The VJ119A1 Version 2 data product is a NOAA-20 Visible Infrared Imaging Radiometer Suite (VIIRS) Land Surface Bidirectional Reflectance Factor (BRF) gridded Level 2 product produced daily at 375 meter (m) and 750 m pixel resolutions using the Rotated Sinusoidal (RSIN) projection. The VJ119A1 product is corrected for atmospheric gases and aerosols using a Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm that is based on a time series analysis and a combination of pixel- and image-based processing. The VIIRS MAIAC Land Surface BRF products provide an estimate of the surface spectral reflectance as it would be measured at ground-level in the absence of atmospheric scattering or absorption.

Provided in the VJ119A1 product are layers for surface reflectance, cosines of solar and view zenith angles, relative azimuth, sun azimuth (SAZ), sensor view azimuth (VAZ), scattering angle and glint angle. Volumetric (Fv) and geometric-optics (Fg) kernels of the Ross-Thick Li-Sparce (RTLS) model for the observation geometry are also included. The 750 m surface reflectance layers are produced in cloud-free conditions from bands M1-M5, M7, M8, M10, and M11, whereas the 375 m layers are produced from bands I1-I3.

Known Issues

• The spatial resolution and projection of this product are listed incorrectly in the VJ119A1 long name. VJ119A1 uses the RSIN projection and is at 375m and 750m resolution. The long name should read “VIIRS/JPSS1 Land Surface BRF Daily L2G Global 375m and 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.