Optimization Method of Beam Position Design for Spaceborne SAR

Abstract

The present invention provides a method for optimizing the beam position design of a spaceborne SAR. Different from the previous idea of ​​using a fixed pulse width as input for all beam positions, the pulse width is designed and output for different beam positions; different from the problem that the previous design has no automatic iteration capability or the iteration method is simple, the automatic iteration function of the design is realized through a three-layer loop iteration step-by-step parameter adjustment method. Beneficial effects of the present invention: the pulse width is designed for different beam positions, instead of using a fixed and unique pulse width as input for all beam positions, which not only avoids the situation that some beam positions have harsh timing constraints due to excessively wide pulse widths, and thus the designable PRF range is too small or non-existent, but also avoids the situation that some beam positions have poor noise equivalent backscatter coefficients due to excessively narrow pulse widths, thus affecting the design results, effectively improving the flexibility of the design and the performance of the design results; at the same time, the design capability of the system is improved and the optimal design results are ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of SAR beam position optimization, and in particular relates to a satellite-borne SAR beam position design optimization method. Background Art

[0002] Synthetic aperture radar SAR has the characteristics of all-weather and all-day, and is widely used in environmental monitoring, military reconnaissance and other fields. Due to the complexity of the SAR payload system and the interrelationship of many parameters, the system design is difficult. Among them, the wave position design is an important part of the parameter design of the spaceborne SAR system. It is necessary to fully consider the imaging performance index requirements, antenna system requirements, timing constraints and other factors to optimize the system.

[0003] Many scholars have conducted relevant research on the design of spaceborne SAR system parameters for different working modes. Among the many parameter analyses in the prior art, some wave position design methods do not have the ability of automatic iterative optimization, and require manual adjustment of input parameters or constraints for redesign, which increases the difficulty of wave position design and reduces the design efficiency; or when designing, the pulse width is used as a known input, that is, in the entire incident angle range, all wave positions use the same fixed pulse width. Such a design may result in: the input fixed pulse width is wider for a certain wave position, resulting in more stringent timing constraints, which in turn affects the design PRF range to become smaller or no; or the input fixed pulse width is lower for a certain wave position, resulting in poor performance of the noise equivalent backscatter coefficient, which in turn affects the wave position design results; in addition, for the design iteration, the methods of the prior art are limited by the selection of the starting empirical value, and some indicators such as the range ambiguity ratio are not used as constraints, which affects the performance of the design results; some prior art provides iterative parameter adjustment methods, but the iteration capability is general, and only a certain parameter can be adjusted. If the adjustment is invalid, the design will fail. Summary of the invention

[0004] In view of this, the present invention aims to propose a spaceborne SAR beam position design optimization method to solve at least one problem existing in the above-mentioned prior art.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A method for optimizing the beam position design of a spaceborne SAR comprises the following steps:

[0007] S1, first initialize i=1 and design the beam parameters of the i-th wave position;

[0008] S2. According to the parameters obtained in step S1, the pulse repetition frequency PRF and pulse width Tp of the i-th wave position are designed;

[0009] S3, judging whether the pulse repetition frequency and pulse width of the current wave position are designed in step S2, if not, proceeding to step S4, if yes, it means that the design of wave position i is completed, proceeding to step S5;

[0010] S4, adjusting the beam pointing direction of the current wave position, calculating the overlap rate, and then proceeding to step S6;

[0011] S5, judging whether all wave positions within the incident angle range have been designed, if all wave positions have been completed, saving the design, ending the design, and exiting; if not, entering step S10;

[0012] S6, judging whether the overlap rate calculated in step S4 is less than the maximum overlap rate requirement, if yes, proceeding to step S1 to redesign the wave position i; if no, proceeding to step S7;

[0013] S7, adjusting the surveying band width or beam width of the wave position, and then proceeding to step S8;

[0014] S8, judging whether the output of S7 meets the minimum mapping band width requirement, if so, proceeding to step S1 to redesign the wave position i; if not, proceeding to step S9;

[0015] S9, updating the overlap rate and the swath width to an initial state, and then reducing the system performance index;

[0016] S10, let i=i+1, then return to step S1 to design the next wave position.

