Pier-based observations of polarized sea surface emission

A Ka band polarimetric radiometer operating at 37 GHz was deployed from the seaward end of a small pier colocated with an X band Doppler scatterometer used to measure the instantaneous wave field. Brightness temperature time series from a small spot on the surface for four linear polarizations were measured: T-V, T-H, T-P, and T-M, corresponding to vertical, horizontal, +4 5 degrees, and -45 degrees, respectively. Expected behavior of the mean val ues of T-V and T-H was observed as a function of incidence and azimuth angl es. Varying sensitivities to the wave field in T-P and T-M were observed as a function of azimuth angle with respect to the upwind direction. To the l eft of upwind, wave-induced modulations of T-P exceeded those of T-M, while the opposite behavior was observed to the right of upwind. Since U is the mean value of the difference of these signals, it is relatively easy to int erpret the sine variation of U with wind-relative azimuth angle. Finally, m odulations of brightness temperatures by the wave field were found to be co nsistent with the "smoothed" slope distribution provided by the radar.