PRELIMINARY ASSESSMENT AND USE OF ERS-1 ALTIMETER WAVE DATA

The satellite ERS-1, launched in July 1991, carries a radar altimeter that provides collocated measurements of significant wave height and wind speed over the oceans. During the calibration period, significant wave height and wind speed simulations from wave models at several national weather forecasting centers were used to assess the accuracy of the altimeter observations. This provided a rapid check on observation quality and assisted in validating the instrument. Comparison with altimeter data showed the U.K. Meteorological Office (UKMO) wave forecast system to be lacking in swell. Verification figures comparing the UKMO wave model to ERS-1 data were similar to those comparing the model against moored buoy data. Once the quality of altimeter data was established, an assimilation trial was run. From the start of November 1991 to the end of January 1992 the altimeter data were assimilated into the UKMO wave forecast system in real time, with the operational wave products as a control. The main impact of assimilating the data was to increase swell in the model fields, and the largest impact was in the central Pacific. For waves up to 6-m height, the mean bias in the model was reduced by 0.3 m. There was little impact for waves higher than 6 m, which were mostly forced by local wind conditions.