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Full catalog/MODISA_L4m_GSM
MODISA_L4m_GSM·v2022.0·dataset

Ocean chlorophyll and particle color from a biology model (Aqua)

Aqua MODIS Level-4 Global Mapped Garver-Siegel-Maritorena Model (GSM) Data, version 2022.0
ocean NASA OB_CLOUD Level 4 active netCDF-4
In plain English

What it measures. Global maps of ocean color properties, including chlorophyll-a (a stand-in for how much microscopic plant life is in the water) plus the absorption and backscattering of light by dissolved material and particles.

How it's made. Created from Aqua MODIS ocean-color measurements run through a physics-based model (the Garver-Siegel-Maritorena model) that pulls several optical properties out of the reflected light at once, then mapped globally.

How & where you'd use it. Helps scientists track ocean plant life and water clarity with a more physics-based approach than simpler chlorophyll methods, useful for studying ocean ecosystems and the carbon cycle.

What's measured

Oceans › Ocean Optics › AbsorptionOCEANS › OCEAN OPTICS › SCATTERINGBIOSPHERE › ECOSYSTEMS › AQUATIC ECOSYSTEMS › PLANKTON › PHYTOPLANKTONEARTH SCIENCE SERVICES › ENVIRONMENTAL ADVISORIES › HYDROLOGICAL ADVISORIES › WATER QUALITYTERRESTRIAL HYDROSPHERE › SURFACE WATEROCEANS › OCEAN OPTICS › CHLOROPHYLL › CHLOROPHYLL CONCENTRATION

Coverage & cadence

  • Time span2002-07-04 → ongoing
  • Measured byAqua (MODIS)
  • Processing levelLevel 4
  • 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 GSM data suite provides ocean-color fields derived by inverting water-leaving reflectance with the Garver–Siegel–Maritorena (GSM/GSM01) semi-analytical model. GSM’s advantage is that it retrieves multiple optical properties simultaneously from a reflectance spectrum and offers a more physics-based alternative to simple band-ratio chlorophyll algorithms. Geophysical variables in this suite include: - adg_443_gsm – Absorption by gelbstoff and detrital material at 443 nm, GSM algorithm (m⁻¹) - bbp_443_gsm – Particulate backscattering at 443 nm, GSM algorithm (m⁻¹) - chl_gsm – Chlorophyll-a concentration, GSM model (mg m⁻³)

Get the data

modisa_l4m_gsm_access.py
import earthaccess
earthaccess.login(strategy="netrc")          # free Earthdata Login

results = earthaccess.search_data(
    short_name="MODISA_L4m_GSM",
    version="2022.0",
    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.