Broadband phenomena in oceanic passive wind direction signatures: The sensitivity to wave asymmetry, foam, and atmospheric profile

An inherently broadband asymmetric-wave geometrical optics (AWGO) model of the upwelling thermal radiation over the ocean was used to investigate the contributions of wave asymmetry, foam, and the downwelling (background) radiation profile to the passive oceanic wind direction signature. Signatures at K- and K_a-band (19 and 37 GHz) were calculated using a Monte-Carlo ocean surface simulation. The investigation showed that at angles near the SSM/I observing angle, T _h and T_U are sensitive but T_ν is insensitive to wave asymmetry. However, T_ν was found to be sensitive and T_U insensitive to the placement of foam on the waves. Sensitivity to the background radiation profile was investigated by varying the atmospheric temperature and humidity profiles. For changes of ≳33% in atmospheric water vapor from a global mean value, only slight variation (~0.2 K) in the upwind/downwind brightness temperature difference for either polarization resulted