CN112684448A - Multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation method and system - Google Patents
Multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation method and system Download PDFInfo
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Abstract
The invention provides a multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation method and system, which comprise the following steps: determining a PRF range, a pulse width range, a protection width range and an observation visual angle range; combining PRF, pulse width and guard width within the range at will; any combination number is used as the total cycle number, and a multi-core parallel computing mode is utilized to extract a corresponding PRF value, a pulse width value and a protection width value under any cycle; calculating the echo time of the front edge and the back edge of a transmitting signal interference band; calculating the echo time of the front edge and the back edge of the satellite point signal interference band; calculating the azimuth ambiguity under the corresponding parameters; calculating the range ambiguity under the corresponding parameters; calculating the system sensitivity under the corresponding parameters; when all the judgments are met, keeping the PRF value, the pulse width value and the protection width value, and keeping corresponding direction ambiguity, distance ambiguity and system sensitivity calculation values; and repeating the execution until all the working conditions are completely calculated and judged.
Description
Technical Field
The invention relates to the technical field of general design of synthetic aperture radar satellites, in particular to a multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation method and system, and more particularly to a multi-parameter combination-oriented high-efficiency satellite-borne SAR wave position calculation and generation method and system.
Background
The space-borne Synthetic Aperture Radar (SAR) is an imaging radar for space-to-ground observation, has the advantages of all weather, all time and penetrating a certain vegetation compared with optical remote sensing, can carry out global observation, and has wide application in the fields of military, agriculture, oceans and the like. In the design process of a satellite-borne SAR system, wave position design is a key step, and firstly, PRF values, pulse widths and protection widths under various observation widths are designed based on system parameters and observation requirements (including antenna size, frequency band, system noise coefficient, system loss, emission power, incidence angle range, imaging width, overlapping degree, resolution ratio and the like) so as to avoid emission signals and satellite point signals; and secondly, calculating and verifying whether the imaging quality meets requirements (including ambiguity, system sensitivity and the like) under the conditions of different PRFs, pulse widths and guard widths.
The conventional design method of the invention is that firstly, a zebra pattern is drawn (the zebra pattern is a group of curves drawn according to the function relation of the incidence angle and the pulse repetition frequency, and the pattern is similar to a diamond shape, so the zebra pattern is often called as the zebra pattern); then wave positions are designed in the rhombic area of the zebra pattern from the initial incident angle, each wave position needs to meet the indexes of azimuth ambiguity, distance ambiguity, system sensitivity and the like, and a certain overlapping degree needs to be formed between the adjacent wave positions. In the conventional wave position design method, the continuous adjustment of the overlapping degree parameter is used as a means of wave position design iteration, and due to the irregularity of the pulse selectable region, only the adjustment of the overlapping degree is that the algorithm design complexity is high; secondly, the design efficiency is low; thirdly, it is difficult to obtain an optimal solution. The conventional wave position design method has the advantages of intuition and visibility, and has the disadvantages that the zebra pattern cannot be adjusted in real time due to the determination of the pulse width and the protection width, the PRF needs to be selected by multiple manual attempts to meet the imaging quality requirement, the time is consumed, and the zebra pattern cannot be dynamically adjusted in real time to obtain multiple available wave position parameters.
The method is based on the dynamic generation of the zebra crossing under the condition of multiple parameters to adapt to wave level design under different parameter conditions, and firstly, the PRF range is determined according to the design value and observation requirements of system parameters; secondly, determining a pulse width range based on the PRF range and the duty ratio constraint; and thirdly, determining the range of the protection width based on the proportional relation between the protection width and the pulse width, finally forming a multi-parameter working condition combination under three-dimensional freedom, and developing an input working condition combination capable of adapting to parallel operation to improve the wave position calculation and generation efficiency. Under the input working condition of multidimensional parameter free combination, adaptive wave position calculation and generation facing different constraint conditions can be dynamically selected, and under any one working condition parameter, the calculation of the echo time of the front edge and the back edge of a satellite point signal and the echo time of the front edge and the back edge of a transmitted pulse signal is carried out and is used as a class of constraint conditions; secondly, calculating distance ambiguity, azimuth ambiguity and system sensitivity, and using the distance ambiguity, the azimuth ambiguity and the system sensitivity as another type of constraint condition; and thirdly, storing and recording the working condition parameters under the condition that all the constraint conditions are met to obtain all wave position generation results meeting the constraint conditions so that designers can screen optimal wave positions in time.
Patent document CN102393514A (application number: 201110327821.2) discloses a method and a system for adaptive wave position design of a synthetic aperture radar satellite, wherein the method comprises the following steps: acquiring the satellite orbit height and the sub-satellite point vector; determining the selection range of the wave position parameters; determining a space limitation condition of a wave position; designing a wave position parameter set; primary screening is carried out on the wave position parameters based on the zebra crossing; wave position parameters are secondarily screened based on SAR performance indexes; and (5) correcting wave position parameters of a large visual angle. The system comprises a satellite orbit height and sub-satellite point earth radius acquisition module, a wave position selection range determination module, a wave position space limitation condition determination module, a wave position parameter set design module, a wave position parameter screening module based on a zebra diagram, a wave position parameter screening module based on SAR performance indexes and a large-view-angle wave position parameter correction module. The patent uses a fixed zebra pattern to perform wave level design and screening.
