AERDB_L2_VIIRS_NOAA20 - VIIRS/NOAA20 Deep Blue Aerosol L2 6-Min Swath 6 km

The Visible Infrared Imaging Radiometer Suite (VIIRS) NASA standard Level-2 (L2) Deep Blue aerosol products from the Joint Polar Satellite System (JPSS) series NOAA-20 instrument provides satellite-derived measurements of Aerosol Optical Thickness (AOT) and their properties over land and ocean in 6-minute data granules with daily global coverage. The Deep Blue algorithm draws its heritage from previous applications to retrieve AOT from Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) over both land and ocean, and Moderate Resolution Imaging Spectroradiometer (MODIS) measurements over land. This L2 description pertains to the VIIRS Deep Blue Aerosol Version 2.0 (V2.0) product, whose record starts from February 17, 2018.

This orbit-level product (Short-name: AERDB_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. The L2 Deep Blue AOT data products, at 550 nm reference wavelengths, are derived from particular VIIRS bands using two primary AOT retrieval algorithms: Deep Blue algorithm over land, and the Satellite Ocean Aerosol Retrieval (SOAR) algorithm over ocean. Although this product is called Deep Blue based on retrievals for the land algorithm, the data includes over-water retrievals as well.

The L2 netCDF product, acquired every 6 minutes, contains 55 Science Data Set (SDS) layers. They include the following:

1. Aerosol_Optical_Thickness_550_Expected_Uncertainty_Land
2. Aerosol_Optical_Thickness_550_Expected_Uncertainty_Ocean
3. Aerosol_Optical_Thickness_550_Land
4. Aerosol_Optical_Thickness_550_Land_Best_Estimate
5. Aerosol_Optical_Thickness_550_Land_Ocean
6. Aerosol_Optical_Thickness_550_Land_Ocean_Best_Estimate
7. Aerosol_Optical_Thickness_550_Ocean
8. Aerosol_Optical_Thickness_550_Ocean_Best_Estimate
9. Aerosol_Optical_Thickness_550_STDV_Land
10. Aerosol_Optical_Thickness_550_STDV_Ocean
11. Aerosol_Optical_Thickness_QA_Flag_Land
12. Aerosol_Optical_Thickness_QA_Flag_Ocean
13. Aerosol_Type_Land
14. Aerosol_Type_Land_Ocean
15. Aerosol_Type_Ocean
16. Algorithm_Flag_Land
17. Algorithm_Flag_Ocean
18. Angstrom_Exponent_Land
19. Angstrom_Exponent_Land_Best_Estimate
20. Angstrom_Exponent_Land_Ocean
21. Angstrom_Exponent_Land_Ocean_Best_Estimate
22. Angstrom_Exponent_Ocean
23. Angstrom_Exponent_Ocean_Best_Estimate
24. Cell_Average_Elevation_Land
25. Cell_Average_Elevation_Ocean
26. Fine_Mode_Fraction_550_Ocean
27. Fine_Mode_Fraction_550_Ocean_Best_Estimate
28. Idx_Atrack
29. Idx_Xtrack
30. Land_Bands
31. Latitude
32. Longitude
33. Number_Of_Pixels_Used_Land
34. Number_Of_Pixels_Used_Ocean
35. Number_Valid_Pixels
36. Ocean_Bands
37. Ocean_Sum_Squares
38. Precipitable_Water
39. Reflectance_Bands
40. Relative_Azimuth_Angle
41. Scan_Start_Time
42. Scattering_Angle
43. Solar_Zenith_Angle
44. Spectral_Aerosol_Optical_Thickness_Land
45. Spectral_Aerosol_Optical_Thickness_Ocean
46. Spectral_Single_Scattering_Albedo_Land
47. Spectral_Surface_Reflectance
48. Spectral_TOA_Reflectance_Land
49. Spectral_TOA_Reflectance_Ocean
50. TOA_NDVI
51. Total_Column_Ozone
52. Unsuitable_Pixel_Fraction_Land_Ocean
53. Viewing_Zenith_Angle
54. Wind_Direction
55. Wind_Speed

Differences between the V2.0 and V1.1 VIIRS Deep Blue Aerosol L2 product

The V2.0 VIIRS deep blue aerosol products are available from both NOAA20 and SNPP platforms. Significant changes have been made to the V2.0 Deep Blue/SOAR algorithms to further improve the data quality. Changes in the retrieval algorithms and data products include the following:

• NOAA20 VIIRS-derived products are now available besides the SNPP VIIRS-derived version.
• New SDS suite for prognostic uncertainties of 550 nm AOT over both land and ocean is added. (Aerosol_Optical_Thickness_550_Expected_Uncertainty_Land, Aerosol_Optical_Thickness_550_Expected_Uncertainty_Ocean, Unsuitable_Pixel_Fraction_Land_Ocean).
• Surface pressure is better accounted for both over-land and over-ocean retrievals by adding surface pressure nodes in the aerosol lookup table. This has improved retrieval accuracy over elevated land surfaces as well as water surfaces.
• A new surface database describing the surface reflectance relationships between visible and 2.2 mm bands in each geographic grid is introduced for the over-land retrievals. This new database mitigates overall biases.
• New fine-mode dominant aerosol optical models are added to existing nonspherical dust models, together replacing the original Deep Blue optical models over land. This has improved retrieval accuracy for fine-mode dominant aerosol cases.
• Optimized global retrieval performance.
• QA filtering and smoke detection scheme has been improved.

Consult the VIIRS Deep Blue Aerosol product user guide for additional information regarding the global attributes, data field attributes, quality flags, software to handle and use these data products, etc.