Anyone can help in explaining how I can apply Quality Control (QC) for MODIS Leaf Area Index (LAI) to extract the valid pixels of LAI using ArcMap?
I assume that you are referring to one of the following MODIS products: MYD15A2, MOD15A2, MCD15A2 or MCD15A3.
The quality control layer for these files is based on using each of the bits in the value as separate flags. ArcMap doesn't know this, and interprets it as a standard 8-bit image (values from 0 to 255). The intended approach would be to use LDOPE to mask the data, but it can be a somewhat daunting task to get a handle on.
Another option is to take a very direct approach, and use reclassify in ArcMap to establish a simplified QC layer. Looking at pages 3 and 4 in this PDF will give you a list of QC flags in the product. These can be translated using this converter.
It should be noted that the order of bits in the MODIS QC layer is from right to left. As such, the simplest usable QC mask you can make from the MODIS QC product would be to only use data where the MODIS QC layer is 0 or 2 (meaning Good Quality & either from the Aqua or Terra satellite).