I was producing vegetation indices in a study area in the tropics with MOD09 product (Land Surface Reflectance, 8-days, 500m) and also with MOD13 (Vegetation index, 16-days, 500m). I got more or less the same result with some small differences due to the fact that the former product is an 8-days composite and the latter is 16-days composite. But I noticed that the quality flag are completely different, the one from MOD09 is very 'permissive', the could masking is almost unnecessary but with MOD13 is the opposite, because I lose a lot of data due to clouds. I think that the QA flag of MOD13 should be the correct one because my study area is in the tropics with high presences of clouds, but I wonder why the QA flag of MOD09 is so different and seems to be unreliable.
Can someone give me a clue?
Thanks for your reply Prof. Hack. And yes, I have used the quality flag as it says in the guidelines. I will take a look to the paper you just recommended me.
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