Hi again, My more careful statements for logrel turned out to be motivated. My comment on "conservative" triggered Ole-Martin to check what I had done. And I had been too quick again. The mapping shall use the retrieved VMR, and not the VMR of the a priori.
Please note that the error estimate after a conversion from logrel to VMR is dependent on the retrieved state. If the retrieved state is too high (due to errors), the error is over-estimated and vice versa. I don't see a solution to this problem now. The warning is still valid, be careful if you use qp2_rel2vmr for logrel data. Right now I just wanted to fix this bug before leaving for the mid-summer weekend (very important here in Sweden!). Bye, Patrick Hi René and all, Sorry, but I don't have time to dig into this now. And will not have before July 4. Until then I leave the detailed answers from our side to Ole-Martin. We have discussed the conversions and we should have the same view on these matters. I will here just point out some basic things.. Qpack1: The idea here is that the retrieval and its diagnostic are in VMR, independent of the retrieval unit. However, there could be mistakes here. And as I remember it, A is not converted which is incorrect. Qpack2: After more recent changes, the retrieval and diagnostic follow the selected retrieval unit, which is clearly a much better approach than the one for Qpack1. After the recent bug fixes, I think this now works. Regarding qp2rel2vmr: The conversion from rel to VMR should be OK. And yes, A shall be converted and this can change this drastically. %/% and VMR/VMR are different things, especially if you have strong gradients in the VMR profile, as for H2O in the troposphere. The conversion from logrel to VMR is less certain. I selected here the most simple expression for converting the errors (see header text). It is OK for small errors, but you could argue that this should be done differently for large errors. One advantage of the selected expression is that it gives a conservative estimate of the error range. And the conversion of A is done for rel. Ole-Martin, do you agree on this point? My advice is to first focus on Qpack2, as the implementation here is much more clean. And when we are sure that all is OK in Qpack2, we should check if there is any disagreement with Qpack1. If yes, I will try to fix it. Bye, Patrick On 2011-06-22 2:10 PM, Rene Bleisch wrote: > Hi Patrick, > I'm a bit confused with the error characterisations when comparing > QPack1 to Qpack2. For the unit='vmr' case, all is clear and consistent. > The use of unit= 'logrel' in Qpack2 resp. "Q.CLS_SPECIES_POS_ON = 1" in > Qpack1 (not x is retrieved but log(x/xa)) as in my retrieval case, leads > to inconsistencies in error calculation between Qpack1 and Qpack2 and in > QPack1 itself. > > Error calculation: > Qp1: S_obs = (unitfac*unitfac') .* (Dy * Se * Dy'); %unitfac: in my > case the a-priori-profile, for the 'vmr' case a vector of ones > A = A - eye(nx,nx); > S_smo = A * Sx * A'; > > Qp2 : So = G * Se * G'; > AI = A - eye(size(A,1)); > Ss = AI * Sx * AI'; > > => eo = sqrt(diag(S_obs)) resp. sqrt(diag(So)) and es = > sqrt(diag(S_smo)) resp. sqrt(diag(Ss)) > => es (Qp1)~ es (Qp2) but eo(Qp1)<<eo(Qp2) > > Up to now, I assumed eo and es being relative to x for both versions. > > The difference of the observation error obviously comes from the > application of unitfac in Qpack1. > > In the QPack2 doc it is suggested to convert the L2 data of Qpack2 from > logrel to vmr with qp2_rel2vmr* (this includes errors and AVK), thus > the converted errors are also in absolute values. Surprisingly the > converted observation error is similar to the one of Qpack1. Does this > mean, that the observation error of Qpack1 in reality is given in > absolute values??. This would be inconsistent as at least es (Qpack1) > seems to be relative. > > Further I'm not sure if it makes sense to also convert the averaging > kernel vom logrel to vmr, as in my case the converted AVK is completely > useless for me. E.g. the maxima are in the stratosphere (whereas the > unconverted AVK is similar to the AVK from Qpack1 with maxima in the > troposphere). Thus I tend to convert only x and xa by an own function. > > Regards > René > > > * in the doc, sect. 6.4.3 a function called "qp2_rel2logrel" is > mentioned, but I think it should be "qp2_rel2vmr" > _______________________________________________ qpack mailing list [email protected] https://www.sat.ltu.se/mailman/listinfo/qpack
