Zhou Yinqing

Analysis on noise reduction method for interferometric SAR image

Noise in SAR interferogram brings much trouble in phase unwrapping. It will also influence the accuracy of digital elevation models. Based on realization of complex mean filtering, pivoting mean filtering, pivoting median filtering three noise reduction algorithms, their computations are analyzed and the effect of noise reduction is given out. In order to get the most optimized balance between computation and effect of noise reduction, a new noise reduction idea - second-time or multiple combined noise reduction is proposed. The algorithm can comprehend the merits of several noise reduction methods. It can preserve edge information well and decrease phase noise dramatically at the cost of adding a little computation. Based on computer simulation, certain terrain is set and the effect of noise reduction of new method is verified. The variance of before and after combined noise reduction is given out. The effect of three-time or more combined noise reduction is not obvious because noise has been reduced by second-time noise reduction. We do not recommend 4 or more-time combined noise reduction for its large computation. ERS-frac12 real data are also used to verify the validity of the new algorithm

A Novel Speckle Filter for SAR Images Based on Information-theoretic Heterogeneity Measurements

Abstract Most adaptive speckle filters are based on the local coefficient of variation, which serves to measure the heterogeneity of synthetic aperture radar (SAR) images. However, the sensitivity of the measurements to speckle and noise of SAR images would greatly deteriorate the speckle reduction. This article, based upon the information theory, presents a novel parameter for the heterogeneity measurement as a general index to quantitate the SAR image heterogeneity. Further, as a new speckle reduction algorithm based on the aforesaid quantitative heterogeneity measurements, it puts forward a heterogeneity-based speckle reduction filter (HBSRF), which uses the information-theoretic heterogeneity measurements as a criterion to classify the SAR images as belonging to homogeneous or heterogeneous regions. Then the finite iteration procedure and edge detection algorithms are adopted to strike the best balance between speckle reduction and edge preservation. The results from the computer simulation have demonstrated that the proposed effective method is superior to the conventional speckle filters based on the local coefficient of variation both in textural preservation and speckle reduction.

Image Formation Algorithm for Topside Ionosphere Sounding with Spaceborne HF-SAR System

The exploration of ionosphere is significant for satellite communication and navigation etc. Spaceborne HF-SAR is utilized for the observation of topside ionosphere, in order to acquire higher spatial resolution, global scale ionospheric electron density map and irregularities distribution. The operation mode and system parameters are introduced. The echo signal of spaceborne HF-SAR has long synthetic aperture time, large range migration, and small depth of focus due to the low carrier frequency. Considering these characteristics of spaceborne HF-SAR, a two dimension time-frequency domain correlation image formation algorithm is presented. The effectiveness of the algorithm is validated by computer simulation results.

Motion error analysis and compensation for airborne formation flying InSAR

Because the stability of plane platform is not good, airborne SAR can not acquire the precise orbit parallelism and velocity as spaceborne SAR. Motion error problem for airborne formation flying InSAR is analyzed here. The plane interval changes (across track baseline changes) can be discussed in three situations: interval increasing, interval decreasing, interval changing according to sine curve. Phase changes with baseline changes are deduced quantiticationally. The simulation result of plane interval changes is given out. It can be concluded that across track baseline changes lead to azimuth slope. The digital relation between across-track baseline error and phase error, height error is concluded by simulation experiment result. The paper presents the method of azimuth slope elimination. Azimuth slope eliminating is adopted in simulation terrain. Two control points are set in topographic area to compensate the phase error of baseline changes. This algorithm can improve the DEM precision for whole area. Even if the plane track is curve, the method in this paper can still compensate most of the motion error.

Realization of quick-look imaging for spaceborne SAR based on parallel processing

Large range cell migration is a severe challenge to imaging algorithm for spaceborne SAR. Based on design of Finite Impulse Response (FIR) filter and Range Doppler (RD) algorithm, a realization of quick-look imaging for large range cell migration is proposed. It realized quick-look imaging of 8 times reduced resolution with parallel processing on memory shared 8 CPU SGI server. According to simulation experiment, this quick-look imaging algorithm with parallel processing can image 16384×16384 SAR raw data within 6 seconds. It reaches the requirement of real-time imaging.Large range cell migration is a severe challenge to imaging algorithm for spaceborne SAR. Based on design of Finite Impulse Response (FIR) filter and Range Doppler (RD) algorithm, a realization of quick-look imaging for large range cell migration is proposed. It realized quick-look imaging of 8 times reduced resolution with parallel processing on memory shared 8 CPU SGI server. According to simulation experiment, this quick-look imaging algorithm with parallel processing can image 16384×16384 SAR raw data within 6 seconds. It reaches the requirement of real-time imaging.

