Dear Gabriele,
This sounds strange. y_aux should indeed contain optical depth. You
don't mix up elevation angle and zenith angle?
However, if you perform a pure transmission measurement it makes more
sense to use
Q.IY_MAIN_AGENDA = { 'iy_main_agenda__Transmission' };
But you then need to also include this setting
Q.IY_TRANSMITTER_AGENDA = { 'iy_transmitter_agenda__UnitUnpolIntensity' };
With these settings y should include atmospheric transmissions.
Bye,
Patrick
On 2017-02-16 19:35, Gabriele Mevi wrote:
Hi all
I'm actually using the atmlab 2.0 code for ARTS and I'm having some
issues in the simulation of atmospheric optical depth.
I work on an instrument that can estimate the optical depth of the
atmosphere at 22.23 GHz, measuring the spectrum of the water vapour
emission line at this frequency.
I should test the instrument simulating with ARTS the optical depth of
some known atmospheric profiles. I used in the calculation as absorbing
species O2, N2 and water vapour. The spectroscopic parameters are
described by the model O2-PWR98 for O2, N2-SelfContStandardType for N2
and by HITRAN 2012 database for water vapour.
The atmlab commands I used are:
Q.IY_MAIN_AGENDA = {'iy_main_agenda__Emission'};
Q.IY_AUX_VARS=['Optical depth'];
The y_aux variable should contain the results of the calculation,
however the values are closer to 1 (about 0.97), not realistic for
optical depth. I don’t know if these values are related to the
transmittance, so the optical depth tau is
tau=-ln(y_aux).
Although this last operation produces realistic values for tau they are
lower of about 20% respect to my measurements.
I should ask if I'm doing something wrong and some suggestions to how
correctly calculate the optical depth.
Best Regards
Gabriele
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