TOPS Time Series Performance Assessment With TerraSAR-X Data

The terrain observation by progressive scans (i.e., TOPS) SAR mode enables a large ground coverage with an azimuth-invariant SNR, while avoiding the drawbacks of scalloping. The implementation of TOPS, obtained by steering the antenna from aft to fore within a burst, introduces an azimuth-dependent Doppler variation on the received signal. The processing of TOPS data needs to account for this signal property, requiring additional care especially when used for SAR interferometry (InSAR) applications. In particular, achieving a high coregistration accuracy is more stringent than for stripmap modes. For the analysis of TOPS InSAR data time series, the required high coregistration accuracy is even more critical, because any small error would translate into a biased estimation of geophysical parameters, such as the surface deformation. In this context, the interferometric processing aspects related to TOPS are discussed in this paper, and several analyses to evaluate the TOPS performance when processing time series are presented. Both permanent scatterers (PS) and small baselines subset (SBAS) techniques will be employed to perform the analysis. Two interleaved time series acquired by the TerraSAR-X sensor in TOPS and stripmap modes are used to evaluate and compare the results.