[0017] Further, in step S1, the beam parameters include a downward viewing angle / incident angle range, a beam width, and corresponding slant range and ground range.

[0018] Further, in step S2, it is determined whether the pulse repetition frequency and pulse width of the current wave position are designed in step S2. If not, the process proceeds to step S4. If yes, it indicates that the design of wave position i is completed, and the process proceeds to step S5, including:

[0019] S2_1, calculate the minimum PRFmin and maximum PRFmax of PRF, set PRF=PRFmin and then enter the loop;

[0020] S2_2, determine whether PRF is less than or equal to PRFmax. If the condition is met, proceed to step S2_3; if not, and the designed PRF array is empty, it means that the design fails, and exit step S2;

[0021] S2_3, searching for a pulse repetition frequency and pulse width that meet the conditions according to the noise equivalent backscatter coefficient constraint and the timing relationship constraint;

[0022] S2_4, determine whether the search result is empty. If it is empty, PRF=RPF+1, and re-enter the loop step S2_2; if it is not empty, it means that the PRF and Tp that meet the constraint conditions are searched out, and then enter step S2_5;

[0023] S2_5, using the PRF and Tp searched out in S2_4 as input, calculate the system performance parameters of this wave position,

[0024] S2_6, judging whether all performance parameters meet the performance index requirements, if all meet, then enter step S2_7; if there is any that do not meet, then PRF=PRF+1, and re-enter the loop step S2_2;

[0025] S2_7, save the PRF and Tp designed in step S2_5 into an array, then PRF=PRF+1, and re-enter the loop step S2_2;

[0026] S2_8. Select PRF and Tp as design results from the non-empty PRF array and pulse array saved in step S2_7.

[0027] Further, in step S2_5, the system performance parameters include the range ambiguity ratio, the azimuth ambiguity ratio and the data rate.

[0028] An electronic device comprises a processor and a memory which is in communication with the processor and is used to store instructions executable by the processor, wherein the processor is used to execute the spaceborne SAR wave position design optimization method.

[0029] A server comprises at least one processor and a memory in communication with the processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes the spaceborne SAR wave position design optimization method.

[0030] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the space-borne SAR wave position design optimization method is implemented.

[0031] Compared with the prior art, the spaceborne SAR wave position design optimization method described in the present invention has the following advantages:

[0032] (1) The spaceborne SAR beam position design optimization method described in the present invention designs different pulse widths for different beam positions to avoid the situation where all beam positions share the same pulse width, which results in some beam positions affecting the noise equivalent backscatter coefficient index due to low duty cycle, or affecting the PRF design due to large pulse width, thereby improving the design capability or the performance of system parameters.

[0033] (2) The spaceborne SAR wave position design optimization method described in the present invention is designed to solve the problem of wave position design failure. The present invention has designed a software automatic step-by-step iteration method with three-layer iteration capability. First, the beam pointing is adjusted step by step, and the wave position is redesigned within the overlap rate requirement range. If the design fails, the outer layer starts a cycle of step-by-step adjustment of the mapping band width, and the inner layer starts a cycle of step-by-step adjustment of the beam pointing. If the double-layer iteration still fails, it means that the performance upper limit of this system cannot meet the index requirements. At this time, the performance index is reduced step by step, and the three-layer iteration of the performance index, mapping band width range and overlap rate range is started at the same time, and finally the optimal performance design that this system can meet can be designed. The advantages of this are: first, there is no need to manually adjust the parameters. Manually adjusting the parameters requires high professional analysis ability of the system designer and a long design cycle; at the same time, manual adjustment is not easy to operate, and all wave positions need to be adapted and adjusted. The success rate of the wave position design result is not high; second, there are three layers of step-by-step loop iteration, which not only takes into account various adjustable situations, but also sets priorities, and can efficiently and quickly design the optimal result. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 This is a schematic diagram of the optimization method flow according to an embodiment of the present invention;

[0036] Figure 2 A detailed schematic diagram of “designing PRF and TP” of the method flow described in an embodiment of the present invention;

[0037] Figure 3 A schematic diagram of the noise backscattering coefficient obtained by the design simulation according to an embodiment of the present invention;

