Directional Stability and Conservation of Scattering (DiSCS)-Based Directional-Ambiguity Removal Algorithm for Improving Wind Fields From Scatterometer: A QuikSCAT Example

A new directional-ambiguity removal algorithm has been developed for improving the wind fields derived from a scatterometer. Exploiting the natural spatial variability of ocean surface wind directions and invoking the conservation of backscattering, a new directional stability-weighted low-pass filter has been designed to complement the circular median filtering. It improves the directional-ambiguity removal by reducing the directional noise while retaining the natural wind flow. On the basis of analysis, which will be described later, indicating the lower spatial stability (conversely, the variability) of the wind direction and the lower direction-retrieval skills of the scatterometer-derived winds at low-intensity winds (< 3 m/s) as compared to those for winds above 3 m/s, the ambiguity removal has been performed separately for these two wind regimes. The proposed Directional Stability and Conservation of Scattering (DiSCS) algorithm is applicable to the full swath of the scatterometer. Using the DiSCS algorithm, the wind fields derived from QuikSCAT Level-2A backscatter data over global oceans for 57 orbits during July 1-4, 2005, have been compared with the winds from the National Centers for Environmental Predictions and European Centre for Medium-Range Weather Forecasts models. Similar comparisons of QuikSCAT Level-2B finished products "direction interval retrieval with thresholded nudging" winds (referred to hereinafter as FP) with the winds from these two models have been performed. The QuikSCAT-derived winds are found to be closer to the model winds as compared to those QuikSCAT FP winds.