The VNP19A2 Version 2 data product is a NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Land Aerosol Optical Depth (AOD) gridded Level 2 product produced daily at 750 meter (m) pixel using the Rotated Sinusoidal (RSIN) projection. The VNP19A2 product provides the atmospheric properties and view geometry used to calculate the Multi-Angle Implementation of Atmospheric Correction (MAIAC) Land Surface Bidirectional Reflectance Factor (BRF) or surface reflectance, VNP19A1 product.

Provided in the VNP19A2 product are layers for AOD, AOD uncertainty and QA, injection height of smoke plume, AOD outside of glint area, fine mode fraction, and cosines of solar and view zenith angles, relative azimuth, scattering angle, glint angle, and Angstrom Exponent over the ocean.

Known Issues

• The spatial resolution and projection of this product are listed incorrectly in the VNP19A2 long name. VNP19A2 uses the RSIN projection and is at 750m resolution. The long name should read “VIIRS/NPP Land Aerosol Optical Depth Daily L2G Global 750m RSIN Grid V002”. This will be rectified in future versions.

• MAIAC Lookup Tables (LUTs) are built assuming pseudo-spherical correction in single scattering which has a reduced accuracy for high sun/view zenith angles. A reduced MAIAC performance is expected at solar zenith angles > 78°.

• MAIAC may be missing bright salt pans in several world deserts. In such cases, it may generate a persistent high Aerosol Optical Depth (AOD) resulting in missing surface retrievals.

• Because of inherent uncertainties of gridding on the coastline, the area of 1-3 pixels from the coastline may contain frequent artifacts in cloud mask (usually over-detection), AOD (higher values) and surface BRF. Users should exercise caution near the coastline as represented by the AOD QA bit 1010 (See Table 5.4 bits 8-11, 1010 -- AOD within +-2km from the coastline is replaced by nearby AOD).

• Atmospheric Correction (AC) over detected snow: as MAIAC does not retrieve AOD over snow, it assumes a low climatology AOD=0.05 globally and 0.02 at high elevations (H>4.2km). Over north-central China, which is often heavily polluted and low AOD assumption can lead to a significant bias, we use AOD averaged over mesoscale area of 150km using reliable AOD retrievals over snow-free pixels. Such approach does improve quality of AC as compared to low-AOD assumption as judged by the reduced boundaries and color artefacts, but it does not account for the aerosol variability inside 150km area.

• Ice mask is currently unreliable.