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Full catalog/CLDMSK_L2_VIIRS_NOAA21
CLDMSK_L2_VIIRS_NOAA21·v1·dataset

Which pixels are cloudy vs clear (VIIRS, NOAA-21)

VIIRS/NOAA21 Cloud Mask and Spectral Test Results 6-Min L2 Swath 750m
atmosphere NASA LAADS Level 2 active NetCDF-4
In plain English

What it measures. A pixel-by-pixel verdict on whether each spot in a satellite scene is cloudy or clear, at 750-meter detail, along with the results of the individual tests used to make that call.

How it's made. Produced from VIIRS data on the NOAA-21 satellite using a cloud-detection algorithm shared across MODIS and VIIRS, processed in 6-minute swath chunks.

How & where you'd use it. A behind-the-scenes building-block product: most people use it indirectly, since cloud flags are needed to clean up nearly every other land, ocean, and atmosphere measurement before it can be trusted.

What's measured

ATMOSPHERE › CLOUDS › CLOUD PROPERTIES › CLOUD FREQUENCYSPECTRAL/ENGINEERING › INFRARED WAVELENGTHS › REFLECTED INFRAREDSPECTRAL/ENGINEERING › INFRARED WAVELENGTHS › INFRARED RADIANCESPECTRAL/ENGINEERING › VISIBLE WAVELENGTHS › VISIBLE RADIANCEATMOSPHERE › CLOUDS › CLOUD PROPERTIESATMOSPHERE › CLOUDS › CLOUD PROPERTIES › CLOUD TOP HEIGHTATMOSPHERE › CLOUDS

Coverage & cadence

  • Time span2023-02-10 → ongoing
  • Measured byNOAA-21 (VIIRS)
  • Processing levelLevel 2
  • Spatial extent-180, -90, 180, 90
  • FormatsNetCDF-4
  • StatusACTIVE

What you can do with it

  • Map air pollutants — NO₂, aerosols, ozone
  • Track greenhouse gases and Earth's energy budget
  • Feed weather and air-quality analysis
Official description

The National Oceanic and Atmospheric Administration (NOAA-21) Visible Infrared Imaging Radiometer Suite (VIIRS) NASA Level-2 (L2) Cloud Mask (VIIRS/NOAA21 Cloud Mask and Spectral Test Results 6-Min L2 Swath 750m) product is one of four continuity products designed to sustain the long-term records of both Moderate Resolution Imaging Spectroradiometer (MODIS) and VIIRS heritages. CLDMSK_L2_VIIRS_NOAA21 is the short-name for the NOAA-21 VIIRS incarnation of the Cloud Mask continuity product derived from the MODIS-VIIRS cloud mask (MVCM) algorithm, which itself is based on the MODIS (MOD35) algorithm. The MVCM describes a continuity algorithm that is central to both MODIS data (from Terra and Aqua missions) and VIIRS data (from Suomi National Polar-orbiting Partnership (SNPP) and Joint Polar Satellite System missions). Please bear in mind that the term MVCM does not appear as an attribute within the product’s metadata. Implemented to consistently handle MODIS and VIIRS inputs, the NOAA-21 VIIRS collection-1 products use calibration-adjusted NASA VIIRS L1B as inputs. The nominal spatial resolution of the NOAA-21 VIIRS L2 Cloud mask is 750 meters. The L2 netCDF product is acquired and processed every 6 minutes. For more information consult Product Page at: https://cimss.ssec.wisc.edu/MVCM/

Get the data

cldmsk_l2_viirs_noaa21_access.py
import earthaccess
earthaccess.login(strategy="netrc")          # free Earthdata Login

results = earthaccess.search_data(
    short_name="CLDMSK_L2_VIIRS_NOAA21",
    version="1",
    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 LAADS
Browsing CMR needs no login. Downloading or streaming bytes needs a free Earthdata Login + the earthaccess package.