Satellite scatterometer model functions are the empirical correlations between observed backscatter and geophysical parameters. One problem is the choice of surface truth for the latter. Currently, buoy data and general circulation model surface analyses have been used to establish 10 m neutrally stratified wind model functions. The correlation between backscatter and surface winds has been the foundation of the scatterrometers. The backscatter is anisotropic with respect to wind direction, allowing wind direction information to be derived from multiple looks at the same patch of ocean. Here the evolution of a model function for the pressure gradient (hence surface geostrophic wind) is given. The European Center for Medium-Range Weather Forecasts surface pressure analyses are used to establish the pressure-based model function. There are limitations and advantages to both geophysical data sets. ¿ 2000 American Geophysical Union