A method for predicting optimal imaging time period for space-based ISAR based on IPP and resolution analysis

Abstract

The present invention discloses a space-based ISAR optimal imaging time period prediction method combining IPP and resolution analysis, including establishing a satellite orbit simulation model, calculating the relative speed and position of the target star relative to the radar detection star; establishing a simulated satellite three-dimensional scattering point model; dividing the imaging interval and obtaining the azimuth resolution change curve and the projection area curve of all intervals; obtaining the optimal imaging interval according to the azimuth resolution change curve and the projection area curve, and obtaining the space-based ISAR optimal imaging time period prediction result; using the normalized resolution to measure the imaging quality of the optimal imaging interval, and outputting the optimal imaging interval and the corresponding normalized imaging resolution. The present invention can predict the time period with a better imaging plane and a higher resolution before the radar is turned on, avoiding the platform energy consumption caused by long-term startup, and at the same time ensuring that the radar obtains an ISAR image that is easy for subsequent target recognition and component segmentation within the startup time period.

Description

Technical Field

[0001] The invention belongs to the technical field of space target imaging, and in particular relates to a method for predicting an optimal imaging time period of space-based ISAR combining IPP and resolution analysis. Background Art

[0002] For ISAR (Inverse Synthetic Aperture Radar) imaging of space targets, high image quality and resolution are required for subsequent use of ISAR images for target classification and recognition. Subsequent component measurement and target attitude estimation require ISAR images to present the basic features of space targets. Therefore, the imaging image should show as many component features as possible.

[0003] In order to improve the imaging rate and resolution of the radar in space, it is essential to select the optimal imaging time period. Existing methods process the echo data and use single criteria such as Doppler center frequency estimation, Doppler broadening estimation or quality evaluation index of the obtained image to complete the selection of the optimal imaging time period. Most of the existing methods ignore the prior information of the spaceborne ISAR platform and the space target. For example, the space target operates in an environment close to vacuum or with a very thin atmosphere and in most cases, it will not move back and forth significantly, that is, the movement of such targets is relatively stable, and the imaging plane and imaging resolution of the target can be predicted in advance. In addition, the radar consumes a lot of power when it is turned on for a long time, and the large amount of storage of echoes with poor imaging effects also leads to a waste of resources. Therefore, it is necessary to propose a new and efficient optimal imaging time period prediction algorithm based on the characteristics of the target. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a space-based ISAR optimal imaging time period prediction method combining IPP (Image Projection Plane) and resolution analysis, predicting the imaging plane through a range-Doppler projection algorithm, combining the relative rotation angle and the corresponding resolution to determine whether the imaging conditions are met and analyzing the time range suitable for imaging, selecting a time period suitable for imaging and turning on the radar in combination with the prediction results of the imaging plane and the effective rotation angular velocity, effectively saving radar power and storage space while receiving echoes with better imaging within the prediction result interval, and obtaining an ISAR image with higher resolution and more complete projection of key components.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] The present invention proposes a space-based ISAR optimal imaging time period prediction method combining IPP and resolution analysis, comprising the following steps:

[0007] S1. Establish a satellite orbit simulation model to obtain the position and velocity of the target star and the radar detection star in the inertial system, and calculate the relative velocity and position of the target star relative to the radar detection star for subsequent resolution prediction.

[0008] S2. Establish a simulated satellite three-dimensional scattering point model for subsequent IPP prediction.

[0009] S3, divide the feasibility analysis time period into several sub-intervals, calculate the effective rotation angular velocity of the target star relative to the radar detection star in each interval according to the relative speed and position in step S1, obtain the relative rotation angle and image azimuth resolution corresponding to each interval, and finally obtain the azimuth resolution change curve of all intervals.

[0010] S4. Calculate the Doppler frequency and echo delay of each scattering point on the target model in each interval according to the simulated satellite three-dimensional scattering point model in step S2 and the sub-intervals divided in step S3, use them to establish a projection plane coordinate system, map the scattering points to the projection plane and calculate the projection area of ​​all scattering points, and finally obtain the projection area curve of all intervals.

[0011] S5. Obtain the optimal imaging interval according to the azimuth resolution change curve in step S3 and the projection area curve in step S4.

[0012] S6: According to the optimal imaging interval in step S5, the optimal imaging time period of space-based ISAR is predicted, and the imaging quality of the optimal imaging interval is measured by normalized resolution, and the optimal imaging interval and the corresponding normalized imaging resolution are output. .

