A SAR imaging method and system for short-time frequency-hopping stepped signals

Abstract

The present invention discloses a SAR imaging method and system of a short-time frequency hopping step signal, and relates to the field of SAR imaging. The method comprises: processing an input short-time frequency hopping step signal through a short-time frequency hopping step signal model to generate a scene echo signal, preprocessing the scene echo signal according to a reference function, performing range migration correction on the preprocessed scene echo signal, performing azimuth matching filtering on the scene echo signal after range migration correction in the frequency domain, and obtaining a SAR image of the short-time frequency hopping step signal. The SAR image obtained by the scheme solves the defects of range defocusing and limited range signal bandwidth in the existing scheme.

Description

Technical Field

[0001] The present invention relates to the field of SAR imaging, and in particular to a SAR imaging method and system of a short-time frequency-hopping stepped signal. Background Art

[0002] In the Synthetic Aperture Radar (SAR) system, a large-bandwidth linear frequency modulation signal (LPM) is generally used to obtain a higher range resolution. The processing of the SAR signal includes matched filtering, curvature correction and azimuth pulse compression. In the SAR radar system using short-time frequency hopping signals, the radar transmit signal waveform uses a costas signal combined with FSK-PSK in the sub-pulses of a pulse group, and each sub-pulse uses a different starting frequency, and there is a certain frequency overlap between the pulse signals. Compared with the traditional linear frequency modulation signal, the short-time frequency hopping step signal is a time series agile waveform, which cannot be coherently processed using the linear frequency modulation matching function, and defocusing occurs in the distance dimension. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a SAR imaging method and system of a short-time frequency-hopping stepped signal in view of the deficiencies in the prior art.

[0004] The technical solution of the present invention to solve the above technical problems is as follows:

[0005] A SAR imaging method of a short-time frequency-hopping stepped signal, comprising:

[0006] S1, processing the input short-time frequency hopping step signal through the short-time frequency hopping step signal model to generate a scene echo signal;

[0007] S2, preprocessing the scene echo signal according to a reference function;

[0008] S3, performing range migration correction on the pre-processed scene echo signal;

[0009] S4, performing azimuth matching filtering on the scene echo signal after range migration correction in the frequency domain to obtain a SAR image of the short-time frequency hopping step signal.

[0010] The beneficial effects of the present invention are as follows: the scheme processes the short-time frequency hopping step signal through a short-time frequency hopping step signal model, pre-processes the scene echo signal obtained by the processing, then performs range migration correction, and then performs azimuth matching filtering to obtain the SAR image of the short-time frequency hopping step signal. The SAR image obtained by the scheme solves the defects of range defocusing and limited range signal bandwidth in the existing scheme.

[0011] Furthermore, it also includes:

[0012] The model of the short-time frequency hopping step signal is constructed according to the following formula:

[0013]

[0014] in, Represents the fast time variable of the sub-pulse signal, i = 1, 2, ..., M; t k represents the slow time variable of the pulse signal; M represents the frequency encoding length of the sub-pulse; f c(k) represents the starting reference frequency of the kth sub-pulse; f m(k) is the frequency code of the kth sub-pulse; represents the phase modulation corresponding to the chip of the kth sub-pulse; T represents the pulse signal time width; j represents a complex number; k represents the transmission signal sequence number, ranging from 1 to positive infinity;

[0015] The short-time frequency-hopping step signal includes a superposition of k sub-pulse signals.

[0016] The beneficial effect of adopting the above further solution is that the model of the short-time frequency hopping step signal in this solution generates a scene echo signal.

[0017] Furthermore, the S2 specifically includes:

[0018] Processing the scene echo signal through mixing filtering to obtain a first echo signal after removing the carrier frequency;

[0019] The first echo signal is subjected to matched filtering according to a reference function, and the first echo signal subjected to matched filtering is used as the preprocessed scene echo signal, thereby completing preprocessing.

[0020] The beneficial effect of adopting the above further scheme is: this scheme performs processing through mixing filtering, and then performs matched filtering according to a reference function to complete the preprocessing of the first echo signal.

