Abstract: The baseline is the key factor in InSAR systems, which will decide the accuracy of the target height calculated from the InSAR. For a two pass InSAR system, the parameter of baseline will change during the flying. And it should be estimated differently. The common way for calculating the Baseline is based on the DEM. Unfortunately, DEM is always difficult to obtain. To use the available data fully, this paper first calculates the baseline by the geometry of orbits. Then depending on the key points, e.g. reflection corners, this paper shows an iterative way to refine the baseline. The raw data of Etna in Italy, has been used to verify this algorithm.

Key words: InSAR, ba seline, estimatio n, o rbit geometry, iterat ion