Three-dimensional InSAR imaging method and system based on OAM

Abstract

The invention discloses a three-dimensional InSAR imaging method and system based on OAM, and the method comprises the steps: building an echo signal model for an SAR imaging scene; constructing a coupling OAM phase item compensation filter; echo signals are received and compensated; performing two-dimensional imaging processing according to the compensated echo signal; solving a three-dimensional coordinate by using a two-dimensional imaging result and a geometrical relationship; constructing a coupling OAM phase item and a BESSEL compensation filter by using the three-dimensional coordinates; compensating the echo signal again, and performing two-dimensional imaging processing according to the compensated echo signal; and solving a new three-dimensional coordinate by using a two-dimensional imaging result and a geometrical relationship. The system comprises a signal modeling unit, a compensation unit, a two-dimensional imaging unit and a three-dimensional imaging unit. According to the invention, high-precision three-dimensional target reconstruction can be realized. The method can be widely applied to the field of high-resolution imaging.

Description

Technical Field

[0001] The present invention relates to the field of radar signal processing, and in particular to a three-dimensional InSAR imaging method and system based on fused orbital angular momentum (OAM). Background Art

[0002] Radar imaging technology, due to its exceptional all-weather and all-day capabilities, has been widely applied in various fields. Based on the imaging principle, radar imaging can be broadly categorized into two types: fixed-field-of-view imaging and synthetic aperture radar (SAR) imaging. Fixed-field-of-view imaging utilizes fixed transmission and reception modes, providing only range resolution but lacking azimuth resolution. In contrast, SAR imaging achieves high azimuth resolution by exploiting the Doppler effect caused by platform motion.

[0003] However, SAR imaging is a complex remote sensing technology that faces multiple technical challenges in practical applications. Traditional SAR imaging reconstructs targets by acquiring two-dimensional target information. However, due to the limitations of two-dimensional features, high-precision target reconstruction cannot be achieved. Summary of the Invention

[0004] In view of this, in order to solve the technical problem that the existing SAR imaging method has low accuracy in three-dimensional target reconstruction due to the limitation of two-dimensional imaging, the present invention proposes a three-dimensional InSAR imaging method based on OAM, which includes the following steps:

[0005] For SAR imaging scenarios, an echo signal model is established;

[0006] Construct coupled OAM phase term compensation filter;

[0007] Receive echo signal and compensate;

[0008] Performing two-dimensional imaging processing according to the compensated echo signal;

[0009] Use the two-dimensional imaging results and geometric relationships to solve the three-dimensional coordinates;

[0010] Reconstruct the coupled OAM phase term and BESSEL term based on the three-dimensional coordinates and perform secondary compensation on the echo signal;

[0011] Performing two-dimensional imaging processing on the echo signal after secondary compensation to generate a new two-dimensional imaging result;

[0012] Based on the new two-dimensional imaging results and geometric relationships, the three-dimensional coordinates are iteratively optimized to achieve high-precision three-dimensional target reconstruction.

[0013] In some embodiments, the step of performing two-dimensional imaging processing based on the compensated echo signal specifically includes:

[0014] First, the compensated echo signal is uniformly compressed to eliminate the coupled phase in the range and azimuth directions;

[0015] Then, Stolt interpolation is performed to correct the nonlinear offset in the wavenumber domain and complete two-dimensional focused imaging.

[0016] In some embodiments, the time domain compensation filter includes a coupled OAM phase term compensation filter and a BESSEL term compensation filter, which are used to correct the phase distortion introduced by orbital angular momentum and the scattering characteristics characterized by the Bessel function, respectively.

[0017] The present invention also proposes a three-dimensional InSAR imaging system based on OAM, the system comprising:

[0018] The signal modeling unit builds an echo signal model including OAM modulation characteristics for SAR imaging scenarios;

[0019] The compensation unit constructs a coupled OAM phase compensation filter; receives the echo signal and compensates it;

[0020] a two-dimensional imaging unit, performing two-dimensional imaging processing according to the compensated echo signal;

[0021] 3D imaging unit, which uses 2D imaging results and geometric relationships to solve 3D coordinates;

[0022] The secondary compensation unit reconstructs the coupled OAM phase term and BESSEL term based on the three-dimensional coordinates and performs secondary compensation on the echo signal;

[0023] The iterative optimization unit performs two-dimensional imaging processing on the echo signal after quadratic compensation to generate a new two-dimensional imaging result; based on the new two-dimensional imaging result and the geometric relationship, the three-dimensional coordinates are iteratively optimized to achieve high-precision three-dimensional target reconstruction;

[0024] In some embodiments, the system further includes a motion compensation module for correcting phase errors introduced by non-ideal motion of the platform to ensure the accuracy of OAM phase modulation.

