Geosat altimeter derived sea surface wind speeds and significant wave heights for the north Indian Ocean and their comparison with in situ data

Abstract

Geosat altimeter data for the period November 1986-October 1987 over the north Indian Ocean have been processed to retrieve wind speeds and significant wave heights. Smoothed Brown algorithm is used to retrieve wind speeds from back-scattering coefficients. From the retrieved wind speeds and significant wave heights, minimum significant swell heights are computed. Three major checks were carried out to prove the accuracy of the data for further analysis. Results are presented in the form of colour coded maps, showing the distribution of mean monthly values of wind and wave parameters over 2.5 degrees square grids. Altimeter derived wind and wave parameters are compared with (1) winds and waves obtained through ships of opportunity and documented in Indian Daily Weather Reports (IDWR), and (2) waves measured through shipborne wave recorders (SWR) and wave rider buoys (WRB). However, comparison of monthly averages of Geosat wind speeds and significant wave heights with those of IDWR values over 2.5 degrees square grids shows good agreement. As expected, significant wave heights and wind speeds are higher during monsoon season than during non-monsoon season. Variability of wind and wave parameters during different seasons is clearly seen in the altimeter data