A Terahertz Video Synthetic Aperture Radar Moving Target Imaging Method Based on Time-Frequency Analysis

Abstract

This application relates to a terahertz video synthetic aperture radar moving target imaging method based on time-frequency analysis. The method includes: constructing a radar echo model of the moving target based on instantaneous range and radar echo; processing the radar echo model by performing a short-time Fourier transform on the compressed echo signal; obtaining the Doppler center frequency of the scene echo from the obtained time-frequency distribution map; performing Doppler frequency zero-padding, range migration correction, and azimuth processing on the compressed echo signal according to a pre-set function; observing the range cell position of the moving target from the obtained imaging results; and extracting and performing time-frequency analysis on the moving target signal. After determining the Doppler center frequency of the moving target through time-frequency analysis and the time-frequency map, velocity estimation is performed; and the image of the moving target is refocused based on the characteristics of the time-frequency distribution line of the moving target echo. This method can quickly achieve velocity estimation and image refocusing of moving targets.

Description

Technical Field

[0001] This application relates to the field of signal processing technology, and in particular to a terahertz video synthetic aperture radar moving target imaging method, apparatus, computer equipment, and storage medium based on time-frequency analysis. Background Technology

[0002] Synthetic Aperture Radar (SAR) was initially developed for high-resolution imaging of static scenes, but imaging of moving targets is crucial in target tracking and traffic monitoring. SAR moving target imaging technology can quickly detect the direction of movement and geographical location of moving targets in complex environments. Therefore, combining video SAR with moving target imaging technology allows for continuous monitoring of moving targets. However, the challenges of moving target imaging are well-known: the presence of velocities in two directions causes image shifts and defocusing in the moving target imaging results.

[0003] However, most of the existing methods for velocity estimation in motion target imaging technology are cumbersome and time-consuming, and involve a lot of formula derivation, resulting in slow velocity estimation efficiency. Summary of the Invention

[0004] Therefore, it is necessary to provide a terahertz video synthetic aperture radar moving target imaging method, device, computer equipment, and storage medium based on time-frequency analysis that can quickly achieve velocity estimation and image refocusing of moving targets, addressing the aforementioned technical problems.

[0005] A terahertz video synthetic aperture radar moving target imaging method based on time-frequency analysis, the method includes:

[0006] To obtain the instantaneous distance and radar echo of the radar reaching the moving target;

[0007] A radar echo model of a moving target is constructed based on instantaneous distance and radar echo. The radar echo model is then windowed and range compressed to obtain the compressed echo signal.

[0008] The compressed echo signal is subjected to short-time Fourier transform to obtain a time-frequency distribution map. The Doppler center frequency of the entire scene echo is obtained from the time-frequency distribution map. The compressed echo signal is compensated according to the pre-set Doppler frequency zero-padding function to obtain the compensated echo.

[0009] Based on the pre-set range migration correction function and azimuth reference function, the compensated echo is processed for range migration and azimuth to obtain preliminary imaging results;

[0010] The range cell position of the moving target is obtained from the preliminary imaging results. After extracting the moving target signal, time-frequency analysis is performed to obtain the Doppler center frequency of the moving target echo.

[0011] The azimuth direction of the preliminary imaging results is calibrated based on the radar pulse repetition frequency. The Doppler frequency caused by the lateral position of the moving target is obtained by using the target shadow. The Doppler center frequency offset is obtained by subtracting the Doppler frequency caused by the lateral position of the moving target from the Doppler center frequency of the moving target echo.

[0012] The radial velocity of the moving target is obtained by calculating the Doppler center frequency shift.

[0013] The initial imaging results are subjected to an inverse Fourier transform in the azimuth direction, and the moving target signal is subjected to a short-time Fourier transform to obtain the transformed time-frequency diagram. The frequency modulation of the azimuth reference function is modified according to the transformed time-frequency diagram until the tilt of the time-frequency distribution line of the moving target disappears, and the frequency modulation of the azimuth signal is obtained.

[0014] Accurate imaging of the moving target is achieved by using its radial velocity, azimuth signal modulation frequency, and phase gradient autofocus function, resulting in the final imaging outcome.

[0015] In one embodiment, constructing a radar echo model of a moving target based on instantaneous distance and radar echo includes:

[0016] A radar echo model of a moving target is constructed based on instantaneous distance and radar echo.

[0017]

[0018] Wherein, R(t) m ) represents the instantaneous distance, rect() represents the window function, exp represents the exponential function with base e, j represents the imaginary unit, t represents the distance-time interval, and T p f is the radar pulse width. c λ is the radar center frequency, λ is the radar wavelength, and k is the center frequency of the radar. r For the range-directed modulation frequency, t m It is a slow time of location, T a denoted as the time to synthesize the aperture, and c as the speed of light.

[0019] In one embodiment, the radar echo model is windowed and range compressed to obtain a compressed echo signal, including:

[0020] The radar echo model is windowed according to the Hanning window to obtain the windowed echo signal.

[0021] The windowed echo signal is subjected to a range-to-Fourier transform to obtain the compressed echo signal.

[0022] In one embodiment, the pre-set Doppler frequency zero-compensation function is exp(-j2πf dct m ), where f dc The Doppler center frequency of the scene echo.

