Evaluation of MODIS ocean colour products at a northeast United States coast site near the Martha's Vineyard Coastal Observatory

Moderate Resolution Imaging Spectroradiometer ( MODIS) marine and atmospheric products were evaluated using match- ups of MODIS and in situ measurements collected by an above- water radiometric system, the SeaWiFS Photometer Revision for Incident Surface Measurements ( SeaPRISM), deployed near the Martha's Vineyard Coastal Observatory from 2004 to 2005. The products evaluated include the normalized water- leaving radiance Lwn in the visible and near- infrared bands, and the aerosol optical thickness at 870nm ta( 870), and the A ngstro m exponent a( 531). With a restricted match- up criterion, the result shows that the MODIS- retrieved Lwn at 488, 531 and 551nm agree very well with SeaPRISM measurements, giving mean per cent differences d(%) of 37%, absolute mean per cent differences | d|(%) of,16%, and coefficient of determination R 2 of 0.84- 0.88. However, the MODIS- retrieved Lwn at 412nm are underestimated significantly with d(%), | d|(%) and R 2 of 235%, 57% and 0.32, respectively, corresponding to a consistent overestimation and underestimation for the MODIS- retrieved ta( 870) and a( 531), respectively. Temporal patterns of match- ups revealing two distinct cases of the discrepancy of MODIS retrievals from in situ SeaPRISM measurements are discussed.