Patent document 102998655a (application No. 201210480438.5) discloses a method for selecting an optimum wave position of a scanning operation mode of a synthetic aperture radar. Respectively designing wave positions of a strip working mode according to the limits of parameters of a distance mapping area, the maximum value of an equivalent backscattering coefficient, the maximum value of a fuzzy ratio and the width of an optional i group of strips to obtain i groups of wave positions with different strip widths, and taking a union set of the wave positions as a wave position set to be selected of a scanning working mode; step two, selecting an initial wave position; step three, constructing a wave position tree; traversing the wave position tree; and step five, selecting an optimal wave potential combination. The patent uses a scan mode wave position design based on a fixed zebra pattern.
The adaptive computing method (modern radar journal) for the satellite-borne SAR global wave position parameters mainly aims at the change of the orbit position to perform dynamic wave position adjustment.
A Zebra-map-based space-based radar PRF design (journal of radar science and technology) is mainly characterized in that a calculation formula of a self-adaptive Zebra map is deduced according to satellite orbits and radar parameters on the basis of a satellite-ground model of a space-based radar, and the influence of the satellite orbits and the earth model of the space-based radar on the Zebra map is effectively solved.
In summary, the prior art disclosed is adaptive zebra map generation around orbit and earth models; secondly, wave position design and screening are carried out based on the fixed zebra crossing; and thirdly, searching for the optional wave position by adjusting the overlapping degree parameter. The innovation point and the novelty of the application are mainly based on the fact that a zebra pattern under multiple working conditions is formed by freely combining PRF, pulse width and protection width, a parallel operation method is designed to carry out wave level parameter technology and generation meeting imaging quality requirements, manual intervention is not needed, computer calculation can be directly carried out to obtain all wave levels meeting the requirements, and firstly, the wave level selectable range can be enlarged; secondly, the efficiency is greatly improved.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation method and system.
The invention provides a multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation method, which comprises the following steps:
step M1: determining a PRF range, a pulse width range, a protection width range and an observation visual angle range according to basic parameters of the satellite-borne SAR system;
step M2: based on the PRF range, the pulse width range and the protection width range, the PRF, the pulse width and the protection width in the range are combined randomly to generate working condition parameters suitable for parallel operation;
step M3: taking any combination number of PRF, pulse width and protection width in the range as the total cycle number, and extracting a corresponding PRF value, pulse width value and protection width value under any cycle by utilizing a computer multi-core parallel computing mode;
step M4: calculating the echo time of the front edge and the back edge of the interference band of the transmitting signal according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
step M5: calculating the front and back edge echo time of the satellite point signal interference band according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
step M6: calculating azimuth ambiguity under corresponding parameters according to the PRF value and basic parameters of the satellite-borne SAR system, and judging whether a preset required value is met;
step M7: calculating the range ambiguity under corresponding parameters according to the PRF value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
step M8: calculating the system sensitivity under corresponding parameters according to the PRF value, the pulse width value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
step M9: when all the judgments are met, keeping the PRF value, the pulse width value and the protection width value, keeping and recording the corresponding azimuth ambiguity, distance ambiguity and system sensitivity calculation value, or else, leaving the current working condition parameter value; and repeatedly executing the steps M3 to M9 until all the working conditions are completely calculated and judged, and generating all the effective wave position parameters.
Preferably, the step M1 includes: determining a PRF range according to a satellite system parameter design value and observation requirements; determining a pulse width range based on the PRF range and the duty cycle constraint; determining a range of the guard width based on a proportional relationship between the guard width and the pulse width; and calculating the observation visual angle range according to the observation belt width and the track height.
Preferably, the step M2 includes: and carrying out three-layer cycle operation by taking the PRF, the protection pulse and the protection width as variables to generate working condition parameters which are freely combined and adapt to parallel calculation, and storing the working condition parameters in a two-dimensional array form.
Preferably, the step M3 includes: and (3) calling a parform loop command in matlab to perform independent parallel operation by taking the number of the combined working conditions as the total loop times, and extracting a PRF value, a pulse width value and a protection width value corresponding to the current loop in any loop.
Preferably, the step M4 includes: and calculating the echo time of the front edge and the back edge of the transmitting signal interference band by utilizing the PRF value, the pulse width value and the protection width value corresponding to the current cycle, the known orbit height value, the PRF maximum and minimum value and the known slope distance maximum and minimum value corresponding to the observation region, and judging whether the effective echo time region is overlapped with the transmitting signal interference band or not according to the judgment result so as to obtain the correct judgment result of the avoidance success.
Preferably, the step M5 includes: and calculating the echo time of the front edge and the back edge of the satellite lower point interference band by utilizing the PRF value, the pulse width value and the protection width value corresponding to the current cycle, the known orbit height value, the PRF maximum and minimum value and the slope distance maximum and minimum value corresponding to the observation region, and judging whether the effective echo time region is overlapped with the transmission signal interference band or not according to the judgment result so as to obtain the correct judgment result of successful avoidance.
