Four level least squares adjustment in Persistent Scatterer Interferometry for the Wide Area Product

Persistent Scatterer Interferometry (PSI) is a well established SAR technique to monitor the Earth´s surface displacements with millimeter accuracy [1]. In the framework of the ESA´s Terrafirma project, a PSI based Wide Area Product (WAP) is developed and demonstrated by DLR [2]. The PSI technique is well applicable for the processing of urban areas, because many persistent scatterers (PSs) are available due to man-made features. However, the mapping of areas with an extension of more hundreds of kilometres is the objective of the WAP. Thus rural and mountainous regions also need to be handled by the processor. In such areas, the distribution of PSs is very inhomogeneous and, typically, the point density is very low. In this paper we address two technical difficulties in the development of the WAP. Firstly, we report on the determination and estimation of a reliable reference network of the processing area in order to estimate and compensate the atmospheric phase screen (APS). Secondly, the mosaiking of independent reference networks into a global consistent data set is described. As basic method, the conventional least squares adjustment is used on four hierarchic levels. Consequently, the error propagation through all these levels can be analyzed and evaluated.