Evaluation of SeaWiFS, MODIS Terra and MODIS Aqua coverage for studies of phytoplankton diurnal variability

Contemporaneous satellite ocean colour data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and MODIS Aqua instruments are consistently calibrated and uniformly processed using equivalent code and algorithms. These sensors cover the globe at different times of a local day. Combining the three instruments provides an unprecedented opportunity to monitor global and local oceanic phytoplankton fluctuations continuously throughout the day. While a daily maximum of 3 hours of coverage is expected from the three sensors, longer observation periods are achieved by combining hourly coverage from a number of consecutive days. The southern hemisphere is then observed continually between 9 am and 3 pm local time. The northern hemisphere is monitored for shorter periods, largely between 10 am and 2 pm local time. This study proposes methodologies to investigate diurnal variability in phytoplankton optical properties from satellite instruments. It also makes an initial attempt to extract diurnal phytoplankton trends from the data and highlights the requirements for accurate instrument calibration and algorithm consistency in ocean colour.