The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
diagrams are subtracted from each other, three- dimensioned 
picture 8-a are gained to show the difference. From the 
diagrams we can see: the height error changes in range,it is 
independent of the azimuth direction and the undulation of 
terrain . In order to compare them more better, the two- 
dimension diagram of picture 8-a is showed as picture 8-b. 
From picture 8-b,we can see: with the increase of the ground 
distance,the height measurement error adds evidently. When the 
ground distance is about 60 kilometers , InSAR height error due 
to neglecting the influence of the earth’s curvature is 1.2 meter. 
Therefore, we can draw the conclusions : no matter what the 
height of terrain is variational, errors caused by the influence of 
the earth’s curvature always add with the increase of ground 
distance. The bigger the area coverage is, the more the errors 
caused . So to spomebome InSAR system, the influence of the 
earth’s curvature should be taken in account , so the precision 
of height measurement is more precise. In addition, with the 
height accuracy specifications , in a definite range, the ground 
may be treated as the plane . 
a The three-dimensioned diagram of the 
height measurement error 
b The height measurement error caused 
by the increase of ground distance 
Picture 8 DEM errors caused by taken the earth’s surface as 
palne 
5. CONCLUSION 
From the above analysis ,we can draw the conclusion: no 
matter what the height of terrain is variational, errors caused by 
the influence of the earth’s curvature always adds with the 
increase of mapping area. So to spomebome InSAR system, the 
influence of the earth’s curvature should taken in account , the 
height accuracy is more precise. The error came from earth 
curvature is well-regulated, and may be corrected. At the same 
time, with the height accuracy specifications, in a definite range, 
the ground can be treated as the plane . 
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