[0021] Furthermore, the S3 specifically includes:

[0022] The pre-processed scene echo signal is corrected for range migration according to the correction function and the two-dimensional pulse pressure.

[0023] The beneficial effect of adopting the above further solution is that: this solution realizes the range migration correction of the scene callback signal through the correction function and the two-dimensional pulse pressure.

[0024] Furthermore, the S4 specifically includes:

[0025] The scene echo signal after range migration correction is subjected to azimuth matching filtering in the frequency domain through an azimuth matching filtering function to obtain a SAR image of the short-time frequency hopping step signal.

[0026] The beneficial effect of adopting the above further scheme is: the SAR image is obtained by azimuth matching filtering of the scheme, the occurrence of defocusing phenomenon is reduced, and the signal bandwidth in the range direction is not limited.

[0027] Another technical solution of the present invention to solve the above technical problems is as follows:

[0028] A SAR imaging system of short-time frequency-hopping stepping signal, comprising: a signal processing module, a preprocessing module, a correction module and a filtering module;

[0029] The signal processing module is used to process the input short-time frequency hopping step signal through the short-time frequency hopping step signal model to generate a scene echo signal;

[0030] The preprocessing module is used to preprocess the scene echo signal according to a reference function;

[0031] The correction module is used to perform range migration correction on the pre-processed scene echo signal;

[0032] The filtering module is used to perform azimuth matching filtering on the scene echo signal after range migration correction in the frequency domain to obtain the SAR image of the short-time frequency hopping step signal.

[0033] The beneficial effects of the present invention are as follows: the scheme processes the short-time frequency hopping step signal through a short-time frequency hopping step signal model, pre-processes the scene echo signal obtained by the processing, then performs range migration correction, and then performs azimuth matching filtering to obtain the SAR image of the short-time frequency hopping step signal. The SAR image obtained by the scheme solves the defects of range defocusing and limited range signal bandwidth in the existing scheme.

[0034] Furthermore, it also includes: a model building module, which is used to build a model of the short-time frequency hopping step signal according to the following formula:

[0035]

[0036] in, Represents the fast time variable of the sub-pulse signal, i = 1, 2, ..., M; t k represents the slow time variable of the pulse signal; M represents the frequency encoding length of the sub-pulse; f c(k) represents the starting reference frequency of the kth sub-pulse; f m(k) is the frequency code of the kth sub-pulse; represents the phase modulation corresponding to the chip of the kth sub-pulse; T represents the pulse signal time width; j represents a complex number; k represents the transmission signal sequence number, ranging from 1 to positive infinity;

[0037] The short-time frequency-hopping step signal includes a superposition of k sub-pulse signals.

[0038] The beneficial effect of adopting the above further solution is that the model of the short-time frequency hopping step signal in this solution generates a scene echo signal.

[0039] Furthermore, the preprocessing module is specifically used to process the scene echo signal through mixing filtering to obtain a first echo signal after carrier frequency removal;

[0040] The first echo signal is subjected to matched filtering according to a reference function, and the first echo signal subjected to matched filtering is used as the preprocessed scene echo signal, thereby completing preprocessing.

[0041] The beneficial effect of adopting the above further scheme is: this scheme performs processing through mixing filtering, and then performs matched filtering according to a reference function to complete the preprocessing of the first echo signal.

[0042] Furthermore, the correction module is specifically used to perform range migration correction on the pre-processed scene echo signal according to the correction function and the two-dimensional pulse pressure.

[0043] The beneficial effect of adopting the above further solution is that: this solution realizes the range migration correction of the scene callback signal through the correction function and the two-dimensional pulse pressure.

[0044] Furthermore, the filtering module is specifically used to perform azimuth matched filtering on the scene echo signal after range migration correction in the frequency domain through an azimuth matched filtering function to obtain the SAR image of the short-time frequency hopping step signal.

[0045] The beneficial effect of adopting the above further scheme is: the SAR image is obtained by azimuth matching filtering of the scheme, the occurrence of defocusing phenomenon is reduced, and the signal bandwidth in the range direction is not limited.

