Stuart, I am also seeing the problem but I have no time to investigate in detail. As a temporary solution, there exists another lineshape called "Mirrored Lorentz" that you can use. Testing your controlfile with it instead, the results are more reasonable. Simply change your
abs_lines_per_speciesAddMirrorLines to abs_lineshapeDefine(shape="Mirrored Lorentz", forefactor="VVW", cutoff=750e9) and you will see the results. (Or just the original "Lorentz" lineshape-call in your main controlfile.) With hope, //Richard Ps. You are running an old version of arts. The controlfile was not working without changing the order of calls around. I attach an updated version. I also recommend that you set ARTS_DATA_PATH to your arts-xml-data path because this makes life easier (export ARTS_DATA_PATH="PATH-TO-DATA" should do the trick). I might have time to look at the details over the weekend and will get back to you later but I hope the temporary solution is good for now. 2017-10-13 14:31 GMT+02:00 Fox, Stuart <stuart....@metoffice.gov.uk>: > Hi all, > > > > I wasn’t sure whether to ask this on arts-user or arts-dev - I’m not sure > whether there’s a bug in ARTS or something wrong with my inputs! > > > > I’m trying to do some clear sky brightness temperature simulations for > Earth using water vapour lines from HITRAN-2016. However, I am getting huge > (over 20K) differences in brightness temperature for a nadir viewing > geometry depending on whether I include the mirror (negative frequency) > lines or not. I don’t get the same thing using HITRAN-2012. > > > > Attached is a fairly minimal example controlfile, and extracts of H2O > lines from the two versions of HITRAN. To see the difference then compare > the two output files depending on which of the line sets is used. (The path > to the data from arts-xml-data will need to be changed according to your > setup). For HITRAN 2012 the numbers are pretty much the same. For HITRAN > 2016 they are very different. > > > > I’ve done some digging and isolated the main cause of the issue to the > lowest frequency H2O-162 line in HITRAN-2016 (at 21764932Hz). It seems to > be a combination of the mirror of this line, the pressure shift and the VVW > forefactor that causes the difference. My guess is that the pressure shift > (at the highest pressures in the profile) is pushing the mirror line to a > frequency very close to zero, possibly causing numerical issues in the > forefactor/lineshape. (I also wonder if the pressure shift is being added > in the wrong direction for the mirror lines?) > > > > Does anyone who knows the ARTS internals better than me fancy digging > around to understand what is happening, or perhaps tell me that I’m doing > something wrong! > > > > Cheers, > > > > Stuart > > > > _______________________________________________ > arts_dev.mi mailing list > arts_dev.mi@lists.uni-hamburg.de > https://mailman.rrz.uni-hamburg.de/mailman/listinfo/arts_dev.mi > >
hitran_2012_2016_example.arts
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