An intelligent quantization compression method and system for spaceborne SAR raw data

Abstract

The present invention discloses an intelligent quantization compression method for raw data of spaceborne SAR, S1: receiving an intermediate frequency radar echo signal, filtering and sampling, and obtaining raw echo data with a bit number of 8 (the first bit is a sign bit); S2: sampling the raw echo data with an M×M block size to obtain a number of block data, storing and calculating the amplitude mean and variance value corresponding to each block data; S3: finding the corresponding compression code value from a preset compression coding table, and compressing the block data according to the compression code value to obtain compressed block data; S4: framing based on the sign bit, the amplitude mean, the variance value and the compressed block data to obtain the compression value. The present invention can improve the quantization compression signal-to-noise ratio of the echo data and reduce the amplitude error and phase error. Through the preset compression coding table and the pre-extraction of the sign bit, the data processing function of any compression ratio such as 8:8 (uncompressed), 8:7, 8:6, 8:5, 8:4, 8:3, etc. can be realized.

Description

Technical Field

[0001] The invention belongs to the field of spaceborne radar data processing, and in particular relates to an intelligent quantization compression method and system for spaceborne SAR raw data. Background Art

[0002] In radar remote sensing applications, high-resolution detection and imaging of targets are usually required. The bandwidth of the corresponding radar echo signal is getting larger and larger, and the data capacity of the radar echo is also getting larger and larger. In order to meet the requirements of data transmission rate between satellite and ground, compression processing of satellite-borne radar echo data has become a design necessity. At present, in practical applications, most synthetic aperture radar (SAR) systems use block adaptive quantization (BAQ) compression method. However, after each loading of the imaging program, the compression ratio in the algorithm is mostly fixed, which is difficult to adapt to the areas with obvious echo strength changes in the observation area. For example, Europe's EnviSAT, Canada's RadarSat, Germany's TerraSAR and India's RISAT all use the traditional multi-level BAQ compression algorithm. The selection of the level needs to be realized by uploading control parameters from the ground. Therefore, improvements based on the traditional BAQ algorithm have become a hot topic of current research. For example, researchers from the Institute of Electronics of the Chinese Academy of Sciences proposed a variety of improvement methods such as anti-saturation and floating-point quantization based on the traditional BAQ compression algorithm with fixed compression bits. However, none of these methods have been implemented in engineering. In order to speed up the intelligent processing of the BAQ-based compression algorithm, the patent not only proposes a compression method with variable bit numbers, but also elaborates on the design steps of the system and provides a quantization compression coding table used for different compression output bit numbers. Summary of the invention

[0003] The technical purpose of the present invention is to provide an intelligent quantization compression method and system for spaceborne SAR raw data to solve the technical problem that the compression ratio is fixed and it is difficult to adapt to the area where the echo strength changes significantly in the observation area.

[0004] To solve the above problems, the technical solution of the present invention is:

[0005] An intelligent quantization compression method for spaceborne SAR raw data comprises the following steps:

[0006] S1: Receive the intermediate frequency radar echo signal, filter and sample the intermediate frequency radar echo signal, obtain the original echo data with a bit number of 8, and obtain the sign bit based on the original echo data;

[0007] S2: Sample the original echo data in M×M blocks to obtain a number of block data, store and calculate the amplitude mean and variance value corresponding to each block data;

[0008] S3: obtaining a corresponding quantization compression bit number based on the variance value, obtaining a comparison result based on the amplitude mean value and the threshold level, searching a preset compression coding table based on the quantization compression bit number and the comparison result to obtain a corresponding compression coding value, and compressing the block data according to the compression coding value to obtain compressed block data;

[0009] S4: Frame processing is performed based on the sign bit, amplitude mean, variance value and compressed block data, and sent to the satellite data transmission system through the TLK2711 high-speed interface for transmission to the ground.

[0010] The different block data are stored in the cache SDRAM through a ping-pong method.

[0011] Further preferably, before step S1, a preset compression coding table needs to be constructed according to a minimum error quantization criterion.

[0012] Specifically, the number of quantization compression bits in the compression coding table includes 2, 3, 4, 5, and 6.

[0013] Wherein, in step S3, the block data is compressed using the max-lloyd rule to obtain compressed block data.

[0014] An intelligent quantization compression system for spaceborne SAR raw data, comprising an AD sampling module, a compression coding selection module, an arbitrary compression ratio selection module and a data compression processing module;

[0015] The AD sampling module is used to receive the intermediate frequency radar echo signal, filter and sample the intermediate frequency radar echo signal, and obtain the original echo data with a bit number of 8;

[0016] The arbitrary compression ratio selection module is used to obtain the corresponding quantization compression bit number based on the variance value of the sampling block;

[0017] The compression coding selection module is used to sample the original echo data in M×M block size to obtain a number of block data, calculate the amplitude mean and variance value corresponding to each block data; obtain a comparison result based on the comparison of the amplitude mean and the threshold level, and obtain the corresponding compression coding value from the preset compression coding table based on the quantization compression bit number and the comparison result;

[0018] The data compression processing module is used to compress the block data according to the compression code value to obtain compressed block data.