[0046] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A schematic flow chart of a SAR imaging method using a short-time frequency-hopping stepped signal provided by an embodiment of the present invention;

[0048] Figure 2 The present invention provides a structural block diagram of a SAR imaging system with a short-time frequency-hopping stepped signal. DETAILED DESCRIPTION

[0049] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0050] like Figure 1 As shown, a SAR imaging method of a short-time frequency-hopping stepped signal provided by an embodiment of the present invention includes:

[0051] S1, processing the input short-time frequency hopping step signal through the short-time frequency hopping step signal model to generate a scene echo signal;

[0052] In one embodiment, establishing a short-time frequency hopping step signal model may include: in the short-time frequency hopping step signal, a duration of Mt b The radar waveform is composed of M chips with different modulation frequencies, and the width of each chip is t b , the intervals between each frequency point are equal, that is:

[0053]

[0054] Where B is the signal bandwidth of the sub-pulse, M is the frequency code f m ={f1, f2, ..., f M-1 , f M}. At the same time, each chip also has a corresponding phase modulation, and the phase modulation of each chip is Therefore, the kth sub-pulse signal in a pulse group can be set as:

[0055]

[0056] Among them, the fast time variable of the sub-pulse signal is Each chip corresponds to the corresponding M is the frequency encoding length of the sub-pulse, f c(k) is the starting reference frequency of the kth sub-pulse, and the frequency of the code chip is the increase based on this frequency, f m(k) is the frequency code of the kth sub-pulse, is the phase modulation corresponding to the code chip of the kth sub-pulse, t k is the slow time variable of the pulse signal.

[0057] The echo signal is:

[0058]

[0059] in:

[0060]

[0061] R is the distance between the scattering point and the radar system, and c is the speed of light.

[0062] S2, preprocessing the scene echo signal according to a reference function;

[0063] In one embodiment, the distance preprocessing of the scene echo signal may include: first, the echo signal after the carrier frequency is removed is obtained by mixing and filtering. Since the signal is an inter-pulse step signal, it is necessary to select the corresponding f c(k) As the mixing signal, the baseband echo signal of the radar is obtained:

[0064]

[0065] Perform matched filtering on the echo signal after carrier removal, and the reference function is:

[0066]

[0067] The frequency domain fast convolution method is used to perform distance-dimensional pulse compression on the signal. formula and The formula is Fourier transformed, and after multiplication in the frequency domain, an inverse Fourier transform is performed to obtain:

[0068]

[0069] S3, performing range migration correction on the pre-processed scene echo signal;

[0070] In one embodiment, the range migration correction may include: defining fr as the range frequency, fa as the azimuth frequency, and the movement correction function as:

[0071] H1=exp(j2πR0 / c*(f a λ / 2v) 2 f r ),

[0072] right The formula is used for two-dimensional pulse pressure, and we get:

[0073]

[0074] Will Formula and S(f r , f a ) formula and perform a two-dimensional inverse Fourier transform to obtain:

[0075]

[0076] S4, performing azimuth matching filtering on the scene echo signal after range migration correction in the frequency domain to obtain a SAR image of the short-time frequency hopping step signal.

[0077] In one embodiment, the azimuth matched filtering may include: an azimuth matched filtering function:

[0078]

[0079] Similarly, the azimuth matched filtering is also performed in the frequency domain, that is:

[0080]

[0081] At this point, the azimuth pulse compression is completed and the short-time frequency-hopping stepped signal SAR image is obtained.

[0082] This scheme processes the short-time frequency hopping step signal through a short-time frequency hopping step signal model, pre-processes the scene echo signal obtained by the processing, then performs range migration correction, and then performs azimuth matching filtering to obtain the SAR image of the short-time frequency hopping step signal. The SAR image obtained by this scheme solves the defects of range defocusing and limited range signal bandwidth in the existing scheme.

