AERDT_L2_VIIRS_NOAA20 - VIIRS/NOAA20 Dark Target Aerosol 6-Min L2 Swath 6 km

The NOAA-20 - formerly the Joint Polar Satellite System-1 (JPSS-1) - Visible Infrared Imaging Radiometer Suite (VIIRS) NASA standard Level-2 (L2) dark target (DT) aerosol product provides satellite-derived measurements of Aerosol Optical Thickness (AOT) and their properties over land and ocean, and spectral AOT and their size parameters over oceans every 6 minutes, globally. The VIIRS incarnation of the DT aerosol product is based on the same DT algorithm that was developed and used to derive products from the Terra and Aqua missions' Moderate Imaging Spectroradiometer (MODIS) instruments. Two separate and distinct DT algorithms exist. One helps retrieve aerosol information over ocean (dark in visible and longer wavelengths), while the second aids retrievals over vegetated/dark-soiled land (dark in the visible wavelengths).

This orbit-level product (Short-name: AERDT_L2_VIIRS_NOAA20) has an at-nadir resolution of 6 km x 6 km, and progressively increases away from nadir given the sensor's scanning geometry and Earth's curvature. Viewed differently, this product's resolution accommodates 8 x 8 native VIIRS moderate-resolution (M-band) pixels that nominally have ~750 m horizontal pixel size. Hence, the Level-2 Dark Target Aerosol Optical Thickness data product incorporates 64 (750 m) pixels over a 6-minute acquisition. This Version-2 set of products is the first collection of the Level-2 Dark Target Aerosol derived from the NOAA-20 VIIRS source. Hence, it bears outlining the differences between the products derived from NOAA-20 VIIRS as against the Suomi National Polar-orbiting Partnership (SNPP) VIIRS.

Level-2 Dark Target Aerosol: NOAA-20 VIIRS v2.0 Improvements

• The NOAA-20 VIIRS v2.0 products use a higher-resolution cloud mask, which is derived from the 375 m image-band red-wavelength to allow for closer, near-cloud retrievals with less cloud contamination. This improved mask is especially visible over ocean, where many high AOD values are revised downward.
• The NOAA-20 VIIRS v2.0 products use NASA's Global Modeling and Assimilation Office (GMAO) inputs as their source of ancillary meteorological data over the previous NOAA's Global Data Assimilation System (GDAS) source.
• The NOAA-20 VIIRS v2.0 products use updated VIIRS Level-1B reflectances with improved calibration over its previous version.
• The NOAA-20 VIIRS v2.0 products now report the mean and standard deviation reflectances over land for all seven wavelength bands compared to only over ocean that the v1.1 products reported.

The L2 netCDF product contains the following 37 Science Data Set (SDS) layers:

1. Aerosol_Cldmask_Land_Ocean
2. Aerosol_Cloud_Fraction_Land
3. Aerosol_Cloud_Fraction_Ocean
4. Aerosol_Type_Land
5. Angstrom_Exponent_1_Ocean
6. Angstrom_Exponent_2_Ocean
7. Asymmetry_Factor_Average_Ocean
8. Average_Cloud_Pixel_Distance_Land_Ocean
9. Backscattering_Ratio_Average_Ocean
10. Cloud_Pixel_Distance_Land_Ocean
11. Corrected_Optical_Depth_Land
12. Effective_Optical_Depth_Average_Ocean
13. Effective_Radius_Ocean
14. Error_Flag_Land_And_Ocean
15. Fitting_Error_Land
16. Image_Optical_Depth_Land_And_Ocean
17. Land_Ocean_Quality_Flag
18. Land_Sea_Flag
19. Least_Squares_Error_Ocean
20. Mass_Concentration_Land
21. Mass_Concentration_Ocean
22. Mean_Reflectance_Land
23. Mean_Reflectance_Ocean
24. Number_Pixels_Used_Land
25. Number_Pixels_Used_Ocean
26. Optical_Depth_By_Models_Ocean
27. Optical_Depth_Land_And_Ocean
28. Optical_Depth_Large_Average_Ocean
29. Optical_Depth_Ratio_Small_Land
30. Optical_Depth_Ratio_Small_Ocean_0p55micron
31. Optical_Depth_Small_Average_Ocean
32. PSML003_Ocean
33. STD_Reflectance_Land
34. STD_Reflectance_Ocean
35. Surface_Reflectance_Land
36. Topographic_Altitude_Land
37. Wind_Speed_Ncep_Ocean

Consult the Dark Target Aerosol Product User Guide for additional information regarding these SDS parameters.