Preferably, the step M6 includes: and calculating the azimuth ambiguity by using the PRF value corresponding to the current cycle and the known antenna parameters, wavelength, azimuth processing bandwidth and azimuth scanning angle, and judging whether the calculated value meets a preset required value or not so as to take the required value as a correct judgment result.
Preferably, the step M7 includes: and calculating the distance direction ambiguity by using the PRF value corresponding to the current cycle and the known antenna parameters and wavelengths, and judging whether the calculated value meets a preset required value or not so as to take the required value as a correct judgment result.
Preferably, the step M8 includes: and calculating the system sensitivity by using the PRF value and the pulse width value corresponding to the current cycle and the known antenna parameters, wavelength, signal bandwidth, transmitting power, system noise coefficient and system damage value, and judging whether the calculated value meets the set required value or not so as to meet the required value as a correct judgment result.
The invention provides a multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation system, which comprises:
module M1: determining a PRF range, a pulse width range, a protection width range and an observation visual angle range according to basic parameters of the satellite-borne SAR system;
module M2: based on the PRF range, the pulse width range and the protection width range, the PRF, the pulse width and the protection width in the range are combined randomly to generate working condition parameters suitable for parallel operation;
module M3: taking any combination number of PRF, pulse width and protection width in the range as the total cycle number, and extracting a corresponding PRF value, pulse width value and protection width value under any cycle by utilizing a computer multi-core parallel computing mode;
module M4: calculating the echo time of the front edge and the back edge of the interference band of the transmitting signal according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
module M5: calculating the front and back edge echo time of the satellite point signal interference band according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
module M6: calculating azimuth ambiguity under corresponding parameters according to the PRF value and basic parameters of the satellite-borne SAR system, and judging whether a preset required value is met;
module M7: calculating the range ambiguity under corresponding parameters according to the PRF value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
module M8: calculating the system sensitivity under corresponding parameters according to the PRF value, the pulse width value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
module M9: when all the judgments are met, keeping the PRF value, the pulse width value and the protection width value, keeping and recording the corresponding azimuth ambiguity, distance ambiguity and system sensitivity calculation value, or else, leaving the current working condition parameter value; and repeatedly triggering the execution of the modules M3 to M9 until all the working conditions are completely calculated and judged, and generating all the effective wave position parameters.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention relates to a multi-parameter combination-oriented high-efficiency satellite-borne SAR wave position calculating and generating method, which is characterized in that three parameters are taken as variables to be freely combined within the range of determined PRF, pulse width and protection width, so that a transmitting signal interference band and a satellite lower point signal interference band similar to a zebra pattern can be dynamically and adaptively generated, and the selectivity of wave position calculation and generation is greatly improved;
2. the efficient spaceborne SAR wave position calculation and generation method facing the multi-parameter combination adopts the idea of distributed parallel operation, and adapts to parallel operation by taking independent working conditions as the principle when PRF, pulse width and protection width are freely combined, so that the wave position calculation and generation efficiency is greatly improved;
3. the invention relates to a multi-parameter combination-oriented high-efficiency satellite-borne SAR wave position calculation and generation method, which comprises the steps of calculating the front and back edge time of a satellite point signal and the front and back edge time of a transmitted pulse signal under any working condition parameter and using the calculation as a class of constraint conditions; secondly, calculating distance ambiguity, azimuth ambiguity and system sensitivity, and using the distance ambiguity, the azimuth ambiguity and the system sensitivity as a class of constraint conditions; and thirdly, when all the constraint conditions are met, the working condition parameters are stored and recorded to be used as a group of output results of wave level calculation and generation, so that calculation and analysis of all the working condition parameters can be quickly and efficiently realized, and all wave level parameter results meeting the constraint conditions are generated to facilitate a designer to screen the optimal wave level in time.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a flow chart of a multi-parameter combination-oriented spaceborne SAR wave position calculation and generation method;
FIG. 2 is a graph of input parameters for simulation calculations according to the present invention;
FIG. 3 is a diagram of simulation calculation results of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
Example 1
The invention provides a multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation method, which comprises the following steps:
step M1: determining a PRF range, a pulse width range, a protection width range and an observation visual angle range according to basic parameters of the satellite-borne SAR system, so as to obtain a range of multi-parameter variables and a minimum visual angle and a maximum visual angle in any observation area;
step M2: based on the PRF range, the pulse width range and the protection width range, the PRF, the pulse width and the protection width in the range are combined randomly to generate working condition parameters suitable for parallel operation;
step M3: taking any combination number of PRF, pulse width and protection width in the range as the total cycle number, and extracting a corresponding PRF value, pulse width value and protection width value under any cycle by utilizing a computer multi-core parallel computing mode;
step M4: calculating the echo time of the front edge and the back edge of the interference band of the transmitting signal according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
step M5: calculating the front and back edge echo time of the satellite point signal interference band according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
step M6: calculating azimuth ambiguity under corresponding parameters according to the PRF value and basic parameters of the satellite-borne SAR system, and judging whether a preset required value is met;
step M7: calculating the range ambiguity under corresponding parameters according to the PRF value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
step M8: calculating the system sensitivity under corresponding parameters according to the PRF value, the pulse width value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
step M9: when all the judgments are met, keeping the PRF value, the pulse width value and the protection width value, and keeping and recording the corresponding azimuth ambiguity, distance ambiguity and system sensitivity calculation value, otherwise, discarding the current working condition parameter value and not doing any operation; and repeatedly executing the steps M3 to M9 until all the working conditions are completely calculated and judged, and generating all the available wave position parameters.
