Hi Pauline and all, Nice that you are so careful!
First I should clarify one thing. Y.F is in fact not used by qpack itself. But it should be good practice to set Y.F and run qp2_check_f as part every retrieval. I had a similar problem some days ago. I tracked that down, and found that it was due to that f_grid could was stored as float in arts_oem_init. This gave a difference of 3 kHz, and this caused a difference of 5 K for limb sounding of the 118 GHz O2 line! I fixed this problem in v2.3 and this made me remember to do it for v2.2 as well. But I don't think this your problem (but maybe update atmlab anyhow). But there are some possible pitfalls here. As Ole Martin wrote, qpack takes data from Y. Note that some HSE settings are taken from Y. Do you have exactly the same values in the Q sent to arts_y? Also note that qpack uses the ATMDATA fields, but not arts_y. For example, if T.ATMDATA is set, qpack overwrites Q.T_FIELD. I hope these things are mentioned in the qpack pdf, but things can always be explained clearer ... Bye, Patrick On 09/04/15 17:45, Pauline Martinet wrote: > Hi everybody, > > I have noticed differences between the forward model calculations when I > call Qpack or the function arts_y. > I am simulating a microwave radiometer between 22 and 60 GHz. > I have a matlab routine where I define the structures Q and O. > Then I call the two functions: > TB=arts_y(Q); > and L2=qpack2(Q,O,Y); > with Y.Y=[] : from what I read in the Qpack documentation it should give > the same results. > > But then I do not obtain the same values of brightness temperatures when > simulating the brightness temperature with Qpack or arts_y: > > This is from Qpack: > > 37.6242 > 36.7163 > 32.3708 > 24.4462 > 22.0529 > 19.4580 > 18.6558 > 110.6579 > 152.7556 > 250.9260 > 279.8277 > 284.9573 > 285.2151 > 285.3064 > > This is from arts_y: > 37.5430 > 36.6337 > 32.2927 > 24.3829 > 21.9958 > 19.4087 > 18.6113 > 110.5074 > 152.5850 > 250.8197 > 279.7959 > 284.9563 > 285.2181 > 285.3116 > > For the call to arts-y I had to define: Q.T_FIELD, Q.Z_FIELD, Q.VMR_FIELD > > but I normally use the same values as the ones defined in Q.ABS_SPECIES > and Q.T for Qpack. > > Do you have any idea on what I am doing wrong ? > > Thank you very much. > > Best regards, > > Pauline > > ----- Météo-France ----- > Dr. Pauline Martinet > Chercheur CNRM/GMEI/LISA > [email protected] > Fixe : +33 561079031 > Site web: www.sites.google.com/site/martinetpauline31 > <https://www.sites.google.com/site/martinetpauline31/> > > > > _______________________________________________ > qpack mailing list > [email protected] > https://www.sat.ltu.se/mailman/listinfo/qpack > _______________________________________________ qpack mailing list [email protected] https://www.sat.ltu.se/mailman/listinfo/qpack
