Sunlight available for ocean plants to grow (NOAA-21)
What it measures. How much sunlight usable by ocean plants for photosynthesis reaches the sea surface, reported as a daily amount of light energy.
How it's made. Derived from the VIIRS instrument on the NOAA-21 satellite as a global mapped product covering the photosynthetic light range.
How & where you'd use it. Helps estimate ocean productivity, interpret phytoplankton blooms, and provide light context for ecosystem and biogeochemical models.
What's measured
Coverage & cadence
- Time span2022-11-10 → ongoing
- Measured byNOAA-21 (VIIRS)
- Processing levelLevel 3
- Spatial extent-180, -90, 180, 90
- FormatsnetCDF-4
- StatusACTIVE
What you can do with it
- Watch sea-surface temperature and marine heatwaves
- Spot algal blooms and ocean-colour shifts
- Support fisheries and coastal monitoring
Official description
The Photosynthetically Available Radiation (PAR) data suite provides satellite-based estimates of the downwelling solar radiation in the 400–700 nm range that is available for photosynthesis at the ocean surface. These products quantify the daily or instantaneous amount of usable light energy, expressed in moles of photons m⁻² (commonly noted as “Einstein m⁻²”), and are widely used to estimate marine primary production, interpret phytoplankton bloom dynamics, provide context for optical and biogeochemical measurements,and support ecosystem models and education on light–biology interactions. Geophysical variables in this suite include: - par — Daily photosynthetically available radiation (mol photons m⁻² d⁻¹)
Get the data
import earthaccess
earthaccess.login(strategy="netrc") # free Earthdata Login
results = earthaccess.search_data(
short_name="VIIRSJ2_L3m_PAR",
version="2025.0",
bounding_box=(-122.5, 37.2, -121.8, 37.9), # your area (W,S,E,N)
temporal=("2024-01-01", "2024-12-31"), # your dates
)
files = earthaccess.open(results) # stream straight from OB_CLOUDBrowsing CMR needs no login. Downloading or streaming bytes needs a free Earthdata Login + the earthaccess package. Official links
- OPeNDAP Site for NOAA-21 VIIRS Standard Mapped Image (SMI) Product USE SERVICE API
- Earthdata Search allows users to search, discover, visualize, refine, and access NASA Earth Observation data. GET DATA
- View the version history of this product. VIEW RELATED INFORMATION
- NASA's Ocean Color Web - Data Distribution Site GET DATA
- NOAA-21 Homepage VIEW RELATED INFORMATION
- VIIRS Homepage VIEW RELATED INFORMATION
- Satellite data procesing can be difficult. We're here to help! Visit the Oceandata Help Hub to navigate learning content for accessing visualizing, and analyzing data products. VIEW RELATED INFORMATION
- Algorithm Theoretical Basis Document for Photosynthetically Available Radiation (PAR) VIEW RELATED INFORMATION