Hi Stuart, All the differences between current 2.5 version and old version that I can think of are:
The Doppler broadening is computed on shifted frequencies instead of on unshifted frequencies. This should be more accurate as far as I am concerned. The normalization factor is computed on the unshifted frequencies instead of on the shifted frequencies. If I have not misunderstood the normalization factors, this should also be closer to the physics since you shouldn't really be scaling the line strengths with the line frequency but by the atmospheric frequency (as in the new LM code). This is potentially an issue. The line shape can no longer be a speed-up Voigt function but you have to use the full calculations. The old code was wrong at a scale of 1e-6 if I understand the old comments. The new code does the mirroring inline unless manually added to the catalog. Before you had to manually add a new line with negative line center. It is possible there's a bug here, since I haven't tested this so accurately before. This changes the cutoff frequency since the old code cutoff at CUTOFF - F0 instead at F0 + CUTOFF for the inline mirrored lines. (Thinking about it practically, this makes the line shape non-symmetric, so I will have to add a check to the lbl-check that there's no cutoff used when mirrored lines are there by inline instead of by copy-pasta.) I would think that the difference in cutoff here is the main difference you are seeing. I think that's about it. There's of course entire different algorithm involved, so some additional differences may be from there. With hope, //Richard Den ons 9 juni 2021 kl 17:21 skrev Fox, Stuart <stuart....@metoffice.gov.uk >: > Hello all, > > > > Thanks for all the work on the line cutoff behaviour in the latest version > of ARTS! However,I’m still struggling to reproduce the absorption line > behaviour between v2.3.1277 and v2.5 even after the latest work on the line > cutoff from Richard. In fact, even without a line cutoff there still seems > to be differences caused by (i) the interaction between a line > normalization factor (e.g. VVH) and the line pressure shift, and (ii) the > treatment of mirror lines. > > > > A simple example of (i) using only a single water vapour line with a > Lorentz profile and VVH pre-factor can be found here, with differences up > to about 0.08K: > > https://github.com/stuartfox/arts-cutoff-problem/tree/single-line > > > > For (ii), if I set the normalization to None but add the mirror lines > (with the SameAsLineShape option) I get differences of 0.001K in this test, > but much larger values in a more realistic case with more lines (0.5-0.6K > below 100GHz). > > > > I’ve no idea which version is more correct, but it would be nice to > understand the causes of these variations! > > > > Thanks for all your help, > > > > Stuart > > > > >