The range determination method is as follows: according to the Nyquist sampling theorem, the PRF minimum value is larger than the azimuth Doppler bandwidth, and meanwhile, the pulse repetition period is required to be larger than the maximum echo receiving window time;
specifically, the step M1 includes: determining a PRF range according to a satellite system parameter design value and observation requirements; determining a pulse width range based on the PRF range and the duty cycle constraint, the pulse width ranges being different for different PRF values, the pulse width range varying with the PRF value; determining the range of the protection width based on the proportional relation between the protection width and the pulse width, wherein the larger the protection time is, the larger the width of the fringe of the area shielded by the echo of the satellite point and the transmitted pulse is, and the smaller the space selected by the wave position is, therefore, the protection width is not recommended to be acquired greatly and is controlled below 50% of the pulse width as much as possible; and calculating the observation visual angle range according to the observation belt width and the track height.
Specifically, the step M2 includes: and carrying out three-layer circulation operation by taking the PRF, the protection pulse and the protection width as variables, wherein the PRF is taken as the variable in the first-layer circulation, the pulse width is taken as the variable in the second-layer circulation, and the protection width is taken as the variable in the third-layer circulation, so that working condition parameters which are freely combined and adapt to parallel calculation are generated and are stored in a two-dimensional array form.
Specifically, the step M3 includes: and (3) calling a parform loop command in matlab to perform independent parallel operation by taking the number of the combined working conditions as the total loop times, and extracting a PRF value, a pulse width value and a protection width value corresponding to the current loop in any loop.
Specifically, the step M4 includes: aiming at a satellite-borne SAR system with one antenna for transmitting and receiving, because a transmitting signal, a satellite down-point signal and an effective echo signal are simultaneously transmitted in the air at any moment, the front and back edge echo time of a transmitting signal interference band is calculated by utilizing a PRF value, a pulse width value, a protection width value, a known track height value, a nearest slant range value, a farthest slant range value and a maximum and minimum value of the slant range corresponding to an observation region in any cycle, and whether the effective echo time region is overlapped with the transmitting signal interference band or not is judged according to the judgment so as to judge the success of avoiding as a correct judgment result.
Specifically, the step M5 includes: aiming at a satellite-borne SAR system with one antenna for transmitting and receiving, because a transmitting signal, a satellite down-point signal and an effective echo signal exist in the air at any moment, the front and back edge echo time of a satellite down-point interference band is calculated in any cycle by utilizing a PRF value, a pulse width value, a protection width value, a known orbit height value, a PRF maximum and minimum value and an observation area corresponding to a slant range maximum and minimum value corresponding to the current cycle, and whether the effective echo time area is overlapped with the transmitting signal interference band or not is judged according to the judgment so as to avoid success as a correct judgment result.
Specifically, the step M6 includes: and calculating the azimuth ambiguity by utilizing the PRF value corresponding to the current cycle and known basic system parameter values such as antenna parameters, wavelength, azimuth processing bandwidth, azimuth scanning angle and the like in any cycle, and judging whether the calculated value meets a preset required value or not so as to meet the required value as a correct judgment result.
The azimuth ambiguities are defined as follows:
for conventional spaceborne SAR, the doppler spectrum of the echo signal is weighted by the antenna azimuth directional transmit-receive two-way directional pattern and sampled by the system at PRF, the doppler spectrum above PRF is folded into the azimuth processing bandwidth, mixing with the main signal causes azimuth ambiguity, and the ratio of such ambiguity signal to the desired signal is defined as the Azimuth Ambiguity Signal Ratio (AASR).
Specifically, the step M7 includes: and calculating the distance direction ambiguity by using the PRF value corresponding to the current cycle and the known antenna parameters and wavelengths, and judging whether the calculated value meets a preset required value or not so as to take the required value as a correct judgment result.
The range-wise ambiguity is defined as follows:
the range ambiguity refers to some echo signals in the range of slant range and its nearby area, the delay time of which is different from the echo delay time of the current mapping zone by integral multiple of pulse repetition period, and these unwanted echoes arrive at the receiver together with the echo in the mapping zone, thus causing interference to the mapping zone. The distance blurring causes bright spots of different intensities to appear in the image of the point target in the distance direction. The magnitude of the distance blur is represented by a distance blur ratio RASR, which is defined as: the ratio of the total energy of the echo signals in all the fuzzy areas to the required energy of the echo signals in the mapping zone.
Specifically, the step M8 includes: and calculating the system sensitivity by using the PRF value and the pulse width value corresponding to the current cycle and known basic system parameter values such as antenna parameters, wavelength, signal bandwidth, transmitting power, system noise coefficient, system damage value and the like in any cycle, and judging whether the calculated value meets the set required value or not so as to meet the required value as a correct judgment result.