[0013] Furthermore, the calculation of the relative speed and position of the target star relative to the radar detection star includes the following:

[0014] The satellite orbit simulation model is established using STK software. The calculation formula for the relative speed and position of the target star relative to the radar detection star is:

[0015]

[0016] in, represents the relative speed, represents the speed of the target star in the inertial system within the interval, represents the speed of the radar detection satellite in the inertial system within the interval, Indicates relative position. represents the position of the target star in the inertial system within the interval, Indicates the position of the radar detection satellite in the inertial system within the interval.

[0017] Furthermore, in step S2, the coordinates of the scattering points are input using Matlab software to establish a three-dimensional scattering point model of a simulated satellite.

[0018] Furthermore, in step S3, obtaining the azimuth resolution change curves of all intervals includes the following sub-steps:

[0019] S301, calculating the azimuth and elevation angle of the target star relative to the radar detection star.

[0020] S302: Calculate the tangential velocity of the target star relative to the radar and the effective rotation angular velocity in the current interval, and obtain the effective rotation angle in the current interval.

[0021] S303, calculating the azimuth resolution according to the effective rotation angle in step S302, the specific formula is:

[0022]

[0023] in, represents the signal wavelength, represents the azimuth resolution, Indicates the effective rotation angle.

[0024] S304. Repeat steps S301-S303 for each sub-interval to obtain azimuth resolution change curves for all intervals.

[0025] Furthermore, in step S4, obtaining the projection area curves of all intervals includes the following sub-steps:

[0026] S401, calculating the distance from the radar detection star to the scattering point on the target star at the imaging plane prediction time, and obtaining the time delay of the scattering point relative to the target center point. The specific formula is:

[0027]

[0028] Among them, R i Indicates the distance from the radar detection star to the scattering point, R o Indicates the distance from the radar detection star to the target center, B w represents the bandwidth of the transmitted signal, c represents the speed of light, Indicates delay.

[0029]

[0030] in, represents the position of the radar detection star, represents the position of the kth scattering point.

[0031] S402. Obtain the Doppler frequency according to the satellite's rotation vector and the rotation radius of the scattering point. The specific formula is:

[0032]

[0033] in, represents the radar line of sight direction vector, represents the tangential velocity vector of the scattering point, Indicates the Doppler frequency.

[0034] S403, repeat steps S401-S402 to calculate the time delay and Doppler frequency of all scattering points.

[0035] S404: Establish a projection plane coordinate system according to the time delays and Doppler frequencies of all scattering points in step S403, map the scattering points onto the projection plane and calculate the projection areas of all scattering points.

[0036] S405. Repeat steps S401-S404 for each sub-interval to obtain projection area curves of all intervals.

[0037] Furthermore, in step S5, obtaining the optimal imaging interval includes the following contents:

[0038] According to the obtained relative rotation angle and azimuth resolution, if the relative rotation angle between the radar detection star and the target star exceeds 2 degrees within this interval, that is, the azimuth resolution exceeds 0.42m, it is considered that imaging can be achieved and the interval is considered as imaging interval 1.

[0039] The projection area curve obtained in step S4 is normalized, and the interval in which the normalized projection area is greater than the set threshold is set as imaging interval 2.

[0040] The overlapping portion of the imaging interval 1 and the imaging interval 2 is set as the optimal imaging interval.

[0041] Furthermore, in step S6, the larger the normalized imaging resolution is, the higher the imaging quality is.

[0042] Furthermore, the present invention also proposes an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method for predicting the optimal imaging time period of space-based ISAR combining IPP and resolution analysis as described above are implemented.

[0043] Furthermore, the present invention also proposes a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the method for predicting the optimal imaging time period of space-based ISAR combining IPP and resolution analysis as described above is executed.

[0044] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0045] (1) The present invention uses IPP and resolution prediction to calculate the interval with better imaging before the radar is turned on, avoiding power consumption of the radar due to long-term startup, and at the same time ensuring that the radar receives data with better imaging during the startup period.

[0046] (2) The present invention uses IPP combined with a resolution prediction model to perform dual-criteria prediction while taking into account the actual space target motion characteristics, and has the characteristics of fast calculation speed and high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is an overall implementation flow chart of the present invention.

