VENEZIA

The main objectives of VENEZIA have been to define and implement a land subsidence monitoring service in the Lagoon of Venice based on the combined used of differential SAR interferometry (DInSAR) and Interferometric Point-Target Analysis (IPTA) integrated with ground based levelling surveys and GPS measurements. In the lagoon of Venice, traditionally subsidence rates are monitored with varying temporal and spatial frequency depending on the ground measurement networks.

The use of satellite derived subsidence measurements helps to improve the spatial and temporal frequency to every 25m and at least 35 days (repeat pass orbits in the case of ERS and ASAR) in the case of DInSAR and IPTA. The combination of ground and satellite measurements helps to confirm the accuracy and cross validation of the satellite derived measurements as well as providing improved and more detailed maps of subsidence in the Lagoon and surrounding area.

A new development for subsidence monitoring in the Lagoon of Venice, has been the use of IPTA processing and the generation of subsidence maps. DInSAR is limiting for subsidence mapping in rural areas due to temporal phase de-correlation. However through the use of long time series SAR images, phase stable point targets within a scene can be identified. These are usually returns from man-made structures or buildings. In the Lagoon and surrounding area, these are distributed in both urban and rural areas. So there is further potential to improve the spatial coverage for subsidence mapping. An important aspect of the study has been the development of the IPTA processing chain and removal of atmospheric artefacts that cause within scene and between scene random phase noise signal variations.