bug: cam-fv and cam-se can't assimilate radiance obs

🐛 cam assimilations can't handle radiance obs

Describe the bug

both cam models (se and fv) on the current main branch cannot assimilate radiance obs if the default setting for 'no_assim_above_model_level' is used.

the interpolation routine rejects locations called from the rttov forward operator code which is contructing columns of values for various fields.

(there may be other reasons radiance obs fail, i.e. if the cam state doesn't include enough variables for what rttov needs.)

Error Message

all radiance obs fail with QC=4.

Which model(s) are you working with?

cam-se and cam-fv

Version of DART

main branch

Have you modified the DART code?

Yes - i pushed a branch no_assim_high_cam_obs with the minor changes needed in both cam model_mods. this fix requires the rest of the QC=8 issues to be addressed but it is a separate issue once those are fixed.

this change results in the high obs returning with a QC of 8 (failed vertical convert) which is a non-zero QC code so the observation is not assimilated. that means the namelist item is still correctly named. it should be documented somewhere why these obs fail the vert convert (because they're too high, not because of any other reason.) note that the test for high obs moved from interpolate to the obs vertical conversion routine, not get_close.

i realize everyone is working on AGU and AMS right now, plus it is the holiday season, so i don't expect this to be addressed for a while. but i had already made these changes and i didn't want to lose them or this issue in the meantime.

this code change is an offshoot from discussion #436 but that discussion has wound around many other issues. this is addressing one facet of those issues.

Build information

any, but i built it with gfortran on my laptop.

Start with the cam-se and cam-fv model_mods and the no_assim_high_cam_obs branch, then reproduce radiance assimilation using the default no_assim_above_model_level setting. Trace the interpolation routine, RTTOV forward operator, and observation vertical-conversion path; done means valid radiance observations no longer all receive QC=4, while overly high observations receive QC=8 with the failure documented.