[0048] Figure 2 This is an example diagram of the STK simulated radar and track model according to an embodiment of the present invention.

[0049] Figure 3 It is the Matlab satellite simulation three-view drawing of the embodiment of the present invention.

[0050] Figure 4 It is the resolution prediction result of the embodiment of the present invention.

[0051] Figure 5 It is the IPP prediction result of the embodiment of the present invention.

[0052] Figure 6 This is an imaging result diagram obtained according to the echo data segment of the prediction result in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0054] The present invention proposes a method for predicting the optimal imaging time period of space-based ISAR by combining IPP and resolution analysis. Figure 1 As shown, the following steps are included:

[0055] S1. Use STK software to establish the orbit simulation model of the radar detection star and the target star, and obtain the position of the target star in the inertial system within the interval. and speed , the position of the radar detection satellite in the inertial system within the interval and speed , the target satellite and the detection satellite are both in high orbit, and the orbital three-dimensional model is as follows Figure 2 As shown in (a), the 2D local enlarged model is as follows Figure 2As shown in (b). In this embodiment, the target star first approaches the radar detection star and then moves away, wherein the closest distance between the target star and the radar detection star is 3.5 km. In the process of the target star approaching the radar, the relative distance between the target star and the radar detection star is represented by the negative absolute value of the distance; in the process of the target star moving away from the radar, the relative distance between the target star and the radar detection star is represented by the absolute value of the distance.

[0056] Then calculate the relative speed and position of the target star relative to the radar detection star. The specific formula is:

[0057]

[0058] in, represents the relative speed, and ; represents relative position, and .

[0059] S2. Use Matlab software to input the coordinates of the scattering points and establish a three-dimensional scattering point model of the simulated satellite. The model and its three-view drawing are shown in the figure. Figure 3 As shown, the model is 6.2m long and 1.8m wide. The target is the simulated scattering point model of the long hockey satellite, which contains a total of 279 scattering points. Figure 3 (a) is the display result of the target model in three-dimensional space. Figure 3 (b)-(d) are respectively the top view, front view and side view of the target three-dimensional model. In this embodiment, the observable stage when the target is less than 20 km away from the radar is selected as the simulation scene, which is 1411.3 seconds in total.

[0060] S3, push 60 minutes back from the current moment as the imaging feasibility analysis time period, divide the feasibility analysis time period into several sub-intervals, each interval length Na is 128, the sampling time is 0.1s, that is, each interval is 12.8s. According to the relative speed and position in step S1, calculate the effective rotation angular velocity of the target star relative to the radar detection star in each interval, obtain the relative rotation angle and image azimuth resolution corresponding to each interval, and obtain the azimuth resolution change curve of all intervals; including the following sub-steps:

[0061] S301, calculating the azimuth and elevation angle of the target star relative to the radar detection star, the specific formula is:

[0062]

[0063] in, represents the azimuth, represents the pitch angle, Indicates the position of the radar detection star.

[0064] S302, calculating the tangential velocity of the target star relative to the radar and the effective rotation angular velocity in the current interval, and obtaining the effective rotation angle in the current interval. The specific formula is:

[0065]

[0066] in, Represents the radar line of sight direction vector; represents the tangential velocity; represents the effective angular velocity; Indicates the radar detection star to the center of the current target interval (i.e. time), ; represents the effective rotation angle; PRT represents the pulse repetition time.

[0067] S303, calculating the azimuth resolution according to the effective rotation angle in step S302, the specific formula is:

[0068]

[0069] in, represents the signal wavelength, Indicates the azimuth resolution.

[0070] S304. Repeat steps S301-S303 for each sub-interval to obtain azimuth resolution change curves for all intervals.

[0071] In this embodiment, the resolution prediction result is as follows: Figure 4 As shown, the critical value of the rotation angle is calculated by a resolution of 0.42m and an interval duration of 12.8s.

[0072] S4, calculating the Doppler frequency and echo delay of each scattering point on the target model in each interval according to the simulated satellite three-dimensional scattering point model in step S2 and the sub-intervals divided in step S3, establishing a projection plane coordinate system using the delay and Doppler frequency, mapping the scattering points to the projection plane and calculating the projection area of ​​all scattering points, and obtaining the projection area curve of all intervals; comprising the following sub-steps:

[0073] S401, calculating the distance from the radar detection star to the scattering point on the target star at the imaging plane prediction time, and obtaining the time delay of the scattering point relative to the target center point. The specific formula is:

[0074]

[0075]

[0076] in, represents the distance from the radar detection star to the kth scattering point, represents the transmit signal bandwidth, represents the speed of light, Indicates delay, represents the position of the kth scattering point.

