ISO Spectral access and QUANTITY discussion

[David Berry]

Pedro,


>  --------------------------------------------
>  Use of dimensional equation for the metadata
>  --------------------------------------------
>
>  Our data fluxes, in the case of LWS, are given in "w/cm^2/um", whereas
>  the data for SWS are given in Jy.
>
>  We thus need a way to convert from one to the other. Let's try
>  to convert the LWS spectrum units (w/cm^2/s) to the SWS spectrum units
>  (in Jy) and then display both in the same browse tool.
>
>  According to our server, the SWS flux (in Jy) dimensional equation is:
>
>  [SWS] = MT-2
>
>  and the LWS (w/cm^2/um) dimensional equation is:
>
>  [LWS] = MLT-3
>
>
>  So, to represent one with respect to the other, we will have to divide
>  both dimensional equations:
>
>  [SWS]     MT-2
>  ----- = ------- = LT
>  [LWS]   ML-1T-3
>
>
>  as the only quantities we can use in the transformation are those
> coming from the conversion between "wavelength" and "frequency", to go
> from one to the other we will have to use a combination of "LAMBDA" and
> "c" (wavelength and light velocity).

I can see this works nicely for the case of this spectral axis
transformation. How would it work in the case of an arbitrary Quantity?
In the above, because of your knowledge of the problem, you knew that the
dimensional inequality between SWS and LSW needed to be balanced by some
combination of "LAMBDA" and "c". I am wondering how this would work in the
general case. If you know the MLT dimensions of 2 quantities, what would
the general algorithm be for determining what other values needed to be
used to equate the dimensions?

David

----------------------------------------------------------------------
Dr David S. Berry    (dsb at ast.man.ac.uk)

STARLINK project		 |	Centre for Astrophysics
(http://www.starlink.ac.uk/)	 |	University of Central Lancashire
Rutherford Appleton Laboratory	 |	PRESTON
DIDCOT				 |	United Kingdom
United Kingdom			 |	PR1 2HE
OX11 0QX