Algorithm Descriptions
The Ocean Biology Processing Group (OBPG) produces 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.
All products produced by the OBPG are distributed and archived by the Ocean Biology Distributed Actice Archive Center (OB.DAAC).
Flags:
View Level-2 ocean color product quality indicators.
View SST product quality indicators.
Standard
- 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
- Inherent Optical Properties from GIOP Algorithm (IOP, m-1)
- Spectral marine absorption and backscattering coefficients of water column constituents
- 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
- 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
- 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.
- Sea Surface Temperature, 11µm (SST; °C)
- Sea surface temperature derived from long-wave (11-12 µm) thermal radiation
- Sea Surface Temperature, 4µm (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
Provisional/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
- Aerosol Optical Properties
- The algorithms used to produce aerosol optical depth.
- 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.
- Cloud Mask
- The algorithm that defines whether a given pixel is likely to be partially or fully covered by a cloud ("cloudy") or not ("cloud-free" or "clear").
- Cloud Optical Properties
- This product provides the cloud optical depth (COD) and cloud effective radius (CER).
- Cloud Phase
- The thermodynamic phase of a cloudy pixel: liquid water, or ice crystals.
- Cloud Top Pressure
- The cloud top pressure (CTP) and cloud top height (CTH) for cloudy pixels.
- 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.
- 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.
- Sea Surface Temerature, Physical Deterministic (PD) Method
- Sea surface temperature using a physical deterministic method
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
- Calcite (ci2)
- Calcite concentration derived from particulate inorganic carbon
- 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.