The system sensitivity is defined as follows:
in a space-borne SAR system, the system sensitivity is expressed as NE σ0Noise equivalent scattering coefficient (NESZ), one of the important indicators affecting imaging quality, characterizes the ability of the spaceborne SAR to detect small and weak targets, and NE σ allows the system conditions0The lower the value design, the better, in remote sensing applications, the distributed target (or planar target) is generally considered, and the system sensitivity is defined as the average backscattering coefficient divided by the radar signal-to-noise ratio.
Specifically, the step M9 performs comprehensive decision by using the determination results of the steps M4 to M8, and stores and records the PRF value, the pulse width value, the protection width value, the calculated ambiguity value and the calculated system sensitivity value corresponding to the cycle when the determination results of the steps M4 to M8 are both correct. Under the condition that an echo time window corresponding to an observation area is not overlapped with a transmitting signal interference area time area and a satellite point signal interference area time area, and azimuth ambiguity, distance ambiguity and system sensitivity meet index requirements, a PRF value, a pulse width value and a protection width value corresponding to the cycle can be comprehensively judged to be used as wave level parameter results, and meanwhile, a corresponding ambiguity value and a system sensitivity value are recorded. And repeatedly circulating the operations of the step M3 to the step M9 until all the working conditions are completely calculated and judged, and generating all the available wave position parameters (including the PRF parameter value, the pulse width parameter value and the protection width parameter value).
The invention provides a multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation system, which comprises:
module M1: determining a PRF range, a pulse width range, a protection width range and an observation visual angle range according to basic parameters of the satellite-borne SAR system, so as to obtain a range of multi-parameter variables and a minimum visual angle and a maximum visual angle in any observation area;
module M2: based on the PRF range, the pulse width range and the protection width range, the PRF, the pulse width and the protection width in the range are combined randomly to generate working condition parameters suitable for parallel operation;
module M3: taking any combination number of PRF, pulse width and protection width in the range as the total cycle number, and extracting a corresponding PRF value, pulse width value and protection width value under any cycle by utilizing a computer multi-core parallel computing mode;
module M4: calculating the echo time of the front edge and the back edge of the interference band of the transmitting signal according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
module M5: calculating the front and back edge echo time of the satellite point signal interference band according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
module M6: calculating azimuth ambiguity under corresponding parameters according to the PRF value and basic parameters of the satellite-borne SAR system, and judging whether a preset required value is met;
module M7: calculating the range ambiguity under corresponding parameters according to the PRF value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
module M8: calculating the system sensitivity under corresponding parameters according to the PRF value, the pulse width value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
module M9: when all the judgments are met, keeping the PRF value, the pulse width value and the protection width value, and keeping and recording the corresponding azimuth ambiguity, distance ambiguity and system sensitivity calculation value, otherwise, discarding the current working condition parameter value and not doing any operation; and repeating the execution of the modules M3 to M9 until all the working conditions are completely calculated and judged, and generating all the available wave position parameters.
Example 2
Example 2 is a modification of example 1
As shown in fig. 1, in this embodiment, the invention relates to the overall system design of a synthetic aperture radar satellite, and in particular, to an accurate and efficient multi-parameter combination-oriented high-efficiency space-borne SAR wave position calculation and generation method. With the continuous development of the synthetic aperture radar satellite technology, not only higher resolution and larger observation width are required to be obtained, but also imaging quality with lower ambiguity and better system sensitivity is required to be obtained. In the overall design of the SAR satellite, the design and selection of the wave position are very important for the design of a satellite-borne SAR system, and are directly related to the imaging quality and the engineering realizability of the satellite-borne SAR. The wave position design is an optimal solution problem under multi-parameter free combination, and different combinations of PRF, pulse width and protection width need to be selected to achieve the purposes of avoiding the interference of off-satellite point signals, transmitting the signal interference and meeting the imaging quality.
The method comprises the steps that firstly, the PRF, the pulse width and the protection width are used as multi-dimensional variable parameters to be freely combined, all possible inputs are provided for wave position calculation and generation, and the method has the condition of parallel operation to meet the requirement of rapid calculation; secondly, calculating the time of the interference zone of the transmitted signal, calculating the time of the interference zone of the satellite point, calculating the ambiguity and calculating the system sensitivity based on the respective combination state parameters; and thirdly, comprehensively judging whether conflicts exist with the interference zone time region or not and whether the set imaging quality requirements are met or not. Through simulation design verification under actual system parameters, the wave position calculation and generation method provided by the invention can screen out all available PRF values, pulse width values and protection width values in a full range, greatly improves the realizability of design, and improves the efficiency of design screening through parallel operation.
