Hi, thanks Richard for your feedback. I'm not sure, though, whether I really understand it (incl. wondering why you talk about jacobians here...). *scratches head*
we're trying to pin down where the wind is blowing in a 1D atm setup. 1D allows us to have vertical (w) and horizontal (v) winds that affect the signal. let's forget about the vertical, that one is clear. for the horizontal, there is two possible wind directions in a 1D case - a head wind (aka blowing in the observer's face) and a tail wind (aka blowing from the observer's back). which of these corresponds to a positive, which to a negative wind(_v) speed. starting from your "For the 'absolute' wind speed option, a positive retrieved sign is equivalent to a red-shift" and equating a red-shift with observer moving away from source (or source from observer...), a positive wind should mean a tail wind. which actually seems indeed in agreement with info I dig from the ARTS documentation (not that easy to find and combine for a beginner...): wind_v doc says positive v-winds are winds blowing south to north (which alone isn't very helpful for 1D setups - there is no north in 1D...); sensor_los doc says for the 2D case (allowing positive and negative zenith angles - in order to distinguish two possible viewing directions) that positive angles are equivalent to viewing towards higher latitudes, ie towards north. assuming this is valid for 1D, too (ie in 1D the observer always looks towards north) means for the 1D case positive winds (blowing to north) equate tail winds (for an observer looking north), negative winds are head winds. to confirm this, Rita, you could have a look where the line peak moves (prefereably in a high-spectral resolution simulation) for positive and negative winds, respectively. for positive it should move to lower freqs, for negative to higher. best wishes, Jana On Wed, Apr 3, 2019 at 12:03 PM Richard Larsson <ric.lars...@gmail.com> wrote: > Hi Rita, > > For the directional components, the sign of a retrieved component with the > ARTS Jacobian is positive along the axes themselves. The direction the > sensor is looking only influences the scale of the Jacobian, not the sign > of the direction of the retrieval calculation. If you look parallel or > anti-parallel to the field, the values inside the Jacobian switch signs > accordingly to work on the external field. As an example, you should be > able to make measurements at several different directions and, if you > assume the field is uniform, retrieve just one field without any > transformation on the components themselves inside the calculations. > > For the 'absolute' wind speed option, a positive retrieved sign is > equivalent to a red-shift, or a Doppler shift below unity if you wish. > This is much messier to work with during ARTS iterations, so make sure your > signal is easy to interpret if you use it. This is of course closer to the > physics of what is going on with the signal itself, since all we really can > see of the wind is how much it is blue- or red-shifting the signal. > > With hope, > //Richard > > Ps. Oliver, please sent another email when it is fixed. > > > > Den ons 3 apr. 2019 kl 13:36 skrev Oliver Lemke < > oliver.le...@uni-hamburg.de>: > >> Hi all, >> >> Sorry if you received the mail below already. We're currently >> investigating a mail delivery problem to Gmail adresses. If you've already >> received the mail from Rita yesterday please disregard this mail. >> >> Cheers, >> Oliver >> >> >> > From: Rita Edit Kajtar <rita.edit.kaj...@ltu.se> >> > Subject: Wind calculations >> > Date: 2 April 2019 at 10:36:54 CEST >> > To: "arts_users.mi@lists.uni-hamburg.de" < >> arts_users.mi@lists.uni-hamburg.de> >> > >> > >> > Hello! >> > >> > >> > I have a short question regarding wind calculations. >> > >> > What is the general convention assumed for determining the sign of the >> wind speeds having the measuring instrument as the reference point? Are the >> winds blowing towards the instrument considered positive and those blowing >> away from the instrument negative or the other way around? >> > >> > The ARTS documentation provides information for how the sign should be >> considered regarding the four cardinal directions, but not relative to a >> measuring device. >> > >> > >> > Best regards, >> > Rita Kajtar >> >> >> _______________________________________________ >> arts_users.mi mailing list >> arts_users.mi@lists.uni-hamburg.de >> https://mailman.rrz.uni-hamburg.de/mailman/listinfo/arts_users.mi >> > _______________________________________________ > arts_users.mi mailing list > arts_users.mi@lists.uni-hamburg.de > https://mailman.rrz.uni-hamburg.de/mailman/listinfo/arts_users.mi > -- ===================================================================== Jana Mendrok, Ph.D. (Geoscience) Email: jana.mend...@gmail.com Phone : +46 (0)708 860 729 =====================================================================
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