[0025] Based on the above scheme, the present invention provides a three-dimensional InSAR imaging method and system based on OAM. Compared with the limitations of traditional SAR imaging and the problems of OAM signal phase coupling and energy leakage, the present invention achieves high-precision three-dimensional target reconstruction. Traditional SAR imaging can only obtain two-dimensional imaging results, while SAR imaging combined with OAM can obtain three-dimensional imaging results by utilizing the unique phase wavefront distribution of vortex waves. By coupling the OAM phase term and the BESSEL term for joint compensation, the mode dispersion problem in vortex electromagnetic wave imaging is solved; the iterative compensation mechanism of three-dimensional coordinate feedback is adopted to break through the limitation of baseline length of traditional InSAR elevation measurement; combining time domain filtering and wavenumber domain interpolation, efficient suppression of OAM modal interference is achieved, significantly improving the three-dimensional reconstruction accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flowchart of the steps of a three-dimensional InSAR imaging method based on OAM of the present invention;

[0027] Figure 2 1 is a schematic diagram of a geometric scene of a strip vortex SAR in a side-view mode according to a specific embodiment of the present invention;

[0028] Figure 3 Schematic diagram of Bessel function curves of different modes according to a specific embodiment of the present invention;

[0029] Figure 4 2 is a schematic diagram comparing the imaging results of the specific embodiments S1 and S2 of the present invention;

[0030] Figure 5 This is a schematic diagram of three-dimensional imaging of multiple target points according to a specific embodiment of the present invention;

[0031] Figure 6 It is a schematic diagram of three-dimensional imaging of a single target point in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] It should be noted that, for ease of description, only the parts related to the invention are shown in the drawings. In the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0034] It should be understood that the terms "system," "device," "unit," and / or "module" used in this application are a method for distinguishing different components, elements, parts, portions, or assemblies at different levels. However, if other terms can achieve the same purpose, the terms may be replaced by other expressions.

[0035] As used in this application and the claims, unless the context clearly indicates an exception, the terms "a," "an," "an," and / or "the" are not intended to refer to the singular and may include the plural, unless the context clearly indicates otherwise. Generally speaking, the terms "comprises" and "include" only indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include other steps or elements. The phrase "comprises a..." does not preclude the presence of additional identical elements in the process, method, product, or apparatus that includes the elements.

[0036] In the description of the embodiments of this application, "plurality" refers to two or more than two. The terms "first" and "second" below are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0037] In addition, flow charts are used in this application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, the steps may be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0038] Reference Figure 1 , which is a flow chart of an optional example of the OAM-based three-dimensional InSAR imaging method proposed in the present invention. The method can be applied to a computer device. The imaging method proposed in this embodiment may include but is not limited to the following steps:

[0039] Step S1: performing signal modeling based on the imaging scene and constructing an expression of the echo signal;

[0040] Step S2: constructing a coupled OAM phase term compensation filter based on the expression of the echo signal;

[0041] Step S3, receiving the echo signal;

[0042] Step S4: compensating the echo signal based on the coupled OAM phase term to obtain a compensated echo signal;

[0043] Step S5: performing two-dimensional imaging processing according to the compensated echo signal to obtain a two-dimensional imaging result;

[0044] Step S6: generating three-dimensional coordinates according to the two-dimensional imaging results and the geometric relationship.

[0045] Step S7: constructing a coupled OAM phase term and a BESSEL term according to the three-dimensional coordinates;

[0046] Step S8: compensating the echo signal based on the coupled OAM phase term compensation filter and the BESSEL term compensation filter to obtain a compensated echo signal;

[0047] Step S9: performing two-dimensional imaging processing according to the compensated echo signal to obtain a two-dimensional imaging result;

[0048] Step S10: Generate new three-dimensional coordinates according to the two-dimensional imaging results and the geometric relationship.