The invention relates to a multi-parameter combination-oriented high-efficiency satellite-borne SAR wave position calculation and generation method, which mainly comprises the following steps:
1. multi-parameter free combination condition generation
The multi-parameter free combination working condition generation mainly completes the determination of a PRF range, the design of a pulse width range and the determination of a protection width range, wherein the PRF range determination is determined by the azimuth imaging resolution, and the PRF minimum value is larger than the azimuth Doppler bandwidth and is set as PRF _ min according to the Nyquist sampling theorem; secondly, the receiving window time corresponding to the imaging width is determined, the pulse repetition period is required to be larger than the maximum echo receiving window time, and the maximum PRF value is set as PRF _ max. The pulse width range setting is generally determined based on the PRF value and the maximum duty cycle limit, the pulse width ranges are different for different PRF values, the range of pulse widths is varied with the PRF value, and the minimum duty cycle and the maximum duty cycle are set to k1, k 2. The protection width range is determined by carrying out corresponding proportion calculation on the basis of a pulse width value, the larger the protection time is obtained, the larger the width of a zone stripe shielded by an echo of a satellite point and a transmitted pulse is, and the smaller the space of wave position selection is, therefore, the protection width is not recommended to be obtained to be large, the protection width is controlled to be below 50% of the pulse width as much as possible, and the minimum proportion and the maximum proportion are set to be p1 and p 2. The generation result of the multi-parameter free combination working condition is as follows:
PRF＝PRF_min:PRF_step:PRF_max (1)
tau＝k1·PRF:tau_step:k2·PRF (2)
tau_g＝p1·tau:tau_g_step:p2·tau (3)
PRF _ step is a pulse repetition frequency change step value, tau _ step is a pulse width change step value, and tau _ g _ step is a guard width step value.
The method comprises the specific steps of carrying out random combination based on a PRF range, a protection pulse width range and a protection width range to generate working condition parameters capable of adapting to parallel computation, and specifically, carrying out three-layer cycle operation, wherein a PRF is used as a variable in a first-layer cycle, a pulse width is used as a variable in a second-layer cycle, a protection width is used as a variable in a third-layer cycle, N combinations are formed after the cycle is finished, the combinations are represented and stored by two-dimensional arrays of 3 rows and N columns, the arrays are named as parameters, wherein the 1 st row represents a PRF value, the 2 nd row represents a pulse width value, the 3 rd row represents a protection width value, and the columns represent each combination sequence.
2. Multi-constraint computation
Under any multi-parameter free combination working condition, the current PRF value, the pulse width value and the protection width value are determined, the front and back edge echo time of a signal interference band transmitted under the working condition of the current parameter and the front and back edge echo time of a signal interference band at an off-satellite point can be calculated according to relevant system parameters such as a visual angle range, a track height, an antenna size and the like, and meanwhile, the azimuth ambiguity, the distance ambiguity and the system sensitivity value under the current parameter can also be calculated, and the specific calculation method is as follows.
(1) Echo time of front and back edges of transmitting signal interference band
Calculating the front and back edge time of the interference band of the transmission signal corresponding to any PRF, tau and tau _ g, and respectively representing by T1 and T2:
T1＝i/PRF-tau-tau_g (4)
T2＝i/PRF+tau+tau_g (5)
in the formula: i ═ imin,imin+1,...,imax，imin＝int(Tn·PRF_min)，imax＝int(Tf·PRF_max)，
RnAt the nearest slant distance, RfThe farthest skew distance.
Wherein PRF is the pulse repetition frequency, tau is the pulse width, tau _ G is the guard width, PRF _ min is the minimum value of the set pulse repetition frequency, PRF _ max is the maximum value of the set pulse repetition frequency, c is the speed of light, int represents the integer function, f is the Doppler frequency, G is the antenna gain directional diagram
(2) Echo time of front and back edges of satellite point signal interference band
Calculating the front and back edge time of the satellite point signal interference band corresponding to any PRF, tau and tau _ g, and respectively using Tnad1 and Tnad2 to represent:
wherein j is jmin,jmin+1,...,jmax，jmin＝imin-int[(Tnad+tau+ 2·tau_g)·PRF_min，jmax＝imax-int(Tnad·PRF_max)，
H is the track height
(3) Ambiguity of azimuth
For conventional spaceborne SAR, the doppler spectrum of the echo signal is weighted by the antenna azimuth directional transmit-receive two-way directional pattern and sampled by the system at PRF, the doppler spectrum above PRF is folded into the azimuth processing bandwidth, mixing with the main signal causes azimuth ambiguity, and the ratio of such ambiguity signal to the desired signal is defined as the Azimuth Ambiguity Signal Ratio (AASR). The calculation formula of the azimuth ambiguity mainly includes two cases of azimuth non-scanning and azimuth scanning, wherein the azimuth non-scanning mainly corresponds to a strip imaging mode, a SCAN imaging mode and the like, and the azimuth scanning mainly corresponds to a beam-bunching imaging mode, a sliding beam-bunching imaging mode, a TOPS imaging mode and the like, and the specific calculation formula is as follows.
Wherein, thetaaFor azimuthal scan angle, θa∈(-θamax,θamax)，θamaxAt the maximum scan angle, GθaFor a scanning angle of thetaaAzimuthal antenna gain pattern of time, BpFor azimuthal processing bandwidth, the azimuthal direction is set at θziFor a scan step, equation (5) may be changed to:
wherein K ═ K +1, …,0, K-2, K-1, K, K ═ int (θ)amax/θzi)。
Wherein, BpIndicating the azimuth processing bandwidth, f is the doppler frequency, and PRF is the pulse repetition frequency; g (f) is the azimuth antenna gain pattern.
