Micromotion is an important target feature,although the target micromotion has an unfavorable influence on the synthetic aperture radar (SAR) image interpretation due to defocusing.This paper introduces micromotion parameters into the scattering center model to obtain a hybrid micromotion-scattering center model,and then proposes an optimization algorithm based on the maximal likelihood estimation to solve the model for jointly obtaining target motion and scattering parameters.Initial value estimation methods using targets’ghost images are then presented to guarantee the global and fast convergence.Simulation results show the effectiveness of the proposed algorithm especially in high precision estimation and multiple targets processing.
The sparse recovery algorithms formulate synthetic aperture radar(SAR) imaging problem in terms of sparse representation(SR) of a small number of strong scatters' positions among a much large number of potential scatters' positions,and provide an effective approach to improve the SAR image resolution.Based on the attributed scatter center model,several experiments were performed with different practical considerations to evaluate the performance of five representative SR techniques,namely,sparse Bayesian learning(SBL),fast Bayesian matching pursuit(FBMP),smoothed l0 norm method(SL0),sparse reconstruction by separable approximation(SpaRSA),fast iterative shrinkage-thresholding algorithm(FISTA),and the parameter settings in five SR algorithms were discussed.In different situations,the performances of these algorithms were also discussed.Through the comparison of MSE and failure rate in each algorithm simulation,FBMP and SpaRSA are found suitable for dealing with problems in the SAR imaging based on attributed scattering center model.Although the SBL is time-consuming,it always get better performance when related to failure rate and high SNR.
The problems of joint adaptive waveform design and baseline range design for bistatic radar to maximize the practical radar resolution were considered.Distinguishing from the conventional ambiguity function(AF)-based resolution which is only related with the transmitted waveform and bistatic geometry and could be regarded as the potential resolution of a bistatic radar system,the practical resolution involves the effect of waveform,signal-to-noise ratio(SNR)as well as the measurement model.Thus,it is more practical and will have further significant application in target detection and tracking.The constraint optimization procedure of joint adaptive waveform design and baseline range design for maximizing the practical resolution of bistatic radar system under dynamic target scenario was devised.Simulation results show that the range and velocity resolution are enhanced according to the adaptive waveform and bistatic radar configuration.
The original nonlinear chirp scaling(NCS) algorithm was extended for high precision processing of the highly squinted curvilinear trajectory synthetic aperture radar(CTSAR).Based on the analysis of slant range model and the frequency spectrum characteristics of the echo signal,a novel nonlinear chirp scaling function and more complex phase compensation factors with both velocity and acceleration parameters were proposed in the new algorithm for accommodation to curvilinear trajectory.The processing flow and computational complexity of modified NCS algorithm were fundamentally the same as the original NCS algorithm.However,the higher order phase compensation,range cell migration correction(RCMC) and range-variant secondary range compression(SRC) caused by the non-linear aperture and the severe range-azimuth coupling were accomplished accurately and efficiently without interpolation.Simulation results show that data acquired with a curvilinear aperture and a squint angle up to about 50° for X-band can be processed with no evident degradation of impulse response function.
Inverse synthetic aperture radar(ISAR) imaging can be regarded as a narrow-band version of the computer aided tomography(CT). The traditional CT imaging algorithms for ISAR, including the polar format algorithm(PFA) and the convolution back projection algorithm(CBP), usually suffer from the problem of the high sidelobe and the low resolution. The ISAR tomography image reconstruction within a sparse Bayesian framework is concerned. Firstly, the sparse ISAR tomography imaging model is established in light of the CT imaging theory. Then, by using the compressed sensing(CS) principle, a high resolution ISAR image can be achieved with limited number of pulses. Since the performance of existing CS-based ISAR imaging algorithms is sensitive to the user parameter, this makes the existing algorithms inconvenient to be used in practice. It is well known that the Bayesian formalism of recover algorithm named sparse Bayesian learning(SBL) acts as an effective tool in regression and classification,which uses an efficient expectation maximization procedure to estimate the necessary parameters, and retains a preferable property of the l0-norm diversity measure. Motivated by that, a fully automated ISAR tomography imaging algorithm based on SBL is proposed.Experimental results based on simulated and electromagnetic(EM) data illustrate the effectiveness and the superiority of the proposed algorithm over the existing algorithms.
