A real-time BAQ compression method for raw echo data of spaceborne synthetic aperture radar

Abstract

The invention provides a real-time BAQ compression method for raw echo data of a spaceborne synthetic aperture radar, the method comprising the following steps: within a preset azimuth block size, sequentially read the cached raw echo data according to the distance block size to obtain distance block data, and obtain several table lookup parameters of the first block data being read; synthesize the table lookup address of the first block data from several table lookup parameters; and read the raw echo data cached after the first block data according to the distance to obtain the second block data, and obtain several table lookup parameters of the second block data; use the obtained table lookup address to search the quantization coding table to obtain the quantization coding result of each block data. In the invention, BAQ real-time compression processing is performed on two block data at the same time, which can shorten the compression processing time by nearly half, and improve the timeliness of SAR system data processing.

Description

Technical Field

[0001] The invention belongs to the technical field of digital signal processing, and in particular relates to a real-time BAQ compression method for raw echo data of a spaceborne synthetic aperture radar. Background Art

[0002] Synthetic Aperture Radar (SAR) is a modern high-resolution microwave imaging radar that can operate in all weather conditions and at all times. It uses the relative motion between the radar and the target to synthesize a smaller real antenna aperture into a larger equivalent antenna aperture using data processing methods. Synthetic aperture radar is characterized by high resolution, all-weather operation, and the ability to effectively identify camouflage and penetrate cover. Synthetic aperture radar is mainly used in aerial surveying, aerial remote sensing, satellite ocean observation, space reconnaissance, image matching guidance, deep space exploration, etc. The radar system often uses the block adaptive quantization (BAQ) compression algorithm to compress the SAR raw echo data.

[0003] The principle of the block adaptive quantization (BAQ) compression algorithm is as follows: the SAR raw echo data is divided into blocks in the range and azimuth directions according to the pre-configured block size, the amplitude mean of the block data is calculated, and the amplitude mean is mapped to the standard deviation, each block data is normalized using the standard deviation, and then the Lloyd-Max quantizer is applied for quantization encoding, and the compressed data is obtained by table lookup.

[0004] However, with the development of science and technology, SAR technology is developing towards high resolution, multi-function and multi-mode, which makes SAR system gradually develop towards multi-polarization, multi-band and multi-mode, which makes the raw data rate of SAR increase rapidly, usually up to tens of Gbps. Although the block adaptive quantization (BAQ) algorithm has become the first practical SAR raw data compression algorithm due to its good compromise between compression performance and hardware implementation complexity, the existing data compression measures cannot compress and output the raw echo data collected by the SAR system in real time in real time, and must consume storage resources to cache the echo data, which brings the problem of high hardware overhead and poor real-time performance to the SAR system.

[0005] Therefore, in order to alleviate the pressure on the storage capacity of solid-state memory and the transmission rate and time of the data transmission link, how to compress the SAR raw data without affecting it is becoming an important issue in the design of SAR systems. Summary of the invention

[0006] In view of this, the present invention aims to propose a real-time BAQ compression method for raw echo data of a spaceborne synthetic aperture radar to solve the problem of poor timeliness in traditional radar signal processing.

[0007] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0008] A real-time BAQ compression method for raw echo data of a spaceborne synthetic aperture radar comprises the following steps:

[0009] Within the preset azimuth block size, sequentially read the cached original echo data according to the range block size to obtain range block data, and obtain several table lookup parameters of the first block data being read;

[0010] The table lookup address of the first block data is synthesized by a plurality of table lookup parameters; and the original echo data cached after the first block data is obtained according to the distance to obtain the second block data, and a plurality of table lookup parameters of the second block data are obtained;

[0011] The obtained table lookup address is used to search the quantization coding table to obtain the quantization coding result of each block data.

[0012] Furthermore, the block size in the azimuth direction is 1.

[0013] Furthermore, the table lookup parameters include the amplitude mean of the block data and the intra-block data of the block data.

[0014] Furthermore, the method for obtaining the amplitude mean of the block data is:

[0015] Obtaining the absolute value of each original echo data in the block data, and accumulating and summing the absolute values ​​of all the original echo data in the block data to obtain the cumulative sum of the block data;

[0016] The accumulated sum of the block data is used as the dividend and the distance block size S is used as the divisor to calculate the amplitude mean of the block data.