[0023] In one embodiment, the pre-set distance migration correction function is exp(-j4πf r Vsinθt m / c), f r Where θ is the range frequency, V is the radar platform velocity, and θ is the radar angle of view.

[0024] In one embodiment, the pre-set azimuth reference function is: k a Frequency is tuned to the azimuth direction of the signal.

[0025] In one embodiment, the radial velocity of the moving target is obtained by calculating the Doppler center frequency shift, including:

[0026] The radial velocity of the moving target is obtained by calculating the Doppler center frequency shift.

[0027] v r =λf shift / -2

[0028] Among them, f shift This represents the Doppler center frequency shift.

[0029] A terahertz video synthetic aperture radar moving target imaging device based on time-frequency analysis, the device comprising:

[0030] The radar echo model construction and processing module is used to acquire the instantaneous range and radar echo of the radar reaching the moving target; based on the instantaneous range and radar echo, a radar echo model of the moving target is constructed; the radar echo model is windowed and range compressed to obtain the compressed echo signal.

[0031] The echo signal compensation module is used to perform a short-time Fourier transform on the compressed echo signal to obtain a time-frequency distribution map. The Doppler center frequency of the entire scene echo is obtained from the time-frequency distribution map, and the compressed echo signal is compensated according to the preset Doppler frequency zero-padding function to obtain the compensated echo.

[0032] The time-frequency analysis module is used to perform range migration correction and azimuth processing on the compensated echo according to the pre-set range migration correction function and azimuth reference function to obtain preliminary imaging results; the range cell position of the moving target is obtained from the preliminary imaging results, and the moving target signal is extracted and then subjected to time-frequency analysis to obtain the Doppler center frequency of the moving target echo;

[0033] The Doppler center frequency offset calculation module is used to calibrate the azimuth of the preliminary imaging results based on the radar pulse repetition frequency. It obtains the Doppler frequency caused by the lateral position of the moving target by using the target shadow. It subtracts the Doppler frequency caused by the lateral position of the moving target from the Doppler center frequency of the moving target echo to obtain the Doppler center frequency offset.

[0034] The imaging module is used to calculate the Doppler center frequency shift to obtain the radial velocity of the moving target; to perform an inverse azimuth Fourier transform on the preliminary imaging results and a short-time Fourier transform on the moving target signal to obtain the transformed time-frequency map; to modify the modulation frequency of the azimuth reference function based on the transformed time-frequency map until the tilt of the time-frequency distribution line of the moving target disappears, thus obtaining the azimuth signal modulation frequency; and to perform precise imaging of the moving target based on the radial velocity, the azimuth signal modulation frequency, and the phase gradient self-focusing function to obtain the final imaging result.

[0035] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program performing the following steps:

[0036] To obtain the instantaneous distance and radar echo of the radar reaching the moving target;

[0037] A radar echo model of a moving target is constructed based on instantaneous distance and radar echo. The radar echo model is then windowed and range compressed to obtain the compressed echo signal.

[0038] The compressed echo signal is subjected to short-time Fourier transform to obtain a time-frequency distribution map. The Doppler center frequency of the entire scene echo is obtained from the time-frequency distribution map. The compressed echo signal is compensated according to the pre-set Doppler frequency zero-padding function to obtain the compensated echo.

[0039] Based on the pre-set range migration correction function and azimuth reference function, the compensated echo is processed for range migration and azimuth to obtain preliminary imaging results;

[0040] The range cell position of the moving target is obtained from the preliminary imaging results. After extracting the moving target signal, time-frequency analysis is performed to obtain the Doppler center frequency of the moving target echo.

[0041] The azimuth direction of the preliminary imaging results is calibrated based on the radar pulse repetition frequency. The Doppler frequency caused by the lateral position of the moving target is obtained by using the target shadow. The Doppler center frequency offset is obtained by subtracting the Doppler frequency caused by the lateral position of the moving target from the Doppler center frequency of the moving target echo.

[0042] The radial velocity of the moving target is obtained by calculating the Doppler center frequency shift.

[0043] The initial imaging results are subjected to an inverse Fourier transform in the azimuth direction, and the moving target signal is subjected to a short-time Fourier transform to obtain the transformed time-frequency diagram. The frequency modulation of the azimuth reference function is modified according to the transformed time-frequency diagram until the tilt of the time-frequency distribution line of the moving target disappears, and the frequency modulation of the azimuth signal is obtained.

[0044] Accurate imaging of the moving target is achieved by using its radial velocity, azimuth signal modulation frequency, and phase gradient autofocus function, resulting in the final imaging outcome.

[0045] A computer-readable storage medium having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0046] To obtain the instantaneous distance and radar echo of the radar reaching the moving target;

[0047] A radar echo model of a moving target is constructed based on instantaneous distance and radar echo. The radar echo model is then windowed and range compressed to obtain the compressed echo signal.

[0048] The compressed echo signal is subjected to short-time Fourier transform to obtain a time-frequency distribution map. The Doppler center frequency of the entire scene echo is obtained from the time-frequency distribution map. The compressed echo signal is compensated according to the pre-set Doppler frequency zero-padding function to obtain the compensated echo.

[0049] Based on the pre-set range migration correction function and azimuth reference function, the compensated echo is processed for range migration and azimuth to obtain preliminary imaging results;

[0050] The range cell position of the moving target is obtained from the preliminary imaging results. After extracting the moving target signal, time-frequency analysis is performed to obtain the Doppler center frequency of the moving target echo.

