SAR Applications The ERS-2 Synthetic Aperture Radar (SAR) produces all-weather, day and night detailed images of a 100-km strip of the earth's surface. An impressive range of scientific investigations has been carried out in oceanography, glaciology, and climate research. Operational systems have been developed for mapping sea ice, oil slick monitoring and ship detection. SAR data are being used for agricultural monitoring, forest mapping, geological exploration and flood mapping, while SAR interferometric measurements of topography and small topographic changes are making major contributions to environmental risk assessment involving earthquakes and land subsidence. The ASAR now operating on Envisat is a step forward in terms of system flexibility and the scientific values of its data sets, howeever, the demand for ERS-2 SAR data remains relatively unchanged. "The fixed geometry of the ERS-2 SAR provides a very consistent and reliable product, one which is proving to be highly beneficial for many interferometric appolications and operations requiring frequent repeat data sets. The long time series of images means that new ERS-2 acquisitions are especially valuable for the analysis and monitoring of stable targets in urban areas." Professor Fabio Rocca, Politecnico Milando ASIA TSUNAMI 2004 - Little Nicobar: The combination of a pre-tsunami ERS-1 image with a post-tsunami ERS-2 images shows (in red) changes in low-lying areas adjacent to the coast. There is a clear role for ERS-2 data to contribute to the International Charter "Space and Major Disasters" There have been remarkably accurate results using the long sequence of ERS-1 and ERS-2 SAR measurements of land surface deformations. From repeated SAR observations it is possible to select ground targets which maintain their coherence for a long period of time. Once these so-called Permanent Scatterers are identified, it is possible to measure their motion along the ERS-2 line of sight. Moreover, by combining ascending and descending passes, it is possible to separate vertical from horizontal motion to centrimetric precision.   Dynamic Ocean Topography   Ocean Wave Heights The SAR Wave Mode imagettes taken every 200 km along track are an important source of ocean wave information, including significant wave height, mean wavelength and propagation direction. Data are used inteh assimilation of numerical ocean wave forcasts and also to check whether the observed extreme waves are within the standard wave statistics currently used for marine design.   Cyclonic Wind Direction in West Ireland    Weather Nowcasting After the loss of the onboard ERS-2 tape recorders, ESA has more than tripled the data acquisition rate, allowing data coverage in the North Atlantic and adjacent seas within 30 minutes. This is unprecedented for scatterometer winds, available nominally in about 150 minutes, and for the first time has allowed the use of scatterometer winds for weather nowcasting. At KNMI, a procedure has been developed to provide unique on-the-fly scatterometer winds, i.e. swath overlaps are taken out and incomplete Wind-Vector-Cells are combined for completion. KNMI produces easily available real-time ERS-2 scatterometer wind products.   Hurricane Kate   Improving hurricane prediction Hurricane Kate was a category 3 Atlantic event, active between 25 September and 7 October 2003. Kate was captured twice by ERS-2 on 5 October at 12.00 UTCS and 14.00 UTC. When the scatterometer data are not assimilated, a positional error relative to subsequent analysis of 200 km is observed. Not only does the positional error improve when scatterometer data are used, but the vortex is shown with increased intensity which more closely matches the real situation.   Wind field at the Heart of Hurricane Isabel   Wind Scatterometer The WS works by firing a trio of high-frequency radar beams down to the earth's surface and recording the characteristics of the backscatter returned to the satellite. Wind-driven ripples on the ocean surface modify the radar backscatter and as the energy in these ripples increases with wind velocity, the scatterometer is able to measure wind speed and direction across the water surface. It is practically unaffected by heavy rain, and so can return useful wind data from extreme weather events such as hurricanes and tornadoes. In this way ERS-2 is helping to preserve life and minimise damage to property. The data are used operationally within routine weather forecasting assimilation algorithms. This is the only scatterometer of this type currently in orbit. "For the first time ERS-2 results are available for nowcasting, which is a whole new applicationn for the satellite. You want observations of current weather on your desk immediately, otherwise you are already getting behind the actual facts." Ad Stoffelen of the Royal Dutch Meteorological Institute, KNMI.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry