Interferometric coherence analysis with high resolution space-borne synthetic aperture radar

Recently high spatial resolution space-borne synthetic aperture radar (SAR) systems with various polarizations have launched and have operated successfully. Interferometric SAR (InSAR) processing with the high resolution space-based observations acquired by these systems can provide more detail information for various geodetic applications [1-5]. Coherence is regarded as a critical parameter in the evaluating the quality of an InSAR pair. In this study, we evaluate the coherence characteristics of high-resolution data acquired by TerraSAR-X (X-band) and ALOS (L-band) and intermediate-resolution data acquired by Envisat (C-band) over western Texas, U.S.A. Our coherence analysis reveals that the high-resolution X-band TSX (3.1 cm) data has a high coherence level (0.3-0.6), similar to that of the L-band ALOS data (23.5 cm) in short temporal baselines (Fig. 1). Furthermore, the TSX coherence values are significantly higher than those of the C-band (5.6 cm) Envisat data (Fig. 1). The higher coherence of the TSX dataset is a surprising result, because common scattering theories suggest that the longer wavelength SAR data maintain better coherence. In vegetated areas the shorter wavelength radar pulse interacts mostly with upper sections of the vegetation and, hence, does not provide good correlation over time in InSAR pairs. Thus, we suggest that the higher coherence values of the TSX data reflect the data´s high-resolution, in which stable and coherent scatterers are better maintained. Although, however, the TSX data show a very good coherence with short temporal baseline (11-33 days), the coherences are significantly degraded as the temporal baselines are increased (Fig. 2). This result confirms previous studies showing that the coherence has a strong dependency on the temporal baseline [1-2]. We will continue this preliminary study by conducting additional coherence analyses over various environments and develop appropriate relationship that will account for data reso- - lution in the coherence calculations.