VIIRS Cloud (CLDPROP·CLDMSK)¶

MODIS-VIIRS Continuity Cloud Properties (CLDPROP_L2, D3, M3, V1.1) and Cloud Mask (CLDMSK_L2, V2) — Suomi NPP, NOAA-20 and NOAA-21 VIIRS and Aqua MODIS (continuity cloud record built on common bands)

Available

At a glance¶

Note on period: Aqua MODIS versions (CLDPROP_*_MODIS_Aqua, CLDMSK_L2_MODIS_Aqua) from 2002-07-04, Suomi NPP from 2012-03-01 (delivery due to end 2026-11-02), NOAA-20 from 2018-02-17 (L3 daily from 2018-03-17, monthly from 2018-04), and the NOAA-21 cloud mask from 2023-02-10. The LAADS transition table lists the Aqua MODIS versions as starting in 2012, but CMR holds data from July 2002 (checked 2026-10-13).

Overview¶

NASA continuity cloud products built to join the MODIS and VIIRS cloud records. VIIRS lacks the MODIS CO2 absorption (around 13 µm) and water vapour (6.7 and 7.3 µm) bands, and its shortwave infrared band sits at a different wavelength (2.25 µm against 2.13 µm), so the MODIS standard algorithms cannot be carried over directly. Instead the same algorithm, using only bands common to both sensors, is applied to VIIRS and to Aqua MODIS. The cloud mask (CLDMSK) is the MODIS-VIIRS Cloud Mask (MVCM), descended from MOD35; the cloud properties (CLDPROP) combine NOAA CLAVR-x cloud top and phase algorithms with MOD06-heritage optical properties (optical thickness, effective radius, water path), with 1° daily and monthly gridded statistics. The key feature is the Aqua MODIS version, which allows an afternoon record made with one algorithm from 2002 onward.

What changes with the successor¶

CLDMSK V1 (MVCM continuity cloud mask) → CLDMSK V2¶

Transition: 2026-04

Continuity cloud mask V2 (Suomi NPP and NOAA-20 VIIRS, Aqua MODIS) was released on 28 April 2026, along with two new masks that combine an imager with a sounder (AIRS, CrIS). V2 takes calibration-adjusted VIIRS L1B as input and adds a daytime 375 m I-band mask. As of 2026-10-13 the NOAA-21 mask exists only as V1, and no decommissioning date has been announced for the V1 collections.

Sources: Release of MODIS-VIIRS Cloud Mask Version 2.0 Collection Products (LAADS, 2026-04-28) · CLDMSK_L2_VIIRS_SNPP V2 collection description (CMR metadata)

Available variables¶

Names from the CMR variable records (UMM-Var). Files are NetCDF-4, with L2 science variables inside the geophysical_data/ group. Variable names are the same in Aqua MODIS, SNPP and NOAA-20 files. Some variables are stored as integers with scale_factor and add_offset attributes (for example cloud top temperature, scale about 0.0079 and offset 100), so read them with a tool that converts automatically, such as xarray.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

Cloud mask L2 (CLDMSK_L2_VIIRS_NOAA20, NOAA21, SNPP; CLDMSK_L2_MODIS_Aqua)¶

Cloud properties L2 — cloud top and phase (CLDPROP_L2_VIIRS_NOAA20, SNPP; CLDPROP_L2_MODIS_Aqua)¶

Cloud properties L2 — optical properties, daytime (CLDPROP_L2_*)¶

Cloud properties L3 daily and monthly 1° (CLDPROP_D3, CLDPROP_M3 _VIIRS_NOAA20, SNPP, _MODIS_Aqua)¶

The full variable list is in the official documentation.

