SAR imaging method for large-angle diving hypersonic vehicle based on two-dimensional frequency domain interpolation

Abstract

The present invention relates to a SAR imaging method for a large-angle dive hypersonic aircraft based on two-dimensional frequency domain interpolation, comprising: constructing the instantaneous slant range of the reference point for a reference point in a scene, and performing series expansion of the instantaneous slant range of the reference point in azimuth slow time; constructing the corresponding instantaneous slant range of any point in the scene and performing series expansion, and performing three-dimensional Taylor expansion of the instantaneous slant range of the arbitrary point after the series expansion; compensating the instantaneous slant range of the reference point in the received radar echo signal through a consistent compensation function in the azimuth dimension frequency domain distance dimension time domain, and reconstructing and converting the compensated radar echo signal into a radar echo signal in the two-dimensional frequency domain; performing nonlinear phase decoupling on it; performing consistent compensation on the reference item, and obtaining the imaging result through CZT interpolation. The present invention can solve the problem of poor imaging quality of HSV SAR under large dive conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing, and relates to a SAR imaging method carried by a large-angle diving hypersonic aircraft based on two-dimensional frequency domain interpolation. Background Art

[0002] HSV is a multivariable system with strong coupling and parameter uncertainty, which plays an important role in the design of future aircraft. Due to its high speed, strong nonlinearity and complex motion trajectory, it has a high survival rate even in harsh environments. The synthetic aperture radar (SAR) installed on the HSV platform can obtain two-dimensional high-resolution ground images, greatly improving the environmental perception capability.

[0003] However, the existing SAR imaging method uses small aperture frequency domain imaging with nonlinear frequency modulation scaling to suppress the cross-range unit migration caused by linear range migration and acceleration, and uses a new geometric correction method based on back projection to eliminate the negative impact of imaging processing.

[0004] However, this method does not take into account the HSV SAR in a large dive flight state (similar to a vertical trajectory). This method, which mainly performs imaging processing on the horizontal plane, will result in poor HSV SAR imaging quality under large dive conditions.

[0005] Therefore, how to improve the imaging quality of HSV SAR under large dive conditions has become an urgent problem to be solved. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] The embodiment of the present invention provides a SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation, comprising the following steps:

[0008] S1. constructing instantaneous slant distances of reference points in the scene, and performing series expansion of the instantaneous slant distances of the reference points in azimuth slow time;

[0009] S2, constructing the corresponding instantaneous slant distance of any point in the scene and performing series expansion, performing three-dimensional Taylor expansion on the instantaneous slant distance of the arbitrary point after series expansion, wherein the three-dimensional Taylor expansion term includes the instantaneous slant distance of the reference point after expansion, and performing second-order parameter fitting on each level in the three-dimensional Taylor expansion term to obtain the simplified instantaneous slant distance of the arbitrary point;

[0010] S3, receiving a radar echo signal in a difference frequency domain; compensating the instantaneous slant range of the reference point in the radar echo signal by using a consistent compensation function in the azimuth-frequency-domain, distance-time-domain, and reconstructing the compensated radar echo signal, and converting the reconstructed radar echo signal into a radar echo signal in a two-dimensional frequency domain by using a stationary phase principle;

[0011] S4, performing nonlinear phase decoupling on the two-dimensional frequency domain radar echo signal, wherein the two-dimensional frequency domain radar echo signal after the nonlinear phase decoupling includes: a reference item, a function only related to the distance, and a function only related to the azimuth;

[0012] S5, performing consistent compensation on the reference item, and mapping the function related only to the distance and the function related only to the azimuth to the two-dimensional frequency domain to obtain the distance dimension frequency and the azimuth dimension frequency respectively;

[0013] S6. Acquire an imaging result through CZT interpolation according to the distance dimension frequency and the azimuth dimension frequency.

