Dear everybody,
I already sent a message a while ago for a proper pencil beam simulation with
ARTS but I am still confused thus I need some help.
We are trying to compare ARTS with a new fast radiative transfer model for
ground-based microwave radiometers and we would like to start the comparison
with pencil beam calculation but I would be interested in also knowing how the
band-averaged brightness temperatures (BT) are computed with ARTS and if I am
doing that properly.
I am using Qpack for simulations of band-averaged BT but for pencil beam
computation I use arts_y since your advice last time.
I) Questions about band-averaged BT
In our fast radiative transfer model, the band-averaged BTs are computed from
three frequencies only: central frequency (cf), cf-df/2 and cf+df/2 with df
the spectral bandwidth of each channel.
To do that in Qpack, I normally declare Q.SENSOR_RESPONSE.F_BACKEND = central
frequencies of the 14 channels of the MWR
and for each of the 14 channel I declare the
Q.SENSOR_RESPONSE.BACKEND_CHANNEL_RESPONSE as:
{df(i)/2*[-1 1]}
where df corresponds to the spectral band of channel i. Thus for me it seems
that I am doing an averaging of the BT over 2 frequencies: the central
frequency minus the spectral band
divided by 2 and the central frequency plus the spectral band divided by 2.
Am I right ?
If I want to mimic the fast radiative transfer model by averaging over 3
frequencies, should I just add one value to the vector defining the
BACKEND_CHANNEL_RESPONSE ?
like this:
{-df(i)/2*1 0 df(i)/2*1]}
Here I put a zero to consider the central frequency TB also in the averaging.
Could you explain to me what is the role of Q.F_GRID in qpack ? I am confused
because we already define the frequency grid we want to simulate and the
frequency averaging in Q.SENSOR_RESPONSE.F_BACKEND and
Q.SENSOR_RESPONSE.BACKEND_CHANNEL_RESPONSE. Thus why do we need another vector
defining again a frequency grid ?
II) Pencil beam calculations
To do the pencil beam calculations I do not use Qpack but arts_y, this time I
define my 14 frequency grid in Q_F.GRID and I switched Q.SENSOR_DO to false.
Could you just confirm that with this configuration, pencil beam calculations
means no modelling of the antenna beam-width ?
Thank you very much for your kind help
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
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