Study On The Imaging Algorithms Of One-stationary Bistatic Synthetic Aperture Radar In High-resolution And Wide-swath Model

One-stationary bistatic synthetic aperture radar(OS BiSAR)refers to a new type of BiSAR system with a transmitter deployed on a stationary platform and a receiver deployed on a moving platform(and vice versa).This kind of SAR configuration not only possesses many advantages of general BiSAR,but also is relatively easier to be built and deployed,which has broad application prospect in both military and civilian fields,like military reconnaissance,regional monitoring,and resource exploration.Although,OS BiSAR is relatively easier to be deployed,its imaging processing is extremely difficult.Due to the fact that the relative position between the transmitter and the receiver changes with the azimuth time,the echo will be subject to the characteristic of the two-dimensional spatial variance of the range cell migration(RCM)and the azimuth variance of the Doppler phases,which will bring relatively serious adverse effect in high-resolution and wide-swath cases.To deal with the above imaging difficulties,this dissertation launches the following innovative work:Firstly,according the characteristic of the bistatic range history of the echo,an ellipse model for describing the range-azimuth space-variant property of the echo is proposed.Based on this model,a quadratic RCM correction(RCMC)method is deduced to improve the range processing.On the basic of linear range walk correction(LRWC),keystone transform(KT),and bulk RCMC(BRCMC),this method is able to effectively correct the residual high-order RCM component,which is especially suitable for high-resolution and wide-swath OS BiSAR imaging.Secondly,based on the ellipse spatial model above,an improved nonlinear chirp scaling(NLCS)algorithm is proposed to enhance the performance of the azimuth focusing.The ellipse model is used to model the Doppler frequency modulation(FM)rate as a first-approximated expression,and then improved functions of the Doppler chirp scaling and the azimuth compression are derived,which accomplishes the azimuth focusing.Compared with the NLCS algorithm based on the traditional range model,the improved NLCS algorithm based on the ellipse spatial model proposed by this dissertation can achieve higher-quality SAR focused images,especially in high-resolution and wide-swath imaging cases.Lastly,a quadratic ellipse spatial model is proposed,and then an extended NLCS(ENLCS)algorithm based on this model is derived to further enlarge the depth of the azimuth focusing.By using the quadratic ellipse spatial model,the Doppler FM rate is expanded as a second-order approximated expression.According to this expression and the principle of the ENLCS algorithm,improved Doppler chirp scaling function is deduced to accomplish the azimuth equalization.Compared with the NLCS algorithm based on the ellipse spatial model,due to fully considering the spatial properties of the high-order term of the Doppler FM rate,the ENLCS algorithm based on quadratic ellipse spatial model is able to process higher-resolution and wider-swath OS BiSAR data.