[0014] In one embodiment of the present invention, the expression of the instantaneous slant distance of the reference point is:

[0015] |r C (η)|=|r C -vη-aη 2 / 2-bη 3 / 6|:

[0016] Wherein, C is the reference point; C (η)| is the instantaneous slant distance vector of the reference point; η represents the azimuth slow time; r C is the shortest slope distance vector of the reference point; v is the velocity vector, a is the acceleration vector, and b is the jerk vector;

[0017] The expression of the instantaneous slope distance of the reference point after expansion is:

[0018]

[0019] in,

[0020]

[0021]

[0022]

[0023] Among them, <, > is the vector inner product, the is the slope distance dependency, is the Doppler center dependency, is a cross-coupling term.

[0024] In one embodiment of the present invention, the expression of the instantaneous slope distance of any point after series expansion is:

[0025]

[0026] Among them, the |r A (η)| is the expression of the instantaneous slant distance vector of any point, and the r A is the shortest slant distance vector of any point in the scene, For r A Taylor expansion coefficient of (η).

[0027] In one embodiment of the present invention, the expression of the instantaneous slope distance of any point after three-dimensional Taylor expansion is:

[0028]

[0029] Where κ0(η), κ1(η) and κ2(η) are the three-dimensional Taylor series expansion coefficients, is the slope distance dependency, is the Doppler center dependency, is a cross-coupling term.

[0030] In one embodiment of the present invention, the expression of the quadratic term during the second-order parameter fitting is:

[0031]

[0032] Among them, the o n , the p n , the q n They correspond to the fitting coefficients of the κ0(η), the κ1(η) and the κ2(η) respectively.

[0033] In one embodiment of the present invention, the simplified expression of the instantaneous slant distance of any point is:

[0034]

[0035] in,

[0036]

[0037]

[0038] In one embodiment of the present invention, the expression of the radar echo signal is:

[0039]

[0040] Wherein, the s0(fr , n) is the radar echo signal, the f c is the carrier frequency, the f r is the distance dimension frequency.

[0041] In one embodiment of the present invention, the expression of the consistent compensation function for performing consistent compensation on the reference item is:

[0042]

[0043] The expression of the compensated radar echo signal is:

[0044]

[0045] The expression of the two-dimensional frequency domain radar echo signal is:

[0046]

[0047] in,

[0048]

[0049]

[0050]

[0051] ξ=(f r +f c ) / c;

[0052] The H0(f r , η) is the consistent compensation function, the s1(f r , η) is the compensated radar echo signal, the s1(f r , f η ) is a two-dimensional frequency domain radar echo signal, is the slope distance dependency, is the Doppler dependence, is a cross-coupling term.

[0053] In one embodiment of the present invention, performing nonlinear phase decoupling on the radar echo signal in the two-dimensional frequency domain includes:

[0054] The coupling terms in the two-dimensional frequency domain radar echo signal are expanded by two-dimensional expansion according to the following expression:

[0055]

[0056] Among them, Ψ0 and Ψ1 are the coefficients of the expansion;

[0057] Performing nonlinear phase decoupling on the radar echo signal in the two-dimensional frequency domain according to the expanded coupling term;

[0058] The phase expression after the nonlinear phase decoupling is:

[0059]

[0060] The compensation function expression for performing consistent compensation on the reference item is:

[0061]

[0062] The expression for mapping the function only related to distance and the function only related to orientation to the two-dimensional frequency domain is:

[0063]

[0064] Among them, f0′ and f1′ are the distance dimension frequency and azimuth dimension frequency after mapping, respectively.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] The HSV SAR slant range history expression proposed by the present invention is more accurate, and the constructed compensation function is more precise, so that the designed imaging algorithm has higher accuracy and less approximation, and is suitable for HSV SAR imaging under any large dive and front oblique angle. The problem of insufficient imaging quality of the existing HSV SAR imaging technology under large dive conditions is solved.