Parallel Distributed CFAR Detection Optimization Based on Genetic Algorithm with Interval Encoding

Aiming at parallel distributed constant false alarm rate (CFAR) detection employing K/N fusion rule, an optimization algorithm based on the genetic algorithm with interval encoding is proposed. N-1 local probabilities of false alarm are selected as optimization variables. And the encoding intervals for local false alarm probabilities are sequentially designed by the person-by-person optimization technique according to the constraints. By turning constrained optimization to unconstrained optimization, the problem of increasing iteration times due to the punishment technique frequently adopted in the genetic algorithm is thus overcome. Then this optimization scheme is applied to spacebased synthetic aperture radar (SAR) multi-angle collaborative detection, in which the nominal factor for each local detector is determined. The scheme is verified with simulations of cases including two, three and four independent SAR systems. Besides, detection performances with varying K and N are compared and analyzed.

A simple implementation of multi-baseline INSAR

Multi-baseline INSAR is a kind of technology that obtains terrain height information using multiple SAR images, therefore, it has a better performance than single-baseline INSAR. There are primarily two methods to increase the accuracy of terrain height estimation. One increases the quality of the interferometric absolute phase image by utilizing several single-look complex images. The other decreases the errors of the terrain height estimation through iterative ways. Integrating the former method and noise-immune phase unwrapping method, this paper presents a realistic method to implement multi-baseline INSAR. This method mainly includes two steps; the first one is about how to obtain multi-baseline interferometric absolute phase image whereas the second one is the unwrapping mechanism. Then, through simulation, the achieved results not only demonstrate the validity and practicability of the method, but also prove that the performance of the multi-baseline INSAR is much better than single-baseline INSAR.

Graphic characteristics of the spaceborne SAR point target in ambiguity zone

Ambiguity phenomenon is a sort of jamming, which is caused by the inherent reasons in synthetic aperture radar (SAR) system. Identify the target in ambiguity zone in SAR image, using the graphic characteristic of the target of the ambiguity zone, can reduce the disturbance made by ambiguity phenomenon on image interpretation and discrimination. In this paper, the graphic characteristic of point target in ambiguity zone was concluded by analyzing the theory of the chirp scaling (CS) algorithm. Target in range ambiguity zone is looked like a line. And target in azimuth ambiguity zone is looked like a block. The computer simulation validates the conclusions.

New method of formation design for both GMTI and InSAR using distributed satellites

This letter proposes a method for designing a specific formation of satellites where the flying motion only exists in a circle orbit plane of the reference satellite, which means that the orbit eccentricity is zero. This method combines the Hill equation, the Kepler equation, and the geometrical meaning of orbit elements. It creates the redundancy condition to simplify the deducing process, utilizes multiple conditions to solve the orbit elements for the satellite formation, and obtains the analytical relationship of the orbit elements for the formation satellites with the formation parameters and the orbit elements of the reference satellite. Using these formulations, the orbit elements and formation parameters for the formation satellites can be solved for the given orbit elements of the reference satellite. The letter describes the proposed double-ellipse formation for both GMTI and InSAR, and the validity of the formation is demonstrated via simulation.

Formation Flying InSAR Configuration Error Simulation and Compensation

Configuration error for airborne formation flying InSAR was studied. The aircraft interval changes are the most important error. Interval decreasing is taken as an example. Phase changes with baseline changes were derived in formula. The simulation result of plane interval changes is given out. A pentahedron on flat ground is set to show influence of the configuration error. Correct phase compensation is the key technology to get accurate interferogram. So azimuth slope eliminating was adopted. Two control points were arranged in observing area to compensate the phase error introduced by configuration error. This algorithm can improve the DEM precision for whole area. The pentahedron terrain is employed to verify compensation algorithm. The simulation terrain and compensation results prove that the algorithm is effective and efficient.