Just wanted to put a note here on using RTTOV and conda (with Python 3) since it took me awhile to get my environment right (using linux-64). These were the approximate steps I needed (RTTOV 12.3):
1. conda create -n rttov123 -c conda-forge python=3 hdf5 gfortran_linux-64 netcdf4 netcdf-fortran
2. conda activate rttov123
3. Copy build/arch/gfortran to build/arch/gfortran-conda
4. Update FC, FC77, and CC using the results from echo $FC and echo $CC
5. Update LDFLAGS: $ LDFLAGS=”-shared $LDFLAGS”
6. Compile RTTOV (use “gfortran-arch”)