[0067] Other aspects and features of the present invention will become apparent from the following detailed description with reference to the accompanying drawings. It should be understood, however, that the drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention, as reference should be made to the appended claims. It should also be understood that, unless otherwise indicated, the drawings are not necessarily drawn to scale and are intended merely to conceptually illustrate the structures and processes described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 A schematic flow chart of a SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation provided in an embodiment of the present invention;

[0069] Figure 2 The geometric model of the large-dive ultra-high-speed missile-borne SAR in the Cartesian coordinate system adopted by the present invention;

[0070] Figure 3 This is a simulated imaging diagram of the geometric model of the large-dive ultra-high-speed missile-borne SAR located in a Cartesian coordinate system adopted by the present invention. DETAILED DESCRIPTION

[0071] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0072] HSV is a multivariable system with strong coupling and parameter uncertainty, and plays an important role in the design of future aircraft. Due to its high speed, strong nonlinearity and complex motion trajectory, it has a high survival rate even in harsh environments. The synthetic aperture radar (SAR) installed on the HSV platform can obtain two-dimensional high-resolution ground images, greatly improving the environmental perception capability. Compared with airborne SAR, HSV SAR has a greater speed and can provide timely and rapid response and high-resolution imaging and rapid detection. In addition, the higher its flight altitude means that the beam coverage area is larger, so more information can be obtained. Compared with spaceborne SAR, HSV SAR has greater flexibility, so it can provide timely response and comprehensive detection of areas of interest. It also has lower transmission power and higher signal-to-noise ratio. In addition, HSVSAR has an extremely high forward squint angle, which can obtain more potentially useful information for rapid response and decision-making. The imaging method of traditional SAR is ineffective for the HSV platform because the latter has an extremely high forward squint angle, so it is necessary to reconsider the design of imaging methods suitable for HSV SAR.

[0073] In an article published on TGRS, titled "A Frequency-Domain Imaging Algorithm for Highly Squinted SAR Mounted on Maneuvering Platforms With Nonlinear Trajectory" (DOI: 10.1109 / TGRS.2016.2535391), a frequency interpolation algorithm based on an approximate slant range model was proposed. Small-aperture frequency domain imaging with nonlinear frequency modulation scaling was used to suppress linear range migration and cross-range unit migration caused by acceleration, and a new geometric correction method based on back projection was used to eliminate the negative effects of imaging processing. However, this method does not take into account the HSV SAR in a large dive flight state (approximately a vertical trajectory). This method, which mainly performs imaging processing on the horizontal plane, will have significant residuals due to the high front tilt angle and large vertical velocity of the HSV. At the same time, due to the large coupling between the range and azimuth dimensions, high-precision approximation processing cannot be performed, which will reduce the imaging quality.

[0074] From the above analysis, we can see that the shortcomings of existing HSV SAR imaging technology mainly include:

[0075] (1) The traditional slant range expression is not accurate enough due to the maneuvering trajectory, hypersonic speed, and large dive of HSV SAR, which results in poor imaging quality of HSV SAR under large dive conditions in existing technologies.

[0076] (2) The three-dimensional velocity, acceleration, jerk and other parameters brought about by the HSV SAR's large dive flight, as well as the extremely large forward squint angle, cause the characteristics of the radar echo signal to change dramatically compared with traditional SAR. On the one hand, it causes the echo sampling signal results to be mixed, and on the other hand, it causes the range-azimuth coupling characteristics and the two-dimensional space-varying characteristics to change dramatically. The time-frequency characteristics of the echo are no longer similar to the linear frequency modulation characteristics of traditional SAR, and the imaging effect of the traditional algorithm is poor or even impossible.

[0077] In view of the shortcomings of the prior art, the present invention proposes a high-angle dive hypersonic vehicle-borne SAR imaging method based on two-dimensional frequency domain interpolation. The method re-derives a new slant range equation and a two-dimensional frequency interpolation function through quadratic fitting and three-dimensional expansion. The problem of range-azimuth cross-coupling and large spatial variation existing in the prior art when applied to HSV SAR with a near-high dive trajectory is solved, and the imaging quality of HSV SAR under high dive conditions is improved.

[0078] See also Figure 1 , Figure 1 A flow chart of a method for SAR imaging of a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation provided by an embodiment of the present invention. The present invention provides a method for SAR imaging of a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation, and the imaging method comprises the following steps:

[0079] S1. Construct the instantaneous slant distance of the reference point in the scene, and expand the instantaneous slant distance of the reference point in series in the azimuth slow time;

[0080] The reference point is the point where all parameters are known.

