IMOS - Satellite Remote Sensing - MODIS - 01 day - Net Primary Productivity (GSM 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_gsm) use the Garver-Siegel-Maritorena (GSM) method implemented in the SeaDAS processing software l2gen and described in “Chapter 11, and references therein, of IOCCG Report 5, 2006, (http://ioccg.org/wp-content/uploads/2015/10/ioccg-report-05.pdf). This product is recommended for use in the VGPM model. The product Eppley_NPP_chl_gsm is experimental, in the sense that it is challenging to validate due to the scarcity of insitu measurments. It should only be used with caution informed by understanding of the algorithms.

Production of contemporary MODIS data ceased at 2024/12/26. Users requiring similar Ocean Colour Radiometry data beyond 2024 should consider the VIIRS instruments on the SNPP and NOAA20+ series of satellites, also provided by IMOS.

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Organization: Australian Ocean Data Network