Earth Data School
About
Full catalog/VIIRSJ2_L3m_CHL_NRT
VIIRSJ2_L3m_CHL_NRT·v2025.0·dataset

Tiny ocean plants (chlorophyll), near-real-time (NOAA-21)

NOAA-21 VIIRS Level-3 Global Mapped Chlorophyll (CHL) - Near Real-time (NRT) Data, version 2025.0
ocean NASA OB_CLOUD Level 3 active netCDF-4
In plain English

What it measures. The concentration of chlorophyll-a at the ocean surface, a stand-in for how much tiny floating plant life (phytoplankton) is present.

How it's made. Derived from the VIIRS instrument on the NOAA-21 satellite and mapped into global composites. This is the fast near-real-time version, so its inputs and calibration are less refined than the final product.

How & where you'd use it. Tracks phytoplankton over time, flags unusual blooms, and supports fisheries and ecosystem work. Readings can be less reliable in murky coastal or inland waters.

What's measured

Oceans › Ocean Optics › Chlorophyll › Chlorophyll ConcentrationBIOSPHERE › VEGETATION › CHLOROPHYLLOCEANS › OCEAN CHEMISTRY › CHLOROPHYLLOCEANS › OCEAN CHEMISTRY › PIGMENTS › CHLOROPHYLLTERRESTRIAL HYDROSPHERE › WATER QUALITY/WATER CHEMISTRY › WATER CHARACTERISTICS › CHLOROPHYLL CONCENTRATIONSBIOSPHERE › ECOSYSTEMS › AQUATIC ECOSYSTEMS › PLANKTON › PHYTOPLANKTON

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 Ocean Biology DAAC produces near real-time (NRT) products using the best-available combination of ancillary data from meteorological and ozone data. As such, the inputs and the calibration used are less than optimal. Near real-time products provide a snapshot of the data during a short time period within a single orbit. The Chlorophyll-a data suite provides global, gridded composites of surface chlorophyll-a concentration (a proxy for phytoplankton biomass). CHL supports time-series and climatologies, anomaly detection, ecosystem and fisheries applications, and teaching/training, and pairs well with AVW, PAR, Kd(490), SST, and winds for environmental context. Note: retrievals in optically complex coastal/inland waters may carry higher uncertainty—refer to the mission/algorithm documentation (e.g., OCx/OCI) for details. Geophysical variables in this suite include: - chlor_a — Chlorophyll-a concentration (mg m⁻³)

Get the data

viirsj2_l3m_chl_nrt_access.py
import earthaccess
earthaccess.login(strategy="netrc")          # free Earthdata Login

results = earthaccess.search_data(
    short_name="VIIRSJ2_L3m_CHL_NRT",
    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_CLOUD
Browsing CMR needs no login. Downloading or streaming bytes needs a free Earthdata Login + the earthaccess package.