[0051] The azimuth direction of the preliminary imaging results is calibrated based on the radar pulse repetition frequency. The Doppler frequency caused by the lateral position of the moving target is obtained by using the target shadow. The Doppler center frequency offset is obtained by subtracting the Doppler frequency caused by the lateral position of the moving target from the Doppler center frequency of the moving target echo.

[0052] The radial velocity of the moving target is obtained by calculating the Doppler center frequency shift.

[0053] The initial imaging results are subjected to an inverse Fourier transform in the azimuth direction, and the moving target signal is subjected to a short-time Fourier transform to obtain the transformed time-frequency diagram. The frequency modulation of the azimuth reference function is modified according to the transformed time-frequency diagram until the tilt of the time-frequency distribution line of the moving target disappears, and the frequency modulation of the azimuth signal is obtained.

[0054] Accurate imaging of the moving target is achieved by using its radial velocity, azimuth signal modulation frequency, and phase gradient autofocus function, resulting in the final imaging outcome.

[0055] The aforementioned terahertz video synthetic aperture radar moving target imaging method, device, computer equipment, and storage medium based on time-frequency analysis first acquire the instantaneous range of the radar to the moving target and the radar echo; then, a radar echo model of the moving target is constructed based on the instantaneous range and radar echo; the radar echo model is then windowed and range compressed to obtain the compressed echo signal; the purpose of windowing is to suppress the sidelobes of the signal and thus improve the resolution. The compressed echo signal is subjected to a short-time Fourier transform to obtain a time-frequency distribution map. The Doppler center frequency of the scene echo is obtained from the time-frequency distribution map, and the compressed echo signal is compensated according to a pre-set Doppler frequency zero-padding function to obtain the compensated echo. The compensated echo is then processed for range migration correction and azimuth direction according to a pre-set range migration correction function and azimuth reference function to obtain preliminary imaging results. The range cell position of the moving target is observed from the preliminary imaging results. Then, the moving target signal is extracted and analyzed in time and frequency to obtain the Doppler center frequency of the moving target echo. The azimuth direction of the preliminary imaging results is calibrated according to the radar pulse repetition frequency. The Doppler frequency caused by the lateral position of the moving target is obtained by using the target shadow. The Doppler center frequency of the moving target echo is then subtracted from the lateral position of the moving target. The Doppler frequency shift is obtained by analyzing the Doppler frequency shift caused by the target's position. The radial velocity of the moving target is then calculated using the Doppler center frequency shift formula, enabling rapid velocity estimation. An inverse Fourier transform of the azimuth direction is performed on the initial imaging results, followed by a short-time Fourier transform of the moving target signal to obtain the transformed time-frequency map. The frequency modulation of the azimuth reference function is modified based on this transformed time-frequency map until the tilt of the moving target's time-frequency distribution line disappears, yielding the azimuth signal frequency modulation. The azimuth frequency modulation is corrected by observing the time-frequency distribution of the moving target echo, achieving image refocusing of the moving target and eliminating the need for parameter estimation. Finally, precise imaging of the moving target is performed based on its radial velocity, azimuth signal frequency modulation, and phase gradient autofocus function, resulting in the final imaging result. This application enables rapid velocity estimation of moving targets, simplifies the estimation process, and thus achieves rapid imaging of moving targets. On the other hand, when refocusing images of moving targets, it continuously optimizes the imaging results based on the time-frequency distribution map without parameter estimation, which saves time and achieves rapid imaging and image refocusing of moving targets based on velocity estimation. The velocity estimation and image refocusing of moving targets can be completed using only time-frequency analysis. The parameter estimation process is simple and the imaging efficiency is high. Attached Figure Description

[0056] Figure 1 This is a flowchart illustrating a terahertz video synthetic aperture radar moving target imaging method based on time-frequency analysis in one embodiment.

[0057] Figure 2 This is a schematic diagram of the imaging geometry model in one embodiment;

[0058] Figure 3 Here are specific imaging results and echo time-frequency distribution diagrams for a radial velocity greater than zero in one embodiment; where (a) is the imaging result diagram and (b) is the echo time-frequency distribution diagram.

[0059] Figure 4 Here are specific imaging results and echo time-frequency distribution diagrams for a radial velocity less than zero in one embodiment; where (a) is the imaging result diagram and (b) is the echo time-frequency distribution diagram.

[0060] Figure 5 This is a time-frequency distribution diagram of scene echoes in a certain frame of one embodiment;

[0061] Figure 6 This is an image of the Doppler center after compensation in one embodiment;

[0062] Figure 7 This is a magnified image of the result from one embodiment;

[0063] Figure 8 This is a time-frequency distribution diagram of the echo of a moving target in one embodiment;

[0064] Figure 9 Here are time-frequency distribution diagrams of a moving target before and after focusing in one embodiment; where (a) is the time-frequency distribution diagram of the moving target focusing, and (b) is the time-frequency distribution diagram of the moving target after focusing.