[0077] S402. Obtain the Doppler frequency according to the satellite's rotation vector and the rotation radius of the scattering point. The specific formula is:

[0078]

[0079] in, represents the tangential velocity vector of the scattering point, Indicates the Doppler frequency.

[0080] S403, repeat steps S401-S402 to calculate the time delay and Doppler frequency of all scattering points.

[0081] S404: Establish a projection plane coordinate system according to the time delay and Doppler frequency of all scattering points in step S403, map the scattering points onto the projection plane and calculate the projection area of ​​all scattering points. The specific formula is as follows:

[0082]

[0083] Where S represents the projection area, k represents the kth scattering point, and m represents the total number of scattering points. Indicates the expansion point position, P k represents the position of the kth scattering point in the time delay and Doppler frequency projection coordinate system.

[0084] S405. Repeat steps S401-S404 for each sub-interval to obtain projection area curves of all intervals.

[0085] S5, obtaining the optimal imaging interval according to the azimuth resolution change curve in step S3 and the projection area curve in step S4, including the following contents:

[0086] According to the variation of the azimuth resolution with the interval obtained in step S3, if the relative rotation angle between the radar detection star and the target star exceeds 2 degrees in a certain interval, that is, the azimuth resolution exceeds 0.42m, it is considered that imaging is possible, and this interval is considered as imaging interval 1. The projection area curve obtained in step S4 is normalized, and the part greater than 0.4 is considered as imaging interval 2. The overlapping part of imaging interval 1 and imaging interval 2 is considered as the optimal imaging interval.

[0087] In this embodiment, the IPP prediction results are as follows: Figure 5 shown.

[0088] S6: According to the imaging interval in step S5, the optimal imaging time period of space-based ISAR is predicted, and the imaging quality of the optimal imaging interval is measured by normalized resolution, and the optimal imaging interval and the corresponding normalized imaging resolution are output. .

[0089] Since the imaging interval condition is that the resolution exceeds 0.42m, the maximum value of the azimuth resolution is set to 0.5, and the normalized resolution calculation method is as follows:

[0090]

[0091] in, represents the normalized imaging resolution.

[0092] Table 1 gives the algorithm results and time, mainly including the resolution prediction interval, IPP prediction interval, optimal imaging interval and total program time.

[0093] Table 1 Algorithm results and time

[0094]

[0095] According to Table 1, the range with the best imaging effect is predicted to be -4.4km to 3.7km between the radar and the target, which is 164.6s in total. The echo of the data from 4.4km to 3.7km is simulated and the imaging result is obtained as shown in the figure. Figure 6 (a)-(d), the corresponding normalized resolutions are 0.534, 0.61, 0.697, and 0.636, respectively. It can be seen that receiving echoes and imaging within the prediction result interval can obtain ISAR images with higher resolution and more complete projection, and effectively save radar power and storage space.

