Satellite remote sensing

Currently the most useful satellite wave measuring instrument is the satellite altimeter. This instrument can provide significant wave height measurements close to the accuracy of a buoy from an orbit of typically 1,000 km. Measurements are provided each second, as the satellite covers a repeated net of ground tracks at about 6 km/s. This provides enormous amounts of wave data worldwide, and with, at present, a steady flow of new data from 3 or more operational satellites, millions of new observations are becoming available each month. Altimeter measurements have been performed during 1985-1989 (US Navy’s Geosat), from 1991 by ESA’s ERS-1 and ERS-2 satellites, and from the US/French Topex/Poseidon mission since 1992.

Algorithms for the correct interpretation of the back-scattered radar return pulse have been gradually improved, and the values presently derived show an accuracy close to buoy data (see Figure below and Krogstad and Barstow, 1999). However, some uncertainty still exists in the high wave height range, and this can influence the evaluation of extreme conditions when extrapolating satellite data alone or using the altimeter data to calibrate wave model data.

In Eurowaves, we are using data from the Topex and Geosat altimeters in all areas (Atlantic, Mediterranean, Baltic and Black Sea) up to the northern limit of the satellite’s coverage, which is 66 and 72 deg. N respectively. The data being used are quality controlled and calibrated data from OCEANOR’s World Wave Atlas data base. The ground tracks for these two satellites are shown here. Coming Soon.

Figure. Comparison of significant wave height between the Topex altimeter and NOAA buoys for 1,365 coincident data (from Krogstad and Barstow, 1999).

National Technical
University of Athens

Oceanographic
Company of Norway

Istituto Studio
Dinamica Grandi Masse

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