Hi René, My answer is in line with the one of Stefan. The first step is to check if you get the same spectrum from the two forward models, for the same input. That is, no inversions involved. First test without sensor. And if OK, include also the sensor.
Looking a bit on the retrieval part. The logrel unit is the most tricky one. If the tests above are all OK, please compare weighting functions for rel/frac. Just ask if anything is unclear. I want of course to know if there is a bug soemwhere. That can happen even in ARTS/Qpack ;-) Bye, Patrick On 06/15/2011 12:47 PM, Rene Bleisch wrote: > Hi all, > I use Qpack to retrieve tropospheric water vapour profiles from spectra > of our 22GHz radiometer MIAWARA. The setup is like this: > - nonlinear Marquardt-Levenberg > - polyfit (1st grade, coefficients are part of the state vector and are > retrieved) > > Till recently, I used the old Qpack1 and it worked well. Some months ago > I started trying to setup the same retrieval with QPack2. As it didn' > work well and I had a lack of time, I gave it then up. Now I retried it > and it works quite well with QPack2 after setting the retrieval unit to > logrel (implicitly the Qpack1-retrieval was set to logrel, what I only > discovered thanks to Patriks suggestions). > > Still the results with QPack2 differ from the results with QPack1, as > the vmr is generally up to 20% too low in upper troposphere and 10-20% > too high in lower troposphere. More detailed analyses revealed that > there is a difference between the weighting functions in Qpack1 and > Qpack2 (even in the first iteration step), the tropospherical maxima of > the weighting functions in Qpack2 are generally up to 10% lower than in > Qpack1. > > Does anyone have an idea where this difference could come from? > (spectroscopy and pTz setup are identical) > > Maybe it has to do something with the sensor/backend-part, which should > in principle be the same for both. In Qpack1 the H-matrix (y=H*F(x,b)) > summarizes the entire sensor/backend stuff. I wanted to compare H with > its equivalent in QPack2, but I could not find it. Does there exist a > similar H-matrix in Arts2/QPack2? > > Regards > René > > _______________________________________________ qpack mailing list [email protected] https://www.sat.ltu.se/mailman/listinfo/qpack