[0065] Figure 10 Here are the results before and after focusing on a moving target in one embodiment; where (a) is the result of focusing on the moving target, and (b) is the result after focusing on the moving target;

[0066] Figure 11 This is a structural block diagram of a terahertz video synthetic aperture radar moving target imaging device based on time-frequency analysis in one embodiment;

[0067] Figure 12 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0068] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0069] In one embodiment, such as Figure 1 As shown, a terahertz video synthetic aperture radar moving target imaging method based on time-frequency analysis is provided, including the following steps:

[0070] Step 102: Obtain the instantaneous distance and radar echo of the moving target; construct a radar echo model of the moving target based on the instantaneous distance and radar echo, and perform windowing processing and range compression on the radar echo model to obtain the compressed echo signal.

[0071] Based on the phase term of the radar echo model, the azimuth Doppler frequency of the moving target echo can be obtained as follows:

[0072]

[0073] The Doppler center frequency of the echo is f. mdc =-2(x0v) x -x0v+y0v y ) / (λR0), 2x0v / (λR0) are the Doppler center frequencies caused by radar motion, or the Doppler center frequencies caused by the lateral position of the target itself, while the Doppler center frequency offset caused by the target's own motion is f. shift =-2(x0v) x +y0v y The term ) / (λR0) causes the imaging result of the moving target to deviate from its original position. The azimuth Doppler frequency modulation is... This factor affects the focusing effect of moving target imaging results. For ease of analysis, this application specifies f... shift To simplify further, in reality, the target's lateral position is much smaller than its longitudinal position, so -2(x0v) x The smaller the value of ) / (λR0), the better for f shift The impact is minimal and can be ignored; at this point, f shift =-2(y0v y ) / (λR0), and This application defines v r Let f be the radial velocity of the moving target. shift =-2v r / λ.

[0074] Therefore, the radial velocity of a moving target will cause the imaging result to deviate from its original position, while the presence of azimuth velocity will cause the imaging result to be out of focus. Thus, knowing the velocities in both directions allows us to determine the Doppler center frequency shift and the azimuth signal modulation frequency of the moving target, and then use these two parameters to accurately image the moving target. The obtained echo is then subjected to windowing and range compression. Range compression improves range resolution. Here, the window function used in this application is the Hanning window. The window function is directly called and multiplied with the signal. The purpose of windowing is to suppress the sidelobes of the signal, thereby improving resolution. Then, a range Fourier transform is directly performed on the signal; this step is equivalent to range compression.

[0075] Step 104: Perform a short-time Fourier transform on the compressed echo signal to obtain a time-frequency distribution map. Obtain the Doppler center frequency of the entire scene echo from the time-frequency distribution map, and compensate the compressed echo signal according to the pre-set Doppler frequency zero-padding function to obtain the compensated echo.

[0076] The compressed echo signal is subjected to short-time Fourier transform to draw a time-frequency distribution diagram. Then, the Doppler center frequency of the scene echo is obtained by observing the time-frequency distribution. The compressed signal is multiplied by a Doppler frequency zero-padding function to compensate for the Doppler center frequency of the scene echo, thereby ensuring that the imaging result is in the center position.

[0077] Step 106: Perform range migration correction and azimuth processing on the compensated echo according to the pre-set range migration correction function and azimuth reference function to obtain preliminary imaging results; obtain the range cell position of the moving target from the preliminary imaging results, extract the moving target signal and perform time-frequency analysis to obtain the Doppler center frequency of the moving target echo.

[0078] After range compression and zero-padding of the scene Doppler center frequency, the next step is range migration correction. Because video synthetic aperture radar (SAR) uses a spotlight mode, the synthetic aperture time is relatively long. However, in image processing, we use segmented data, where each segment has a very short synthetic aperture time, which can be approximated as strip SAR data, and each segment is also called a frame. This application uses a range-Doppler algorithm for data processing, and sets the range migration correction function expression as follows:

[0079] exp(-j4πf r Vsinθt m / c)

[0080] Where f r Where θ is the range frequency, V is the radar platform velocity, and θ is the radar angle of view.

[0081] Because the synthetic aperture is very short, the range migration caused by target motion is not significant. Therefore, both the range migration caused by target motion and the range migration caused by radar motion can be compensated for by the above formula. After range migration correction, the next step is azimuth processing. The first step is to multiply the azimuth time domain by an azimuth reference function, and then perform an azimuth Fourier transform. Observe the range cell position of the moving target from the imaging results, and then extract the moving target signal separately for time-frequency analysis. When performing time-frequency analysis on the moving target signal, first compensate for the Doppler center frequency of the scene echo to obtain the accurate Doppler center frequency of the moving target, and then obtain the Doppler center frequency of the moving target echo from the time-frequency distribution map.

[0082] Step 108: Calibrate the azimuth of the preliminary imaging result according to the radar pulse repetition frequency, obtain the Doppler frequency caused by the lateral position of the moving target by using the target shadow, and obtain the Doppler center frequency offset by subtracting the Doppler frequency caused by the lateral position of the moving target from the Doppler center frequency of the moving target echo.

[0083] The azimuth direction of the imaging results is calibrated based on the radar pulse repetition frequency (PRF), ranging from -PRF / 2 to PRF / 2. It can be observed that the Doppler center frequency at the center of the scene is zero, and the Doppler frequency caused by the lateral position of the moving target can also be observed. The Doppler center frequency of the moving target echo is obtained from the time-frequency distribution map. Subtracting the Doppler frequency caused by the target's own position yields the Doppler center frequency shift due to the moving target's motion. Finally, the formula f is used... shift =-2v r / λ gives the radial velocity of the moving target at this moment.

