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Case #:PM_MYD09_20010   Opening date: 04/10/20   Last update: 05/28/20
Status: Note
The aerosol quantity flag in the C6 MODIS Surface Reflectance product (MOD09/MYD09) 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. This is more relevant for areas with brighter surfaces and high-aerosols. This has been corrected in C61, using a new approach that is also consistent across the two sensors, MODIS Terra/Aqua and VIIRS S-NPP. 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 C61 product only corrects the quantification of the aerosol correction impact and does not change the retrieved land surface reflectance (LSR) values. Any impact from this, on the downstream L3 dailies are minimal and are seen to produce small differences in the different 'n-day' products that are dependent on LSR. For a more detailed discussion on the changes and impact on different downstream products please refer to the following document.

Examples below show RGB composite images of surface reflectance bands 1, 4 and 3 with areas flagged as high aerosol removed from the images: The images on the bottom are from the C61 surface reflectance product generated using the old approach to flag the aerosol (as in the C6 products) and the associated aerosol quantity. The images on the top are from the C61 surface reflectance product generated using the new approach to flag aerosols. Use of the new approach to flag aerosol results in fewer retrievals being flagged as high aerosol.

Comparison of old and new approaches to flag aerosols in C6 and C61.
Land Surface Reflectance Bands 1, 4, and 3 (MYD09, 2018.193).

Occurrence: C6 MYD09, and downstream products, corrected in C61

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