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I am trying to filter the best quality nLw using the l2_flags in the Aqua/MODIS L2_LAC files. The Ocean Level-2 Data Products document (http://oceancolor.gsfc.nasa.gov/DOCS/Ocean_Level-2_Data_Products.pdf
) indicates that the l2_flags is INT32 and has the bit setting described in Table 3 on p. 9. In looking at a sample granule, A2003303180500.L2_LAC, the range of the integers is [-2147483648, 679510848]. To use the l2_flags, should I convert it to UINT32 first, then go in and extract each bit according to the definitions shown in the Ocean Level-2 Data Products document? According to the bit definitions, the best quality pixels would have bit 1 to 29 set to 0 and bit 32 set to 1. Am I correct?
You are right. You may use SeaDAS's Read & Profileo function to help
you better understand those L2 flag use.
Function -> Read & Profile -> Pixel bit data display + cursor motion
If you wish to write an IDL program, SeaDAS's 'sdp_read_bit_dsp.pro'
is your good reference.