Hi Ole Martin
answers below
Regards
René
On 22.06.2011 15:10, Ole Martin Christensen wrote:
> The error analysis in Qpack to should now be consistent so that if the
> calculations are preformed in logrel or rel the errors(all of them)
> should come out relative units. To convert to vmr the qp2_rel2vmr is used.
>
> Im not sure about the error quantities in Qp1. But it very well might be
> as you suggest that the observation error comes out in absolute units in
> Qp1. What are the values for smoothing and observation error in Qp1 and
> Qp2 before and after converting?
>
>
One example of the errors at surface altitude (xa= 0.0101 in vmr units),
all values are as delivered by Qpack1/2:
Qp1: e_obs = 3.5972e-05, e_smo = 0.0902
Qp2: eo = 0.0034, es = 0.0908
Qp2(converted) eo = 3.4277e-05, es = 9.6232e-04
> You write that your apriori profile is a vector of ones for the vmr
> case, wouldn't this imply a huge amount of water (1 000 000 ppm?). Could
> you attach your two Q-files with your response so I can have a look at them?
>
I didn't do testings for the 'vmr' case, I just had a look on the Qpack1
routines. The error calculations are done in qpcls.m L776ff. unitfac
comes from qp_x2X.m, where it is defined as ones(length (profile)) for
the absolute (unit='vmr') case, resp. xa for the 'logrel' case.
In summary, the (unitfac*unitfac') correction term doesn't do anything
in 'vmr' cases, as it then is just ones(length (profile),length (profile))
> Regarding the averaging kernels, they should be converted, even though
> it means that their peak is at the wrong height. The reason for this
> comes from the definition of the averaging kernel(see attached file).
> This means that the averaging kernels for retrieving the relative change
> from xa and the absolute vmr ARE different. If you try and run the
> inversion with the same settings converted into vmr(can be a bit tricky
> depending on your inversion settings) you will see that the averaging
> kernels will look like the converted ones.
>
>
In my case, it is a retrieval of tropospheric water vapour (nonlinear
with Marquartd-Levenberg iteration). Due to the large tropospheric H2O
gradient an absolute ('vmr') retrieval doesn't make sense. Earlier
tests showed tremendous oscillations with negative xret values.
> Ill also fix the documentation.
>
> Regards
>
> Ole Martin
>
>
>
>
> On 22/06/11 14:10, 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"
>>
>>
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--
René Bleisch
Institute of Applied Physics
University of Bern
Sidlerstr.5
3012 Bern
Switzerland
Phone: +41 31 631 89 59
Mail: [email protected]
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