[0038] Figure 4 A schematic diagram of an azimuth ambiguity ratio (ie, the worst azimuth ambiguity ratio in dB) obtained by a design simulation according to an embodiment of the present invention;

[0039] Figure 5 A schematic diagram of a distance fuzzy ratio diagram obtained by design simulation according to an embodiment of the present invention;

[0040] Figure 6 This is a schematic diagram of a zebra diagram (i.e., a blue emission cutoff area and a red sub-satellite point echo window) obtained by the design simulation described in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0042] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0043] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0044] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0045] like Figures 1 to 6 As shown, the spaceborne SAR beam position design optimization method, the first purpose of the present invention is to design different pulse widths for different beam positions, to avoid the situation that the pulse repetition frequency of some beam positions is difficult to select or the duty cycle is low due to the fixed pulse width, which affects the noise equivalent backscatter coefficient performance (as well as the situation that the design of some beam positions fails or the performance of the design result does not reach the optimal level);

[0046] The second objective of the present invention is to design a method for automatic step-by-step iteration of software for the case where a certain wave position design fails. By step-by-step adjusting geometric parameters (such as beam pointing or mapping band width, etc.), the beam angle is modified and the wave position design of this wave position is re-performed, thereby improving the degree of automation of the design. Neither manual adjustment nor adjustment of all wave positions is required. It is very flexible and convenient and improves the design efficiency. At the same time, if the performance parameters of the wave position after adjustment still cannot meet the performance index requirements, this wave position will jump back to the initial unadjusted state (that is, the geometric parameters of the wave position are consistent with those before adjustment), and the optimal performance parameters that the system can meet are achieved through design, and are output as design results. The advantage of such a design is that, when the adjustment is effective, the flexibility and design efficiency of the wave position design are improved through the automatic adjustment of the system, and when the adjustment fails, it can be guaranteed that this wave position is the optimal performance wave position that the system can achieve.

[0047] The optimization algorithm steps of SAR beam position design are as follows:

[0048] First initialize i=1, and then perform the following steps:

[0049] Step S1: Design the beam parameters of the i-th wave position, such as the following geometric parameters: viewing angle / incident angle range, beam width, and corresponding slant range and ground distance;

[0050] Step S2: According to the parameters obtained in step S1, the pulse repetition frequency (PRF) and pulse width (Tp) of the i-th wave position are designed;

[0051] Step S3: Determine whether the pulse repetition frequency and pulse width of the current wave position have been designed in step S2. If not, proceed to step S4. If yes, it means that the design of wave position i is completed, and proceed to step S5.

[0052] Step S4: adjust the beam pointing direction of the current wave position, calculate the overlap rate, and then proceed to step S6;

[0053] Step S5: Determine whether all wave positions within the incident angle range have been designed. If all wave positions have been completed, save the design, end the design, and exit; if not, enter step S10;

[0054] Step S6: determine whether the overlap rate calculated in step S4 is less than the maximum overlap rate requirement. If yes, proceed to step S1 to redesign the wave position i; if no, proceed to step S7;

[0055] Step S7: adjusting the swath width or beam width of the wave position, and then proceeding to step S8;

[0056] Step S8: Determine whether the output of S7 meets the minimum swath width requirement. If so, proceed to step S1 to redesign the wave position i; if not, proceed to step S9;

[0057] Step S9: updating the overlap rate and the swath width to an initial state, and then reducing the system performance index;

[0058] Step S10: Let i=i+1, then proceed to step S1 to design the next wave position.

[0059] Among them, step S2 is the key step of wave position design, which mainly includes the following steps:

[0060] Step S2_1: Calculate the minimum PRFmin and maximum PRFmax of PRF, set PRF=PRFmin and then enter the loop;

[0061] Step S2_2: Determine whether the current PRF is less than or equal to PRFmax. If the condition is met, enter S2_3; if not, and the designed PRF array is empty, it means that the design fails, and exit S2;

[0062] Step S2_3: searching for a pulse repetition frequency and a pulse width that meet the conditions according to the noise equivalent backscatter coefficient constraint and the timing relationship constraint;