[0049] In some feasible embodiments, step S1 specifically includes:

[0050] Figure 2 The strip vortex SAR imaging scene in the side-view mode is demonstrated. In this system, the number of UCA elements is N, and the center O of the concentric uniform circular array (UCA) motion trajectory is used as the origin of the coordinate system to establish a right-handed rectangular coordinate system: the radar platform flies at a constant speed in the positive direction of the x-axis, the downward viewing angle of the UCA is 90 degrees, the y-axis coincides with the direction of the vortex beam center, and the z-axis is perpendicular to the xOy plane and points to the ground. The system uses a concentric uniform circular array as the transmitting array, and the transmitting signal uses a linear frequency modulation (LFM) waveform. At the same time, the receiving array elements are arranged at the geometric center of the UCA to form a transmitting and receiving split structure of the vortex electromagnetic wave.

[0051] In the imaging scene, O' is the center of the imaging scene, the position coordinates of UCA are (vη,0,0), and the position coordinates of the target are P T =(x T ,y T ,z T ), under far-field conditions, the transmitted signal is:

[0052]

[0053] In the formula, t is the fast time variable, η is the slow time variable, and c is the propagation speed of the vortex electromagnetic wave. is the linear frequency modulation ratio, f c is the center frequency, l is the mode of the vortex electromagnetic wave, ω a (·) is the azimuthal envelope, ω r(·) is the range envelope, and the distance from the target to the origin is:

[0054]

[0055] The shortest slant distance from the target point to the UCA is The instantaneous distance to the target is:

[0056]

[0057] is the azimuth at time 0, and the instantaneous azimuth is:

[0058]

[0059] θ0 is the pitch angle at time 0, and the instantaneous pitch angle is:

[0060]

[0061] k=2π{K r [tR η / c]+f c} / c is the wave number, a is the array radius, J l [kasinθ η ] is the Bessel function of the first kind.

[0062] The echo signal can be obtained by superimposing the signals obtained by all array elements:

[0063]

[0064] Where σ is the scattering coefficient of the signal.

[0065] As can be seen from formula (6), compared with traditional radar imaging, the echo signal received by vortex imaging not only contains range and Doppler information, but also adds a spiral phase term related to the azimuth angle. This term carries the orbital angular momentum information of the target, which can obtain more dimensional information.

[0066] In some feasible embodiments, steps S2, S3 and S4 specifically include:

[0067] Analyzing the echo signal formula, the azimuth term in the coupled OAM phase term varies with slow time. This term can provide azimuth information, but it will affect the imaging results after consistent compression and Stolt interpolation. In the same scenario, the echo signals of two sets of different modes can be expressed as:

[0068]

[0069] The conjugate multiplication of the two sets of echo signals can be obtained:

[0070]

[0071] According to Euler's formula, we can get:

[0072]

[0073] According to the reference point of the initial azimuth, judge For example, when l1=1, l2=-1, When φ=sin -1 (φ); when When φ=π-sin -1 (φ); when When φ=2π+sin -1 (φ). Whenever A change of π / 2 will cause φ to change by 2π. Finally, the instantaneous azimuth is extracted:

[0074]

[0075] In order to avoid the influence of coupled OAM phase on two-dimensional imaging, a time-domain compensation filter (Equation 13) is designed to eliminate phase coupling interference.

[0076]

[0077] In some feasible embodiments, step S5 specifically includes:

[0078] The echo formula after compensation is:

[0079]

[0080] The WK algorithm is used to process the echo (14) into two-dimensional imaging. The specific processing steps are: In the two-dimensional frequency domain, use H(f τ ,f a ) performs uniform compression on the echo signal, H(f τ ,f a ) can be expressed as:

[0081]

[0082] Then, Stolt interpolation is performed to convert the original distance frequency f τ Mapped to the new distance frequency f τ ' makes the echo signal linear. Among them, f a is the azimuth frequency.

[0083] The point spread function of the target is obtained as:

[0084]

[0085] Where Δfr is the bandwidth of the signal.

[0086] In some feasible embodiments, step S6 specifically includes:

[0087] The maximum value point corresponds to the coordinates of the target point. T ,t T ,l1)=|s1(η,t,l1)| max Solve the target's azimuth coordinate x T and distance R T .

[0088] R T =ct T (18)

[0089] x T =vη T (19)

[0090] Substituting the formula and the formula into the formula, we can get

[0091]

[0092] Combining the formula, formula, formula and formula, we can get

[0093]

[0094] In some feasible embodiments, the following further comprises:

[0095] The Bessel terms introduced in imaging will affect the extraction of target features to a certain extent, such as Figure 3 As shown in the figure, under the premise of consistent antenna size and initial frequency, the zero points and energy distribution of the Bessel terms of different modes are different. In vortex echo signals, the Bessel terms affect the signal energy distribution and the imaging results after processing by some existing two-dimensional imaging algorithms.

