Anxi Yu

An Efficient and Adaptive Approach for Noise Filtering of SAR Interferometric Phase Images

This letter presents a new efficient phase filtering algorithm for synthetic aperture radar interferometric phase images. Based on the additive noise model, we assume that the phase without noise is composed of principal phase components and residual phase components. A new two-step adaptive filtering algorithm based on this assumption is then developed. First, the principal phase components are adaptively estimated using the frequency spectrum with an adaptive bound and removed from the original noisy phase; thus, a residual noisy phase is obtained. Second, spatial filtering is carried out on this residual noisy phase image using four directional masks. The filter equals three other common filters when three different special bound parameters are set accordingly. This algorithm is effective, particularly for the interferometric phase images with tightly packed fringes or low coherence. Numerical results obtained with synthetic and real data show a significant improvement with respect to other conventional filtering algorithms in some situations of the proposed approach.

High-precision, fast DEM reconstruction method for spaceborne InSAR

The primary objective of the spaceborne interferometric synthetic aperture radar (InSAR) system is to develop a consistent global digital elevation model (DEM). The improvement of the processing speed in global interferometry missions while maintaining the accuracy is becoming an important issue. DEM reconstruction is the most time-consuming step in the data processing required for spaceborne InSAR. Based on a DEM reconstruction principle analysis, we exploited two basic characteristics of the mapping relation between the interferometric phase and 3-D position of target point. First, the relation between the 3-D position of the target point and the interferometric phase can be approximated using polynomials. Second, the corresponding polynomials change slowly in the local SAR images. Also, we verified the foundations of the two mentioned characteristics theoretically. Then, we proposed a fast method of DEM reconstruction based on this analysis. Detailed descriptions of the step and key parameters of the fast algorithm are provided. Finally, the repeat-pass interferometric data obtained using TerraSAR-X was used to test the presented method. The experimental results showed that a significant reduction in computation time is achieved with only a small loss in accuracy. The effectiveness and correctness of the proposed method were also validated.

A multi-mode space-borne SAR simulator based on SBRAS

A multi-mode space-borne Synthetic Aperture Radar (SAR) simulator is presented in this paper. The simulator is based on the Space-borne Radar Advance Simulator (SBRAS), and supports the parameter design, raw data simulation, data focusing and performance evaluation of strip-map mode, spotlight mode, sliding spotlight mode, ScanSAR mode, Terrain Observation by Progressive Scans (TOPS) mode and mosaic mode. The hardware architecture and software composition are described below. At last, an application example of high resolution sliding spotlight with point targets and another application example of wide swath TOPS mode with distributed targets are provided.

An improved DBS algorithm based on Doppler localization equations

This paper proposes an improved Doppler Beam Sharpening (DBS) algorithm for missile-borne Synthetic Aperture Radar (SAR) based on Doppler localization equations, to gain a better azimuth resolution and reduce the heavy localization computation afford. Firstly, the azimuth resolution is improved by a modified reference function, with little extra computation. Then Doppler localization equations are introduced to increase the speed of localization computation. At last, the simulation result shows that the proposed DBS algorithm can effectively gain high resolution image in short time, compared with traditional DBS algorithm.

Spaceborne SAR raw signal simulation of ocean scene

According to fractal ocean surface model, electromagnetic scattering model under Kirchhoff approximation and the raw signal simulation procedure of dynamic scene based on time domain, spaceborne synthetic aperture radar (SAR) raw signal of ocean scene is generated. The SAR images obtained from the echo of both simple cosine wave and complex fractal ocean surface are in accordance with the tilt modulation and the velocity bunching theoretically, and also with the statistical properties of real ocean SAR images, which validate the simulation procedure. The raw signal could be the input data of studying along-track InSAR (ATI) for ocean current measurements.

Improved geometrical SAR image registration based on elevation correction

Accurate co-registration of SAR image is a crucial step in interferometry SAR (InSAR) processing, and lower registration accuracy will lead to more interferometry phase error. The most commonly used is 2-D polynomial function registration method (2-DR), which is simple and works well in most conditions. But in the case of long baselines and complex terrain scene, (2-DR) can not meet the precision requirements. The DEM-assisted geometrical SAR image registration method (GeoR), which use the external DEM and orbit data to calculate offsets, can theoretically achieve an ideal precision for any baseline and terrain. In GeoR, corresponding elevation value of each pixel in the master image needs to extracted from the external DEM. Unfortunately, there are errors in the DEM data and the orbit data, which often result in approximate horizontal shift error and mismatch between DEM and SAR image, caused low precision elevation value extraction and eventually degrade the registration performance. In this paper, the influences of DEM error and orbital error in elevation value extraction are firstly analyzed, and then an improved geometrical SAR image registration method based on elevation correction (I-GeoR) is proposed. In elevation correction, Elevation value in DEM can be correctly assigned to each pixel of the image, which is achieved by deformation extraction that based on SAR image simulation. Finally, two ALOS-PALSAR images are processed to vaidate the new method. The result shows that I-GeoR can effectively correct the elevation and has a higher registration precision.

Testing and evaluation of permanent scatterers candidates selection methods

This paper develops a method to evaluate the accuracy of permanent scatterers selection by using the proportion from the number of lines in the initial PS network to the number of lines in the refined PS network. Taking advantage of this method, two main PSC selection methods: amplitude dispersion method and coherence method were tested using 20 Envisat ASAR acquisitions. The results show that, when the number of image is more than 11, the permanent scatterers candidates selected by amplitude dispersion method is more accurate than the ones selected by coherence method, the opposite conclusion can be drawn when the number of images is less than 11. The results are consistent with the conclusions drawn by other qualitative analysis, which prove the method developed in the paper is effective.

A fast InSAR raw signal simulation based on GPGPU

Under the precision constraint of interferometric SAR simulation applications, a range frequency fast algorithm is proposed to increase the InSAR raw signal simulation efficiency and the GPGPU technique is used to implement the raw signal simulation of large 10km×10km nature scene. The experiment results validate the proposed fast algorithm and the GPGPU technique. The total speedup of GPU over CPU is 4, and some local grogram speedup is over 14, which makes the InSAR raw signal simulation more practical in the InSAR system simulation.