Impact of the assimilation of ERS-1 and ERS-2 data into a North Atlantic regional version of WAM

Abstract

The routine availability of SAR wave data from ERS-1 and 2 has dramatically increased the volume of wave observations available to weather services for monitoring and forecasting the sea state. To make optimal use of the data, we have developed a data assimilation system for use with our operational version of the WAM model. The assimilation method is sequential, one-pass Cressman type, with an influence region of 5 degrees of latitude. SAR spectra are converted to estimates of wave spectra at the observation locations using the inversion methods of Hasselmann and Hasselmann (1991), with some updates.

We have tested the system on a storm case and on a one running month, using ERS-1 data. Recently, the necessary conversions were made to test the system on ERS-2 data. We assessed the impact of the data both on forecasts and analyses from the model, in terms of summary parameters of the wave spectrum, significant wave height, average period and wave direction. We used independent observational data from buoys and the ERS-1 radar altimeter to compare with the analyses and forecasts with and without assimilation.

Results from these experiments will be shown to demonstrate the impact of the data on the wave analyses and forecasts.

Keywords: synthetic aperture radar, data assimilation, ocean waves, wave modelling

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