[0063] Step S2_4: Determine whether the search result is empty. If it is empty, PRF=RPF+1, and re-enter the loop step S2_2; if it is not empty, it means that the PRF and Tp that meet the constraint conditions are searched out, and then enter step S2_5;

[0064] Step S2_5: using the PRF and Tp searched out in S2_4 as input, calculate the system performance parameters of this wave position, such as the range ambiguity ratio, azimuth ambiguity ratio and data rate;

[0065] Step S2_6: Determine whether all performance parameters meet the performance index requirements. If all meet the requirements, enter step S2_7; if any do not meet the requirements, PRF=PRF+1, and re-enter the loop step S2_2;

[0066] Step S2_7: save the PRF and Tp designed in step S2_5 into an array, then PRF=PRF+1, and re-enter the loop step S2_2;

[0067] Step S2_8: According to certain selection criteria, select appropriate PRF and Tp as the design result from the non-empty PRF array and pulse array saved in step S2_7.

[0068] The present invention also proposes an electronic device, comprising a processor and a memory which is communicatively connected to the processor and is used to store instructions executable by the processor, wherein the processor is used to execute the satellite-borne SAR wave position design optimization method.

[0069] The present invention also proposes a server, comprising at least one processor and a memory communicatively connected to the processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes the spaceborne SAR wave position design optimization method.

[0070] The present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program implements the spaceborne SAR wave position design optimization method when executed by a processor.

[0071] Advantages of the present invention:

[0072] (1) The present invention designs different pulse widths for different wave positions to avoid all wave positions sharing the same pulse width, which may cause some wave positions to affect the noise equivalent backscatter coefficient index due to low duty cycle, or affect the PRF design due to large pulse width, thereby improving the design capability or system parameter performance.

[0073] (2) Aiming at the situation where the design of a certain wave position fails, the present invention designs an automatic step-by-step iteration method with three-layer iteration capability. The advantage of such a design is that on the one hand, no manual adjustment is required, and no adjustment is required for all wave positions, which improves the flexibility and efficiency of the design. On the other hand, the designed wave position is the optimal situation under the constraint conditions.

[0074] Example 1

[0075] Table 1

[0076] ;

[0077] If a fixed pulse width is used as the input, we must consider the problem that the pulse width is too large and it is difficult to meet the timing constraints. We must also consider the problem that the pulse width is too small. The near-end wave position may meet the index requirements (but in fact the system performance can be better), but the far-end wave position may not meet the index requirements and thus the design fails.

[0078] Taking the parameter input in Table 1 as an example, if a fixed pulse width of 40 microseconds is used, the pulse width, PRF and NESZ design results of wave positions 1 to 3 are shown in the following table:

[0079] Table 2

[0080] ;

[0081] As can be seen from Table 2, the duty cycles (duty cycle = PRF multiplied by pulse width) of beam position 1 and beam position 2 are 22.97% and 23.85% respectively, and the beam edge NESZ meets the index of better than -20dB; however, when the pulse width of beam position 3 is 40 microseconds, although there is a PRF set that meets the timing constraint, the NESZ index cannot be met due to the low duty cycle; therefore, the feasibility of beam position design can be improved by designing a variable pulse width;

[0082] If the present design method is used to design the wave position, some design parameters are shown in Table 3. At this time, the pulse width of wave position 1 is automatically designed, and the PRF of wave position 1 is lower than the PRF designed for wave position 1 in Table 2, which reduces the data rate, while increasing the duty cycle and slightly improving the NESZ performance. The same is true for wave position 2. At the same time, the pulse width and duty cycle of wave position 3 are both improved relative to the design in Table 2, and the PRF design can be achieved.

[0083] Table 3

[0084] ;

[0085] Example 2

[0086] If there is no automatic iterative update function in the wave position design method, when the design fails, it is necessary to manually adjust one or more input parameters and then redesign.

