Ocean Color Continuity From VIIRS Measurements Over Tampa Bay

Ocean color continuity calls for consistent observations from multiple sensors in order to establish a seamless data record to address earth science questions. Currently, both Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites are being operated well beyond their designed five-year mission life, and they have shown signs of sensor degradation. It is thus urgent to evaluate whether the most recently launched Visible Infrared Imager Radiometer Suite (VIIRS) instrument (2011 to present) can provide consistent observations should MODIS instruments stop functioning. In this study, the consistency between MODIS/Aqua and VIIRS measurements over the Tampa Bay estuary ( ~ 1000 km²) is assessed for remote sensing reflectance (Rrs, sr^-1), chlorophyll-a concentrations (Chla, mg·m^-3), and absorption coefficient of colored dissolved organic matter (ag(443), m^-1). While Rrs was derived as a standard National Aeronautics and Space Administration product from the SeaDAS software package (reprocessing version R2013.0), Chla and ag(443) were estimated using the recently developed regional algorithms for Tampa Bay. Time-series analysis and statistics both showed that the two sensors provided consistent measurements for most products evaluated, with unbiased mean percentage differences of 25% and mean annual biases within -9% (except for one of the eight cases) for large dynamic ranges in Chla (1.0-20 mg·m^-3) and ag(443) (0.1-1.5 m^-1) in all four bay segments. These estimates are comparable or better than those derived from satellite-in situ comparisons, suggesting that VIIRS will provide observations consistent with MODIS, ensuring ocean color continuity and seamless data records for Tampa Bay. Such observations are crucial in establishing a long-term satellite-based water quality decision matrix for Tampa Bay.