CN107831504B - Processing method for reducing data rate of satellite-borne SAR satellite load - Google Patents

Processing method for reducing data rate of satellite-borne SAR satellite load Download PDF

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CN107831504B
CN107831504B CN201710877188.1A CN201710877188A CN107831504B CN 107831504 B CN107831504 B CN 107831504B CN 201710877188 A CN201710877188 A CN 201710877188A CN 107831504 B CN107831504 B CN 107831504B
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sampling
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路瑞峰
刘艳阳
侯雨生
张丙良
巩彪
曹岸杰
魏春
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Shanghai Institute of Satellite Engineering
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
    • G01S19/05—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing aiding data
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
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    • G01S7/4052—Means for monitoring or calibrating by simulation of echoes

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Abstract

The invention provides a processing method for reducing data rate of satellite-borne SAR satellite loads, which comprises the following steps: inputting SAR echo data; step two, Doppler center estimation; determining down-sampling multiples; step four, constructing a down-sampling interpolation kernel function; step five, resampling on-satellite data; and step six, resampling the signal. The method solves the problem of large data rate caused by high azimuth oversampling rate of SAR system design under the requirements of azimuth ambiguity and zebra pattern design to a certain extent, further effectively ensures the earth observation performance of the SAR system, and has the advantage of signal-to-noise ratio preservation.