(4) Distance direction ambiguity
The range ambiguity refers to some echo signals in the range of slant range and its nearby area, the delay time of which is different from the echo delay time of the current mapping zone by integral multiple of pulse repetition period, and these unwanted echoes arrive at the receiver together with the echo in the mapping zone, thus causing interference to the mapping zone. The distance blurring causes bright spots of different intensities to appear in the image of the point target in the distance direction. The magnitude of the distance blur is represented by a distance blur ratio RASR, which is defined as: the ratio of the total energy of the echo signals in all the fuzzy areas to the required energy of the echo signals in the mapping zone.
Wherein, tau1And τ2Respectively, the minimum delay and the maximum delay, theta, corresponding to the distance to a certain observation bandwidthrIn order to be the distance to the scan angle,
for a scanning angle of thetarDistance in time towards antenna gain pattern, RτAnd Rτ+m/PRFThe respective skew values, eta, corresponding to the time delays tau and tau + m/PRFτAnd ητ+m/PRFThe incident angles corresponding to the time delays tau and tau + m/PRF respectively.
(5) Sensitivity of the system
In a space-borne SAR system, the systemSensitivity NE σ0Noise equivalent scattering coefficient (NESZ), one of the important indicators affecting imaging quality, characterizes the ability of the spaceborne SAR to detect small and weak targets, and NE σ allows the system conditions0The lower the value design the better. In remote sensing applications, a distribution target (or called a plane target) is generally considered, and a specific calculation formula is as follows.
The surface target radar equation is shown as follows:
wherein, PavIs the average power, G is the antenna gain, λ is the wavelength, σ0To distribute the mean backscattering coefficient of the target, δ Rg＝c/(2BRsinη)、BRIs the signal bandwidth, η is the angle of incidence, R is the slant distance between the target and the radar, VstK is the Boltzmann constant, F, is the relative velocity between the satellite and the targetopIs the system noise coefficient, TsIs the total equivalent noise temperature, LmIs the system loss.
The surface target system sensitivity expression is:
3. efficient algorithm design
The satellite-borne SAR wave position calculation and generation firstly calculates the observation visual angle range according to the observation band width and the track height; secondly, generating time regions of an interference band of signals of the satellite points under different PRFs, different pulse widths and different protection widths and time regions of an interference band of transmitted signals; calculating the ambiguity and the system sensitivity; and finally, selecting the PRF, the pulse width and the guard width by using the principle of avoiding the sub-satellite point signal and the transmitted signal and using the ambiguity and the system sensitivity to meet the imaging requirement as constraints until the screening under all the PRF, pulse width and guard width combinations is completed. In order to realize efficient and rapid wave position calculation and generation, any combination is carried out based on PRF, pulse width and protection width so as to adapt to parallel operation, and the specific efficient algorithm is designed as follows:
In summary, the efficient spaceborne SAR wave position calculating and generating method for multi-parameter combination according to the present invention is verified by simulation calculation under actual system parameters, the input parameters of the simulation calculation are as shown in fig. 2, the maximum duty cycle is set to 15%, 0.5% is used as the duty cycle stepping value, the protection width is set to 20% of the pulse width, and the calculation result is as shown in fig. 3. The result proves that the wave position calculation and generation method provided by the invention can screen out all available PRF values, pulse width values and protection width values in a full range, greatly improves the realizability of design, improves the efficiency of design screening by parallel operation, and provides an effective means for the overall design of the SAR satellite.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Those skilled in the art will appreciate that, in addition to implementing the systems, apparatus, and various modules thereof provided by the present invention in purely computer readable program code, the same procedures can be implemented entirely by logically programming method steps such that the systems, apparatus, and various modules thereof are provided in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system, the device and the modules thereof provided by the present invention can be considered as a hardware component, and the modules included in the system, the device and the modules thereof for implementing various programs can also be considered as structures in the hardware component; modules for performing various functions may also be considered to be both software programs for performing the methods and structures within hardware components.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (10)
1. A multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation method is characterized by comprising the following steps:
step M1: determining a PRF range, a pulse width range, a protection width range and an observation visual angle range according to basic parameters of the satellite-borne SAR system;
step M2: based on the PRF range, the pulse width range and the protection width range, the PRF, the pulse width and the protection width in the range are combined randomly to generate working condition parameters suitable for parallel operation;
step M3: taking any combination number of PRF, pulse width and protection width in the range as the total cycle number, and extracting a corresponding PRF value, pulse width value and protection width value under any cycle by utilizing a computer multi-core parallel computing mode;
step M4: calculating the echo time of the front edge and the back edge of the interference band of the transmitting signal according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
step M5: calculating the front and back edge echo time of the satellite point signal interference band according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
step M6: calculating azimuth ambiguity under corresponding parameters according to the PRF value and basic parameters of the satellite-borne SAR system, and judging whether a preset required value is met;
step M7: calculating the range ambiguity under corresponding parameters according to the PRF value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
step M8: calculating the system sensitivity under corresponding parameters according to the PRF value, the pulse width value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
step M9: when all the judgments are met, keeping the PRF value, the pulse width value and the protection width value, keeping and recording the corresponding azimuth ambiguity, distance ambiguity and system sensitivity calculation value, or else, leaving the current working condition parameter value; and repeatedly executing the steps M3 to M9 until all the working conditions are completely calculated and judged, and generating all the effective wave position parameters.
