Whitecap Fraction From Satellite Measurements: Algorithm Description
Abstract
Many air‐sea interaction processes are quantified in terms of whitecap fraction W because whitecaps are the most visible and direct way of observing breaking waves with air entrainment in the open ocean. Photographs or video images of the sea state collected from towers, ships, and aircrafts have been used over the years to obtain W. Satellite remote sensing of W is a recent development that allows long‐term, consistent observations of whitecapping on a global scale. The method for estimating W uses the variations of ocean surface emissivity at microwave frequencies (6 to 37 GHz) due to presence of sea foam on a rough sea surface. Satellite‐borne microwave radiometers detect these variations at the ocean surface as changes of the brightness temperature TB at the top of the atmosphere. We present the physical and parameterized models, as well as the input data, necessary to calculate W from WindSat TB observations with our W (TB) algorithm. We describe the implementation versions through which the W (TB) algorithm has developed. We show that satellite‐based W data vary with the frequency and polarization of the TB observations. The wind speed dependence of the W retrievals at horizontal and vertical polarizations shows different behavior and compares differently with in situ W data and existing wind speed parameterizations W(U10). We discuss the applicability of our methodology to other radiometric data. We indicate possible modifications and tuning of the models in the W (TB) algorithm that can help to further improve the accuracy of the satellite W retrievals.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Mar 01, 2019
- Source ID
- 10.1029/2018jc014630
Entities
People
- Magdalena D. Anguelova
- Michael H. Bettenhausen
Organizations
- Office of Naval Research
- United States Naval Research Laboratory