Retrieving capillary-gravity wave spectrum from polarimetric microwave radiation of ocean surface

Abstract

A new simple two-scale model on the polarimetric microwave emission of ocean surface is derived at first, which can be expressed as an integral of weighting functions (M 0 and M 2) and ocean surface curvature spectrum coefficients (C 0 and C 2). This provides a simple way to investigate the effect of curvature spectrum on ocean emission. It is found that ocean waves with wavelengths both comparable to and much greater than the electromagnetic wavelength can contribute to the harmonics of ocean surface microwave emission, depending on the magnitude of the ocean surface spectrum in these length scales. Brightness temperature predictions differ significantly due to present diverse spectrum models, and thus a study on wave spectrum obtained inversely from brightness temperature measurements is necessary. From the ocean surface radiation data measured by polarimetric microwave radiometer, we derived an ocean wave spectrum with a wider wave number range, using the proposed two-scale model and constrained linear least-squares method. The derived ocean wave spectrum is useful for comparing with present diverse models.