How to get the data¶

• LAADS DAAC (search, order and direct download) — Web search, direct HTTPS download (CLDPROP V1.1 under archive/allData/5111/, CLDMSK V2 under 5200/) / LAADS API-V2 / OPeNDAP
  • Example short names: CLDPROP_L2_VIIRS_NOAA20, CLDPROP_D3_VIIRS_NOAA20, CLDPROP_M3_VIIRS_NOAA20, CLDPROP_*_MODIS_Aqua, CLDMSK_L2_VIIRS_NOAA20, CLDMSK_L2_VIIRS_NOAA21, CLDMSK_L2_MODIS_Aqua (SNPP for Suomi NPP). The CMR version is "1.1" for CLDPROP and "2" for CLDMSK V2 ("1" for the NOAA-21 mask). Since 2026-04-30 OPeNDAP also requires Earthdata Login.
• NASA Earthdata Search — Web search / earthaccess (Python)
  • Searching CLDPROP or CLDMSK lists collections by sensor, satellite and version. There are also L3 products for comparison with the COSP simulator (CLDPROPCOSP_D3, M3).

Example code¶

Downloads a NOAA-20 CLDPROP monthly file with earthaccess and reads the monthly mean cloud fraction with xarray. L3 variables sit inside NetCDF groups, so use the group argument. Check the group and coordinate names in the file.

# pip install earthaccess xarray netCDF4
import earthaccess
import xarray as xr

earthaccess.login()  # free NASA Earthdata account
results = earthaccess.search_data(
    short_name="CLDPROP_M3_VIIRS_NOAA20", version="1.1",
    temporal=("2024-07-01", "2024-07-31"),
)
files = earthaccess.download(results[:1], "cldprop")

import netCDF4
with netCDF4.Dataset(files[0]) as nc:
    print(list(nc.groups))                   # list the variable groups
cf = xr.open_dataset(files[0], group="Cloud_Fraction")["Mean"]
print(float(cf.mean()))

Practical tips¶

• The MODIS standard cloud products (MOD06, MOD08) and these continuity products give different values even for the same Aqua observations (different cloud top algorithm, liquid refractive index, QA and multilayer detection). For MODIS-VIIRS long-term work, use Aqua MODIS CLDPROP instead of MOD06.
• Platnick et al. (2021) report that the VIIRS 2.25 µm versus MODIS 2.13 µm band difference makes 2.x µm effective radius differ systematically between sensors, and that this has not been fully separated from calibration differences. Check whether the 1.6 µm (_16) retrievals show a smaller difference between the sensors.
• VIIRS lacks the MODIS CO2 and water vapour absorption bands, so cloud detection in polar night is weaker. The MVCM user guide says the 13.3 µm test is gone and the loss of 6.7 and 7.3 µm is only partly offset by new tests. Use winter polar cloud masks with care.
• The Suomi NPP versions stop after 2026-11-02, and there is no NOAA-21 CLDPROP yet (mask only). To continue a VIIRS record, switch to the NOAA-20 versions.
• The Aqua MODIS versions are affected by Aqua orbit drift (later overpasses since 2021). Differences between Aqua and VIIRS after 2021 include a time-of-day difference.
• In October 2023 the continuity cloud mask algorithm was updated with a bug fix and switched to OISST input (collection number unchanged, product_version 1.0.5), and data from 2023-01-01 were reprocessed. CLDMSK V2, adding a 375 m mask, followed in April 2026, so check which mask version you have.
• Cloud properties L3 files use NetCDF groups, so xr.open_dataset(path) alone shows no variables. Open the groups with the group= argument or with netCDF4.

