The derived acceleration maps were elaborated starting from SAR ERS satellite data (processed period goes from 1992 to 2000) and ENVISAT (processed period goes from 2003 to 2008). The two sets of data differ for an interval of about four years. In order to have a better discrimination of the areas subject to anomalous movements, for the determination of the hydrogeological risk, it was decided to develop measures of derived accelerations. From the average speeds obtained from the processing of ERS and ENVISAT data, the areas present in both data series and with the same geometry were identified: ERS ascending with ENVISAT ascending. Within these areas, comparisons were made between the speeds estimated in the time interval 1992-2000 with ERS data and those estimated in the time interval 2003-2008 with ENVISAT data: the result of these comparisons is an index of the variation of the speeds estimated in the two time intervals. There are two derived acceleration measurements provided, one relating to the ascending observation geometry and the other relating to the descending observation geometry. Each measurement contains the speed variation indices relating to the points identified and measured by the ERS and ENVISAT calculations within certain areas. The result of the comparison consists of two representative maps of the average speed difference measured in the time interval 1992-2000 with ERS data, and 2003-2008 with ENVISAT data. The differences refer to extension areas of 100 m x 100 m for a total coverage of almost 100,000 sq km in both geometries. The comparison refers to over ten million DPs overall between ERS and ENVISAT.