[0081] Specifically, the slope distance expression of the reference point C is constructed based on the imaging geometry model. The expression of the instantaneous slope distance of the reference point C is:

[0082] |r C (η)|=|r C -vη-aη 2 / 2-bη 3 / 6|;

[0083] Among them, |·| is the absolute value operation symbol; C is the reference point; |r C (η)| is the instantaneous slant distance vector of the reference point; η represents the azimuth slow time; r Cis the shortest slope distance vector of the reference point; v is the velocity vector, a is the acceleration vector, and b is the jerk vector.

[0084] After obtaining the instantaneous slant range expression of the reference point C according to the imaging geometry model, it can be expanded in power series with the azimuth slow time. The expression of the instantaneous slant range of the reference point after expansion is:

[0085]

[0086] in, is the Taylor expansion coefficient, and the first three expressions are as follows:

[0087]

[0088]

[0089]

[0090] Among them, <, > is the vector inner product, is the slope distance dependency, is the Doppler center dependency, is a cross-coupling term.

[0091] S2, constructing the corresponding instantaneous slant distance of any point in the scene and performing series expansion, performing three-dimensional Taylor expansion on the instantaneous slant distance of any point after series expansion, wherein the three-dimensional Taylor expansion term includes the instantaneous slant distance of the reference point after expansion, performing second-order parameter fitting on each level in the three-dimensional Taylor expansion term to obtain the simplified instantaneous slant distance of any point;

[0092] Specifically, for any point A in the scene, an expression for the instantaneous slant distance is constructed and expanded in series. The expression for the instantaneous slant distance of any point after series expansion is:

[0093]

[0094] Among them, |r A (η)| is the expression of the instantaneous slope distance vector at any point, r A is the shortest slope distance vector of any point in the scene, For r A Taylor expansion coefficient of (η).

[0095] In order to reduce the error, the slope distance expression of any point after the series expansion is subjected to a higher precision three-dimensional Taylor expansion. The expression of the instantaneous slope distance of any point after the three-dimensional Taylor expansion is:

[0096]

[0097] Where κ0(η), κ1(η) and κ2(η) are the three-dimensional Taylor series expansion coefficients, is the slope distance dependency, is the Doppler center dependency, is a cross-coupling term.

[0098] The complex three-dimensional Taylor series is fitted by second-order parameters to derive the quadratic term of the simplified slope range history. The expression of the quadratic term during second-order parameter fitting is:

[0099]

[0100] Among them, n , p n ,q n They correspond to the fitting coefficients of κ0(η), κ1(η) and κ2(η), respectively.

[0101] At this time, the simplified expression of the instantaneous slope distance of any point is:

[0102]

[0103] in,

[0104]

[0105]

[0106] Aiming at the problem that the existing HSV SAR slant range history expression is not accurate enough in the state of large dive and hypersonic motion, the present invention proposes a more accurate slant range expression based on three-dimensional Taylor series expansion, and designs a HSV SAR imaging method suitable for large dive angles based on the accurate expression. The algorithm can efficiently obtain high-precision large dive HSV SAR images.

[0107] From the simplified expression of the instantaneous slant range at any point, it can be seen that the two-dimensional spectrum can be easily derived using the principle of fixed phase (POSP). In addition, through the simplified slant range quadratic term, the third-order and higher-order terms corresponding to the azimuth frequency in the two-dimensional spectrum will disappear, the quadratic phase term can be decoupled, and the higher-order phase term can also be avoided.

[0108] It is worth noting that the slant distance expressions in the following steps all use the slant distance expressions after second-order parameter fitting (that is, the instantaneous slant distance of any point after the above simplification). Because the parameters after three-dimensional expansion are very complex and not conducive to the construction of a two-dimensional spectrum, a second-order parameter fitting is performed to simplify the slant distance expression.

