Hi Patrick, - Sensor/backend: removing the sensor/backend part lead to no improvements, the differences are still the same - Forward model: For the same example a-priori vmr, Arts1 delivers a spectrum with 43.1 K at the center frequency of 22.235 GHz, Arts2 a spectrum with only 39.7 K (Rayleigh-Jeans BT) resp. 40.2 K (Planck BT) at 22.235 GHz using the settings from the retrievals, the deviation slightly increases with frequency. Thus choosing Planck or RJ matters, but the difference is small (only 0.5 K in the example).
Hence the problem obviously seems to be in the Forward modelling and not in the retrieval itself. I will now carefully go through the entire forward model setup for both versions (which should be the same). Regards, René PS: During the tests with no sensor/backend part, I discovered that Qpack2 ends with an error, if y is chosen in L2_EXTRA and the sensor/backend are disabled. Qpack2 then crashes because qp2_l2 takes L2.f from Q.SENSOR_RESPONSE_F (line 137). But as the backend is disabled, neither this variable (containing the name of the xml-file with the sensor-response frequency grid) nor the xml-file itself are created during the processing. On 15.06.2011 14:47, Patrick Eriksson wrote: > 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 >> >> > -- René Bleisch Institute of Applied Physics University of Bern Sidlerstr.5 3012 Bern Switzerland Phone: +41 31 631 89 59 Mail: [email protected] _______________________________________________ qpack mailing list [email protected] https://www.sat.ltu.se/mailman/listinfo/qpack
