The Suomi National Polar-orbiting Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) NASA Level-2 (L2) Cloud Mask + Sounder is a continuity product that leverages the synergy between the VIIRS instrument’s higher spatial resolution and the Cross-track Infrared Sounder (CrIS) instrument’s higher spectral resolution. This product is the result of a data fusion process between an imager (VIIRS) and a hyperspectral sounder (CrIS), which provides improved sensitivity in nighttime and polar regions leveraging additional information content from the sounder instrument's absorption channels (water vapor and carbon dioxide). This continuity product is designed to sustain the long-term records of both Moderate Resolution Imaging Spectroradiometer (MODIS) and VIIRS heritages but with cloud mask performance similar to the full-resolution MODIS Cloud Mask.

CLDMSK_L2_VIIRS-CRIS_SNPP is the shortname for the SNPP VIIRS version of this product that is derived from the MODIS-VIIRS Cloud Mask (MVCM) continuity algorithm, which itself is based on the MODIS (MOD35) algorithm. The MODIS (from Terra and Aqua missions) and VIIRS (from SNPP and Joint Polar Satellite System (JPSS) missions) data-derived cloud mask products use the MVCM algorithm. Implemented to consistently handle MODIS and VIIRS inputs, the version 2.0 (v2.0) SNPP VIIRS Cloud Mask + Sounder collection products use calibration-adjusted NASA VIIRS Level-1B as inputs. The nominal spatial resolution of the SNPP VIIRS L2 Cloud mask is 750 meters at nadir. The v2.0 collection starts from March 1, 2012 (2012-061).

The L2 netCDF product, acquired and processed every 6 minutes, contains the following three data groups and Science Data Set (SDS) layers in each group:

Geophysical data

• VIIRS Clear Sky Confidence
• VIIRS Cloud Mask and Spectral Test Results
• CrIS convolve MYD/VIIRS FOV
• VIIRS Integer Cloud Mask
• Quality Assurance for VIIRS Cloud Mask

Geolocation data

• Latitudes of pixel locations
• Longitudes of pixel locations
• Sensor azimuth angle at pixel locations
• Sensor zenith angle at pixel locations
• Solar azimuth angle at pixel locations
• Solar zenith angle at pixel locations

Scanline attributes

• Scan start time (TAI93)

Most of the SDSs are like those in the regular SNPP VIIRS Cloud Mask product, but one unique SDS that deserves some explanation is “CrIS convolve MYD/VIIRS FOV” under Geophysical Data. This convolution is the basis for the data fusion that integrates measurements from CrIS with higher spectral resolution and VIIRS with higher spatial resolution. It helps create a more comprehensive infrared radiance product than what either instrument can produce alone. Note that the reference to “MYD” is from the naming convention for Aqua MODIS, and is not related to this process directly.

Consult the MODIS-VIIRS Cloud Mask Product User Guide for additional information regarding the transition from the MODIS-MOD35 to the MVCM algorithm, inputs to MVCM, output files, file naming conventions, quality flags, and validation. Users are also encouraged to consult the MOD35 Algorithm Theoretical Basis Document (ATBD).