[0109] S3, receiving the radar echo signal in the difference frequency domain; compensating the instantaneous slant range of the reference point in the radar echo signal by using a consistent compensation function in the azimuth-frequency-distance-time domain, and reconstructing the compensated radar echo signal, and converting the reconstructed radar echo signal into a radar echo signal in the two-dimensional frequency domain by using the stationary phase principle;

[0110] Specifically, a radar echo signal in the difference frequency domain is received, and the expression of the radar echo signal is:

[0111]

[0112] Among them, s0(f r ,η) is the radar echo signal, f c is the carrier frequency, f r is the distance dimension frequency.

[0113] The term corresponding to the reference point C is invariant in space and can be eliminated by a consistent compensation function in the azimuth, frequency, distance and time domains to reduce the two-dimensional spectrum. The expression of the consistent compensation function is:

[0114]

[0115] At this time, the expression of the compensated radar echo signal is:

[0116]

[0117] After the consistency compensation and slant range expression are reconstructed, the expression of the two-dimensional frequency domain radar echo signal is obtained through POSP:

[0118]

[0119] in,

[0120]

[0121]

[0122]

[0123] ξ=(f r +f c ) / c;

[0124] H0(f r , η) is the consistent compensation function for compensating the instantaneous slant range of the reference point in the radar echo signal through the consistent compensation function of the azimuth dimension, frequency domain, distance dimension and time domain, s1(f r ,η) is the compensated radar echo signal, s1(f r , f η) is the two-dimensional frequency domain radar echo signal, is the slope distance dependency, is the Doppler dependence, is a cross-coupling term.

[0125] Slope range dependency and Doppler dependence Respectively with f r and f η There is a linear relationship between the two terms, which can be eliminated by consistent compensation. is the cross-coupling term, which corresponds to f r and f η The coupling is affected by the near-submerged trajectory, that is, the larger acceleration and jerk vector, and the space variation is very obvious and must be eliminated.

[0126] S4, performing nonlinear phase decoupling on the two-dimensional frequency domain radar echo signal, wherein the two-dimensional frequency domain radar echo signal after nonlinear phase decoupling includes: a reference term, a function only related to the distance, and a function only related to the azimuth;

[0127] The nonlinear phase decoupling of the two-dimensional frequency domain radar echo signal is performed to eliminate the space-varying error. Specifically:

[0128] For cross-coupling terms To break it down:

[0129]

[0130] Among them, Ψ0 and Ψ1 are the coefficients of the expansion.

[0131] The above process can be understood as expanding the coupling terms in the radar echo signal in the two-dimensional frequency domain by means of two-dimensional expansion.

[0132] can be decoupled into three separable parts, then the original two-dimensional frequency domain radar echo signal s1(f r ,f η ) can be rewritten as:

[0133]

[0134] in, is the reference item; is a function related only to distance; is a function that is only related to the orientation.

[0135] S5, performing consistent compensation on the reference item, and mapping the function only related to the distance and the function only related to the orientation to the two-dimensional frequency domain to obtain the distance dimension frequency and the orientation dimension frequency respectively;

[0136] Specifically, the compensation function expression for consistent compensation of the reference item is:

[0137]

[0138] The expression for mapping the function only related to distance and the function only related to orientation to the two-dimensional frequency domain is:

[0139]

[0140] Among them, f′0 and f1′ are the distance dimension frequency and azimuth dimension frequency after mapping, respectively.

[0141] The present invention proposes a two-dimensional expansion based on radius / angle, which can eliminate cross-coupling and space-variant terms with high precision through multi-level decomposition, thereby obtaining high-quality imaging results.

[0142] S6. Obtain imaging results through CZT interpolation according to the distance dimension frequency and the azimuth dimension frequency.

[0143] Due to the large amount of calculation, the present disclosure adopts CZT interpolation processing to compensate the reference item, distance dimension frequency and azimuth dimension frequency to obtain the imaging result.

[0144] The frequency domain algorithm of the present invention, which performs interpolation compensation based on frequency, effectively eliminates the coupling terms of the range and azimuth dimensions. Compared with time domain algorithms such as FFBP, it has higher accuracy and faster imaging speed and can meet the high real-time requirements of the HSV platform.

