Hi Matthias and all -
Are cell methods the right way to document this? The 'sum' cell method
indicates
that you've summed a number of measurements, and I don't think that's
the case
here.
I'd have thought that providing the the instrument depth and orientation
(upward)
would make it more clear.
This isn't a feature I use routinely, so I could easily be missing
something.
Cheers - Nan
On 5/30/13 6:12 PM, Matthias Lankhorst wrote:
> 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
>>>
>>>
--
*******************************************************
* Nan Galbraith Information Systems Specialist *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 (508) 289-2444 *
*******************************************************
Received on Fri Jun 07 2013 - 13:57:12 BST