[0084] Step 110: Calculate the Doppler center frequency shift to obtain the radial velocity of the moving target; perform an inverse azimuth Fourier transform on the preliminary imaging result and a short-time Fourier transform on the moving target signal to obtain the transformed time-frequency map; modify the modulation frequency of the azimuth reference function according to the transformed time-frequency map until the tilt of the time-frequency distribution line of the moving target disappears to obtain the azimuth signal modulation frequency; perform precise imaging of the moving target based on the radial velocity of the moving target, the azimuth signal modulation frequency, and the phase gradient self-focusing function to obtain the final imaging result.

[0085] The initial imaging results are subjected to an inverse Fourier transform in the azimuth direction, and a short-time Fourier transform is performed on the moving target signal. A time-frequency plot is then drawn, revealing a tilt and jitter in the time-frequency distribution line of the moving target. By observing the time-frequency distribution plot, the tuning frequency of the azimuth reference function is modified until the tilt disappears, while the jitter can be addressed using a phase gradient self-focusing function. After this step, the moving target image can be refocused.

[0086] In the above-mentioned terahertz video synthetic aperture radar moving target imaging method based on time-frequency analysis, the instantaneous range of the radar to the moving target and the radar echo are first obtained; a radar echo model of the moving target is constructed based on the instantaneous range and radar echo; the radar echo model is then windowed and range compressed to obtain the compressed echo signal; the purpose of windowing is to suppress the sidelobes of the signal and thus improve the resolution. The compressed echo signal is subjected to a short-time Fourier transform to obtain a time-frequency distribution map. The Doppler center frequency of the scene echo is obtained from the time-frequency distribution map, and the compressed echo signal is compensated according to a pre-set Doppler frequency zero-padding function to obtain the compensated echo. The compensated echo is then processed for range migration correction and azimuth direction according to a pre-set range migration correction function and azimuth reference function to obtain preliminary imaging results. The range cell position of the moving target is observed from the preliminary imaging results. Then, the moving target signal is extracted and analyzed in time and frequency to obtain the Doppler center frequency of the moving target echo. The azimuth direction of the preliminary imaging results is calibrated according to the radar pulse repetition frequency. The Doppler frequency caused by the lateral position of the moving target is obtained by using the target shadow. The Doppler center frequency of the moving target echo is then subtracted from the moving target's... The Doppler frequency resulting from the lateral position is used to obtain the Doppler center frequency shift. The radial velocity of the moving target is calculated from the Doppler center frequency shift, enabling rapid velocity estimation of the moving target. Then, an inverse azimuth Fourier transform is performed on the preliminary imaging results, and a short-time Fourier transform is performed on the moving target signal to obtain the transformed time-frequency map. Based on the transformed time-frequency map, the modulation frequency of the azimuth reference function is modified until the tilt of the time-frequency distribution line of the moving target disappears, thus obtaining the azimuth signal modulation frequency. The azimuth modulation frequency is corrected by observing the time-frequency distribution map of the moving target echo, achieving the purpose of refocusing the moving target image and eliminating the parameter estimation process. Finally, the moving target is accurately imaged based on the radial velocity, azimuth signal modulation frequency, and phase gradient autofocus function to obtain the final imaging result. This application enables rapid velocity estimation of moving targets, simplifies the estimation process, and thus achieves rapid imaging of moving targets. On the other hand, when refocusing images of moving targets, it continuously optimizes the imaging results based on the time-frequency distribution map without parameter estimation, which saves time and achieves rapid imaging and image refocusing of moving targets based on velocity estimation. The velocity estimation and image refocusing of moving targets can be completed using only time-frequency analysis. The parameter estimation process is simple and the imaging efficiency is high.

[0087] In one embodiment, constructing a radar echo model of a moving target based on instantaneous distance and radar echo includes:

[0088] A radar echo model of a moving target is constructed based on instantaneous distance and radar echo.

[0089]

[0090] Wherein, R(t) m ) represents the instantaneous distance, rect() represents the window function, exp represents the exponential function with base e, j represents the imaginary unit, t represents the distance-time interval, and T p f is the radar pulse width. c λ is the radar center frequency, λ is the radar wavelength, and k is the center frequency of the radar. r For the range-directed modulation frequency, t m It is a slow time of location, T a denoted as the time to synthesize the aperture, and c as the speed of light.

[0091] In one embodiment, the radar echo model is windowed and range compressed to obtain a compressed echo signal, including:

[0092] The radar echo model is windowed according to the Hanning window to obtain the windowed echo signal.

[0093] The windowed echo signal is subjected to a range-to-Fourier transform to obtain the compressed echo signal.

[0094] In one embodiment, the pre-set Doppler frequency zero-compensation function is exp(-j2πf dc t m ), where f dc The Doppler center frequency of the scene echo.

[0095] In one embodiment, the pre-set distance migration correction function is exp(-j4πf r Vsinθt m / c), f r Where θ is the range frequency, V is the radar platform velocity, and θ is the radar angle of view.

[0096] In one embodiment, the pre-set azimuth reference function is: k a Frequency is tuned to the azimuth direction of the signal.

