URBAN

The objective of the URBAN project was to demonstrate the use of differential SAR interferometry to map Earth surface displacement in urban environment, with the perspective to define a service, generate application demonstration material and develop a user community in the research, public and private sector.

Land subsidence occurs in many parts of the world as result of natural compaction of sediments, extraction of underground resources (water, oil, coal, ...) and underground works. An accurate monitoring of land subsidence is required for the assessment of the deformation and to give recommendations for a wise use of underground resources.

Traditionally, land subsidence is determined with leveling surveys. Wide networks of benchmarks have been setup in most of the subsiding cities and lots of measurements are periodically repeated. Leveling allows monitoring of land subsidence along profiles with high precision. Nevertheless this method is time consuming and expensive. Recently, GPS stations were implemented in a few significant points of large subsiding areas in order to have a global, fast and cheap measurement of subsidence rates.

In the context of the traditional surveying techniques, differential SAR interferometry has the potential to provide very important subsidence information over urban areas because of the 2-dimensional coverage, the high temporal coverage, the availability of information in almost real time, the large existing data archive, the expected availability of many more new data in the near future (RADARSAT, ENVISAT, ALOS), and the competitive cost.

In order to prove the usefulness and reliability of differential SAR interferometry, land subsidence maps were generated for four different sites: Ruhrgebiet (Germany), Mexico City (Mexico), Bologna (Italy) and Euganean Geothermal Basin (Italy). These areas are characterized by high (m/year) to low (mm/year) subsidence rate. In all those case studies, very promising results were obtained by InSAR analysis, raising the interest of potential customers in this new and promising technique.