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Full catalog/MODIST_L3m_KD
MODIST_L3m_KD·v2022.0·dataset

How deep sunlight reaches in seawater (Terra MODIS)

Terra MODIS Level-3 Global Mapped Diffuse Attenuation Coefficient of Downwelling Irradiance (KD) Data, version 2022.0
ocean NASA OB_CLOUD Level 3 active netCDF-4
In plain English

What it measures. How quickly blue-green light fades as it goes deeper into seawater, which is a measure of water clarity and how far sunlight can penetrate. Lower values mean clearer water and deeper light reach.

How it's made. Calculated from Terra MODIS ocean-color measurements using a standard clarity algorithm and mapped into a global grid.

How & where you'd use it. Used to estimate the sunlit depth where life can thrive, track coastal water clarity and murkiness, and feed ocean ecosystem models; accuracy can be weaker in cloudy coastal or inland waters.

What's measured

Oceans › Ocean Optics › Attenuation/Transmission

Coverage & cadence

  • Time span2000-02-24 → ongoing
  • Measured byTerra (MODIS)
  • 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 KD data suite provides diffuse attenuation coefficient of downwelling irradiance at 490 nm, Kd_490, which quantifies how quickly blue-green light diminishes with depth—an indicator of water clarity and the depth to which sunlight penetrates. Kd_490 is generated from ocean-color reflectance using the KD2 algorithm. Lower values indicate clearer water (deeper light penetration); users commonly apply Kd_490 to estimate euphotic depth, track coastal water quality and turbidity, interpret bloom/light environments, and supply inputs to biogeochemical and ecosystem models. As with all ocean-color products, uncertainties can be larger in optically complex coastal or inland waters; refer to the file metadata and algorithm documentation for quality flags and usage notes. Geophysical variables in this suite include: - Kd_490 — Diffuse attenuation coefficient of downwelling irradiance at 490 nm, KD2 algorithm (m⁻¹)

Get the data

modist_l3m_kd_access.py
import earthaccess
earthaccess.login(strategy="netrc")          # free Earthdata Login

results = earthaccess.search_data(
    short_name="MODIST_L3m_KD",
    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.