Ding Chibiao

Non-linear chirp scaling algorithm for one-stationary bistatic SAR

This paper points out the non-linear property of the differential RCM along range direction in one-stationary bistatic SAR, and compares it with the monostotic case. Then it deduces out a non-linear chirp scaling factor to identify the RCM of all targets in the swath. The implementary processes of a non-linear chirp scaling algorithm for one-stationary bistatic SAR are then described detailedly. Finally, the simulating results present here validate the correctness of the algorithm.

An advanced 2-D spectrum for high-resolution and MEO spaceborne SAR

In this paper, an advanced range equation is presented for high-resolution and medium-earth-orbit (MEO) synthetic aperture radar (SAR). Besides an additional linear component, this new equation has a similar formalism to conventional hyperbolic range equation (CHRE), so is called the advanced hyperbolic range equation (AHRE). Incorporating with this additional linear coefficient and the other two parameters, the cubic Taylor series expansion of AHRE has exactly the same value as which of the actual range history. Furthermore, a two-dimensional (2-D) spectrum based on AHRE is derived, which is useful for developing efficient SAR algorithms. Simulations validate AHRE and show its advantages in highresolution and MEO spaceborne SAR cases.

3D Reconstruction of Building Based on High-Resolution SAR and Optical Images

In high-resolution SAR image, the building can form the layerover and shade. Basing on the imaging equation of SAR image, we can extract the height, width and location information of the building. The high-resolution optical image can reflect the roof shape and location of the building. But the information in optical image is so rich that it can produce heavy error when extracting the roof of the building with some automatic methods. In order to extract the roof accurately, we attempt to fuse the SAR image with the optical image. Because the buildings layerover can reflect the buildings location, by the imaging equation of SAR image and that of optical image, we use the layerover of building in SAR image to confirm the approximate location of the buildings roof in optical image. Thus, we obtain a small window that includes the roof of the building, and use the ISODATA method to classify the small window to get the roof class. In the end, we use the height, width, location and roof information to reconstruct the building. The result proves that me method is a good idea.

A Fast Method for InSAR Phase Unwrapping Based on Quality Guide: A Fast Method for InSAR Phase Unwrapping Based on Quality Guide

Phase unwrapping is a key issue in InSAR research. As a critical step of InSAR processing, it affects the accuracy of interferometry measurement directly. The efficiency of the traditional quality-guided phase unwrapping method is low due to a great deal of sorting, espceically for large interferogram. This paper proposes a highly efficient quality-guided phase unwrapping method based on heap sort in order to solve the problem. First, the quality map is caculated according to the interferometric complex data or interferogram. Next, with the max-heap acting as the data structure of sorting, its property is maintained while deleting root node and inserting new node, and thus the sorting of quality map is accomplished and the phase can be unwrapped from high quality areas to low quality areas. The improved algorithm reduces the computational complexity greatly compared with traditional methods, which is significant in large area mapping of InSAR. At the end of the paper, the simulated and experimental results show the accuracy and the efficiency of the algorithm. Key word: Interferometric SAR (InSAR); Interferometric phase; Phase unwrapping; Quality map; Heap sort

Large beamwidth spaceborne SAR processing using chirp scaling

The accurate effective platform velocity and the effective closest approach range should be used to get a high resolution image when the chirp scaling algorithm (CSA) is employed in spaceborne SAR processing, especially, in the large beamwidth and squint modes. In this paper the two effective parameters are derived as a function of the Doppler centroid and the Doppler rate. Therefore, the classical clutterlock and autofocus methods can be used in CSA to get precise estimates of the effective parameters. Simulation results show that CSA using the effective velocity and closest slant range is suitable for L-band large beamwidth spaceborne SAR processing.

A novel single-channel SAR-GMTI method based on defocusing shifted difference

A novel single channel SAR-GMTI method is proposed in this paper. When the azimuth mismatch filter performs compression, it induces shifted difference between the stationary and moving targets because of having different Doppler center. The proposed method employs this character to separate moving targets from stationary targets. It can produce two images by pulse compression which make use of two symmetrical mismatch filters in azimuth direction, and then cancel stationary and retain moving targets by subtracting one image from another. Compared with traditional methods, it is applicable to both low and high squint case and the detection capability is significantly improved. The simulation results validate the effectiveness of the proposed method.

