I need to get the percentage of valid data on the resulting image clip of a polygon por each date. I was suggested to create a layer where I obtain 1 if any band has a value distinct of 0 and then use the FIS to get the statistics so the mean would be equivalent to percentage of valid data. When I do that on an image that I know does not cover the 100% of the polygon I still get 100%. I think that that is happening because the area with no date is masked and all calculations of the FIS are done over the unmasked area. So if that is true it would be much easier to get the masked area cover, How can I do that?
Attached is an image of the scene.