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,

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
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