Status: Pending
The VIIRS L2 Land Surface Reflectance product VNP09 seems to consistently flag a larger number of retrievals as 'High Aerosol' in the quality data set QF7 compared to the heritage MODIS reflectance product generated using MODIS observations. This is observed globally but specifically impacts regions in the mid to high latitude, desert, and tropical vegetative areas. Inaccurately flagged high aerosol quality flags in VNP09 directly impact the quality of the downstream VIIRS BRDF Albedo product, i.e. BRDF retrieval algorithm will tend to reject these high aerosol observations and switch from full inversion (high quality retrieval) to magnitude inversion (low quality retrieval) in the case of less than required number of observations to perform the full inversion.
The issue is currently under investigation and more information will be posted when it becomes available. The images below, provided by the BRDF Science Team, show a comparison between the VIIRS and MODIS Surface Reflectance and associated Aerosol Flag over the mid latitudes (Europe). In this example, the first image shows the VIIRS Surface Reflectance where the associated Aerosol Flag shows a large number of pixels flagged as 'High' (Red).
 VNP09GA Surface Reflectance / Aerosol Flag 2016.188, Tile:H19V04 Europe Summer |
The second image shows the same region and day for the MODIS Surface Reflectance and Aerosol Flag, where minimal 'high' aerosol values (red) are observed. |
 MYD09GA Surface Reflectance / Aerosol Flag 2016.188, Tile:H19V04 Europe Summer |
The third and fourth images below show the issue with the flagging of aerosol for a sample tile over desert area, tile h19v06 covering Sahara desert in Northern Africa. The image of the aerosol flag in the L2G surface reflectance product from MODIS Aqua (MYD09GA) shows nearly all retrievals flagged as low (green) or average aerosol (sea green). |
 MYD09GA Surface Reflectance / Aerosol Flag 2016.185, Tile h19v06 (Sahara Desert) |
The fourth image below shows the SNPP VIIRS Surface Reflectance and the associated Aerosol Flag , where most of the area are flagged as 'High' (Red). |
 VNP09GA Surface Reflectance / Aerosol Flag 2016.185, Tile h19v06 (Sahara Desert) |
Occurrence: AS5000, VNP09 and All Downstream products.
PGE: ?