Notices and change history¶

References for your paper¶

Dataset citation¶

CLDPROP_L2_VIIRS_NOAA20 V1.1 (NOAA-20 L2 cloud properties) — DOI 10.5067/VIIRS/CLDPROP_L2_VIIRS_NOAA20.011

@misc{cldprop_l2_noaa20_v11,
  author    = {{NASA VIIRS Atmosphere SIPS}},
  title     = {{VIIRS/NOAA20} Cloud Properties {L2} 6-Min Swath 750 m, Version 1.1},
  year      = {2021},
  publisher = {L1 and Atmosphere Archive and Distribution System (LAADS)},
  doi       = {10.5067/VIIRS/CLDPROP_L2_VIIRS_NOAA20.011}
}

CLDPROP_L2_MODIS_Aqua V1.1 (Aqua MODIS L2 continuity cloud properties) — DOI 10.5067/MODIS/CLDPROP_L2_MODIS_Aqua.011

@misc{cldprop_l2_aqua_v11,
  author    = {{NASA VIIRS Atmosphere SIPS}},
  title     = {{MODIS/Aqua} Cloud Properties {L2} 5-Min Swath 1000 m, Version 1.1},
  year      = {2019},
  publisher = {L1 and Atmosphere Archive and Distribution System (LAADS)},
  doi       = {10.5067/MODIS/CLDPROP_L2_MODIS_Aqua.011}
}

CLDPROP_M3_VIIRS_NOAA20 V1.1 (NOAA-20 L3 monthly) — DOI 10.5067/VIIRS/CLDPROP_M3_VIIRS_NOAA20.011

@misc{cldprop_m3_noaa20_v11,
  author    = {{NASA VIIRS Atmosphere SIPS}},
  title     = {{VIIRS/NOAA20} Cloud Properties Level 3 monthly, 1x1 degree grid, Version 1.1},
  year      = {2021},
  publisher = {L1 and Atmosphere Archive and Distribution System (LAADS)},
  doi       = {10.5067/VIIRS/CLDPROP_M3_VIIRS_NOAA20.011}
}

CLDMSK_L2_VIIRS_NOAA20 V2 (NOAA-20 L2 cloud mask) — DOI 10.5067/VIIRS/CLDMSK_L2_VIIRS_NOAA20.002

@misc{cldmsk_l2_noaa20_v2,
  author    = {{NASA VIIRS Atmosphere SIPS}},
  title     = {{VIIRS/NOAA20} Cloud Mask and Spectral Test Results 6-Min {L2} Swath 750m, Version 2},
  year      = {2025},
  publisher = {L1 and Atmosphere Archive and Distribution System (LAADS)},
  doi       = {10.5067/VIIRS/CLDMSK_L2_VIIRS_NOAA20.002}
}

Reference papers¶

NASA MODIS-VIIRS continuity cloud optical properties products (Platnick et al., 2021) — DOI 10.3390/rs13010002

@article{platnick2021continuity,
  author  = {Platnick, S. and Meyer, K. and Wind, G. and Holz, R. E. and Amarasinghe, N. and Hubanks, P. A. and Marchant, B. and Dutcher, S. and Veglio, P.},
  title   = {The {NASA} {MODIS-VIIRS} Continuity Cloud Optical Properties Products},
  journal = {Remote Sensing},
  volume  = {13},
  number  = {1},
  pages   = {2},
  year    = {2021},
  doi     = {10.3390/rs13010002}
}

Acknowledgements¶

Cite the LAADS dataset DOI of each product and satellite you use (10.5067/VIIRS/.011 for CLDPROP, 10.5067/MODIS/.011 for the Aqua MODIS versions, 10.5067/VIIRS/.002 for CLDMSK V2). Cite Platnick et al. (2021) for cloud optical properties, and the MOD35 ATBD (Ackerman et al.) and the MVCM user guide for the cloud mask, as algorithm references.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• LAADS DAAC — MODIS to VIIRS Transition (continuity product table)
• L2 Cloud Properties User Guide (MODIS and VIIRS CLDPROP, v1.2)
• L3 Continuity Cloud Properties (CLDPROP_L3) User Guide v2.0
• MODIS-VIIRS Cloud Mask (MVCM) User Guide
• CLDPROP_L2_VIIRS_NOAA20 product page (LAADS DAAC)
• CLDMSK_L2_VIIRS_NOAA20 product page (LAADS DAAC)
• Suomi NPP Data Product Delivery to Cease (Earthdata)