[0097] In one embodiment, the radial velocity of the moving target is obtained by calculating the Doppler center frequency shift, including:

[0098] The radial velocity of the moving target is obtained by calculating using the Doppler center frequency shift.

[0099] v r =λf shift / -2

[0100] Among them, f shift This represents the Doppler center frequency shift.

[0101] In a specific embodiment, taking a radar system with a carrier frequency of 220 GHz as an example, a point target is used as the imaging target, the bandwidth is 900 MHz, the pulse repetition frequency is 16000 Hz, the pulse duration is 1 μs, the radar platform speed is 60 m / s, and the platform height is 1300 m. The imaging geometry model is as follows: Figure 2 As shown.

[0102] Simulations revealed that when the radial velocity of the moving target is greater than zero, the imaging result will shift to the left from its original position, and the Doppler center frequency shift of the moving target will be less than zero. However, when the radial velocity of the moving target is less than zero, the imaging result will shift to the right from its original position, and the Doppler center frequency shift of the moving target will be greater than zero. Figure 3 and Figure 4 Specific imaging results and time-frequency distribution diagrams are provided.

[0103] Simulation results show that when the radial velocity of the moving target is greater than zero, the Doppler center frequency of the target's echo is less than zero. Figure 3 As shown in (b), the Doppler center frequency of the moving target echo is -3550Hz, while the Doppler center frequency caused by the target's lateral position can be calculated as 333Hz using the formula 2x0v / (λR0). Therefore, from f mdc It can be seen that the Doppler center frequency shift caused by the motion of the moving target is -3833Hz. From the relationship between radial velocity and Doppler center frequency shift, f... shift =-2v r / λ can be used to obtain v r It is 2.6134 m / s, and then the relationship between radial velocity and distance velocity is... The velocity v in the distance direction can be obtained. y It is 3.0020 m / s. Similarly, when the radial velocity of a moving target is less than zero, such as... Figure 4 As shown in (b), the Doppler center frequency of the moving target echo is greater than zero, at which point f mdc The Doppler center frequency is 4100Hz, and the Doppler center frequency caused by the target's lateral position is 333Hz. Therefore, the Doppler center frequency shift caused by the moving target's motion is 3767Hz. We can then obtain v at this point. r The velocity is 2.5684 m / s, and the range velocity v y It is 2.9503 m / s.

[0104] The following section applies this method to real data. Following the flowchart, the Doppler center frequency of the scene echo is first estimated, then the Doppler center frequency of the scene echo is compensated for, and finally the Doppler center frequency of the moving target is estimated. The time-frequency distribution diagram of a scene echo in a certain frame is shown below. Figure 5As shown, the Doppler center frequency of the scene is 5800Hz. By compensating for this Doppler center frequency, the imaging result will remain in the middle, as shown below. Figure 6 As shown. Next, the imaging results are magnified to observe the Doppler frequency caused by the target's lateral position. Figure 7 The Doppler center frequency resulting from the target's lateral position is 650Hz.

[0105] Next, the moving target signal is extracted and time-frequency analysis is performed to obtain the Doppler center frequency of the moving target, such as... Figure 8 As shown, the Doppler center frequency of the moving target is 4950Hz, and the imaging results indicate that the radial velocity of the moving target is less than zero. Subtracting the Doppler frequency caused by the target's lateral position, we obtain a Doppler center frequency shift of 4300Hz due to the target's motion. Therefore, the radial velocity of the moving target is -2.9861m / s. Next, we address the issue of refocusing the moving target. We perform an inverse Fourier transform of the signal from azimuth to azimuth, extract the moving target signal, perform time-frequency analysis, and plot the time-frequency graph, as shown below. Figure 9 and Figure 10 As shown. From Figure 9 It can be seen that the time-frequency distribution line before the moving target is focused has a certain tilt angle and jitter. The tilt is caused by frequency modulation mismatch, which can be eliminated by modifying the frequency modulation. The jitter is caused by some nonlinear effects, which are then solved by using the phase gradient self-aggregation (PGA) function. After modifying the frequency modulation and using the PGA function, the moving target image is refocused, as shown below. Figure 10 As shown.

[0106] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0107] In one embodiment, such as Figure 11As shown, a terahertz video synthetic aperture radar moving target imaging device based on time-frequency analysis is provided, including: a radar echo model construction and processing module 1102, an echo signal compensation module 1104, a time-frequency analysis module 1106, a Doppler center frequency shift calculation module 1108, and an imaging module 1110, wherein:

[0108] The radar echo model construction and processing module 1102 is used to acquire the instantaneous range and radar echo of the radar reaching the moving target; construct a radar echo model of the moving target based on the instantaneous range and radar echo; perform windowing processing and range compression on the radar echo model to obtain the compressed echo signal.

[0109] The echo signal compensation module 1104 is used to perform a short-time Fourier transform on the compressed echo signal to obtain a time-frequency distribution map. The Doppler center frequency of the entire scene echo is obtained from the time-frequency distribution map, and the compressed echo signal is compensated according to the preset Doppler frequency zero-padding function to obtain the compensated echo.