Description

Processing method for reducing data rate of satellite-borne SAR satellite load
Technical Field
The invention relates to the technical field of signal and information processing, in particular to a processing method for reducing data rate of satellite-borne SAR satellite loads.
Background
Synthetic Aperture Radar (SAR) is widely applied to military and civil fields due to all-weather high-resolution ground observation capability of the SAR all day long, such as battlefield investigation, ocean monitoring, agricultural general survey, topographic mapping and the like, generally, the Radar Pulse Repetition Frequency (PRF) of the SAR system is greater than the doppler bandwidth of the SAR system, which causes that certain redundancy exists in SAR echo data, the data rate of the SAR system echo increases quadratically with the improvement of the Radar high resolution, the data rate of the SAR system is increasingly greater with the continuous improvement of the SAR image resolution demand of people, and the system faces increasingly severe data transmission pressure, at the moment, the research of on-satellite real-time processing to reduce the SAR data rate is an important technical support means for realizing high-resolution imaging of the SAR system in the future.
The on-board real-time data rate reduction processing is a problem that a satellite-borne SAR system designer must consider and cannot avoid. At present, a satellite-borne SAR system mainly reduces the data rate in a satellite data compression mode. Kwok et al propose a Block Adaptive Quantization (BAQ) compression algorithm, which can realize data compression in an equal proportion of 8:3 and 8:4, and the algorithm is widely applied to a satellite-borne SAR system, but the algorithm can only reduce the echo data rate by increasing the compression ratio, which will cause the quantization noise of the SAR image to increase and the quality of the SAR image to decrease.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a processing method for reducing the data rate of a satellite-borne SAR satellite load, which solves the problem of large data rate caused by high azimuth oversampling rate of an SAR system design under the requirements of azimuth ambiguity and zebra pattern design to a certain extent, further effectively ensures the earth observation performance of the SAR system, has the advantage of signal-to-noise ratio preservation, and is realized by carrying out azimuth resampling on echo data received by a satellite.
According to one aspect of the invention, a processing method for reducing data rate of satellite-borne SAR satellite loads is provided, and is characterized by comprising the following steps:
inputting SAR echo data, inputting the SAR echo data into a system, and assuming that the pulse repetition frequency of the system is PRF;
step two, Doppler center estimation;
determining down-sampling multiples;
step four, constructing a down-sampling interpolation kernel function as follows:
Figure BDA0001418354690000021
where t is the azimuth pre-sampling time taSampling time for actual orientation, Ba,pProcessing the bandwidth for the azimuth signal, fdcAs a central estimate, f (t; t)a) Interpolating a kernel function for the downsampling; j represents a complex symbol;
step five, resampling on-satellite data;
step six, resampling the signal, and outputting s (t) according to the format requirementa) And outputs the down-sampling multiple F.
Preferably, the step five specifically includes the following steps:
fifthly, determining the azimuth sampling time, and assuming the SAR echo data starting time to be t0After down-sampling, the sampling time of each direction is as follows:
Figure BDA0001418354690000022
wherein, taFor the actual azimuth sampling time, t0The SAR echo data starting time is represented, PRF is the system pulse repetition frequency, and F is the down-sampling multiple;
fifthly, resampling the signal and determining the azimuth time taResampled signal, as follows:
Figure BDA0001418354690000023
wherein the content of the first and second substances,<·>to round the rounding operator, t is the azimuth pre-sampling time, taFor the actual azimuth sampling time, PRF is the system pulse repetition frequency, f (t; t)a) For the down-sampling interpolation kernel, 2N +1 is the number of down-sampling kernel points.
Preferably, the doppler center estimation in step two is performed by using attitude measurement data or raw echo data, assuming that the doppler center estimation value is fdc。
Preferably, the down-sampling multiple is determined in the third step by using the azimuth signal processing bandwidth Ba,pOf the formula：
F＝Ba,p/PRF
Wherein F is a down-sampling multiple, Ba,pFor azimuth signal processing bandwidth, PRF is the system pulse repetition frequency.
Compared with the prior art, the invention has the following beneficial effects: the invention solves the problem of large data rate caused by high azimuth oversampling rate of SAR system design under the requirements of azimuth ambiguity and zebra pattern design to a certain extent, further effectively ensures the earth observation performance of the SAR system, has the advantage of signal-to-noise ratio preservation, and is realized by carrying out azimuth resampling on echo data received by a satellite.
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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 schematic flow chart 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 variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
As shown in fig. 1, the processing method for reducing the data rate of the satellite-borne SAR satellite load of the present invention includes the following steps:
inputting SAR (synthetic aperture radar) echo data, inputting the SAR echo data into a system, and assuming that the pulse repetition frequency of the system is PRF;
estimating the Doppler center, namely estimating the Doppler center by using attitude measurement data or original echo data, and assuming that the Doppler center estimated value is fdc；
Step three, determining down-sampling multiple, and processing bandwidth B by using azimuth signala,pDetermining a down-sampling factor, as given in (1)：
F＝Ba,p/PRF (1)
Wherein F is a down-sampling multiple, Ba,pFor azimuth signal processing bandwidth, PRF is the system pulse repetition frequency;
step four, constructing a down-sampling interpolation kernel function as the following formula (2):
Figure BDA0001418354690000041
where t is the azimuth pre-sampling time taSampling time for actual orientation, Ba,pProcessing the bandwidth for the azimuth signal, fdcAs a central estimate, f (t; t)a) Interpolating a kernel function for the downsampling; j represents a complex symbol;
step five, resampling on-satellite data, specifically comprising the following steps:
fifthly, determining azimuth sampling time, and assuming that the initial time of SAR (synthetic aperture radar) echo data is t0After down-sampling, the sampling time of each azimuth is as follows (3):
Figure BDA0001418354690000042
wherein, taFor the actual azimuth sampling time, t0The method comprises the steps of taking SAR (synthetic aperture radar) echo data starting time, taking PRF as system pulse repetition frequency, and taking F as down-sampling multiple;
fifthly, resampling the signal and determining the azimuth time taThe resampled signal is expressed by the following equation (4):
Figure BDA0001418354690000043
wherein the content of the first and second substances,<·>to round the rounding operator, t is the azimuth pre-sampling time, taFor the actual azimuth sampling time, PRF is the system pulse repetition frequency, f (t; t)a) The number of points is 2N +1 of the down-sampling kernel function;
step six, resampling the signal, and outputting s (t) according to the format requirementa) And outputs the down-sampling multiple F.
The embodiment relates to a processing method for reducing data rate of satellite-borne SAR satellite loads.
The space-borne Synthetic Aperture Radar (SAR) of the embodiment realizes high-resolution imaging to the ground through the azimuth synthetic aperture, and the azimuth signal bandwidth of the SAR is BaThe following formula (5):
Figure BDA0001418354690000044
wherein D isaIs the antenna size and v is the platform motion speed;
to satisfy Nyquist's sampling, the radar pulse repetition Period (PRF) needs to be greater than the signal bandwidth BaUsually, oversampling of 1.1-1.2 times is adopted to ensure the azimuth ambiguity performance of the system, but azimuth oversampling brings an increase of the data rate.
The on-board data rate is reduced by adopting on-board real-time processing, the basic principle is that the azimuth resampling is realized by constructing an interpolation kernel function through a time domain and multiplying the interpolation kernel function by an original signal receiving signal, the processing performance of on-board real-time processing down-sampling is verified by adopting Japanese XXX satellite SAR (synthetic aperture radar), the bandwidth of the original echo data signal is 2480Hz, the pulse repetition frequency is 2720Hz, and the original echo data rate is reduced by 9.9% after the down-sampling processing.
Compared with the traditional technology, the invention has the following advantages:
firstly, the processing idea is different from the existing data compression method, and the data rate is reduced from the signal sampling principle for the first time at home and abroad;
secondly, the provided on-satellite real-time resampling method has the advantages of signal-to-noise ratio protection and the like;
and thirdly, the problem of large data rate caused by high azimuth oversampling rate of SAR (synthetic aperture radar) system design under the requirements of azimuth ambiguity and zebra pattern design is solved to a certain extent.
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 and 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.

