Following on from post we now inspect satellite images one week apart in order to understand the natural variability found in satellite images of the same area.
Upper panel: average image pixel value for sequences of MTSAT images, 1 hour apart, for almost one day in March 2013 and a week later (red curve). Image pixel values is in arbitrary units but is proportional to pixel brightness. Lower panel: difference between upper panel black and read curves, expressed as a percentage of the mean of ther ed and black curves.
The difference between the two curves is on the order of 10% and varies from 8% to 18% during one day.
This tells us two things: Albedo (or something proportional to albedo) can vary by roughly 10% over a week. Albedo can vary during one day by almost as much.
This is useful information to have when we interpret the earthshine data.
We keep in mind that the smooth variations in the black and red curves in panel one are due to the day/night cycle – not intrinsic albedo variations: but the difference between the curves and the variability in the difference tells us about albedo variations.