Abstract: This paper studies the effects of radar local incident angle and rainfall on coherence time-series variations of six small and medium dams in Gongming reservoir in Shenzhen, using 10 ascending and descending TerraSAR-X images with resolution of 1 m and rainfall data of the continuous weather stations near the dams. The experimental results show that both of coherence of concrete surface and grass surface decrease with the increase of local incident angle. Even though precipitation is relatively small, the average coherence of grass surface will decrease rapidly by approximately 0.1~0.2, and differential interference fringe will be less clear with more noise. Concrete surface is less sensitive to rainfall, while it still can become completely incoherent in case of heavy rainstorms. We concluded that in deformation monitoring of small and medium earth-rock dams, the slope and incident angle of the dams should be taken into account in order to select the optimal radar imaging parameter, and rainfall data should be used to evaluate the coherence of the surfaces and eliminate noise of interferogram.

Key words: TerraSAR-X, earth-rock dam, local incidence angle, rainfall, coherence