SPECTRAL DEPENDENCE OF THE RESPONSE TIME OF SEA STATE TO LOCAL WIND FORCING

Bistatic remote sensing using L-band GPS signals has been proposed as an alternative to using microwave radiometers and monostatic radar scatterometers for spaceborne ocean surface windspeed measurements. L-band scattered signals are sensitive to waves with longer wavelengths than are the signals sensed by conventional radiometers and scatterometers, which typically operate at higher frequencies. It is known that longer surface waves take more time to respond to surface winds, propagate further before decaying, and are generally less directly coupled to the local wind field. These factors could affect the ability of scattered GPS L-band signals to retrieve local wind fields. In this work, we attempt to quantify the relationship between the longwave spectrum and local winds by examining windspeed and surface slope measurements by buoys. Specifically, by applying a lag-correlator, it is observed that the average lag time decreases monotonically as the ocean surface wavelength decreases. It is found that 1 hour serves as a conservative bound on the average response time of L-band waves to local wind forcing.