[0110] The time-frequency analysis module 1106 is used to perform range migration correction and azimuth processing on the compensated echo according to the preset range migration correction function and azimuth reference function to obtain preliminary imaging results; obtain the range cell position of the moving target from the preliminary imaging results, extract the moving target signal and perform time-frequency analysis to obtain the Doppler center frequency of the moving target echo;

[0111] The Doppler center frequency offset calculation module 1108 is used to calibrate the azimuth of the preliminary imaging results based on the radar pulse repetition frequency, obtain the Doppler frequency brought about by the lateral position of the moving target by the target shadow, and obtain the Doppler center frequency offset by subtracting the Doppler frequency brought about by the lateral position of the moving target from the Doppler center frequency of the moving target echo.

[0112] Imaging module 1110 is used to calculate the Doppler center frequency shift to obtain the radial velocity of the moving target; to perform an inverse Fourier transform of the azimuth direction on the preliminary imaging results and a short-time Fourier transform on the moving target signal to obtain the transformed time-frequency map; to modify the modulation frequency of the azimuth reference function according to the transformed time-frequency map until the tilt of the time-frequency distribution line of the moving target disappears, thus obtaining the azimuth signal modulation frequency; and to perform precise imaging of the moving target based on the radial velocity of the moving target, the azimuth signal modulation frequency, and the phase gradient self-focusing function to obtain the final imaging result.

[0113] Specific limitations regarding the terahertz video synthetic aperture radar moving target imaging device based on time-frequency analysis can be found in the limitations of the terahertz video synthetic aperture radar moving target imaging method based on time-frequency analysis mentioned above, and will not be repeated here. Each module in the aforementioned terahertz video synthetic aperture radar moving target imaging device based on time-frequency analysis can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in hardware or independent of the processor in a computer device, or stored in software in the memory of a computer device, so that the processor can call and execute the operations corresponding to each module.

[0114] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 12 As shown, the computer device includes a processor, memory, network interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The network interface is used to communicate with external terminals via a network connection. When the computer program is executed by the processor, it implements a terahertz video synthetic aperture radar moving target imaging method based on time-frequency analysis. The display screen can be a liquid crystal display (LCD) or an e-ink display. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0115] Those skilled in the art will understand that Figure 12 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0116] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0117] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0118] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for imaging moving targets in terahertz video synthetic aperture radar based on time-frequency analysis, characterized in that, The method comprises: acquiring instantaneous distances and radar echoes of a radar to a moving target; constructing a radar echo model of the moving target according to the instantaneous distances and the radar echoes, performing windowing processing and distance compression on the radar echo model to obtain a compressed echo signal; performing short-time Fourier transform on the compressed echo signal to obtain a time-frequency distribution diagram, acquiring a Doppler center frequency of an entire scene echo from the time-frequency distribution diagram, compensating the compressed echo signal according to a pre-set Doppler frequency zero padding function to obtain a compensated echo; performing distance migration correction and azimuth processing on the compensated echo according to a pre-set distance migration correction function and an azimuth reference function to obtain a preliminary imaging result; acquiring a distance unit position where the moving target is located from the preliminary imaging result, extracting a moving target signal, and performing time-frequency analysis to obtain a Doppler center frequency of a moving target echo; scaling the azimuth of the preliminary imaging result according to a radar pulse repetition frequency, obtaining a Doppler frequency caused by a lateral position of the moving target by means of a target shadow, subtracting the Doppler frequency caused by the lateral position of the moving target from the Doppler center frequency of the moving target echo to obtain a Doppler center frequency offset; calculating the Doppler center frequency offset to obtain a radial velocity of the moving target; performing inverse azimuth Fourier transform on the preliminary imaging result and performing short-time Fourier transform on the moving target signal to obtain a transformed time-frequency diagram, modifying a frequency modulation rate of the azimuth reference function according to the transformed time-frequency diagram until an inclination of a time-frequency distribution line of the moving target disappears to obtain an azimuth signal frequency modulation rate; accurately imaging the moving target according to the radial velocity of the moving target, the azimuth signal frequency modulation rate and a phase gradient autofocus function to obtain a final imaging result.

2. The method of claim 1, wherein, The method comprises: acquiring instantaneous distances and radar echoes of a radar to a moving target; where R(t m ) is the instantaneous range, rect() denotes the window function, exp denotes the exponential function with base e, j denotes the imaginary unit, t is the range fast time, T p is the radar pulse width, f c is the radar center frequency, l is the radar wavelength, k r is the range rate, t m is the azimuth slow time, T a is the synthetic aperture time, and c is the speed of light.

3. The method of claim 1, wherein, constructing a radar echo model of the moving target according to the instantaneous distances and the radar echoes, performing windowing processing and distance compression on the radar echo model to obtain a compressed echo signal; performing short-time Fourier transform on the compressed echo signal to obtain a time-frequency distribution diagram, acquiring a Doppler center frequency of an entire scene echo from the time-frequency distribution diagram, compensating the compressed echo signal according to a pre-set Doppler frequency zero padding function to obtain a compensated echo; performing distance migration correction and azimuth processing on the compensated echo according to a pre-set distance migration correction function and an azimuth reference function to obtain a preliminary imaging result; 4. The method of claim 2, wherein, The pre-set Doppler frequency zeroing function is exp(-j2πf dc t m ), where f dc is the Doppler center frequency of the scene echo.

5. The method of claim 4, wherein, The pre-set range migration correction function is exp(-j4πf r Vsinθt m / c), f r is the range frequency, V is the radar platform velocity, and θ is the radar squint angle.

