When we use the BBSO or EFM methods for removing scattered light we end up with a number for the DS flux – usually in a box on the DS.
When we apply the FFM we end up with a number for the terrestrial albedo – based on all pixels in the image.
The precisions of the two approaches is not the same. In a test on synthetic images with added, realistic, noise, and realistic variability in the offset and PSF-parameter alfa we find that the
S.D. of the determined albedo is 0.12%, while the
mean error on DS intensity is 1.2 %.
This difference was seen in the Figures of the paper we submitted. The present results are a re-calculation of those simulations – it looked too good to be true in the paper, but I can conform that it is indeed the case. I speculate that it is due chiefly to more pixels being used to determine the albedo in FFM than the DS flux in the EFM.
Further calculation of the albedo from DS intensity would carry the 10-times larger error forward to the albedo!