[0087] As shown in Table 4, for wave position 10 (system input parameter table 1), under the initial conditions of 20km width and 10% overlap, there is no suitable PRF and pulse width to meet the system indicators, and the design fails. At this time, it is necessary to readjust the input constraint parameters (such as beam overlap rate and other indicators), and then start the design from wave position 1. This may be repeated many times before the design is completed. This design method changes the overlap rate and width between beams to ensure that the overlap rate and width between beams of each wave position do not need to be consistent, and they can be changed within a reasonable range. First, the beam overlap rate is adjusted while ensuring the width. After many adjustments, the wave position is still not designed, and then the width is reduced. The beam overlap rate changes from the initial value. When the width is reduced to 19.75km and the overlap rate is 10%, a reasonable PRF and pulse width are designed to meet the system indicator requirements.

[0088] Table 4

[0089] .

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A spaceborne SAR beam position design optimization method, characterized by: The following steps are involved: S1, first initialize i=1 and design the beam parameters of the i-th wave position; S2. According to the parameters obtained in step S1, the pulse repetition frequency PRF and pulse width Tp of the i-th wave position are designed; S3, judging whether the pulse repetition frequency and pulse width of the current wave position are designed in step S2, if not, proceeding to step S4, if yes, it means that the design of wave position i is completed, proceeding to step S5; S4, adjusting the beam pointing direction of the current wave position, calculating the overlap rate, and then proceeding to step S6; S5, judging whether all wave positions within the incident angle range have been designed, if all wave positions have been completed, saving the design, ending the design, and exiting; if not, entering step S10; S6, judging whether the overlap rate calculated in step S4 is less than the maximum overlap rate requirement, if yes, proceeding to step S1 to redesign the wave position i; if no, proceeding to step S7; S7, adjusting the surveying band width or beam width of the wave position, and then proceeding to step S8; S8, judging whether the output of S7 meets the minimum mapping band width requirement, if so, proceeding to step S1 to redesign the wave position i; if not, proceeding to step S9; S9, updating the overlap rate and the swath width to an initial state, and then reducing the system performance index; S10, let i=i+1, then return to step S1 to design the next wave position; In step S2, it is determined whether the pulse repetition frequency and pulse width of the current wave position are designed in step S2. If not, the process proceeds to step S4. If yes, it indicates that the design of wave position i is completed, and the process proceeds to step S5, including: S2_1, calculate the minimum PRFmin and maximum PRFmax of PRF, set PRF=PRFmin and then enter the loop; S2_2, determine whether PRF is less than or equal to PRFmax. If the condition is met, proceed to step S2_3; if not, and the designed PRF array is empty, it means that the design fails, and exit step S2; S2_3, searching for a pulse repetition frequency and pulse width that meet the conditions according to the noise equivalent backscatter coefficient constraint and the timing relationship constraint; S2_4, determine whether the search result is empty, if it is empty, then PRF = RPF + 1, re-enter the loop step S2_2; if it is not empty, it means that the PRF and Tp that meet the constraint conditions are searched out, then enter step S2_5; S2_5, use the PRF and Tp searched out in S2_4 as input to calculate the system performance parameters of this wave position, S2_6, determine whether all performance parameters meet the performance index requirements, if all meet, then enter step S2_7; if there is any non-satisfaction, then PRF = PRF + 1, re-enter the loop step S2_2; S2_7, save the PRF and Tp designed in step S2_5 into an array, then PRF=PRF+1, and re-enter the loop step S2_2; S2_8. Select PRF and Tp as design results from the non-empty PRF array and pulse array saved in step S2_7.

2. The method for optimizing the spaceborne SAR wave position design according to claim 1, characterized in that: In step S1, the beam parameters include the downward viewing angle / incident angle range, the beam width, and the corresponding slant range and ground range.

3. The method for optimizing the spaceborne SAR wave position design according to claim 1, characterized in that: In step S2_5, the system performance parameters include the range ambiguity ratio, the azimuth ambiguity ratio and the data rate.

4. An electronic device, comprising a processor and a memory connected to the processor for storing instructions executable by the processor, characterized in that: The processor is used to execute the spaceborne SAR wave position design optimization method described in any one of claims 1-3 above.

5. A server, characterized in that: The invention comprises at least one processor and a memory in communication with the processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes the spaceborne SAR wave position design optimization method according to any one of claims 1 to 3.

6. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the spaceborne SAR wave position design optimization method described in any one of claims 1-3 is implemented.

Images