively solves the parameter estimation problem in hypersonic platform radar imaging of moving targets, improving the signal-to-clutter-to-noise ratio and imaging quality of moving targets.
[0006] A patent application (CN118501877A, filed May 16, 2024) discloses a method for translational compensation of highly maneuverable targets under low signal-to-noise ratio (SNR) conditions, relating to the field of radar signal processing technology. The method includes: constructing a translational compensation model using time-domain echo, radial range, and reference range; fitting an initial set of radial range polynomial coefficients to the reference range set; estimating the target's precise motion parameters using the SAO-KOA hybrid optimization algorithm based on the initial set of coefficients; performing translational compensation on the echo based on the precise motion parameters; and processing the result using a range-instantaneous Doppler imaging model based on synchronous extraction transformation to obtain high-quality ISAR imaging results of the target. This method solves the problem of difficult translational compensation for highly maneuverable targets under low SNR conditions, improves imaging resolution, and enables high-focusing-quality imaging results for highly maneuverable targets.
[0007] However, the two patented technologies mentioned above still cannot solve the problems of insufficient parameter estimation accuracy and robustness, dependence on constant motion model assumptions caused by the spatial variation of intrapulse movement error in existing ISAR imaging methods for long-distance high-speed relatively moving targets, and high computational complexity. Summary of the Invention
[0008] This invention addresses the problems of insufficient estimation accuracy and robustness, lack of consideration for the spatial variation of intra-pulse travel compensation methods in inverse synthetic aperture imaging of long-distance high-speed relatively moving targets, reliance on constant motion model assumptions due to the lack of consideration for the spatial variation of intra-pulse travel error, and high computational complexity in existing methods. Therefore, it proposes an intra-pulse travel compensation method for ISAR imaging of long-distance high-speed relatively moving targets.
[0009] The technical solution adopted by the present invention to solve the above problems is as follows: The steps of the present invention include:
[0010] Step 1: Echo signal preprocessing; Step 2: Extract the echo sequence from the scattering points; Step 3: Estimate compensation parameters using the instantaneous frequency tracking method extracted from the time-frequency Ridge line; The instantaneous frequency tracking method extracted by the time-frequency Ridge line is used to perform time-frequency analysis on the echo sequence of each scattering point extracted in step 2, and the corresponding intrapulse travel compensation parameters are estimated. Step 4: Intravascular compensation; Step 5: Finally, obtain the ISAR image.
[0011] Furthermore, in step 1, without considering the envelope, translational compensation is performed on the echo signal to obtain the baseband echo signal, and range-dimensional FFT and matched filtering are applied to it to analyze the parameters required to compensate for intrapulse travel error.
[0012] Furthermore, in step 2, for each scattering point of the target, the echo signal within the corresponding range cell is extracted as described in step 1 to form the echo sequence of that scattering point.
[0013] Furthermore, the specific steps of the parameter estimation method in step 3 are as follows: Step 301: Perform time-frequency analysis on the fast time-dimensional echo signal; For the echo sequence of each scattering point in step 2, perform a short-time Fourier transform on the fast-time signal to obtain its joint time-frequency distribution, i.e., the joint distribution of instantaneous frequency and fast time. Step 302: Instantaneous frequency ridge line extraction; On the joint time-frequency distribution obtained in step 301, for each fast time point, find the frequency value that makes the magnitude of the joint time-frequency distribution reach its maximum value, and obtain a discrete instantaneous frequency Ridge line, which represents the trajectory of the echo signal frequency change with fast time. Step 303: Estimate parameters through linear fitting; In step 302, the absolute value of the slope of the finally obtained discrete instantaneous frequency Ridge line is denoted as... ,So , Since k << 1, we use Taylor series expansion to make a first-order approximate estimate of k, obtaining an estimated value of k as follows: , In the expression for the intrapulse travel error coefficient C, since the order of magnitude of k is much smaller than 1, the estimated value of C is... , Substituting the estimated value of k into the equation, we can obtain C and the absolute value of the slope of the discrete instantaneous frequency Ridge line. The relationship is
[0014] Furthermore, in step 4, since the analysis was performed in step 1... The product term that causes intra-pulse wander error is the term corresponding to the square of the frequency. In step 3, the intra-pulse wander error coefficient corresponding to each scattering point has been estimated. Therefore, in step 4, a compensation function is constructed for the echo data of the scattering point, and compensation is completed in the distance-dimensional frequency domain to obtain the compensated data.