[0083] Preferably, in any of the above embodiments, it further comprises:

[0084] The model of the short-time frequency hopping step signal is constructed according to the following formula:

[0085]

[0086] in, Represents the fast time variable of the sub-pulse signal, i = 1, 2, ..., M; t k represents the slow time variable of the pulse signal; M represents the frequency encoding length of the sub-pulse; f c(k) represents the starting reference frequency of the kth sub-pulse; f m(k) is the frequency code of the kth sub-pulse; represents the phase modulation corresponding to the chip of the kth sub-pulse; T represents the pulse signal time width; j represents a complex number; k represents the transmission signal sequence number, ranging from 1 to positive infinity;

[0087] The short-time frequency-hopping step signal includes a superposition of k sub-pulse signals.

[0088] In one embodiment, establishing a short-time frequency hopping step signal model may include: in the short-time frequency hopping step signal, a duration of Mt b The radar waveform is composed of M chips with different modulation frequencies, and the width of each chip is t b , the intervals between each frequency point are equal, that is:

[0089]

[0090] Where B is the signal bandwidth of the sub-pulse, M is the frequency code f m ={f1, f2, ..., f M-1 , f M}. At the same time, each chip also has a corresponding phase modulation, and the phase modulation of each chip is Therefore, the kth sub-pulse signal in a pulse group can be set as:

[0091]

[0092] Among them, the fast time variable of the sub-pulse signal is Each chip corresponds to the corresponding M is the frequency encoding length of the sub-pulse, f c(k) is the starting reference frequency of the kth sub-pulse, and the frequency of the code chip is the increase based on this frequency, f m(k) is the frequency code of the kth sub-pulse, is the phase modulation corresponding to the code chip of the kth sub-pulse, t k is the slow time variable of the pulse signal.

[0093] The echo signal is:

[0094]

[0095] in:

[0096]

[0097] R is the distance between the scattering point and the radar system, and c is the speed of light.

[0098] The model of the short-time frequency-hopping stepping signal in this scheme generates the scene echo signal.

[0099] Preferably, in any of the above embodiments, S2 specifically includes:

[0100] Processing the scene echo signal through mixing filtering to obtain a first echo signal after removing the carrier frequency;

[0101] The first echo signal is subjected to matched filtering according to a reference function, and the first echo signal subjected to matched filtering is used as the preprocessed scene echo signal, thereby completing preprocessing.

[0102] In one embodiment, the distance preprocessing of the scene echo signal may include: first, the echo signal after carrier frequency removal is obtained by mixing and filtering. Since the signal is an inter-pulse step signal, it is necessary to select the corresponding J c(k) As the mixing signal, the baseband echo signal of the radar is obtained:

[0103]

[0104] Perform matched filtering on the echo signal after carrier removal, and the reference function is:

[0105]

[0106] The frequency domain fast convolution method is used to perform distance-dimensional pulse compression on the signal. formula and The formula is Fourier transformed, and after multiplication in the frequency domain, an inverse Fourier transform is performed to obtain:

[0107]

[0108] This solution performs processing through mixing filtering, and then performs matched filtering according to a reference function to complete the preprocessing of the first echo signal.

[0109] Preferably, in any of the above embodiments, S3 specifically includes:

[0110] The pre-processed scene echo signal is corrected for range migration according to the correction function and the two-dimensional pulse pressure.

[0111] In one embodiment, the range migration correction may include: defining fr as the range frequency, fa as the azimuth frequency, and the movement correction function as:

[0112] H1=exp(j2πR0 / c*(f a λ / 2v) 2 f r ),

[0113] right The formula is used for two-dimensional pulse pressure, and we get:

[0114]

[0115] Will Formula and S(f r , f a ) formula and perform a two-dimensional inverse Fourier transform to obtain:

[0116]

[0117] This scheme realizes the range migration correction of scene callback signal through correction function and two-dimensional pulse pressure.

[0118] Preferably, in any of the above embodiments, S4 specifically includes:

[0119] The scene echo signal after range migration correction is subjected to azimuth matching filtering in the frequency domain through an azimuth matching filtering function to obtain a SAR image of the short-time frequency hopping step signal.

[0120] In one embodiment, the azimuth matched filtering may include: an azimuth matched filtering function:

[0121]

[0122] Similarly, the azimuth matched filtering is also performed in the frequency domain, that is:

[0123]

[0124] At this point, the azimuth pulse compression is completed and the short-time frequency-hopping stepped signal SAR image is obtained.

