Development of a Scientific Permanent Scatterer System: Modifications for Mixed Ers/envisat Time Series

The permanent scatterer technique invented at POLIMI has meanwhile developed into a remarkable operational method. It facilitates innovative data products such as urban subsidence maps or atmospheric delay measurements and permits new geophysical applications. The accuracy and validity of this techniques has been demonstrated in several projects at DLR. Due to the outstanding availability of data, time series of this technique have mainly been produced from data of the compatible satellite sensors ERS-1 and ERS-2. These time series can even span a continuous time range of about twelve years. This long-term observation enables the monitoring of displacements with millimetre accuracy and even facilitates the detection of seasonal periodic effects. The sensor ERS-1 made its last acquisition in 2000. The similarly constructed successor ERS-2 still monitors the Earth's surface even after nine years of operation. But recent acquisitions are unfortunately not suited for general interferometric applications. The reason is a heavily varying Doppler centroid frequency due to failures of gyros. The ERS-2 successor ENVISAT/ASAR is able to pursue the unique continuity in the monitoring of urban areas. But it operates with a slightly different radar frequency compared to the ERS sensors. Consequently the interferometric principle becomes more complicated and the processing has to be modified. We will present the required changes for the permanent scatterer cross interferometry on the developed scientific permanent scatterer system.