| Synthetic Aperture Radar(SAR)obtains information by actively emitting electromagnetic waves to the target area,and can work around the clock regardless of weather or light.It plays an important role in both military and civilian fields.Compared with other platforms,spaceborne SAR has bigger swath and higher resolution.However,the high cost,high risk and long time for the development of the spaceborne platform limit the ways to verify new SAR system performance and new imaging algorithms.Echo simulation technology provides a large amount of reliable data for verification work,which greatly promotes the development of spaceborne SAR technology.The purpose of this paper is to provide a flexible,efficient,stable and easy-to-operate spaceborne SAR echo data simulation platform.We strive to simulate the physical process of SAR signal transmission and reception as realistically and accurately as possible.A large number of spaceborne radar link models and SAR working mode characteristics are studied,and the research results are finally realized in the form of software.The main research contents of this paper are as follows:1.Summarize the research status and devlopment trend of spaceborne SAR system at home and abroad,and introduce the basic theory of spaceborne SAR echo simulation,including geometric relationship,working mode,signal model and system performance evaluation index,involving system design,echo simulation,imaging processing and other fields.2.Through a large quantity of study of the entire link model of signal transmission and reception,the construction of the automatic spaceborne SAR entire link accurate modeling software was completed.The model includes the platform and payload model,the elevation distribution and scattering characteristic model of the target,and the transmission link model.The platform and payload model includes the description of the parameters for the satellite platform,transmitter,radar antenna and receiver;the exact three-dimensional coordinates of the distributed target are obtained by fractal interpolation combined with Monte-Carlo method,and the artificial target is approximated by the point cloud model.The Bistatic scattering coefficient of the target is calculated using the numerical integration method;the transmission link layer model includes data compression downlink and atmospheric effects in the form of nonideal factor errors.3.The non-ideal factors that affect the performance of the spaceborne SAR system are studied,and a complete simulation analysis platform that comprehensively integrates various errors is established,which includs systematic error models and various atmospheric troposphere and ionosphere influence models existing in the traditional spaceborne SAR system.This paper combines theoretical derivation and simulation processing to evaluate the impact of errors on imaging performance;further focuses on the "three-synchronization" issues unique to distributed spaceborne SAR,and realizes synchronization error simulation and the establishment of inter-satellite synchronization links.The synchronous link compensation algorithm can be used to compensate the error signal.4.A none "stop-go" fast time delay compensation algorithm for echo and direct wave is proposed,combined with the method of selecting RTPC model or RFPC model accroding to the type of target.Finally,the OpenMP library in Microsoft Visual Studio2015 is used for parallel acceleration.A faster and more accurate SAR data computing platform is developed by means of algorithms and codes.5.An echo data simulation platform suitable for both traditional SAR systems and new SAR systems is provided.Verify the correctness of the output data through imaging processing algorithms and evaluation algorithms,which proves that the software has the ability for simulating multi-mode SAR echo data. |
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