Near-surface wind speed retrieval from space-based, multi-angle imaging of ocean sun glint patterns

The relationship between the MISR multi-angle observations of sun glint pattern width over ocean and the near-surface wind speed is explored. With this relationship, we develop an algorithm that can constrain the standard, wind-driven glint/white cap model that defines the ocean–surface boundary condition in MISR aerosol retrievals. The key geometric factor determining wind retrieval quality is the angular distance between the reflection vector and the closest MISR multi-angle observation — the minimum Sun Glint Angle (SGA).MISR-retrieved winds are within 2.4 m/s of buoy-measured values for minimum SGA below about 15° for the 38 cases studied, and usually better than 1.1 m/s, except one for which the wind speed was extremely low. For minimum SGA above about 15°, MISR angular glint pattern reflectance sampling is not adequate to perform wind retrievals. An ambiguity in the retrieval that can occur for minimum SGA greater than 6° or 7° is resolved by the minimum observed absolute reflectance. We also confirm the high accuracy of the Cox–Munk ocean surface reflectance model, used to analyze the glint pattern dependence on wind speed. The wind-retrieval method could be used in an operational multi-angle aerosol retrieval algorithm to dynamically constrain the ocean surface boundary condition when glint pattern angular sampling is adequate.