[0145] In the present invention, after obtaining the synthetic aperture radar echo, the range dimension Fourier transform is performed, and then the range dimension compression is performed, and then the slant range expression is reconstructed, and then the azimuth dimension time domain consistent compression, azimuth dimension Fourier transform, azimuth dimension frequency domain consistent compression are performed, fitting is performed in the two-dimensional frequency domain, two-dimensional inverse Fourier transform, and finally the imaging result is obtained.

[0146] Compared with the prior art, the present invention has the following beneficial effects:

[0147] (1) Compared with the prior art, the HSV SAR slant range history expression proposed in the present invention is more accurate, and the compensation function constructed is more precise, so that the designed imaging algorithm has higher accuracy and fewer approximations, and is suitable for HSV SAR imaging under any large dive and front oblique angle. The problem of insufficient imaging quality of the existing HSV SAR imaging technology under large dive conditions is solved.

[0148] (2) The method proposed in the present invention has low computational complexity, strong real-time performance, higher accuracy, and more effective coupling removal, which solves the problems of large dive, cross coupling caused by hypersonic speed, and large space variation in existing HSV SAR technology. It can meet the HSV SAR imaging requirements in practical engineering applications.

[0149] Simulation experiments can further demonstrate the beneficial effects of the present invention.

[0150] Figure 2 The geometric model of the high-speed missile-borne SAR based on a large dive is located in the Cartesian coordinate system adopted by the present invention, Q point is the azimuth center moment (ACM), l is the flight trajectory of the radar carrier, v, a and b represent the velocity vector, acceleration vector and platform jerk vector of the platform respectively, r C and r A They represent the slant distance vectors of the reference point C and any point A in the scene, h is the flight altitude of the platform, θ is the beam pitch angle, is the angle between the beam and the velocity vector of the ACM, defined as the foreslant angle.

[0151] Table 1 is the measured parameters:

[0152] Table 1 Measured parameters

[0153]

[0154] The selection in the image is mainly due to the phase rotation, from Figure 3 It can be seen from the figure that under the condition of large viewing angle, the method proposed in the present invention can effectively perform imaging.

[0155] In summary, the algorithm of the present invention can be applied to HSV SAR imaging. SAR imaging itself has the characteristics of working all day and all weather. It has been widely valued by countries around the world and has been successfully applied to geology, hydrology, oceanography, mapping, environmental monitoring, agriculture, forestry, meteorology, military and other fields. HSV has a high survival rate even in harsh environments due to its high speed, strong nonlinearity and complex motion trajectory. The synthetic aperture radar (SAR) installed on the HSV platform can obtain two-dimensional high-resolution ground images, which greatly improves the environmental perception ability. Compared with airborne SAR, HSV SAR has a higher speed and can provide timely and rapid response and high-resolution imaging and rapid detection. In addition, the higher the flight altitude, the more information can be obtained. Compared with spaceborne SAR, HSV SAR has greater flexibility, so it can provide timely response and comprehensive detection of areas of interest. It also has lower transmission power and higher signal-to-noise ratio. In addition, HSV-SAR has a very high forward-looking squint angle, which can obtain more potentially useful information for rapid response and decision-making. This algorithm can be applied to HSVSAR imaging, which is of great significance in target perception, recognition, tracking and other aspects.

[0156] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0157] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or special data points described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or special data points described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0158] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation, characterized in that: The following steps are involved: S1. constructing instantaneous slant distances of reference points in the scene, and performing series expansion of the instantaneous slant distances of the reference points in azimuth slow time; S2, constructing the corresponding instantaneous slant distance of any point in the scene and performing series expansion, performing three-dimensional Taylor expansion on the instantaneous slant distance of the arbitrary point after series expansion, wherein the three-dimensional Taylor expansion term includes the instantaneous slant distance of the reference point after expansion, and performing second-order parameter fitting on each level in the three-dimensional Taylor expansion term to obtain the simplified instantaneous slant distance of the arbitrary point; S3, receiving a radar echo signal in a difference frequency domain; compensating the instantaneous slant range of the reference point in the radar echo signal by using a consistent compensation function in the azimuth-frequency-domain, distance-time-domain, and reconstructing the compensated radar echo signal, and converting the reconstructed radar echo signal into a radar echo signal in a two-dimensional frequency domain by using a stationary phase principle; S4, performing nonlinear phase decoupling on the two-dimensional frequency domain radar echo signal, wherein the two-dimensional frequency domain radar echo signal after the nonlinear phase decoupling includes: a reference item, a function only related to the distance, and a function only related to the azimuth; S5, performing consistent compensation on the reference item, and mapping the function related only to the distance and the function related only to the azimuth to the two-dimensional frequency domain to obtain the distance dimension frequency and the azimuth dimension frequency respectively; S6. Acquire an imaging result through CZT interpolation according to the distance dimension frequency and the azimuth dimension frequency.