[0125] The SAR image is obtained by azimuth matching filtering in this scheme, which reduces the occurrence of defocusing and the signal bandwidth in the range direction is not limited.

[0126] In one embodiment, if Figure 2 As shown, a SAR imaging system of a short-time frequency-hopping step signal includes: a signal processing module 1101, a preprocessing module 1102, a correction module 1103 and a filtering module 1104;

[0127] The signal processing module 1101 is used to process the input short-time frequency hopping step signal through a short-time frequency hopping step signal model to generate a scene echo signal;

[0128] The preprocessing module 1102 is used to preprocess the scene echo signal according to a reference function;

[0129] The correction module 1103 is used to perform range migration correction on the pre-processed scene echo signal;

[0130] The filtering module 1104 is used to perform azimuth matching filtering on the scene echo signal after range migration correction in the frequency domain to obtain the SAR image of the short-time frequency hopping step signal.

[0131] This scheme processes the short-time frequency hopping step signal through a short-time frequency hopping step signal model, pre-processes the scene echo signal obtained by the processing, then performs range migration correction, and then performs azimuth matching filtering to obtain the SAR image of the short-time frequency hopping step signal. The SAR image obtained by this scheme solves the defects of range defocusing and limited range signal bandwidth in the existing scheme.

[0132] Preferably, in any of the above embodiments, it further comprises: a model building module, used to build a model of the short-time frequency hopping step signal according to the following formula:

[0133]

[0134] in, Represents the fast time variable of the sub-pulse signal, i = 1, 2, ..., M; t k represents the slow time variable of the pulse signal; M represents the frequency encoding length of the sub-pulse; f c(k) represents the starting reference frequency of the kth sub-pulse; fm(k) is the frequency code of the kth sub-pulse; represents the phase modulation corresponding to the chip of the kth sub-pulse; T represents the pulse signal time width; j represents a complex number; k represents the transmission signal sequence number, ranging from 1 to positive infinity;

[0135] The short-time frequency-hopping step signal includes a superposition of k sub-pulse signals.

[0136] The model of the short-time frequency-hopping stepping signal in this scheme generates the scene echo signal.

[0137] Preferably, in any of the above embodiments, the pre-processing module 1102 is specifically used to process the scene echo signal through mixing filtering to obtain a first echo signal after carrier frequency removal;

[0138] The first echo signal is subjected to matched filtering according to a reference function, and the first echo signal subjected to matched filtering is used as the preprocessed scene echo signal, thereby completing preprocessing.

[0139] This solution performs processing through mixing filtering, and then performs matched filtering according to a reference function to complete the preprocessing of the first echo signal.

[0140] Preferably, in any of the above embodiments, the correction module 1103 is specifically configured to perform range migration correction on the pre-processed scene echo signal according to the correction function and the two-dimensional pulse pressure.

[0141] This scheme realizes the range migration correction of scene callback signal through correction function and two-dimensional pulse pressure.

[0142] Preferably, in any of the above embodiments, the filtering module 1104 is specifically used to perform azimuth matched filtering on the scene echo signal after range migration correction in the frequency domain through an azimuth matched filtering function to obtain a SAR image of the short-time frequency hopping stepped signal.

[0143] The SAR image is obtained by azimuth matching filtering in this scheme, which reduces the occurrence of defocusing and the signal bandwidth in the range direction is not limited.

[0144] It can be understood that in some embodiments, some or all of the optional implementation modes in the above embodiments may be included.

[0145] It should be noted that the above embodiments are product embodiments corresponding to the previous method embodiments. For the description of the optional implementation methods in the product embodiments, reference can be made to the corresponding description in the above method embodiments, which will not be repeated here.

[0146] The reader should understand that 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 characteristics 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 representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics 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 and the features of different embodiments or examples without contradiction.

[0147] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0148] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the embodiments of the present invention.

