Hi, yes you have defined the data argument correct, just make sure Q.SENSOR_RESPONSE.SENSOR_NORM = true
also the center frequency is superfluous, but no problem if you leave it there. Ole Martin ________________________________ From: [email protected] [[email protected]] on behalf of Pauline Martinet [[email protected]] Sent: Monday, July 27, 2015 10:02 AM To: Ole Martin Christensen Cc: [email protected]; ARTS Users Subject: Re: [arts-users] pencil beam calculation/band width averaging Dear Ole Martin, Thank you very much for your answer. I think I managed to run qpack with a band-averaged TB over 3 frequencies but I want to know what means the variable: Q.SENSOR_RESPONSE.BACKEND_CHANNEL_RESPONSE.data ? I have defined the grid argument as a cell array with 3 frequencies: grids = { df(i)/2*[-1 0 1]}; to have : -the central frequency of the receiver minus the spectral bandwith divided by 2 - the central frequency of the receiver - the central frequency of the receiver plus the spectral bandwith divided by 2 Thus I defined the data argument as: Q.SENSOR_RESPONSE.BACKEND_CHANNEL_RESPONSE.data=[1 1 1] Is it correct ? When this data vector is used in the computation of the averaged TB ? Thank you very much again. 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/> ________________________________ De: "Ole Martin Christensen" <[email protected]> À: "Pauline Martinet" <[email protected]>, "ARTS Users" <[email protected]>, [email protected] Envoyé: Mardi 21 Juillet 2015 14:45:53 Objet: RE: pencil beam calculation/band width averaging The answers are embedded in the text below. ________________________________ From: [email protected] [[email protected]] on behalf of Pauline Martinet [[email protected]] Sent: Tuesday, July 21, 2015 2:28 PM To: ARTS Users; [email protected] Subject: [arts-users] pencil beam calculation/band width averaging 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 ? => Jupp, just make sure that Q.SENSOR_RESPONSE.SENSOR_NORM = true so that your backend response is normalized to have a unit area. 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. => Jupp, just make sure that when you define your backend channel response two values are needed a vector containing frequencies and another the response at these frequencies. The example given in qpack2_demo2.m in the demo folder shows you how to do this. 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 ? => The radiative transfer model calculations are done on the grid specified by Q.F_GRID, and thereafter it is interpolated onto the grid of each channel (F_BACKEND / BACKEND_CHANNEL_RESPONSE). 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 ? => Jupp 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 <https://www.sites.google.com/site/martinetpauline31/>
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