This processor is used to derive absorption and backscattering coefficients of MERIS L2 images. Only pixels that are determined to be water are processed, other pixels (land, clouds) will be assigned a "No Data" vlaue on all bands. The L2_Flag band is used to determine if a pixel is water, land or cloud. Any flag band value below the cloud threshold (4194304) is considered to be water. Also, only bands that are under 650nm are used in the Quasi-Analytical Algorithm. Using the default MERIS band wavelengths, the first 6 bands are used in processing.
There are two flag bands in the output product of the Quasi-Analytical Processor. The flag band titled l2_flags is the flag band simply copied over from the input L2 Product. The flag band titled analytical_flags contains Quasi-Analytical Processor specific flags.
The values of the flag band do not contain any information besides to specify which flag(s) that location should have marked. The meaning of Quasi-Analytical Processor specific flags are as follows:
| Name | Value | Description |
| nomral | 1 | A valid water pixel. |
| Imaginary number | 2 | Classified as water, but an imaginary number would have been produced. |
| Negative Adg | 4 | Classified as water, but one or more of the bands contain a negative Adg value. |
| non-water | 8 | Not classified as a water pixel (land/cloud). |
Terrain classification (land, cloud, water) is based off of the l2_flags band.