[0096] The embodiment of the present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. It should be noted that when the processor in the above electronic device executes the computer program, it corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not described in detail in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0097] The embodiment of the present invention further provides a computer-readable storage medium storing a computer program. It should be noted that when the computer program in the computer-readable storage medium is executed by the processor, it corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not described in detail in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0098] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present application may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0099] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0100] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0101] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0102] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0103] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A space-based ISAR optimal imaging time period prediction method combining IPP and resolution analysis, characterized in that: The following steps are involved: S1. Establish a satellite orbit simulation model, obtain the position and velocity of the target star and the radar detection star in the inertial system, and calculate the relative velocity and position of the target star relative to the radar detection star; S2, establish a three-dimensional scattering point model of simulated satellite; S3, taking 60 minutes backward from the current moment as the imaging feasibility analysis period, dividing the feasibility analysis period into several sub-intervals, calculating the effective rotation angular velocity of the target star relative to the radar detection star in each interval according to the relative velocity and position in step S1, obtaining the relative rotation angle and image azimuth resolution corresponding to each interval, and obtaining the azimuth resolution change curve of all intervals; S4, according to the simulated satellite three-dimensional scattering point model in step S2 and the sub-intervals divided in step S3, the Doppler frequency and echo delay of each scattering point on the target model in each interval are calculated, and a projection plane coordinate system is established according to the Doppler frequency and echo delay, and the scattering points are mapped onto the projection plane and the projection area of ​​all scattering points is calculated. The specific formula is as follows: ； Where S represents the projection area, k represents the kth scattering point, and m represents the total number of scattering points. Indicates the expansion point position, P k represents the position of the kth scattering point in the time delay and Doppler frequency projection coordinate system; Calculate the projection area of ​​all scattering points for each sub-interval to obtain the projection area curve of all intervals; S5, obtaining the optimal imaging interval according to the azimuth resolution change curve in step S3 and the projection area curve in step S4; the specific content is: In the interval, when the azimuth resolution between the radar detection star and the target star exceeds 0.42m, it is considered that imaging is possible, and the interval is set as imaging interval 1; the projection area curve obtained in step S4 is normalized, and the interval with the normalized projection area greater than the set threshold is set as imaging interval 2; the overlapping part of imaging interval 1 and imaging interval 2 is set as the optimal imaging interval; S6: According to the optimal imaging interval in step S5, the optimal imaging time period of space-based ISAR is predicted, and the imaging quality of the optimal imaging interval is measured by normalized resolution, and the optimal imaging interval and the corresponding normalized imaging resolution are output. .

2. The method for predicting the optimal imaging time period of space-based ISAR by combining IPP and resolution analysis according to claim 1, characterized in that: In step S1, calculating the relative speed and position of the target star relative to the radar detection star includes the following: The satellite orbit simulation model is established using STK software. The calculation formula for the relative speed and position of the target star relative to the radar detection star is: ； in, represents the relative speed, represents the speed of the target star in the inertial system within the interval, represents the speed of the radar detection satellite in the inertial system within the interval, Indicates relative position. represents the position of the target star in the inertial system within the interval, Indicates the position of the radar detection satellite in the inertial system within the interval.

3. The method for predicting the optimal imaging time period of space-based ISAR by combining IPP and resolution analysis according to claim 1, characterized in that: In step S2, the coordinates of the scattering points are input using Matlab software to establish a three-dimensional scattering point model of the simulated satellite.

4. The method for predicting the optimal imaging time period of space-based ISAR by combining IPP and resolution analysis according to claim 1, characterized in that: In step S3, obtaining the azimuth resolution change curves of all intervals includes the following sub-steps: S301, calculating the azimuth and elevation angle of the target star relative to the radar detection star; S302, calculating the tangential velocity of the target star relative to the radar and the effective rotation angular velocity in the current interval, and obtaining the effective rotation angle in the current interval; S303, calculating the azimuth resolution according to the effective rotation angle in step S302, the specific formula is: ； in, represents the signal wavelength, represents the azimuth resolution, Indicates the effective rotation angle; S304. Repeat steps S301-S303 for each sub-interval to obtain azimuth resolution change curves for all intervals.

5. The method for predicting the optimal imaging time period of space-based ISAR by combining IPP and resolution analysis according to claim 4, characterized in that: In step S4, obtaining the Doppler frequency and echo delay of each scattering point includes the following sub-steps: S401, calculating the distance from the radar detection star to the scattering point on the target star at the imaging plane prediction time, and obtaining the time delay of the scattering point relative to the target center point. The specific formula is: ； Among them, R i Indicates the distance from the radar detection star to the scattering point, R o Indicates the distance from the radar detection star to the target center, B w represents the bandwidth of the transmitted signal, c represents the speed of light, Indicates delay; ； in, represents the position of the radar detection star, represents the position of the kth scattering point; S402. Obtain the Doppler frequency according to the satellite's rotation vector and the rotation radius of the scattering point. The specific formula is: ； in, represents the radar line of sight direction vector, represents the tangential velocity vector of the scattering point, represents the Doppler frequency; S403, repeat steps S401-S402 to calculate the time delay and Doppler frequency of all scattering points.

6. The method for predicting the optimal imaging time period of space-based ISAR by combining IPP and resolution analysis according to claim 1, characterized in that: In step S6, the calculation formula of the normalized imaging resolution is: ； in, Indicates the maximum value of the azimuth resolution. represents the normalized imaging resolution.

7. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 6 is performed.

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