[0015] Furthermore, in step 5, after completing intrapulse travel compensation for all scattering points, the compensated data is subjected to range-oriented IFFT to convert it back to the range-dimensional time domain. Finally, azimuth-dimensional FFT processing is performed to obtain a high-resolution ISAR image.
[0016] The beneficial effects of this invention are: 1. This invention estimates motion parameters in the time-frequency domain and combines time-frequency analysis with instantaneous frequency ridge line extraction and fitting, thereby improving the accuracy of parameter estimation, robustness of parameter estimation, and focus quality of the final image.
[0017] 2. This invention obtains the relationship between instantaneous frequency and fast time by performing time-frequency analysis on the pulse echo signal, which enables the method to adapt to the spatial variation of intrapulse movement error and effectively overcomes the problem of incomplete compensation caused by the reliance on the constant speed assumption of traditional methods.
[0018] 3. The core algorithms used in this invention, including short-time Fourier transform, Ridge line extraction, and linear fitting, all have low computational complexity, avoiding the high computational cost process in traditional parameter search methods, thereby significantly improving computational efficiency and making it easier to achieve real-time or near-real-time processing under conditions of limited computing resources. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the intrapulse movement error in step 1 of a specific embodiment of the present invention; Figure 2 This is a flowchart of the intrapulse migration compensation method for ISAR imaging of long-distance, high-speed relatively moving targets in this invention embodiment; Figure 3 This is a result diagram of the combined time-frequency distribution of an embodiment of the present invention; Figure 4 This is a diagram showing the result of instantaneous frequency ridge line extraction according to an embodiment of the present invention; Figure 5 This is a point target imaging result diagram without intrapulse movement compensation in an embodiment of the present invention; Figure 6 This is a contour map of the point target imaging result without intrapulse movement compensation in this embodiment of the invention; Figure 7 This is a point target imaging result image after intrapulse motion compensation according to an embodiment of the present invention; Figure 8 This is a contour map of the point target imaging result after intrapulse movement compensation in an embodiment of the present invention. Detailed Implementation
[0020] Specific Implementation Method 1: A high-precision intra-pulse motion compensation method for inverse synthetic aperture imaging of high-speed relatively moving targets, the specific steps of which include: Step 1: Echo signal preprocessing; A schematic diagram of intrapulse movement error is shown below. Figure 1 As shown, by Figure 1It can be seen that, assuming the radar remains stationary, if the distance between the radar and the target reaches the target when the leading edge of the transmitted pulse is... And when within the pulse The time interval between the arrival of the fast-time sampling point at time t and the arrival of the leading edge of the transmitted pulse at the target is . We can obtain the following expression: (1) Furthermore in At time t, the expression for the intra-pulse travel delay of the target when it is received by the radar due to its high-speed motion is: (2) In formula (2), Indicates in The intra-pulse travel delay of the target when it is received by the radar, which is caused by the high-speed movement of the target.
[0021] Will Replace with This allows us to obtain any time within the pulse. The expression for the intrapulse travel time delay introduced by the high-speed motion of the target is: (3) In formula (3), Indicates at any time The intra-pulse travel delay introduced by the high-speed movement of the target when it is received by the radar, the first term It can be eliminated by translational compensation, so it will not be considered in the subsequent derivation; only the second term of the above equation will be considered.
[0022] Since the motion between the radar and the target is relative, similarly, assuming the target remains stationary, at any moment within the pulse... The expression for the intra-pulse travel delay introduced by the high-speed movement of the radar is: (4) In formula (4), Indicates at any time The intra-pulse travel delay introduced by the high-speed movement of the radar target when it is received by the radar.
