Methodology
A Cross-Calibrated Multi-Platform Ocean Surface Wind Velocity Product for Meteorological and Oceanographic Applications
The methodology that we use is described in Atlas et al. (1996) and is similar to that described by Hoffman (1984) with modifications to accommodate for the special attributes of the satellite surface wind data as well as some additional tuning of the data quality checking and filter weights. The variational analysis generates a gridded surface wind analysis which minimizes an objective function F measuring the misfit of the analysis to the background, the data and certain a priori constraints. The following expression is used for F:
where the lamdas are weights controlling the amount of influence each constraint has on the final analysis. The following table describes each term:
The a priori constraints are: (1) the analysis should be "close" to the background field, (2) the differences between the analyzed and background wind, vorticity, and divergence should be smooth, and (3) the estimated time rate of change of the vorticity of the analysis should be small. These constraints control the degree to which the analysis can use the data to modify the background field. The analysis procedures also include a simple quality control; initially, data far from the background are withheld , but after an initial analysis the withheld data are then reconsidered in a second pass using tighter acceptance criteria. For further details see Hoffman (1982, 1984) and Atlas et al. (1993, 1996).
Methodology
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