[0017] Further, the method of synthesizing the table lookup address of the block data from a plurality of table lookup parameters is as follows:

[0018] The block data is read sequentially, and the highest bit of the 8-bit width data in each block is inverted and concatenated with the amplitude mean of the block data to form 15-bit data as the lookup address of the quantization coding table.

[0019] An electronic device comprises a processor and a memory which is in communication with the processor and is used to store instructions executable by the processor. The processor is used to execute the above-mentioned real-time BAQ compression method for raw echo data of a space-borne synthetic aperture radar.

[0020] A server includes at least one processor and a memory in communication with the processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes the above-mentioned real-time BAQ compression method for raw echo data of a space-borne synthetic aperture radar.

[0021] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the above-mentioned real-time BAQ compression method for raw echo data of a space-borne synthetic aperture radar.

[0022] Compared with the prior art, the real-time BAQ compression method for raw echo data of spaceborne synthetic aperture radar created by the present invention has the following advantages:

[0023] The present invention creates a real-time BAQ compression method for raw echo data of a satellite-borne synthetic aperture radar. The method adopts a method of performing logical time-division multiplexing on a RAM storing a quantization coding table, and simultaneously performs BAQ real-time compression processing on two block data in the range direction of a single pulse repetition period (PRT). The compression processing time can be shortened by nearly half, and the timeliness of data processing of the SAR system is improved. It is ensured that the range echo data collected in each PRT during the imaging task of the SAR system is compressed and transmitted to the on-board fixed storage device in real time, and there is no situation where additional on-chip storage resources need to be occupied to cache echo data due to insufficient processing rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0025] Figure 1 A flow chart of a real-time BAQ compression method for raw echo data of a spaceborne synthetic aperture radar according to an embodiment of the present invention is shown;

[0026] Figure 2 A data compression flow chart of each block data in an embodiment of the present invention is shown;

[0027] Figure 3 A schematic diagram of a splicing method for synthesizing a table lookup address from the amplitude mean of the block data and the data within the block of the block data in an embodiment of the invention is shown;

[0028] Figure 4 A schematic diagram of a dual-thread compression process of a real-time BAQ compression method for raw echo data of a spaceborne synthetic aperture radar according to an embodiment of the present invention when the total number of raw echo data blocks is an even number is shown;

[0029] Figure 5 A schematic diagram of a dual-thread compression process of a real-time BAQ compression method for raw echo data of a spaceborne synthetic aperture radar described in an embodiment of the present invention when the number of raw echo data blocks is an odd number is shown. DETAILED DESCRIPTION

[0030] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0031] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0032] Figure 1 The flowchart of the real-time BAQ compression method of raw echo data of spaceborne synthetic aperture radar described in the embodiment of the invention is shown.

[0033] Figure 2 A data compression flow chart of each block data in an embodiment of the present invention is shown.

[0034] like Figure 1 and Figure 2 As shown, the real-time BAQ compression method S100 for raw echo data of spaceborne synthetic aperture radar includes the following steps:

[0035] Step S110, within the preset azimuth block size, the cached original echo data are sequentially read according to the range block size to obtain range block data, and a number of table lookup parameters of the first block data being read are obtained.

[0036] Since the acquisition rate of range echo data by each PRT is greater than the rate of BAQ compression processing, in order to prevent data loss, the original echo data is cached in FIFO before compression processing.

[0037] As a preferred solution, in this embodiment, the azimuth block size of the original echo data is set to 1 to ensure the real-time performance of the compression process and reduce the consumption of storage resources.

[0038] Specifically, after the BAQ compression process is started, S block data (data width 8 bits) are sequentially read out from the echo data cache FIFO each time according to the pre-configured range block size (such as range block size S: 128 / 256 / 512 / 1024 / 2048) parameter.

[0039] For example, when the azimuth block size is 1, assuming that the length of each PRT range echo data is 16384, S is configured as 1024, and when performing BAQ compression processing, 1024 block data with a bit width of 8 bits are read out from the FIFO each time. The entire process needs to read the block data from the FIFO 16 times, which means that the echo data is divided into 16 sub-blocks.