[0096] In the time domain, the echo signal s r2 (η,t,l2) is compensated:

[0097] s2(η,t)=s2(η,t,l2)·H(η,l1)·BE(22)

[0098] BE=1 / B (23)

[0099]

[0100] Based on the above imaging method, the present invention also provides relevant simulation examples:

[0101] Single target point comparison:

[0102] Figure 4This is a comparison of the imaging results of the vortex echo signal S1 and the vortex echo signal S2. From the azimuth envelope diagram, it can be seen that the azimuth quality performance parameters change little before and after compensation. After Bessel compensation, the side lobes in the range envelope are significantly suppressed, such as Figure 4 As shown in .

[0103] As can be seen in Table 1, the azimuth quality performance parameters and range resolution remain essentially unchanged, while the range integrated sidelobe ratio and peak sidelobe ratio have both significantly improved. The range integrated sidelobe ratio (ISLR) has improved by over 10dB.

[0104] Table 1 Imaging quality performance parameters

[0105]

[0106] Multi-target point comparison:

[0107] from Figure 5 It can be seen from the three-dimensional coordinate diagram shown that the reconstructed target point basically coincides with the preset target point, proving that the algorithm can successfully process the vortex echo data of multiple target points, realize three-dimensional imaging of multiple target points, and simultaneously solve the coordinate values of multiple target points.

[0108] Table 2 Comparison of real coordinates and reconstructed coordinates

[0109]

[0110]

[0111] Table 3 below shows the relative root mean square error (RRMSE) results for five different modal echo signals. The RRMSE calculation method is shown in the formula. The RRMSE is less than 0.008.

[0112]

[0113] Table 3 Relative root mean square error results

[0114] Parameters RRMSE Position(l1=1,l2=-1) 0.0050 Position(l1=2,l2=1) 0.0077 Position(l1=2,l2=-1) 0.0052 Position(l1=1,l2=-2) 0.0053 Position(l1=2,l2=-2) 0.0051

[0115] Single target imaging

[0116] System Configuration:

[0117] The co-located transmitter and receiver system uses the UCA array. The target point coordinates are: PT1 = (20, 1000, 1000). The target point P T1 The distance R from the origin O T1 It is 1414.35m. The system parameters are shown in Table 1;

[0118] Table 4 System parameters

[0119] Simulation parameters Numerical Carrier frequency 2GHz PRF 2000Hz Signal bandwidth 150MHz Sampling frequency 250MHz Radar flight speed 50m / s Mode l1 1 Mode l2 -1

[0120] Signal processing:

[0121] Perform phase compensation, Bessel correction and ωK algorithm processing according to the flowchart. The coordinates of the target point are solved as PT1'=(20.21,1000,999.79). The three-dimensional target point diagram is as follows Figure 6 shown.

[0122] Result verification: Target point PT1 = (20, 1000, 1000) PT1 = (20, 1000, 1000), the reconstructed coordinates are:

[0123] (20.21,1000,999.79)(20.21,1000,999.79), the error is less than 0.3% ( Figure 6 ).

[0124] Multi-target imaging

[0125] System Configuration:

[0126] The co-located transmitter and receiver system uses a UCA array, and the system parameters are shown in Table 1. Six target points are preset (Table 2). After processing, the error between the reconstructed coordinates and the true coordinates is less than 0.5% ( Figure 5 ).

[0127] A three-dimensional InSAR imaging system based on OAM, comprising:

[0128] A signal modeling unit, configured to execute step S1;

[0129] A compensation unit, configured to execute steps S2-S4;

[0130] A two-dimensional imaging unit, configured to execute step S5;

[0131] a three-dimensional imaging unit, configured to execute step S6;

[0132] A secondary compensation unit, configured to execute steps S7-S8;

[0133] The iterative optimization unit is used to execute steps S9-S10.

[0134] The contents of the above method embodiments are all applicable to the present system embodiments. The functions specifically implemented by the present system embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0135] A three-dimensional InSAR imaging device based on OAM:

[0136] at least one processor;

[0137] at least one memory for storing at least one program;

[0138] When the at least one program is executed by the at least one processor, the at least one processor implements the above-mentioned three-dimensional InSAR imaging method based on OAM.

