nPP Algorithm

Primary Productivity - nPP

The algorithm from Behrenfeld and Falkowski (1997):

nPP = 0.66125 * P^Bop * PAR/(PAR + 4.1) * Z_eu * CHL * D_irr

Satellite measurements

CHL - Surface Chlorophyll_a Concentration

PAR - Photosynthetically Active Radiation

SST - Sea Surface Temperature

Derived parameters

P^Bop - Optimum Photosynthetic Rate

The maximum carbon fixation rate within a water column, mg C mg^-2 chl h^-l

P^Bop = -3.27E^-8 * SST⁷ + 3.4132E^-6 * SST⁶ - 1.348E^-4 * SST⁵ + 2.462E^-3 * SST⁴ - 0.0205 * SST³ + 0.0617 * SST^{^2} + 0.2749 * SST + 1.2956

PAR/(PAR + 4.1) - Fraction of realized P^Bop

This parameter

Z_eu - euphotic depth

Depth where irradiance is 1% of surface irradiance

Z_eu = 568.2 ∗ CHL^−0.746 when CHL_eu > 10.0

Z_eu = 200.0 ∗ CHL^−0.293 when CHL_eu ≤ 10.0

Where

CHL_eu = 38.0 ∗ CHL^0.4250 when CHL ≤ 1.0

CHL_eu = 40.2 ∗ CHL^0.5070 when CHL > 1.0

D_irr - Daylength in hours

Determined from the day of the year and latitude.

Satellite Data Used in the Algorithm

Legacy Product

The original nPP product made by CoastWatch West Coast Node uses chlorophyll, sea surface temperature and photosynthetically active radiation derived from the MODIS sensor on the Aqua satellite. The dataset spans the years from 2002 to 2024. A daily, weekly, and monthly version of the dataset are produced.

VIIRS SNPP Interim Product

The new interim nPP product uses chlorophyll, sea surface temperature and photosynthetically active radiation derived from the VIIRS sensor on the SNPP satellite. The dataset spans the years from 2012 to the present. A daily, weekly, and monthly version of the dataset are produced.

Planned NOAA-20 Interim Product

An additional interim nPP product will be generated that uses chlorophyll, sea surface temperature and photosynthetically active radiation derived from the VIIRS sensor on the NOAA-20 satellite. The dataset spans the years from 2018 to the present. A daily, weekly, and monthly version of the dataset will be produced.

Additional Information

Data Sources

MODIS Aqua nPP

MODIS nPP

MODIS Aqua input data for legacy nPP

VIIRS SNPP nPP

VIIRS nPP

VIIRS SNPP input data for interim nPP

References

Behrenfeld and Falkowski. (1997) Photosynthetic rates derived from satellite-based chlorophyll concentration Limnol. Oceanogr. . 42:1-20. https://doi.org/10.4319/lo.1997.42.1.0001.

Project Team and Funding

The project team included: Dale Robinson, Cara Wilson, Sunny Hospital, Veronica Lance, Johnaton Sherman, Kim Hyde, Andrea VanderWoude, Kari Stlaurent, Melanie Abecassis, Ryan Rykaczewski, Ryan Vandermeulen, Menghua Wang

A special thanks to Jesse Espinosa who made important contribution to the project including helping to generate the production Python code to produce the nPP products

The project was supported by funding from the Portfolio Management Branch of NESDIS, NOAA CoastWatch, and CSU COAST