A novel 3-D reconstruction approach based on group-sparsity of array InSAR

As an advanced technology, synthetic aperture radar tomography (Tomo SAR) provides the feasibility to solve the layover problem caused by the inherent side-view mode in SAR sensors. However, the conventional nonparametric spectral estimation methods, such as truncated singular value decomposition (TSVD), are limited by the poor elevation resolution and cannot meet the needs of practical applications. Currently, SAR 3-D imaging methods based on compressive sensing are typically used; nevertheless, classic compressive sensing algorithms such as BP and OMP still exhibitproblems such as low efficiency, weak super-resolution performance, and poor anti-interference ability. Therefore, an algorithm with high robustness and super-resolution performance is significantly demanded.In this paper, a novel array InSAR 3-D reconstruction algorithm based on group-sparsity is proposed. It is improved based on the existing compressive sensing algorithm and exhibits better super-resolution and robustness. Based on the simulation data and the actual data of the first domestic 3-D imaging experiment by an airborne array InSAR, the super-resolution ability ofthe algorithm is verified, and the 3-D imaging results of the buildings are obtained.

Geo-referencing airborne interferometric SAR data

Synthetic aperture radar (SAR) plays an important role in the earth observation system owing to its all-weather capability. Having the ability of getting the altitude of ground and image simultaneously, interferometric SAR (InSAR) technology becomes used in many fields in recent years. Airborne InSAR system is also developed successfully in June 2004 in China and now many flight tests have been conducted. We can get the SAR backscatter energy and altitude of ground i.e. SAR image and DEM through unwrapping the phase. But the reference coordinates of DEM and SAR image are imaging geometry coordinates which use range number and azimuth number as reference. The imaging geometry coordinates must be changed into geographic coordinates if DEM and SAR image are used in practice, this procedure is called geo-referencing. Owing to its side looking property, the undulation of ground height influences SAR image severely, nevertheless the altitude of ground which is very useful to eliminate the influence of ground undulation can be generated through InSAR. It is very difficult to get the precise position and velocity of airplane in the past, but now we can get precisely position, velocity and attitude using GPS/INS integrated system with the development of inertial navigation system (INS) and the mature of GPS, especially differential carrier phase GPS. The position and orientation system(POS) of Applanix company can provide high accurate position, velocity and attitude, and its position accuracy can reach 0.05~0.30m and velocity 0.0005m/s by post processing using GPS and INS combined filter algorithm We apply Doppler and range equations to geo-reference the DEM and image of InSAR based on the position and velocity of platform which is determined by POS/AV system. The principle and accuracy of geo-referencing InSAR data are discussed in the paper and the test data are processed using this method. Error estimation and field accuracy checking are also presented and the result is satisfactory.

Applying chirp-modulated back-projection to very high resolution spaceborne sliding spotlight SAR data processing

This paper proposed a new approach to focus the very high resolution spaceborne sliding spotlight synthetic aperture radar (SAR) data. The main singularity of the approach is accommodating the space dependent range histories by a back projection method on reduced apertures achieved by chirp modulation method. Besides, in the range spectrum domain, a dechirp method is employed to reduce the Doppler bandwidth to be within one PRF interval. Additionally, range splitting method is employed to mitigate the range dependence of effective velocities. Furthermore, the image grid is placed on the earth surface instead of the slant range plane, and the routine geometry projection processing becomes dispensable. The proposed approach was validated by simulation results of nine point targets.

Ionosphere estimation and correction for geosynchronous SAR based on point target deviation between range sub-images

Ionosphere is an important factor in high-resolution spaceborne synthetic aperture radar (SAR) and geosynchronous (GEO) SAR. An approach based on point target deviation between range sub-images is proposed in this paper to estimate and correct the ionosphere. Due to the dispersion effect, the ionosphere causes propagation delay deviation in range subimages with different carrier frequency. This deviation can be used to estimate the total electron content (TEC) along the propagation path, and then the ionospheric effects can be corrected according to the signal model deduced out in this paper. The simulation results show that our approach is valid and robust.