The instrument triplets (platform, satellite, and sensor ID) in the namelist can be ranked in any order. More detail about the convention of instrument triples can be found on the web page http://nwpsaf.eu/deliverables/rtm/rttov_description.html or in tables 2 and 3 in the RTTOV v11 User’s Guide (http://nwpsaf.eu/deliverables/rtm/docs_rttov11/users_guide_11_v1.3.pdf)