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As an active microwave remote sensing imaging sensor, Synthetic Aperture Radar（SAR） plays an important role in earth observation. Here we establish a SAR system based on the platform of the moon. This will aid large-scale, constant, and long-term dynamic Earth observations to better meet the needs of global change research and to complement the space borne and airborne earth observations. Lunar-based SAR systems have the characteristics of high resolution and wide swath width. The swath width could be thousands of kilometers in the stripe mode and it could cover 40% of earth＇s surface with 10 meters or even higher spatial resolution in the scanning mode. Using the simplified observation model, here we quantitatively analyze the spatial resolution and coverage area of lunar-based SAR and simulate the observation on the Qinghai-Tibet plateau and the Amazon plain. The results show that this system could provide near 100% daily coverage of the Qinghai-Tibet plateau, whereas 40% to 70% daily coverage of the Amazon plain. Lunar-based SAR could provide large-scale, long-term and stable time series data in order to support future research of global change.

In recent years, the repeat-pass GBSAR （ground based synthetic aperture radar） system has demon- strated its capacity to acquire deformation. Nevertheless, in a variety of applications, it needs to measure the deformation with the precision up to 0.1 mm, which could not be reached by utilizing the traditional PS （permanent scatterer） algorithm in most cases. Generally, one of the main reasons could be summarized into the phase error caused by the rail determination error, because the precision of rail determination might degrade during long working hours. However, the traditional PS algorithm could not compensate for the phase error caused by the rail determination error. In order to solve the problems, we modify the conventional PS algorithm. Firstly, we deduced the transformation relationship between the rail determination error and its correspond- ing interferometrie phase error. Then, the phase errors caused by the atmosphere and the rail determination error were jointly compensated. The experimental data, which were obtained in Fangshan District in Beijing （China）, were used to test and verify the performance of the new algorithm. After the comparison between the results processed by the new algorithm and those processed by the traditional algorithm, the proposed method demonstrated its ability to obtain high-precision deformation.

An equivalent system model（ESM） that can be used to calibrate a SAR system affected by both the effect of system errors and the Faraday rotation（FR） is proposed. This ESM contains only systemdistortion-like parameters but includes a distortion matrix（DM） that is identical to the original, which contains the effects of both the system errors and the Faraday rotation angle（FRA）. With this model, the conventional distributed-target-based（DT-based） algorithms which have not taken FR effect into account are readily applicable. The conditions on FRA for the successful application of DT-based algorithms are studied, and the results suggest that reliable estimates can be obtained for a well-designed system whose true system crosstalk level is lower than-20 d B provided that the mean FRA at the calibration site is within±15？ and that the FRA can be suitably modeled as Gaussian. Thus, the requirements on the crosstalk level or the FRA that are commonly employed in other calibration methods designed for data affected by FR are relaxed.

Forest-height inversion using airborne double-antenna synthetic aperture radar（SAR） systems has been widely researched, leading to increasing accuracy. Polarimetric SAR Interferometry（PolInSAR） data from spaceborne single-antenna SAR systems, which are influenced by temporal decorrelation, have difficulty inverting forest height. Given the temporal decorrelation effect, the classical random volume over ground（RVoG） model has been proven to invert forest height with significant errors, using repeat-pass PolInSAR data. In consideration of this problem, the temporal decorrelation RVoG（TD-RVoG; based on the RVoG） model was proposed. In this study, an improved TD-RVoG model is presented, with a new temporal decorrelation function. Compared with TD-RVoG, the new model has fewer unknown parameters and can be applied in a three-stage inversion procedure. Validity of the new model is demonstrated by Advanced Land Observing Satellite/Phased Array type L-band SAR（ALOS/PALSAR） data. Results show that the improved TD-RVoG has better accuracy, with inversion error less than 1.5 m.

