I have several NDVI and EVI rasters from different time points across a study period. These are of a region in Burkina Faso, and during the rainy season pixel reliability can be low. I have first masked each raster using the pixel reliability raster so that each NDVI and EVI raster has only the pixels that had a quality score of 0 or 1 (scores are 0, 1 or 3 with 3 being less reliable). I used GRASS r.mask.rast to do this. To get NDVI/EVI across the region I need to combine 6 layers for each index and get the mean values for each pixel.
I have tried to do this using the QGIS raster calculator (my input screenshot 1), cell statistics (my input screenshot 2) and GRASS r.series.accumulate (my input screenshot 3) but I get quite different results for each. The calculator gives me almost no actual pixels back. The cell statistics gives me all the pixels but they look a lot paler (lower values) for the mean than I expected, as does the max value. This might be accurate and I might be being stupid. For the accumulate I get something more like what i would expect with all the pixels, but I do get several warning messages when I run it (the log closes before I can copy them to paste!). All of my rasters are set to ESPG 32630 UTM zone 30N
calculator Cell stats accumulate
If none of these things is the correct process, is there a better process?