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Full catalog/MODISA_L3m_KD
MODISA_L3m_KD·v2022.0·dataset

How quickly light fades with ocean depth (Aqua)

Aqua 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. Shows how quickly blue-green light fades as it goes deeper into seawater, which is a measure of water clarity and how far sunlight reaches. Lower values mean clearer water and deeper light penetration.

How it's made. Calculated from ocean-color measurements taken by the MODIS instrument on NASA's Aqua satellite, then turned into a global gridded map using the KD2 method.

How & where you'd use it. Used to estimate how deep sunlight reaches in the ocean, track coastal water quality and murkiness, interpret algae bloom conditions, and feed ocean ecosystem models. Accuracy is lower in murky coastal or inland waters.

What's measured

Oceans › Ocean Optics › Attenuation/Transmission

Coverage & cadence

  • Time span2002-07-04 → ongoing
  • Measured byAqua (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

modisa_l3m_kd_access.py
import earthaccess
earthaccess.login(strategy="netrc")          # free Earthdata Login

results = earthaccess.search_data(
    short_name="MODISA_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.