Abstract
The first geostationary ocean color satellite mission (geostationary ocean color imager, or GOCI) has provided eight hourly observations per day over the western Pacific region since June 2010. GOCI imagery has been widely used to track the short-term dynamics of coastal and inland waters. Few studies have been performed to comprehensively assess the advantages of GOCI images in obtaining valid observations and estimating diurnal changes within the water column. Using the entire mission dataset between 2011 and 2017, these knowledge gaps were filled by comparing the daily percentages of valid observations (DPVOs) between GOCI and MODIS Aqua (MODISA) and by examining the diurnal changes in Chl-a over the East China Sea. The mean DPVOs of GOCI was 152.6% over the clear open ocean, suggesting that a daily valid coverage could be expected with GOCI. The GOCI DPVOs were ~26 times greater than the MODISA DPVOs; this pronounced difference was caused by the combined effects of their different observational frequencies and the more conservative quality flag system for MODISA. Diurnal changes in the GOCI-derived Chl-a were also found, with generally higher Chl-a in the afternoon than the morning and pronounced heterogeneities in the temporal and spatial domains. However, whether such diurnal changes are due to the real dynamics of the oceanic waters or artifacts of the satellite retrievals remains to be determined. This study provides the first comprehensive quantification of the unparalleled advantages of geostationary ocean color missions over polar orbiters, and the results highlights the importance of geostationary ocean color missions in studying coastal and inland waters.
Highlights
Over the past few decades, various satellite ocean color instruments have been launched into space by many agencies, including the U.S National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administsaration (NOAA) and the European Space Agency (ESA) [1]
The mean daily percentages of valid observations (DPVOs) for moderate resolution imaging spectroradiometer (MODIS) Aqua (MODISA) Chl-a was 5.2% ± 0.6%, which is more than one order of magnitude less than that of geostationary ocean color mission (GOCI) (112.0% ± 0.1%)
2017 for (a) MODIS Aqua (MODISA), (b) GOCIMODISA and (c) GOCI, which were estimated as the mean values of 81 monthly DPVOs between April 2011 and December 2017
Summary
Over the past few decades, various satellite ocean color instruments have been launched into space by many agencies, including the U.S National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administsaration (NOAA) and the European Space Agency (ESA) [1]. More than one cloud-free observation is expected over the Intra-Americas Sea when geostationary satellite observations are available [19] given the mean daily cloud coverage of 72% for the global ocean [21] Such statistics are based on meteorological satellite data rather than real ocean color observations; the extent to which the valid data coverage of ocean color retrievals can be improved through geostationary missions remains unknown. Compare the daily percentages of valid observations (DPVOs) of Chl-a between MODISA and hourly and daily GOCI measurements and assess the diurnal changes in ocean color products at different locations; Demonstrate how differences in satellite orbits, observational frequencies and data processing methods could impact the data coverage and ocean color measurements; Discuss how the results of this study could be used to help both mission plan of future geostationary ocean color missions and associated algorithm development
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