Dear Gabriele, the absolute value of dry air absorption is actually somewhat uncertain. Both in the model, due to perhaps missing continuum emission and probably in the measurement. You can add the N2 continuum (there is a model in ARTS). I don’t think it has a large effect at this low frequency, but just try it. This will increase the ARTS opacities slightly.
One other known issue is that right now ARTS does not check that the different input VMRs add up to one. That means, if you have a moist atmosphere, then ARTS does not automatically reduce the VMR of oxygen and nitrogen accordingly. We will add a method to do this at some point. If you want to make sure that this aspect is handled correctly in your simulations, then you should manually supply oxygen input profiles, where the standard oxygen VMR value is multiplied by (1-VMRH2O) at each altitude. This will reduce the ARTS opacities slightly. Finally, if you are actually doing stratospheric measurements, perhaps the PWR model is not the best to use. It is mostly intended to get the right total absorption in the troposphere, including the continuum part. You could try using “H2O, H2O-ForeignContCKDMT252, H2O-SelfContCKDMT252”, together with a HITRAN spectrocopy file, or one of the Perrin spectroscopy files that come with arts-xml-data. Then you can set the lineshape yourself; VoigtKunz6 should be a good one. It depends a bit on in which way the simulation deviates from the measurement which of my suggestions I would recommend you to follow. If the difference is an offset everywhere, then the first part of this mail is relevant. If it is a deviation close to the line center, then the last part is relevant. Best wishes, Stefan > On 26 Jul 2016, at 14:22, Gabriele Mevi <gabriele.m...@ingv.it> wrote: > > Thank you for your answer. I'm simulating the optical depth of some > radiosonde profiles and comparing them with my spectrometer measures. The > results of the simulation is higly correlated with the measures but there is > a bias of 0.02 between them that I don't understand. I'll try to check again > all the parameter of the simulation but they seem all correct. > Best wishes > Gabriele > > 2016-07-26 13:55 GMT+02:00 Stefan Buehler <stefan.bueh...@uni-hamburg.de>: > Dear Gabriele, > > I think at that frequency you should be fine with only H2O and O2. If the > simulation looks very different from your real measurements there likely is > some other bug in your setup. Possibilities, from the top of my head: Looking > angle; units (radiance or brightness temperature); bugs in the input > profiles, for example wrong unit for water vapor concentration. I would start > by simulating a larger part of the spectrum, then see if you find the right > spectral lines where you expect them to be, and if you are in a reasonable > range of brightness temperatures. > > Best wishes, > > Stefan > >> On 25 Jul 2016, at 20:00, Gabriele Mevi <gabriele.m...@ingv.it> wrote: >> >> Hi everybody >> I'm a PHD student and I'm simulating the emission of atmosphere at 22.23 GHz >> to built a forward model for a water vapour retrieval. In my simulation I >> assume a clear sky condition. I'm actually using the "H2O-PWR98" model for >> water vapour and "O2-PWR98" for oxygen but the results I obtained do not >> match the measures of a 22.23 GHz spectrometer. Which other chemical species >> and models should I include in the simulation? >> Thank you for the help >> Gabriele >> _______________________________________________ >> arts_users.mi mailing list >> arts_users.mi@lists.uni-hamburg.de >> https://mailman.rrz.uni-hamburg.de/mailman/listinfo/arts_users.mi > > _______________________________________________ arts_users.mi mailing list arts_users.mi@lists.uni-hamburg.de https://mailman.rrz.uni-hamburg.de/mailman/listinfo/arts_users.mi