[0149] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0150] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0151] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A SAR imaging method using a short-time frequency-hopping stepped signal, characterized in that: include: S1, processing the input short-time frequency hopping step signal through the short-time frequency hopping step signal model to generate a scene echo signal; S2, preprocessing the scene echo signal according to a reference function; S3, performing range migration correction on the pre-processed scene echo signal; S4, performing azimuth matched filtering on the scene echo signal after range migration correction in the frequency domain to obtain a SAR image of the short-time frequency hopping step signal; Also includes: The model of the short-time frequency hopping step signal is constructed according to the following formula: ， in, represents the fast time variable of the sub-pulse signal, ; A slow-time variable representing a pulse signal; Indicates the frequency encoding length of the sub-pulse; Indicates the starting reference frequency of the kth sub-pulse; is the frequency code of the kth sub-pulse; represents the phase modulation corresponding to the chip of the kth sub-pulse; Indicates the pulse signal width; Represents a complex number; k is the transmission signal sequence number, ranging from 1 to positive infinity; The short-time frequency-hopping step signal includes a superposition of k sub-pulse signals.

2. The SAR imaging method of a short-time frequency-hopping stepped signal according to claim 1, characterized in that: The S2 specifically includes: Processing the scene echo signal through mixing filtering to obtain a first echo signal after removing the carrier frequency; The first echo signal is subjected to matched filtering according to a reference function, and the first echo signal subjected to matched filtering is used as the preprocessed scene echo signal, thereby completing preprocessing.

3. The SAR imaging method of a short-time frequency-hopping stepped signal according to claim 1, characterized in that: The S3 specifically includes: The pre-processed scene echo signal is corrected for range migration according to the correction function and the two-dimensional pulse pressure.

4. The SAR imaging method of a short-time frequency-hopping stepped signal according to claim 1, characterized in that: The S4 specifically includes: The scene echo signal after range migration correction is subjected to azimuth matching filtering in the frequency domain through an azimuth matching filtering function to obtain a SAR image of the short-time frequency hopping step signal.

5. A SAR imaging system with short-time frequency-hopping stepped signals, characterized in that: include: Signal processing module, preprocessing module, correction module and filtering module; The signal processing module is used to process the input short-time frequency hopping step signal through the short-time frequency hopping step signal model to generate a scene echo signal; The preprocessing module is used to preprocess the scene echo signal according to a reference function; The correction module is used to perform range migration correction on the pre-processed scene echo signal; The filtering module is used to perform azimuth matching filtering on the scene echo signal after range migration correction in the frequency domain to obtain the SAR image of the short-time frequency hopping step signal; It also includes: a model building module, which is used to build a model of the short-time frequency hopping step signal according to the following formula: ， in, represents the fast time variable of the sub-pulse signal, ; A slow-time variable representing a pulse signal; Indicates the frequency encoding length of the sub-pulse; Indicates the starting reference frequency of the kth sub-pulse; is the frequency code of the kth sub-pulse; represents the phase modulation corresponding to the chip of the kth sub-pulse; Indicates the pulse signal width; Represents a complex number; k is the transmission signal sequence number, ranging from 1 to positive infinity; The short-time frequency-hopping step signal includes a superposition of k sub-pulse signals.

6. The SAR imaging system of short-time frequency-hopping stepped signal according to claim 5, characterized in that: The preprocessing module is specifically used to process the scene echo signal through mixing filtering to obtain a first echo signal after the carrier frequency is removed; The first echo signal is subjected to matched filtering according to a reference function, and the first echo signal subjected to matched filtering is used as the preprocessed scene echo signal, thereby completing preprocessing.

7. The SAR imaging system of short-time frequency-hopping stepping signal according to claim 5, characterized in that: The correction module is specifically used to perform range migration correction on the pre-processed scene echo signal according to the correction function and the two-dimensional pulse pressure.

8. The SAR imaging system of short-time frequency-hopping stepping signal according to claim 5, characterized in that: The filtering module is specifically used to perform azimuth matching filtering on the scene echo signal after range migration correction in the frequency domain through an azimuth matching filtering function to obtain the SAR image of the short-time frequency hopping step signal.

Images