OB.DAAC Logo
NASA Logo
Algorithm Descriptions

Algorithm Descriptions

The Ocean Biology Processing Group (OBPG) produces and distributes a standard suite of ocean color products for all compatible sensors at Level-2 and Level-3, plus sea surface temperature (SST) products from MODIS and VIIRS. The OBPG also produces a suite of Level-3 evaluation products. The descriptions and references for these standard and evaluation products (provided below) are intended to satisfy the Algorithm Theoretical Basis Document (ATBD) requirement as defined by the NASA Earth Observing System Project Science Office.

Ocean Color Products

Flags: View quality indicators of Level-2 Ocean Color products.

Standard

Remote Sensing Reflectance (Rrs; sr-1)
The at-surface spectral remote-sensing reflectances observed by the satellite instrument after atmospheric correction. The aerosol optical thickness and aerosol Ångström exponent products are also described.
Chlorophyll a (chlor_a; mg m-3)
The concentration of the photosynthetic pigment chlorophyll a
Diffuse attenuation coefficient for downwelling irradiance at 490 nm (Kd; m-1)
The diffuse attenuation coefficient for downwelling irradiance over the first optical attenuation layer
Particulate Organic Carbon (POC; mg m-3)
The concentration of particulate organic carbon
Particulate Inorganic Carbon (PIC; mol m-3)
The concentration of particulate inorganic carbon
Photosynthetically Available Radiation (PAR; Einstein m-2 d-1)
Daily mean photosynthetically available radiation at the ocean surface
Instantaneous Photosynthetically Available Radiation (iPAR; Einstein m-2 s-1)
PAR at the ocean surface at the time of the satellite observation
Normalized Fluorescence Line Height (nFLH; mW cm-2 µm-1 sr-1)
Relative measure of water-leaving radiance associated with chlorophyll fluorescence
Inherent Optical Properties from GIOP Algorithm (IOP, m-1)
Spectral marine absorption and backscattering coefficients of water column constituents

Provisional/Developmental

PIC - Color Index
This algorithm derives the concentration of particulate inorganic carbon (PIC) in mol m-3, calculated using an empirical relationship derived from in situ measurements of PIC and remote sensing reflectance ($R_{rs}$) in the green-to-red region of the visible spectrum.
Apparent Visible Wavelength (AVW)
This algorithm returns the weighted harmonic mean of the visible-range (400 – 700 nm) remote sensing reflectance (Rrs) wavelengths, outputting the Apparent Visible Wavelength (AVW) in units of nanometers.
Quality Water Index Polynomial (QWIP)
This algorithm returns the Quality Water Index Polynomial (QWIP) score, representing a quantitative metric to evaluate the quality of ocean color remote sensing reflectance (Rrs) data (Dierssen et al. 2022).
Phytoplankton Carbon Concentration (carbon_phyto)
This algorithm returns the concentration of the phytoplankton carbon.

Special

Inherent Optical Properties from GSM Algorithm (GSM; m-1)
Spectral marine absorption and backscattering coefficients of water column constituents
Inherent Optical Properties from QAA Algorithm (QAA; m-1)
Spectral marine absorption and backscattering coefficients of water column constituents
Euphotic Depth from Lee Algorithm (ZLEE; m-1)
Depth of the euphotic zone
Land Reflectance from NDVI algorithm (LAND)
Land reflectance generated from the Normalized Difference Vegetation Index (NDVI) algorithm

Test

Net Primary Production (NPP) Suite
The Net Primary Production (NPP) Suite tracks the proportion of phytoplankton-sequestered carbon that is available to enter into the trophic cascades of the oceanic food web.
Calcite (ci2)
Calcite concentration derived from particulate inorganic carbon

Sea Surface Temperature Products

Flags: View quality indicators of SST products.

Standard

11 µm Sea Surface Temperature (SST; °C)
Sea surface temperature derived from long-wave (11-12 µm) thermal radiation
4 µm Sea Surface Temperature (SST4; °C)
Sea surface temperature derived from short-wave (3-4 µm) thermal radiation
Triple-Window Sea Surface Temperature (SST3; °C)
Sea surface temperature returned in three mid- and long-wave infrared bands

Developmental

This section lists algorithms that have been proposed and are under review. If accepted, the status will be updated to "Provisional" or "Standard". As developmental algorithms, those listed below ARE NOT used in OBPG data processing.

Aerosol correction for VIIRS SST
Aerosol correction for sea surface temperature
Physical Deterministic (PD) SST
Sea surface temperature using a physical deterministic method