[0019] More preferably, it also includes a storage module, and the storage module is used to perform time-sharing processing on the block data through a ping-pong method.

[0020] Due to the adoption of the above technical solution, the present invention has the following advantages and effects compared with the prior art:

[0021] Compared with the conventional BAQ data compression method with a fixed compression ratio in the prior art, the new method proposed by the present invention can improve the quantization compression signal-to-noise ratio of echo data and reduce amplitude error and phase error. Through the preset compression coding table and the pre-extraction of the sign bit, the data processing function of any compression ratio such as 8:8 (uncompressed), 8:7, 8:6, 8:5, 8:4, 8:3 can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various advantages and benefits will become apparent to those of ordinary skill in the art by reading the following detailed description of the preferred embodiments.The drawings are only for the purpose of illustrating the preferred embodiments and are not to be construed as limiting the invention.

[0023] Figure 1 This is a flow chart of an intelligent quantization compression method for spaceborne SAR raw data of the present invention;

[0024] Figure 2 This is a structural diagram of an intelligent quantization compression system for raw data of spaceborne SAR of the present invention;

[0025] Figure 3 The present invention is a data transmission schematic diagram of an intelligent quantization compression system for raw data of spaceborne SAR. DETAILED DESCRIPTION

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work.

[0027] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0028] The following is a further detailed description of the intelligent quantization compression method and system for spaceborne SAR raw data proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims.

[0029] Example 1

[0030] See also Figure 1 and Figure 3 This embodiment provides an intelligent quantization compression method for spaceborne SAR raw data, comprising the following steps:

[0031] First, in step S1, the intermediate frequency radar echo signal transmitted from the outside is received, and the intermediate frequency radar echo signal is filtered and sampled to obtain the original echo data with a bit number of 8. For the original echo data, its sign bit is first obtained. Generally, the first bit of the 8-bit data is the sign bit, and then the absolute value is taken and then step S2 is entered.

[0032] Preferably, before implementing step S1, it is also necessary to construct a preset compression coding table with quantization compression bit numbers including 2, 3, 4, 5, and 6 according to the minimum mean square error quantization criterion. The minimum mean square error quantization criterion refers to quantizing the compression coding value according to the rule so that the mean square error between the decompressed result and the original eight-bit raw data is minimized. The preset compression coding table can be found in Table 1 below.

[0033] Table 1 Compression coding table

[0034]

[0035]

[0036] Then in step S2, the original echo data in step S1 is sampled and divided into blocks with a size of M×M to obtain a number of block data. Different block data are stored in the cache SDRAM through a ping-pong method, and the amplitude mean and variance values ​​corresponding to each block data are calculated in turn.

[0037] Then in step S3, after the variance value is obtained, according to the variance size of each block data, more quantization compression output bits are allocated to the block with larger variance, so that different block data obtain different quantization compression bits. For example, assuming that the mean value of the compression coding bit is 4 bits, the quantization compression bit number of the i-th block data can be obtained by the following formula:

[0038]

[0039]

[0040] Where A is the logarithm of the variance of the block data, is the mean of the logarithm of the variance of each block data, and M is the total number of block data.

[0041] Then, the comparison result is obtained by comparing the amplitude mean with the threshold level. The threshold level refers to the critical value of different compression coding values. By using the quantization compression bit number and the comparison result as the query address, the corresponding compression coding value is found in the preset compression coding table, and then the max-lloyd rule is used to compress the corresponding block data using the compression coding value to obtain the compressed block data. Among them, the max-lloyd rule is an optimal nonlinear quantization coding method for the standard Gaussian distribution. Its design idea is to obtain the optimal quantization compression coding value according to the minimum mean square error criterion. The mean square error is expressed by the following formula

[0042]

[0043] Among them, x is the original 8-bit data, y k It is the decompressed value of the quantized coded value. Since this method is lossy compression, it changes in steps.

[0044] According to the above compression coding table, by pre-extraction of the sign bit, this method can realize data processing functions of any compression ratio such as 8:8 (uncompressed), 8:7, 8:6, 8:5, 8:4, 8:3, etc.

[0045] Finally, in step S4, the sign bit obtained in step S1, the amplitude mean and variance value obtained in step S2, and the compressed block data obtained in step S3 are framed and then sent to the data transmission system through the TLK2711 high-speed interface, and then transmitted to the ground for subsequent processing.

[0046] Example 2

[0047] See also Figure 2 This embodiment provides an intelligent quantization compression system for spaceborne SAR raw data, and its application is the intelligent quantization compression method for spaceborne SAR raw data in Embodiment 1. From the perspective of hardware structure, this embodiment mainly includes ADC, FPGA and SDRAM. According to the function, it can be divided into AD sampling module, compression coding selection module, arbitrary compression ratio selection module, data compression processing module and storage module.