[0040] However, if the azimuth block size is greater than 1, additional on-chip storage resources are required to cache at least 1 more PRT of range echo data, which cannot guarantee the real-time performance of the compression processing and increases the consumption of storage resources (the larger the azimuth size, the more storage resources are required).

[0041] In this embodiment, the table lookup parameters include the amplitude mean of the block data and the intra-block data of the block data, more specifically, the intra-block data after the value domain is positively shifted.

[0042] Specifically, the method for obtaining the amplitude mean of the block data is:

[0043] Obtaining the absolute value of each original echo data in the block data, and accumulating and summing the absolute values ​​of all the original echo data in the block data to obtain the cumulative sum of the block data;

[0044] The accumulated sum of the block data is used as the dividend, S is used as the divisor, and the divider is used to calculate the amplitude mean of the block data.

[0045] It is worth noting that the lower 7 bits of the divider output result are taken as the effective mean value, and the absolute value of the original echo data in the block data is taken because the original echo data in each block data is a signed number.

[0046] While obtaining the amplitude mean of the block data, the block data read out from the FIFO of the original echo data buffer needs to be buffered in the small-size FIFO to be used by sub-process 2.

[0047] Step S120, synthesizing a table lookup address of the first block data by using a plurality of table lookup parameters; and reading the original echo data cached after the first block data according to the distance to obtain the second block data, and obtaining a plurality of table lookup parameters for the second block data.

[0048] That is, while synthesizing the lookup address of the first block data, start reading the original echo data cached behind the first block data according to the distance to obtain the second block data. The second block data becomes the new first block data as the block data being read, and repeats the operation step S110, thereby realizing the cycle of S110 and S120 until the data compression is completed.

[0049] In this embodiment, the method of synthesizing the table lookup address of the block data from a plurality of table lookup parameters is as follows:

[0050] Read the block data sequentially, invert the highest bit of the 8-bit width data in each block, and concatenate it with the amplitude mean of the block data to form 15-bit data as the lookup address of the quantization coding table. Figure 3 shown.

[0051] It is worth noting that the operation of inverting the highest bit of the 8-bit width data in each block here is because the data in each block is a signed number, and the RAM lookup address is a positive number. Therefore, before it is spliced ​​with the amplitude mean of the block data to form the lookup address, its highest bit is inverted to achieve a positive value offset in the numerical domain, thereby achieving an offset in the numerical domain from (-128~127) to (0~255).

[0052] Continue to refer Figure 2 As shown, in this embodiment, the BAQ compression processing flow of each block data can be divided into two sub-flows. Sub-flow 1 reads the block data from the distance echo data cache FIFO and adds and averages the block data. At the same time, the read block data is cached in a small-size FIFO to be used by sub-flow 2. Sub-flow 2 forms a lookup table address based on the calculated block data amplitude mean and the data in the block data cached in the FIFO, and then looks up the table to obtain the compressed quantization encoding result.

[0053] Step S130, using the obtained table lookup address to search the quantization coding table to obtain the quantization coding result of each block data.

[0054] Specifically, the 8-bit quantization coding result is read from the RAM storing the quantization coding table according to the table lookup address, and the quantization coding result is truncated according to the compression ratio to remove the invalid bit width, and finally a valid quantization coding result is obtained. Each original echo data in the block data completes the table lookup in the above manner to obtain a valid quantization coding result.

[0055] Exemplarily, assuming that the compression ratio is configured as 8:4, the lower 4 bits of the 8-bit quantization encoding result are intercepted as the effective quantization encoding result.

[0056] The real-time BAQ compression method for raw echo data of a spaceborne synthetic aperture radar provided in this embodiment divides the processing flow of block data into sub-flow 1 and sub-flow 2 with basically the same processing time, and based on this, adopts a method of time-sharing multiplexing of the quantization coding table RAM to improve data compression efficiency.

