Interpreting floating-point QC values from OPeNDAP MOD21A1D
Posted: Thu Jan 27, 2022 10:33 am America/New_York
With MOD11 data from OPeNDAP, and with MOD21A1D HDF files from EarthData Search, I've been able to interpret values of the `QC` variable with bitwise operations and the appropriate user guide. In these cases, `QC` is provided as integers. But in the case of MOD21A1D data from OPeNDAP, `QC` is given as floating-point numbers (`Float32` in OPeNDAP parlance), and I can't see how it's meant to represent the bit patterns described in the user guide (Table 10 on pages 24-26 of [link] ://lpdaac.usgs.gov/documents/620/MOD21_User_Guide_V61.pdf ).
For example, in the file `MOD21A1D.A2003001.h12v04.061.2020084062741.hdf` I got from EarthData Search, the first five `QC` values are all 54 (hexadecimal 36). The corresponding values from OPeNDAP, available at [link] ://opendap.cr.usgs.gov/opendap/hyrax/MOD21A1D.061/h12v04.ncml.ascii?QC%5B766:1:766%5D%5B0:1:0%5D%5B0:1:4%5D , are all -0.509091 (hexadecimal 86b56fbf in 32-bit IEEE floating point). So how can I interpret the OPeNDAP version?
For example, in the file `MOD21A1D.A2003001.h12v04.061.2020084062741.hdf` I got from EarthData Search, the first five `QC` values are all 54 (hexadecimal 36). The corresponding values from OPeNDAP, available at [link] ://opendap.cr.usgs.gov/opendap/hyrax/MOD21A1D.061/h12v04.ncml.ascii?QC%5B766:1:766%5D%5B0:1:0%5D%5B0:1:4%5D , are all -0.509091 (hexadecimal 86b56fbf in 32-bit IEEE floating point). So how can I interpret the OPeNDAP version?