Coverage opportunities for global ocean color in a multimission era

The international community, recognizing the importance of global ocean color observations in the global carbon cycle, has proposed or flown six global ocean color missions over the next decade: the Ocean Color and Temperature Sensor (OCTS), Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Moderate Resolution Imaging Spectrometer-AM (MODIS-AM), Medium Resolution Imaging Spectrometer (MERIS), Global Imager (GLI), and MODIS-PM. Each of these missions contains the spectral band complement considered necessary to derive oceanic pigment concentrations (i.e., phytoplankton abundance). This paper assesses whether assembling and merging data from these missions can improve ocean coverage, since clouds and sun glint prevent any single satellite from observing more than about 15% of the ocean surface in a single day, and whether new information about diel cycles of phytoplankton abundance is possible. Extensive numerical analysis, given the orbit and sensor characteristics of each mission, showed that merging data from three satellites can produce better ocean coverage in less time. Data from three satellites can improve coverage by 58% for a single day, including the obscuring effects of clouds and sun glint. Thus, observation of approximately 25% of the ocean can be provided, instead of only about 15-16% from a single satellite. After four days, approximately 62% of the ocean surface was observed, an increase from 43 % observed by a single satellite. The addition of more satellites produced diminishing returns. Since the proposed missions have different orbits, they view the same location of the ocean at different times of day. This leads to the possibility of using data from the set of six missions to help understand diel phytoplankton dynamics. The missions produced colocated observations as much as 16 h apart in the high latitudes. However, given the distributions of land masses and ice cover, only a maximum of 14-h spacing could actually be achieved, and this only at high latitudes at the solstices. However, large differences of 4-10 h are readily available at other latitudes and in frequencies numbering in the tens of thousands at 20 [degrees] latitude bands. This suggests that combinations of these missions can support new observations of the higher frequency dynamics of phytoplankton populations in the oceans and help determine how well observations taken at a single time represent the daily abundance. Index Terms - Biology, remote sensing, sea surface.