[0057] like Figure 4 and Figure 5As shown, after the first block data is read from the distance echo data cache FIFO to complete sub-process 1, while the first block data starts sub-process 2, the second block data is read from the distance echo data cache FIFO to perform the operation of sub-process 1, and while the first block completes sub-process 2, the second block completes sub-process 1. At this time, the third block data is read from the distance echo data cache FIFO to perform the operation of sub-process 1, and the second block performs sub-process 2, and so on and so forth until the last block n completes sub-process 2. At this point, a BAQ compression processing flow of the range echo data collected by a PRT is terminated.

[0058] The conventional compression processing flow is to start processing the next block only after the two sub-flows of the current block data finish outputting the quantized coded data. This method is simple to implement, but because it is a serial implementation structure, it consumes more processing time. When the data rate of the echo data is high, it cannot process the current PRT data in real time, resulting in the loss of echo data. The process designed by this method, without increasing the RAM, uses time-sharing multiplexing of the quantized coding table RAM. Although a small-size FIFO for the block data cache is added, the processing time is reduced by nearly half, and the FIFO size of the front-end cache distance to the echo data can be reduced by half accordingly. Compared with the serial implementation method, this method reduces FPGA storage resources and improves processing timeliness.

[0059] The distance block data collected by each PRT is Figure 4 and Figure 5 The process shown in the figure is compressed, and the compressed quantization coding result is transmitted to the on-board storage. At the same time, the distance-direction block data cache FIFO is released, and the echo data acquisition, BAQ compression processing and transmission to the on-board storage process are repeated after the next PRT is turned on until the imaging task is completed. Before each PRT ends, the distance-direction echo data cache FIFO is reset to release its space for the storage of the echo data collected by the next PRT, realizing the reuse of storage resources.

[0060] Those of ordinary skill in the art will appreciate that the units and method steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0061] In the several embodiments provided in the present application, it should be understood that the disclosed methods and systems can be implemented in other ways. For example, the division of the units described above is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. The above-mentioned units may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the embodiments of the present invention.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A real-time BAQ compression method for raw echo data of spaceborne synthetic aperture radar, characterized in that: The steps include: Within the preset azimuth block size, the cached original echo data is sequentially read according to the range block size to obtain the range block data, and a number of table lookup parameters of the first block data being read are obtained; the azimuth block size is 1; The table lookup address of the first block data is synthesized by a plurality of table lookup parameters; and the original echo data cached after the first block data is simultaneously read according to the distance to obtain the second block data, and a plurality of table lookup parameters of the second block data are obtained; The obtained table lookup address is used to search the quantization coding table to obtain the quantization coding result of each block data.

2. The real-time BAQ compression method for raw echo data of spaceborne synthetic aperture radar according to claim 1, characterized in that: The table lookup parameters include the amplitude mean of the block data and the intra-block data of the block data.

3. The real-time BAQ compression method for raw echo data of spaceborne synthetic aperture radar according to claim 2 is characterized in that: The method for obtaining the mean amplitude of the block data is: Obtaining the absolute value of each original echo data in the block data, and accumulating and summing the absolute values ​​of all the original echo data in the block data to obtain the cumulative sum of the block data; The accumulated sum of the block data is used as the dividend and the distance block size S is used as the divisor to calculate the amplitude mean of the block data.

4. The real-time BAQ compression method for raw echo data of spaceborne synthetic aperture radar according to claim 1, characterized in that: The method of synthesizing the lookup address of block data from several lookup table parameters is: The block data is read sequentially, and the highest bit of the 8-bit width data in each block is inverted and concatenated with the amplitude mean of the block data to form 15-bit data as the lookup address of the quantization coding table.

5. An electronic device, comprising a processor and a memory connected to the processor for storing instructions executable by the processor, characterized in that: The processor is used to execute the real-time BAQ compression method for raw echo data of a space-borne synthetic aperture radar as described in any one of claims 1-4.

6. A server, characterized in that: The invention comprises at least one processor and a memory in communication with the processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor so that the at least one processor executes the real-time BAQ compression method for raw echo data of a space-borne synthetic aperture radar as described in any one of claims 1 to 4.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the real-time BAQ compression method for raw echo data of a space-borne synthetic aperture radar as described in any one of claims 1 to 4 is implemented.

Images