6. The method of claim 4, wherein, The pre-set azimuth reference function is k a is the signal azimuth frequency modulation rate.

7. The method of claim 2, wherein, acquiring a distance unit position where the moving target is located from the preliminary imaging result, extracting a moving target signal, and performing time-frequency analysis to obtain a Doppler center frequency of a moving target echo; scaling the azimuth of the preliminary imaging result according to a radar pulse repetition frequency, obtaining a Doppler frequency caused by a lateral position of the moving target by means of a target shadow, subtracting the Doppler frequency caused by the lateral position of the moving target from the Doppler center frequency of the moving target echo to obtain a Doppler center frequency offset; v r = λf shift -2 where f shift is the Doppler center frequency offset.

8. A terahertz video synthetic aperture radar moving target indication device based on time-frequency analysis, characterized in that, calculating the Doppler center frequency offset to obtain a radial velocity of the moving target; performing inverse azimuth Fourier transform on the preliminary imaging result and performing short-time Fourier transform on the moving target signal to obtain a transformed time-frequency diagram, modifying a frequency modulation rate of the azimuth reference function according to the transformed time-frequency diagram until an inclination of a time-frequency distribution line of the moving target disappears to obtain an azimuth signal frequency modulation rate; accurately imaging the moving target according to the radial velocity of the moving target, the azimuth signal frequency modulation rate and a phase gradient autofocus function to obtain a final imaging result. The method comprises: acquiring instantaneous distances and radar echoes of a radar to a moving target; constructing a radar echo model of the moving target according to the instantaneous distances and the radar echoes, performing windowing processing and distance compression on the radar echo model to obtain a compressed echo signal; performing short-time Fourier transform on the compressed echo signal to obtain a time-frequency distribution diagram, acquiring a Doppler center frequency of an entire scene echo from the time-frequency distribution diagram, compensating the compressed echo signal according to a pre-set Doppler frequency zero padding function to obtain a compensated echo; performing distance migration correction and azimuth processing on the compensated echo according to a pre-set distance migration correction function and an azimuth reference function to obtain a preliminary imaging result; acquiring a distance unit position where the moving target is located from the preliminary imaging result, extracting a moving target signal, and performing time-frequency analysis to obtain a Doppler center frequency of a moving target echo; scaling the azimuth of the preliminary imaging result according to a radar pulse repetition frequency, obtaining a Doppler frequency caused by a lateral position of the moving target by means of a target shadow, subtracting the Doppler frequency caused by the lateral position of the moving target from the Doppler center frequency of the moving target echo to obtain a Doppler center frequency offset; calculating the Doppler center frequency offset to obtain a radial velocity of the moving target; performing inverse azimuth Fourier transform on the preliminary imaging result and performing short-time Fourier transform on the moving target signal to obtain a transformed time-frequency diagram, modifying a frequency modulation rate of the azimuth reference function according to the transformed time-frequency diagram until an inclination of a time-frequency distribution line of the moving target disappears to obtain an azimuth signal frequency modulation rate; accurately imaging the moving target according to the radial velocity of the moving target, the azimuth signal frequency modulation rate and a phase gradient autofocus function to obtain a final imaging result. The method comprises: acquiring instantaneous distances and radar echoes of a radar to a moving target; constructing a radar echo model of the moving target according to the instantaneous distances and the radar echoes, performing windowing processing and distance compression on the radar echo model to obtain a compressed echo signal; an echo signal compensation module, configured to perform short-time Fourier transform on the compressed echo signal to obtain a time-frequency distribution map, obtain a Doppler center frequency of an entire scene echo from the time-frequency distribution map, compensate the compressed echo signal according to a pre-set Doppler frequency zero-filling function, and obtain a compensated echo; a time-frequency analysis module, configured to perform range migration correction and azimuth processing on the compensated echo according to a pre-set range migration correction function and an azimuth reference function, to obtain a preliminary imaging result, obtain a distance unit position where a moving target is located from the preliminary imaging result, extract a moving target signal, and perform time-frequency analysis on the moving target signal to obtain a Doppler center frequency of a moving target echo; a Doppler center frequency offset calculation module, configured to scale an azimuth of the preliminary imaging result according to a radar pulse repetition frequency, obtain a Doppler frequency caused by a moving target lateral position by means of a target shadow, subtract the Doppler frequency caused by the moving target lateral position from the Doppler center frequency of the moving target echo, and obtain a Doppler center frequency offset; an imaging module, configured to calculate the Doppler center frequency offset to obtain a radial velocity of the moving target, perform inverse azimuth Fourier transform on the preliminary imaging result and short-time Fourier transform on the moving target signal to obtain a transformed time-frequency map, modify a frequency modulation rate of the azimuth reference function according to the transformed time-frequency map until an inclination of a time-frequency distribution line of the moving target disappears, to obtain an azimuth signal frequency modulation rate, and perform accurate imaging on the moving target according to the radial velocity of the moving target, the azimuth signal frequency modulation rate, and a phase gradient autofocus function, to obtain a final imaging result. 9.A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the computer device is configured to perform the method according to any one of claims 1-8 when the computer program is executed by the processor. The processor executes the computer program to implement the steps of the method in any one of claims 1 to 7.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the method in any one of claims 1 to 7.

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