[0023] Since the radar emits a linear frequency modulated signal, the expression for the baseband echo signal obtained after translational compensation of the echo signal, without considering the envelope, is as follows: (5), (6), In formulas (1) to (6), This indicates the center frequency of the radar's transmitted signal carrier. This represents the time-domain form of the baseband echo signal. Represents the imaginary unit. This indicates the intrapulse travel delay of the echo signal after translational compensation and The ratio, Indicates a fast time. This indicates the frequency modulation frequency of the linear frequency modulated signal transmitted by the radar. Represents the speed of light. Indicates slow time. The rotation term represents the instantaneous slant range between the radar and the target. This represents the radial velocity component of the target. This represents the radial velocity component of the radar. Will By performing an FFT along the fast time dimension using the phase-stationary principle and then applying matched filtering, we obtain... The expression is: (7), In formula (7), , , ; The first term is a constant and does not affect the imaging result. The second term is a linear term with respect to frequency, which only causes a shift in the position of the scattering point in the range dimension and does not cause defocus. The fourth term is only used to obtain the target's coordinates in the image and also does not cause image defocus. The third term is a quadratic term with respect to frequency. This term will cause the main lobe of the range dimension impulse response to expand and the side lobes to increase, thus leading to image defocus, i.e., intrapulse travel error. Therefore, parameter C should be accurately estimated to accurately compensate for intrapulse travel error.
[0024] Step 2: Extract the echo sequence from the scattering points; For each scattering point of the target to be imaged, the echo signal within the corresponding range cell is extracted as described in step 1 to form the echo sequence of that scattering point; Step 3: Compensation parameters based on instantaneous frequency tracking estimation method extracted from time-frequency Ridge line; For the echo sequence of each scattering point in step 2, the corresponding intrapulse travel compensation parameters are estimated. The specific steps include: Step 301: For the echo sequence of each scattering point in Step 2, perform fast-time signal analysis. Perform a short-time Fourier transform to obtain its joint time-frequency distribution. This refers to the combined distribution of instantaneous frequency and fast time: (8), In formula (8), For A Gaussian window function centered at the center; Step 302: Instantaneous frequency ridge line extraction; From formula (5), we know that the phase of the echo signal is: (9), instantaneous frequency The expression is: (10) In formula (10), the first two terms are constant terms, and the third term is a constant with respect to time. The first term, therefore the instantaneous frequency is with respect to fast time. A linear function; The joint time-frequency distribution obtained in step 301 Above, for each fast time point , search for The frequency value at which the modulus reaches its maximum value A discrete instantaneous frequency ridge line is obtained. This line characterizes the frequency of the signal within the pulse as a function of fast time. The trajectory of change; Step 303: Estimate parameters through linear fitting; In step 302, the absolute value of the slope of the finally obtained discrete instantaneous frequency Ridge line is denoted as... ,but: (11), Since k is much less than 1, Taylor series expansion is used to... Perform a first-order linear approximation estimate to obtain The estimated value is: (12) Intrapulse movement error coefficient In the expression, because The order of magnitude is much smaller than 1, so The estimated value is: (13) Will Substituting the estimated value into formula (13), we get The absolute value of the slope of the discrete instantaneous frequency Ridge line The relation is: (14); Step 4: Intravascular compensation; exist In this context, the product term that causes intrapulse motion error is the coefficient corresponding to the square of the frequency. In step 3, the parameters corresponding to each scattering point have been... Make an estimate, so that for the first Echo data from each scattering point The constructed compensation function is: (15) Compensation is performed in the distance-dimensional frequency domain, and the expression for the compensated data is: (16) In formula (16), This represents the slow time of the nth scattering point; Step 5: Finally, obtain the ISAR image; After completing the intrapulse travel compensation for all scattering points according to the above steps, the compensated data is subjected to range IFFT to convert it back to the range dimension time domain. Finally, azimuth dimension FFT is performed along the slow time to obtain a high-resolution ISAR image.
[0025] Example The key steps mentioned in the point target imaging process are simulated with set parameters. The radar system carrier frequency is set to 5.4 GHz, belonging to the C-band; the minimum slant range between the radar and the target is 100 km; the transmitted signal bandwidth is 300 MHz; and the pulse width is 40 microseconds. The joint time-frequency distribution results obtained after short-time Fourier transform are as follows: Figure 3 As shown, in Figure 2 Find the frequency value that maximizes the magnitude of TF(t,f). From this, a discrete instantaneous frequency Ridge line can be obtained {( , The results of instantaneous frequency Ridge line extraction are as follows: Figure 4 As shown, the slope of the obtained instantaneous frequency is -7.4874 × Hz / s, pulse travel compensation parameter The estimated value is 2.2382 × The point target imaging result without intrapulse travel error compensation is shown in the figure below. Figure 5 As shown, the corresponding imaging result contour map is as follows: Figure 6 As shown; the point target imaging result after intrapulse motion compensation is shown in the figure. Figure 7 As shown, the corresponding imaging result contour map is as follows: Figure 8 As shown. In the above imaging process, the final range IFFT and azimuth FFT processing are both interpolated and zero-padded with three times the number of range and azimuth cells respectively to reduce spectral leakage. The imaging result contour map is drawn from the range and azimuth cells near the point target in the imaging result map.
