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Case #:PM_NPP_SRFL_20101a   Opening date: 04/10/20   Last update: 04/27/20
Status: Pending
The C1 S-NPP VIIRS L2 VNP09 Land Surface Reflectance (LSR) product aerosol quantity flag may have been in error and may not have correctly presented the spatial distribution of different aerosol quantities (low, average and high) over the globe. VNP09, tends to show a larger number of retrievals as 'High Aerosol', mainly over brighter surfaces in the mid to high latitude, such as over the Sahara desert, and Arabian Peninsula. This is likely to have an impact on the retrieval of other downstream LSR dependent land science parameters like VIIRS BRDF/Albedo, Nighttime Lights, and VI. This will be corrected in the soon to be operational C2 VNP09 products that will use a new approach to flag the aerosol impact. The new approach has also been verified to be consistent across different sensors like MODIS Terra/Aqua and S-NPP VIIRS in flagging the aerosol impact. Please note that the flag value corresponds to three level quantification of the uncertainty in aerosol correction to the surface reflectance. The new approach adopted in the C2 only corrects the quantification of the aerosol correction impact and does not change the retrieved land surface reflectance (LSR) values.

Examples below shows RGB composite images of surface reflectance with retrievals for area flagged as high aerosol removed from C1 SNPP VIIRS surface reflectance product that use the old approach (image on the left). The middle and right images show C2 SNPP VIIRS surface reflectance and the MODIS Aqua surface reflectance product, which both use the new approach to flag the aerosol impact. Use of the new approach to flag aerosol results in fewer retrievals being flagged as high aerosol. A similar note for MODIS has been described here.

Note: C2 SNPP VIIRS Land Surface Reflectance is only a test sample.

Land Surface Reflectance Bands 5,4,3 (VNP09, 2018.193)
using old approach to flag aerosol as in C1

Land Surface Reflectance Bands 5,4,3 (VNP09, 2018.193)
using new approach to flag aerosol as in C2

Land Surface Reflectance Bands 1,4,3 (MYD09, 2018.193)
using new approach used in C61

Occurrence: AS5000, VNP09 and All Downstream products.
PGE: C1 PGE511

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