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

Abstract

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 L _wn in the visible and near‐infrared bands, and the aerosol optical thickness at 870 nm τ_a(870), and the Ångström exponent α(531). With a restricted match‐up criterion, the result shows that the MODIS‐retrieved L _wn at 488, 531 and 551 nm agree very well with SeaPRISM measurements, giving mean per cent differences δ(%) of 3–7%, absolute mean per cent differences |δ|(%) of ∼16%, and coefficient of determination R ² of 0.84–0.88. However, the MODIS‐retrieved L _wn at 412 nm are underestimated significantly with δ(%), |δ|(%) and R ² of −35%, 57% and 0.32, respectively, corresponding to a consistent overestimation and underestimation for the MODIS‐retrieved τ_a(870) and α(531), respectively. Temporal patterns of match‐ups revealing two distinct cases of the discrepancy of MODIS retrievals from in situ SeaPRISM measurements are discussed.

Acknowledgements

The authors are grateful to the AERONET staffs and G. Zibordi in the Joint Research Centre, Ispra, Italy for their technical comments during the MVCO SeaPRISM instrument deployment and data processing, and to M. Dowell in the Joint Research Centre for his insightful thought to initiate this project. Two anonymous reviewers are greatly acknowledged for their helpful comments. The MODIS project and the GSFC DAAC are also acknowledged for providing the Level‐2 MODIS data. Thanks also go to J. Fredericks and many others in the Woods Hole Oceanographic Institute for their logistic support to access to the MVCO tower. This work was supported by a NASA MODIS Instrument Team Contract (no. NNG04HZ37C) and by the UNH/NOAA Center for Coastal Ocean Observation and Analysis (NOAA award NA160C2740). H. Feng also acknowledges the financial support from GEST/NASA‐GSFC.