2. The method for calculating and generating the multi-parameter combination-oriented spaceborne SAR wave position as claimed in claim 1, wherein the step M1 comprises: determining a PRF range according to a satellite system parameter design value and observation requirements; determining a pulse width range based on the PRF range and the duty cycle constraint; determining a range of the guard width based on a proportional relationship between the guard width and the pulse width; and calculating the observation visual angle range according to the observation belt width and the track height.
3. The method for calculating and generating the multi-parameter combination-oriented spaceborne SAR wave position as claimed in claim 1, wherein the step M2 comprises: and carrying out three-layer cycle operation by taking the PRF, the protection pulse and the protection width as variables to generate working condition parameters which are freely combined and adapt to parallel calculation, and storing the working condition parameters in a two-dimensional array form.
4. The method for calculating and generating the multi-parameter combination-oriented spaceborne SAR wave position as claimed in claim 1, wherein the step M3 comprises: and (3) calling a parform loop command in matlab to perform independent parallel operation by taking the number of the combined working conditions as the total loop times, and extracting a PRF value, a pulse width value and a protection width value corresponding to the current loop in any loop.
5. The method for calculating and generating the multi-parameter combination-oriented spaceborne SAR wave position as claimed in claim 1, wherein the step M4 comprises: and calculating the echo time of the front edge and the back edge of the transmitting signal interference band by utilizing the PRF value, the pulse width value and the protection width value corresponding to the current cycle, the known orbit height value, the PRF maximum and minimum value and the known slope distance maximum and minimum value corresponding to the observation region, and judging whether the effective echo time region is overlapped with the transmitting signal interference band or not according to the judgment result so as to obtain the correct judgment result of the avoidance success.
6. The method for calculating and generating the multi-parameter combination-oriented spaceborne SAR wave position as claimed in claim 1, wherein the step M5 comprises: and calculating the echo time of the front edge and the back edge of the satellite lower point interference band by utilizing the PRF value, the pulse width value and the protection width value corresponding to the current cycle, the known orbit height value, the PRF maximum and minimum value and the slope distance maximum and minimum value corresponding to the observation region, and judging whether the effective echo time region is overlapped with the transmission signal interference band or not according to the judgment result so as to obtain the correct judgment result of successful avoidance.
7. The method for calculating and generating the multi-parameter combination-oriented spaceborne SAR wave position as claimed in claim 1, wherein the step M6 comprises: and calculating the azimuth ambiguity by using the PRF value corresponding to the current cycle and the known antenna parameters, wavelength, azimuth processing bandwidth and azimuth scanning angle, and judging whether the calculated value meets a preset required value or not so as to take the required value as a correct judgment result.
8. The method for calculating and generating the multi-parameter combination-oriented spaceborne SAR wave position as claimed in claim 1, wherein the step M7 comprises: and calculating the distance direction ambiguity by using the PRF value corresponding to the current cycle and the known antenna parameters and wavelengths, and judging whether the calculated value meets a preset required value or not so as to take the required value as a correct judgment result.
9. The method for calculating and generating the multi-parameter combination-oriented spaceborne SAR wave position as claimed in claim 1, wherein the step M8 comprises: and calculating the system sensitivity by using the PRF value and the pulse width value corresponding to the current cycle and the known antenna parameters, wavelength, signal bandwidth, transmitting power, system noise coefficient and system damage value, and judging whether the calculated value meets the set required value or not so as to meet the required value as a correct judgment result.
10. A multi-parameter combination-oriented satellite-borne SAR wave position calculation and generation system is characterized by comprising:
module M1: determining a PRF range, a pulse width range, a protection width range and an observation visual angle range according to basic parameters of the satellite-borne SAR system;
module M2: based on the PRF range, the pulse width range and the protection width range, the PRF, the pulse width and the protection width in the range are combined randomly to generate working condition parameters suitable for parallel operation;
module M3: taking any combination number of PRF, pulse width and protection width in the range as the total cycle number, and extracting a corresponding PRF value, pulse width value and protection width value under any cycle by utilizing a computer multi-core parallel computing mode;
module M4: calculating the echo time of the front edge and the back edge of the interference band of the transmitting signal according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
module M5: calculating the front and back edge echo time of the satellite point signal interference band according to the PRF value, the pulse width value and the protection width value, and performing evasion judgment;
module M6: calculating azimuth ambiguity under corresponding parameters according to the PRF value and basic parameters of the satellite-borne SAR system, and judging whether a preset required value is met;
module M7: calculating the range ambiguity under corresponding parameters according to the PRF value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
module M8: calculating the system sensitivity under corresponding parameters according to the PRF value, the pulse width value and the basic parameters of the satellite-borne SAR system, and judging whether the preset required value is met;
module M9: when all the judgments are met, keeping the PRF value, the pulse width value and the protection width value, keeping and recording the corresponding azimuth ambiguity, distance ambiguity and system sensitivity calculation value, or else, leaving the current working condition parameter value; and repeatedly triggering the execution of the modules M3 to M9 until all the working conditions are completely calculated and judged, and generating all the effective wave position parameters.
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