Observing MODIS ocean color patterns under severe sun glint

Abstract

Observing eddies and other oceanographic patterns in the subtropical and tropical oceans during summer time can be problematic, because sea surface temperature often lacks spatial contrast and satellite altimetry provides coarse resolution data with some time lag. MODIS ocean color observations are supposed to provide timely information, but they suffer from sun glint contamination when the glint reflectance, Lg, is > 0.01 sr -1 . Here, an empirical approach is demonstrated to remove sun glint and clouds using MODIS Rayleigh-corrected reflectance (Rrc) at 469, 555, 645, 859, and 1240-nm. A color index (CI) is derived from the 469-555-645 bands using a baseline subtraction. The CI color patterns appear consistent from adjacent days when different glint and aerosol patterns are present, suggesting the validity of the approach. Applications of the approach over the Gulf of Mexico and other tropical and subtropical regions further validate the approach's general applicability. The new products at 1-km and 500-m resolutions make it possible to observe ocean eddies at both large and small scales. The simple design of the approach also makes it straightforward to implement for other regions when a qualitative MODIS CI is desired to infer circulation patterns and to detect eddies under severe sun glint.