Special attention has been devoted to multi-input multi-output（MIMO）synthetic aperture radar（SAR）systems in recent years.The applications of MIMO SAR systems which involve 3D imaging,highresolution wide-swath remote sensing,and multi-baseline interferometry are seriously limited to the orthogonal waveforms.Although orthogonal frequency division multiplexing（OFDM）chirp waveforms can be used for MIMO SAR systems to avoid intra-pulse interferences,there is a small frequency shift between the transmitted OFDM pulses.This vulnerable shift,which can not only affect the waveform orthogonality,but also introduce residual phase error,renders the OFDM waveforms impractical.In this paper,an improved OFDM chirp waveform which works without the mentioned shift is presented,along with the novel modulation and efficient demodulation procedures.Comparison between the improved and the conventional OFDM chirp waveforms is detailed.The influence of random noise,quantization error,and Doppler shift on the orthogonality of OFDM waveform is also investigated in this paper.Theoretical analysis and simulation results illustrate the feasibility of this waveform scheme.

This paper proposed a new focusing approach for the bistatic SAR systems with a GNSS （Global Navigation Satellite System） satellite as the transmitter. Because of the long integration time the inherited curvature of the transmitter＇s trajectory was adopted and the spatial variance of the equivalent velocity was derived under the principal of equivalent slant range model in the system signal model. The proposed focusing approach consists of two-step processing. Firstly, the general Doppler phase from constant velocity of the echo data is focused by modified Stolt mapping. Secondly, the residual nonlinear Doppler phase due to velocity variation is compensated by means of block-processing-based adaptive phase compensation to achieve large scene focusing. The simulation and experimental results validate the proposed algorithm in GNSS-based BiSAR systenls.

Codebook of conventional VQ cannot be generally used and needs real time onboard updating,which is hard to implement in spaceborne SAR system.In order to solve this problem,this paper analyses the characteristic of space-borne SAR raw data firstly,and then utilizes the distortion function of multidimensional space as criterion,and finally the adaptive code book design algorithm is proposed according to the joint probability density function of the input data.Besides,the feasibility of the new algorithm in cascade with entropy coding and the robustness of the algorithm when error occurs during transmission are analysed based on the encoding and decoding scheme.Experimental results of real data show that codebook deriving from the new algorithm can be generally used and designed off-line,which makes VQ a practical algorithm for space-borne SAR raw data compression.

In the synthetic aperture radar （SAR） system with low pulse repetition frequency （PRF） sampling, it is difficult for the motion parameters estimation of the moving targets, because of the Doppler spectrum ambiguity and Doppler centroid frequency ambiguity of the echo signals. Considering that moving targets are sparsely distributed in the observed scene, their positions and velocities can be reconstructed by using the compressed sensing （CS） technique. In this paper, the range-walk correction are implemented by the Keystone transform and the sparse range-walk correction （SRWC）, then the CS technique is proposed to reconstruct motion parameters by processing the azimuth signals of the moving targets. Experiments using the simulated and real data are performed, and the results confirm the validity of the proposed method.

Many ship target detection methods have been developed since it was verified that ship could be imaged with the space-based SAR systems. Most developed detection methods mostly emphasized ship detection rate but not computation time. By making use of the advantages of the K-distribution CFAR method and two-parameter CFAR method, a new CFAR ship target detection algorithm was proposed. In that new method, we use the K-distribution CFAR method to calculate a global threshold with a certain false-alarm rate. Then the threshold is applied to the whole SAR imagery to determine the possible ship target, pixcls, and a binary image is given as tile preliminary result. Mathematical morphological filter are used to filter the binary image. After that step, we use tile two-parameter CFAR method to detect the ship targets. In the step, the local sliding window only works in the possible ship target pixels of the SAR imagery. That step avoids the statistical calculation of the background pixels, so the method proposed can much improve the processing speed. In order to test the new method, two SAN imagery with different background were used, and the detection result shows that that method can work well in different background circumstances with high detection rate. Moreover, a synchronous ship detection experiment was carried out in Qingdao port in October 28, 2005 to verify the new method and one ENVISAT ASAR imagery was acquired to detect ship targets. It can be concluded from the experiment that the new method not only has high detection rate, but also is time-consuining, and is suitable for the operational ship detection system.