449 
RESEARCH ON SPACEBORNE INSAR IMAGES REGISTRATION 
AND REMOVAL OF THE EFFECT OF THE FLAT EARTH 
H. Lin 3 *, L.P. Zhang 3 , Z. L. Hu b , H.T. Jing 3 
3 School of geodesy and geomatics of XuZhou Normal University, XuZhou, 221116, PR China. 
b City & Environment College XuZhou Normal University, XuZhou, 221116, PR China. 
Commission I, WG 1/2 
KEY WORDS: Interferometric SAR, Images Registration, Removal of the Effect of the Flat Earth, Interferogram 
The correlation coefficient method, paraboloid fitting method, least square fitting method 
ABSTRACT: 
Interferometric Synthetic Aperture Radar (INSAR) is a good technique to produce high resolution digital elevation model (DEM), to 
detect small earth motions, and so on. Therefore, it is very useful to study this technique. In this paper, some methods about data 
preprocessing, control points determining, image registration and removal of the phase of the flat earth are introduced, which are one 
big key step in INSAR technique. Usually, the original data is in a complex format. Only a few white points can be seen from this 
image, and it can be overcome by image histogram equalization or gray contrast enhancement. It has been tested that they improve 
the reliability of image registration. Image registration deals with pixel intensity transformation and geometrical transformation. In 
this paper, they are done separately. Histogram specialization is used to correct the former roughly, for it can satisfy requirements. 
The latter has two steps. At first, two images are registered coarsely by determining range and azimuth offsets because the two 
satellite orbital paths are very close together. Then sufficient identical points are selected by Forstner method on left image and their 
conjugation points are determined using normalized correlation coefficient based on the subpixel shifts between homologous areas 
or using the paraboloid polynomial. Finally, with the help of these control points, the geometric registration is performed by means 
of linear polynomials. Whose coefficients are computed with least -squares approximation. After image registration has been 
performed, the interferogram can be obtained by multiply each pixel in the left image by the corresponding pixel in the second 
image. Thus the phase difference can be gotten .This interferogram includes two parts: phase difference caused by terrain and phase 
difference caused by flat earth. A method called Removal of the Phase of the Flat Earth is performed. In this research, ERS-1, ERS-2 
complex data in the area of Zhangbei is used. All experiments tried with methods discussed above have shown those methods are 
practically largely. 
1. INTRODUCTION 
Synthetic Aperture Radar records not only electromagnetic 
energy of backscattering, but also phase delay at the same time. 
Therefore researchers may use the phase information of the 
radar signal to extract three-dimensional information of the 
earth surface, which is called interferometric Synthetic Aperture 
Radar (INSAR). It makes global digitization possible, being 
extensively applied to produce digital elevation map, exploring 
slight deformation of the earth surface, calculating glacier 
movement, appraising calamity etc. So research on spacebome 
INSAR is of much significance. 
At present, spacebome INSAR has only one pair of antenna, so 
it can only utilize repetition of the satellite track to survey in 
interferometic mode, namely, repetition track interferometric 
measurement. We know, the track data of the satellite have 
errors, some are inherent but difficult to eliminate, data 
precision provided for users does not usually meet the demand 
of interferometry; but time correlation-resistant caused by 
repetition track and geometric deformation arising from slant 
distance imaging are difficult to correct effectively, which can 
result in gradual reduction of grey correlation of homologous 
images points , and the difficulty for complex images 
registration of interferometry , removal of the phase of the flat 
earth of interferogram and DEM production. This paper lays 
special emphasis on the former two aspects for discussion. 
2. COMPLEX IMAGES REGISTRATION OF 
SPACEBORNEINSAR 
In order to forming interferogram, a pair of single vision 
interferometry complex images must be registered, and 
registration precision of repetition track interferometry should 
reach sub-pixel level even more. At present, interferometry 
registration has two methods: Registration on the basis of the 
grey, like coefficient correlation method; Registration on the 
basis of the phase, like the average fluctuation function method. 
This paper adopts the former to study registration of complex 
images of spacebome INSAR. 
2.1 Preprocessing 
As everyone knows, in general, original grey images obtained 
by using complex images SLC according to g = ^/ 2 + q 2 (i is 
imagine part, q is real part, g is grey value) shows only some 
light spots and hides partial object information, and difference 
exists in the grey radiation characteristics of a pair of 
homologous images. So before registration, you must 
* Email:linhuixznu@126.com ;Phone : 13852002411 ;