Mean Monthly Sea Surface Chlorophyll-a Concentration (mg/m3) for 2010-2019 - MODIS

This dataset contains rasters and a metadata file for global mean monthly ocean chlorophyll concentration (mg/m3) from 2010-2019. Rasters are in WGS84 coordinate system (EPSG 4326) . Chlorophyll-a is the light-harvesting pigment found in all photosynthetic plants. Its concentration in the ocean is used as an index of phytoplankton biomass and, as such, is a key input to primary productivity models. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA's Terra and Aqua satellites measures ocean color every day, from which global chlorophyll-a concentrations are derived.

Ocean phytoplankton chemically fix carbon through photosynthesis, taking in dissolved carbon dioxide and producing oxygen. Through this process, marine plants capture about an equal amount of carbon as does photosynthesis by land vegetation. Changes in the amount of phytoplankton indicate the change in productivity of the oceans and provide a key ocean link for global climate change monitoring. Scientists use chlorophyll in modeling Earth's biogeochemical cycles such as the carbon cycle or the nitrogen cycle. Additionally, on short time scales, chlorophyll can be used to trace oceanographic currents, jets, and plumes. The 1-km resolution and nearly daily global coverage of the MODIS data thus allows scientists to observe mesoscale oceanographic features in coastal and estuarine environments, which are of increasing importance in marine science studies.

The MODIS Chlorophyll-a product provides an estimate of the near-surface concentration of chlorophyll calculated using an empirical relationship derived from in situ measurements of chlorophyll and remote sensing reflectances (Rrs) in the blue-to-green region of the visible spectrum. The implementation is contingent on the availability of three or more sensor bands spanning the 440 - 670 nm spectral regime. The current implementation for the default chlorophyll algorithm (chlor_a) employs the standard band ratio algorithm (OCx) merged with the color index (CI) of Hu et al. (2012). As described in that paper, this refinement is restricted to relatively clear water, and the general impact is to reduce artifacts and biases in clear-water chlorophyll retrievals due to residual glint, stray light, atmospheric correction errors, and white or spectrally-linear bias errors in Rrs. As implemented, the algorithm diverges slightly from what was published in Hu et al. (2012) in that the transition between the CI and OCx now occurs at 0.15 < CI < 0.2 mg/m-3 to ensure a smooth transition.

These imagery are produced using 2014.0 OCI chlorophyll data.

References for above: Hu, C., Z. Lee, and B.A. Franz (2012). Chlorophyll-a algorithms for oligotrophic oceans: A novel approach based on three-band reflectance difference, J. Geophys. Res., 117, C01011, doi:10.1029/2011JC007395.

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timestamp Wed, 07/21/2021 - 03:16
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