Assimilation of Altimeter Wave Measurements into Wavewatch III

摘要

Assimilation of altimeter measured significant wave heights (SWH) into a global implementation of the Wavewatch III model was performed for March 2004, using SWH data obtained from ENVISAT and JASON satellites. The wave model is forced by 3-hourly Navy Operational Global Atmospheric Prediction System (NOGAPS) marine surface winds. A 6-hour time window about the synoptic time is used to select the altimeter SWH data for the assimilation. The satellite measurements are quality controlled and bias corrected before being used in the analysis An Optimum Interpolation (OI) scheme is used to compute the SWH increment field from the altimeter SWH innovations. The 'first guess: 6-hr model forecast directional wave spectra are then corrected by the ratio of the analysis wave height over the first guess wave height. This correction is distributed uniformly over the wave model spectra Prior to the March 2004 assimilation run, a 6- month analysis-only run (no forecast model update) was performed. Wavewatch III prediction errors at the 6-hr. forecast period, and spatial covariance functions. Observation errors are found to vary with satellite , prediction errors are found to vary with position, and a second- order autoregressive function is found to be an adequate fit to the bin- averaged spatial autocorrelation estimates. Spatial correlation analysis of the analysis residuals shows that the analysis is effectively extracting all of the information in the altimeter SWH measurements.