Claims (3)

1. A processing method for reducing data rate of satellite-borne SAR satellite loads is characterized by comprising the following steps:
inputting SAR echo data, inputting the SAR echo data into a system, and assuming that the pulse repetition frequency of the system is PRF;
step two, Doppler center estimation;
determining down-sampling multiples;
step four, constructing a down-sampling interpolation kernel function as follows:
Figure FDA0002789516010000011
where t is the azimuth pre-sampling time taSampling time for actual orientation, Ba,pProcessing the bandwidth for the azimuth signal, fdcAs a central estimate, f (t, t)a) Interpolating a kernel function for the downsampling; j represents a complex symbol;
step five, resampling on-satellite data;
step six, resampling the signal, and outputting s (t) according to the format requirementa) And outputting a down-sampling multiple F;
the fifth step specifically comprises the following steps:
fifthly, determining the azimuth sampling time, and assuming the SAR echo data starting time to be t0After down-sampling, the sampling time of each direction is as follows:
Figure FDA0002789516010000012
wherein, taSampling instants for actual orientation，t0The SAR echo data starting time is represented, PRF is the system pulse repetition frequency, and F is the down-sampling multiple;
fifthly, resampling the signal and determining the azimuth time taResampled signal, as follows:
Figure FDA0002789516010000013
wherein the content of the first and second substances,<·>to round the rounding operator, t is the azimuth pre-sampling time, taFor the actual azimuth sampling time, PRF is the system pulse repetition frequency, f (t, t)a) For the down-sampling interpolation kernel, 2N +1 is the number of down-sampling kernel points.
2. The method for processing data rate reduction of loading of SAR satellite on board of claim 1, wherein the Doppler center estimation in the second step is performed by using attitude measurement data or raw echo data, assuming that the Doppler center estimation value is fdc。
3. The method for processing data rate reduction of satellite borne SAR satellite loading according to claim 1, characterized in that the step three for determining the down-sampling multiple is to utilize azimuth signal processing bandwidth Ba,pThe following formula:
F＝Ba,p/PRF
wherein F is a down-sampling multiple, Ba,pFor azimuth signal processing bandwidth, PRF is the system pulse repetition frequency.
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JP2010048603A (en) * 2008-08-20 2010-03-04 Mitsubishi Electric Corp Synthetic aperture radar device
CN101483777A (en) * 2008-12-19 2009-07-15 西安电子科技大学 SAR image denoising compressing method based on adaptive multi-dimension Bandelet packet
US8159387B1 (en) * 2010-03-15 2012-04-17 The United States Of America As Represented By The Secretary Of The Navy Multi-transmitter interferometry
CN102298137A (en) * 2010-06-25 2011-12-28 中国科学院电子学研究所 Method for compressing adaptive data-rate original data of satellite-borne SAR (Synthetic Aperture Radar)

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