Satellite - Ocean Colour - MODIS - 1 day - Net Primary Productivity (OC3 model and Eppley-VGPM algorithm)

The Aqua satellite platform carries a MODIS sensor that observes sunlight reflected from within the ocean surface layer at multiple wavelengths. These multi-spectral measurements are used to infer the concentration of chlorophyll-a (Chl-a), most typically due to phytoplankton, present in the water. Modelling is then used to compute an estimate of the Net Primary Productivity (NPP).

The model used is based on the standard vertically generalised production model (VGPM). The VGPM is a "chlorophyll-based" model that estimates net primary production from chlorophyll using a temperature-dependent description of chlorophyll-specific photosynthetic efficiency. For the VGPM, net primary production is a function of chlorophyll, available light, and the photosynthetic efficiency. The only difference between the Standard VGPM and the Eppley-VGPM is the temperature-dependent description of photosynthetic efficiencies, with the Eppley approach using an exponential function to account for variation in photosynthetic efficiencies due to photoacclimation. The similarity between these models (VGPM vs E_VGPM) is described more extensively in a paper by Elena-Carr et al (2006.). VGPM is a Depth Integrated Model(DIM) described by Behrenfeld and Falkowski (1997), with modification due to Eppley (1972) as implemented by Antoine and Morel (1996).

There are multiple retrieval algorithms for estimating Chl-a. These data (eppley_npp_chl_oc3) use the OC3 method implemented by the NASA Ocean Biology Processing Group in the SeaDAS processing software l2gen. The OC3 algorithm is described at https://oceancolor.gsfc.nasa.gov/atbd/chlor_a/  (and links therein). The Eppley_NPP_chl_oc3 product (based on the IMOS chl_oc3 product) is experimental and was created for comparison purposes with Eppley_NPP_chl_gsm, which is the recommended NPP product. It should only be used with full understanding of the algorithms. If you do not know which product to use, then go with Eppley_NPP_chl_gsm.