[0026] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.
Claims
1. A high-precision intra-pulse migration compensation method for inverse synthetic aperture imaging of high-speed relatively moving targets, characterized in that, The specific steps include: Step 1: Echo signal preprocessing; Step 2: Extract the echo sequence from the scattering points; Step 3: Estimate compensation parameters using the instantaneous frequency tracking method extracted from the time-frequency Ridge line; The instantaneous frequency tracking method extracted by the time-frequency Ridge line is used to perform time-frequency analysis on the echo sequence of each scattering point extracted in step 2, and the corresponding intrapulse travel compensation parameters are estimated. Step 4: Intravascular compensation; Step 5: Finally, obtain the ISAR image.
2. The high-precision intra-pulse migration compensation method for inverse synthetic aperture imaging of high-speed relatively moving targets according to claim 1, characterized in that, In step 1, without considering the envelope, translational compensation is performed on the echo signal to obtain the baseband echo signal. Then, range-dimensional FFT and matched filtering are applied to it to analyze the parameters required to compensate for intra-pulse travel error.
3. The high-precision intra-pulse migration compensation method for inverse synthetic aperture imaging of high-speed relatively moving targets according to claim 1, characterized in that, In step 2, for each scattering point of the target, the echo signal within the corresponding range cell is extracted as described in step 1 to form the echo sequence of that scattering point.
4. The high-precision intra-pulse migration compensation method for inverse synthetic aperture imaging of high-speed relatively moving targets according to claim 1, characterized in that, The specific steps of the parameter estimation method in step 3 are as follows: Step 301: Perform time-frequency analysis on the fast time-dimensional echo signal; For the echo sequence of each scattering point in step 2, perform a short-time Fourier transform on the fast-time signal to obtain its joint time-frequency distribution, i.e., the joint distribution of instantaneous frequency and fast time. Step 302: Instantaneous frequency ridge line extraction; On the joint time-frequency distribution obtained in step 301, for each fast time point, find the frequency value that makes the magnitude of the joint time-frequency distribution reach its maximum value, and obtain a discrete instantaneous frequency Ridge line, which represents the trajectory of the signal frequency within the pulse with fast time. Step 303: Estimate parameters through linear fitting; In step 302, the absolute value of the slope of the finally obtained discrete instantaneous frequency Ridge line is denoted as... ,So ， Since k << 1, we use Taylor series expansion to make a first-order approximate estimate of k, obtaining an estimated value of k as follows: ， In the expression for the intrapulse travel error coefficient C, since the order of magnitude of k is much smaller than 1, the estimated value of C is... ， Substituting the estimated value of k into the equation, we can obtain C and the absolute value of the slope of the discrete instantaneous frequency Ridge line. The relationship is 。 5. The high-precision intra-pulse migration compensation method for inverse synthetic aperture imaging of high-speed relatively moving targets according to claim 1, characterized in that, In step 4, since the analysis was already performed in step 1... The product term that causes intra-pulse wander error is the term corresponding to the square of the frequency. In step 3, the intra-pulse wander error coefficient corresponding to each scattering point has been estimated. Therefore, in step 4, a compensation function is constructed for the echo data of the scattering point, and compensation is completed in the distance-dimensional frequency domain to obtain the compensated data.
6. The high-precision intra-pulse migration compensation method for inverse synthetic aperture imaging of high-speed relatively moving targets according to claim 1, characterized in that, In step 5, after completing intra-pulse motion compensation for all scattering points, range-oriented IFFT is performed on the compensated data to convert it back to the range-dimensional time domain. Finally, azimuth-dimensional FFT processing is performed to obtain a high-resolution ISAR image.