2. The SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation according to claim 1 is characterized in that: The expression of the instantaneous slope distance of the reference point is: |r C (h)|=|r C -vη-aη 2 / 2-b 3 / 6|; Wherein, C is the reference point; C (η)| is the instantaneous slant distance vector of the reference point; η represents the azimuth slow time; r C is the shortest slope distance vector of the reference point; v is the velocity vector, a is the acceleration vector, and b is the jerk vector; The expression of the instantaneous slope distance of the reference point after expansion is: in, Among them, <, > is the vector inner product, the is the slope distance dependency, is the Doppler center dependency, is a cross-coupling term.

3. The SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation according to claim 2 is characterized in that: The expression of the instantaneous slope distance of any point after series expansion is: Among them, the |r A (η)| is the expression of the instantaneous slant distance vector of any point, and the r A is the shortest slant distance vector of any point in the scene, For r A Taylor expansion coefficient of (η).

4. The SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation according to claim 3 is characterized in that: The expression of the instantaneous slope distance of any point after three-dimensional Taylor expansion is: Where κ0(η), κ1(η) and κ2(η) are the three-dimensional Taylor series expansion coefficients, is the slope distance dependency, is the Doppler center dependency, is a cross-coupling term.

5. The SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation according to claim 4 is characterized in that: The expression of the quadratic term during the second-order parameter fitting is: Among them, the o n , the p n , the q n They correspond to the fitting coefficients of the κ0(η), the κ1(η) and the κ2(η) respectively.

6. The SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation according to claim 5, characterized in that: The simplified expression of the instantaneous slope distance of any point is: in, 7. The SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation according to claim 6 is characterized in that: The expression of the radar echo signal is: Wherein, the s0(f r , n) is the radar echo signal, the f c is the carrier frequency, the f r is the distance dimension frequency.

8. The SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation according to claim 7, characterized in that: The expression of the consistent compensation function corresponding to the instantaneous slant range of the reference point in the radar echo signal is compensated by the consistent compensation function of the azimuth dimension, frequency domain, distance dimension and time domain: The expression of the compensated radar echo signal is: The expression of the two-dimensional frequency domain radar echo signal is: in, ξ=(f r +f c ) / c; The H0(f r , η) is the consistent compensation function of the azimuth dimension frequency domain distance dimension time domain, the s1(f r , n) is the compensated radar echo signal, the s1(f r , f η ) is a two-dimensional frequency domain radar echo signal, is the slope distance dependency, is the Doppler dependence, is a cross-coupling term.

9. The SAR imaging method for a large-angle dive hypersonic vehicle based on two-dimensional frequency domain interpolation according to claim 8, characterized in that: The performing nonlinear phase decoupling on the radar echo signal in the two-dimensional frequency domain comprises: The coupling terms in the two-dimensional frequency domain radar echo signal are expanded by two-dimensional expansion according to the following expression: Among them, Ψ0 and Ψ1 are the coefficients of the expansion; Performing nonlinear phase decoupling on the radar echo signal in the two-dimensional frequency domain according to the expanded coupling term; The phase expression after the nonlinear phase decoupling is: The compensation function expression for performing consistent compensation on the reference item is: The expression for mapping the function related only to distance and the function related only to orientation to the two-dimensional frequency domain is: Among them, f0′ and f1′ are the distance dimension frequency and azimuth dimension frequency after mapping, respectively.

Images