Hi,
thanks already for these comments. Roy's suggested name sounds pretty to my
ears.
Trying to explain my "cell_methods" thing:
The instrument is sitting at a fixed spot on the seafloor, so unlike the echo
sounder on a ship, the distance does not change (well, there are tides, but we
filter them out). The remaining signal variance is variability in
environmental sound speed, which is mostly a measure of sea water temperature.
The data, although measured by an instrument at one spot, are dependent on the
vertical distance that the acoustic signal travels, i.e. represent some space
other than a single point. Chapter 7 of the CF document that I found online
explains it this way: "When gridded data does not represent the point values
of a field but instead represents some characteristic of the field within
cells of finite "volume," a complete description of the variable should
include metadata that describes the domain or extent of each cell..."
In my example, let us assume my IES sits at 4500m depth looking up. The
acoustic signal travel time (roundtrip) will be about 6 seconds (sound speed
is ca. 1500 m/s). My data will be numbers that are closer to 5.9 seconds if it
is warm (faster sound speed), and more like 6.1 seconds if it is cold.
If my instrument were instead sitting in the same body of water at 3000m depth
(let's assume there is a mountain nearby), all of my numbers would be
something close to 4 seconds. Now... I don't want the user to think I am still
in 4500m depth in outrageously hot water!
Bottom line: I need to tell the user what depth range I am covering (0-4500 or
0-3000), and in my limited understanding of the situation this is done via the
cell_methods and cell_bounds attributes.
Best wishes, Matthias
On Thursday, May 30, 2013 09:49:29 am Lowry, Roy K. wrote:
> Hi John,
>
> Not exactly. The travel time in both water column echosounding and
> seismics is a proxy for distance and therefore provides information on the
> vertical distribution of returned signal intensity.
>
> Cheers, Roy.
>
> ________________________________________
> From: John Graybeal [graybeal at marinemetadata.org]
> Sent: 30 May 2013 15:22
> To: Lowry, Roy K.
> Cc: mlankhorst at ucsd.edu; cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] standard_name for acoustic travel time from echo
> sounder
>
> +1 for Roy's choice.
>
> Can you explain the following for the acoustically naive? "I assume the
> data would need some additional description to denote the vertical extent
> of the measurement, such as cell_bounds and cell_methods='Z:sum'."
>
> John
>
> On May 30, 2013, at 06:45, "Lowry, Roy K." <rkl at bodc.ac.uk> wrote:
> > Dear All,
> >
> > Of Matthias's suggestions I have a strong preference for a slight
> > extension of roundtrip_acoustic_travel_time_in_sea_water, namely
> > acoustic_signal_roundtrip_travel_time_in_sea_water. 'two-way' is a
> > possible alternative to 'roundtrip' but I think the former carries
> > unfortunate seismic semantic implications, so 'roundtrip' is better for
> > IES. Including 'in_sea_water' is also essential to clearly distinguish
> > it from seismic data.
> >
> > Cheers, Roy.
> > ________________________________________
> > From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] On Behalf Of
> > Matthias Lankhorst [mlankhorst at ucsd.edu] Sent: 30 May 2013 13:16
> > To: cf-metadata at cgd.ucar.edu
> > Subject: [CF-metadata] standard_name for acoustic travel time from echo
> > sounder
> >
> > Dear CF,
> >
> > I have oceanographic data from IES instruments (inverted echo sounder)
> > that I would like to publish via OceanSITES in a CF-compliant form. The
> > data in question are acoustic travel times from the echo sounding
> > device. This means the time it took for the acoustic signal to run from
> > the instrument (which sits on the seafloor) to the sea surface and back
> > to the instrument. These data are commonly used as a proxy for ocean
> > heat content.
> >
> > I don't think there is a suitable CF standard_name out there, and ask for
> > your help in finding/creating one. Which of the following sound good?
> >
> > acoustic_travel_time
> > vertical_acoustic_travel_time
> > roundtrip_acoustic_travel_time_in_sea_water
> > echo_sounder_acoustic_travel_time
> >
> > ...I could think of a couple more combinations using the words above, but
> > would like to hear other people's opinions.
> >
> > The canonical units would obviously be seconds.
> >
> > I assume the data would need some additional description to denote the
> > vertical extent of the measurement, such as cell_bounds and
> > cell_methods='Z:sum'.
> >
> > Any comments?
> >
> > Kind regards, Matthias
> >
> >
--
_______________________________________
Dr. Matthias Lankhorst
Scripps Institution of Oceanography
9500 Gilman Drive, Mail Code 0230
La Jolla, CA 92093-0230
USA
Phone: +1 858 822 5013
Fax: +1 858 534 9820
E-Mail: mlankhorst at ucsd.edu
http://www-pord.ucsd.edu/~mlankhorst/
Received on Thu May 30 2013 - 16:12:10 BST