[0048] The AD sampling module, namely ADC, is used to receive the intermediate frequency radar echo signal, filter and sample the intermediate frequency radar echo signal, and obtain the original echo data with a bit number of 8. The sampling clock of ADC is provided by the external clock distribution circuit.

[0049] FPGA is used for compression coding selection module, arbitrary compression ratio selection module and data compression processing module, and the FPGA working clock is also provided by the external clock distribution circuit. The arbitrary compression ratio selection module is used to obtain the corresponding quantization compression bit number according to the variance value. The compression coding selection module is used to sample the original echo data with an M×M block size to obtain a number of block data, and calculate the amplitude mean and variance value corresponding to each block data. Then, the corresponding quantization compression bit number is obtained according to the variance value, and the comparison result is obtained based on the comparison of the amplitude mean and the threshold level. The corresponding compression coding value is obtained by searching the preset compression coding table through the quantization compression bit number and the comparison result. The data compression processing module is used to receive the compression coding value and then process the corresponding block data to obtain the compressed block data.

[0050] The storage module is SDRAM, which is connected to the FPGA signal and stores and processes the divided block data in a ping-pong manner.

[0051] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the protection scope of the present invention.

Claims

1. An intelligent quantization compression method for spaceborne SAR raw data, characterized in that: The steps include: S1: receiving an intermediate frequency radar echo signal, filtering and sampling the intermediate frequency radar echo signal, obtaining original echo data with a bit number of 8, and obtaining a sign bit based on the original echo data; S2: The original echo data is sampled according to the block size to obtain a plurality of block data, and the amplitude mean and variance value corresponding to each of the block data are stored and calculated; S3: obtaining a corresponding quantization compression bit number based on the variance value, obtaining a comparison result based on the comparison of the amplitude mean value and the threshold level, searching a preset compression coding table based on the quantization compression bit number and the comparison result to obtain a corresponding compression coding value, and compressing the block data according to the compression coding value to obtain the compressed block data; S4: performing frame processing based on the sign bit, the amplitude mean, the variance value and the compressed block data, and sending the frame to the satellite data transmission system through the TLK2711 high-speed interface to be transmitted to the ground; In step S3, after obtaining the variance value, according to the variance of each block data, a design is made to allocate more quantization compression output bits to blocks with larger variances, so that different block data obtain different quantization compression output bits; Assuming that the average number of compressed coding bits is 4 bits, the number of quantized compressed bits of the i-th block data is obtained by the following formula: in, is the logarithm of the variance of the block data, is the mean of the logarithm of the variance of each block data, The total number of block data.

2. The intelligent quantization compression method for spaceborne SAR raw data according to claim 1, characterized in that: In the step S2, the different block data are stored in a cache SDRAM by a ping-pong method.

3. The intelligent quantization compression method for spaceborne SAR raw data according to claim 1, characterized in that: Before step S1, the preset compression coding table is constructed according to the minimum error quantization criterion.

4. The intelligent quantization compression method for spaceborne SAR raw data according to claim 3 is characterized in that: The number of quantization compression bits in the compression coding table includes 2, 3, 4, 5, and 6.

5. The intelligent quantization compression method for spaceborne SAR raw data according to claim 1, characterized in that: In the step S3, the block data is compressed using the max-lloyd rule to obtain the compressed block data.

6. An intelligent quantization compression system for spaceborne SAR raw data, characterized in that: It includes an AD sampling module, a compression coding selection module, an arbitrary compression ratio selection module and a data compression processing module; The AD sampling module is used to receive the intermediate frequency radar echo signal, and filter and sample the intermediate frequency radar echo signal to obtain the original echo data with a bit number of 8; The arbitrary compression ratio selection module is used to obtain the corresponding quantization compression bit number based on the variance value of the sampling block; The compression coding selection module is used to The original echo data is sampled according to the block size to obtain a number of block data, and the amplitude mean and variance value corresponding to each of the block data are calculated; a comparison result is obtained based on the comparison of the amplitude mean and the threshold level, and a corresponding compression code value is obtained by searching from a preset compression code table based on the quantization compression bit number and the comparison result; The data compression processing module is used to compress the block data according to the compression code value to obtain the compressed block data; After the variance value is obtained, according to the variance of each block data, a design is adopted in which more quantization compression output bits are allocated to the block with larger variance, so that different block data obtain different quantization compression output bits; Assuming that the average number of compressed coding bits is 4 bits, the number of quantized compressed bits of the i-th block data is obtained by the following formula: in, is the logarithm of the variance of the block data, is the mean of the logarithm of the variance of each block data, The total number of block data.

7. The intelligent quantization compression system for spaceborne SAR raw data according to claim 6, characterized in that: It also includes a storage module, which is used to perform time-sharing processing on the block data in a ping-pong manner.

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