[0139] The contents of the above method embodiments are all applicable to the present device embodiments. The functions specifically implemented by the present device embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0140] A storage medium stores processor-executable instructions, which, when executed by a processor, are used to implement the above-mentioned OAM-based three-dimensional InSAR imaging method.

[0141] The contents of the above method embodiments are all applicable to the present storage medium embodiment. The functions specifically implemented by the present storage medium embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0142] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A three-dimensional InSAR imaging method based on OAM, characterized in that: The following steps are involved: Perform signal modeling based on the imaging scenario and construct an expression for the echo signal; Constructing a coupled OAM phase term compensation filter based on an expression of the echo signal; receiving echo signals; Compensating the echo signal based on the coupled OAM phase term compensation filter to obtain a compensated echo signal; performing two-dimensional imaging processing according to the compensated echo signal to obtain a two-dimensional imaging result; generating three-dimensional coordinates according to the two-dimensional imaging results and the geometric relationship; reconstructing the coupled OAM phase term and the BESSEL term based on the three-dimensional coordinates, performing secondary compensation on the echo signal to obtain a secondary compensated echo signal; The three-dimensional coordinates are iteratively optimized according to the quadratically compensated echo signal.

2. The OAM-based three-dimensional InSAR imaging method according to claim 1, characterized in that: The expression of the echo signal is as follows: Where η represents the slow time variable, t represents the fast time variable, l represents the mode of the vortex electromagnetic wave, σ represents the scattering coefficient of the signal, N represents the number of elements of the uniform circular array, ω α (·) represents the azimuthal envelope, x T represents the x-axis coordinate of the target point in the three-dimensional coordinate system, v represents the movement speed of the uniform circular array, ω r (·) represents the range envelope, R η represents the distance from the target to the center of the uniform circular array, c represents the propagation speed of the vortex electromagnetic wave, i represents the imaginary number, K r represents the linear frequency modulation ratio, represents the instantaneous azimuth of the target, f c represents the center frequency, k represents the wave number, a represents the array radius, J l [kasinθ η ] represents the Bessel function of the first kind, θ η Indicates the instantaneous pitch angle of the target.

3. The OAM-based three-dimensional InSAR imaging method according to claim 1, characterized in that: The expression of the coupled OAM phase term compensator is expressed as follows: Where l1 represents the mode of the first group of uniform circular arrays.

4. The OAM-based three-dimensional InSAR imaging method according to claim 2, characterized in that: The step of performing two-dimensional imaging processing according to the compensated echo signal to obtain a two-dimensional imaging result specifically includes: uniformly compressing the compensated echo signal in a two-dimensional frequency domain to obtain a compressed signal; Stolt interpolation is performed on the compressed signal to map the original range frequency to a new range frequency to obtain a two-dimensional imaging result.

5. The OAM-based three-dimensional InSAR imaging method according to claim 4, characterized in that: The point spread function of the target in the two-dimensional imaging result is expressed as follows: Where Δf r Indicates the bandwidth of the signal.

6. The OAM-based three-dimensional InSAR imaging method according to claim 1, characterized in that: The step of generating three-dimensional coordinates based on the two-dimensional imaging results and the geometric relationship specifically includes: Determine the x-axis coordinate and distance of the target based on the maximum point in the two-dimensional imaging result; The y-axis coordinate and the z-axis coordinate of the target are solved based on the x-axis coordinate of the target, the distance and the instantaneous azimuth.

7. A three-dimensional InSAR imaging system based on OAM, characterized in that: include: A signal modeling unit performs signal modeling based on the imaging scene and constructs an expression of the echo signal; A compensation unit, constructing a time domain compensation filter based on an expression of the echo signal; receiving echo signals; Compensating the echo signal based on the time domain compensation filter to obtain a compensated echo signal; a two-dimensional imaging unit, configured to perform two-dimensional imaging processing according to the compensated echo signal to obtain a two-dimensional imaging result; A three-dimensional imaging unit, configured to generate three-dimensional coordinates based on the two-dimensional imaging results and the geometric relationship; a secondary compensation unit, which reconstructs the coupled OAM phase term and the BESSEL term based on the three-dimensional coordinates, performs secondary compensation on the echo signal, and obtains a secondary compensated echo signal; The iterative optimization unit is used to iteratively optimize the three-dimensional coordinates according to the echo signal after the quadratic compensation.

8. A three-dimensional InSAR imaging device based on OAM, characterized in that: include: at least one processor; at least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements the OAM-based three-dimensional InSAR imaging method as described in any one of claims 1 to 6.

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