About the draft itself Re: WD-SIA-2.0

[Douglas Tody]

Yes, wavelength is a lousy unit for high energy.  But since we have
to pick one unit for the entire EM spectrum it is a reasonable choice.
For discovery purposes of HE data probably the main usage is merely to
check for a wavelength smaller than some upper limit, to find or exclude
HE data, for which it will work ok (this is all rather pointless, I just
don't like people bashing the poor defenseless meter and feel I need to
stick up for it).  - Doug


On Tue, 6 May 2014, François Bonnarel wrote:

> Le 06/05/2014 19:37, Douglas Tody a écrit :
>>> PS-Yes, wavelength in meters - no one's first choice :-)
>> 
>> Wavelength in meters is actually quite a natural unit for radio
>> telescopes, which predominantly observe in the centimeter, millimeter,
>> and sometimes meter wavelength ranges, although it is true that
>> frequency is more commonly used to describe the radio bands.  O/IR and
>> UV predominantly use angstroms, microns, and nanometers, all of which
>> are wavelength measures.  (But I am sure this will always be a topic
>> for heated discussion :-)
>
> and Xray observers use Kev , Mev gamma ray use GeV and Tev. That's pretty 
> small in meters.
> I encountered the problem once in discussing with Hess/CTA group
>
> Regards
> François
>> 
>> 
>> 
>> On Mon, 5 May 2014, Patrick Dowler wrote:
>> 
>>> 
>>> 
>>> On 14/04/14 01:00 PM, Arnold Rots wrote:
>>>> And what is "barycentric wavelength"? Conversion from frequency to
>>>> wavelength as applied at the gravitational potential at the barycenter?
>>>> Or does it mean to reduce the spectral coordinate to the barycenter only
>>>> dynamically? That's pretty inconvenient for people who are doing
>>>> Galactic work.
>>> 
>>> The intent here is that the BAND parameter only supports one unit (m) and 
>>> one reference position/time/scale/hard-to-remember thing.
>>> 
>>> Since we have to pick one, can you tell me the one most suitable that 
>>> would apply to BAND and TIME parameters. Note that the draft currently 
>>> just refers to the same restricted time metadata as DALI uses for literal 
>>> values (time scale UTC and unknown reference position). What should we use 
>>> for wavelength values in the BAND parameter, knowing that implementers 
>>> will actually just query the wavelength(s) they have in files, filter 
>>> lookup tables, or spectral wcs already.
>>> 
>>> PS-Yes, wavelength in meters - no one's first choice :-)
>>> 
>>> -- 
>>> 
>>> Patrick Dowler
>>> Canadian Astronomy Data Centre
>>> National Research Council Canada
>>> 5071 West Saanich Road
>>> Victoria, BC V9E 2E7
>>> 
>>> 250-363-0044 (office) 250-363-0045 (fax)
>>> 
>