GPS Discussion

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GPS Discussion

Andrew Mercer-2
I would like to start a discussion on the relative merits of different dGPS receivers and their associated software.
During discussions with colleagues it has become apparent that dGPS is a common source of frustration and irritation. Expensive cable and cable port breakages are frequent and the post processing software and the survey control software seem to lack user friendliness that might encourage a more positive view of GPS work. The cold conditions inevitable on glaciers and ice sheets are not conducive good battery performance.

Here in Stockholm we have used Trimble products for several years and the above problems have applied to all the units.

It should be noted that this discussion is about geodetic GPS (kinematic and static) and not about the small, handheld "Garmin" type units.


Andrew Mercer

Room X433
Department of Physical Geography & Quaternary Geology
Stockholm University
SE-10691
Stockholm

Telephone: 08 164959
e-mail: [hidden email]
Skype: andrewpmercer
AIM: mercergeoinfo

http://people.su.se/~anme4406/






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Re: GPS Discussion

Matt King
Hi Andrew

Your email poses some useful questions, although I suspect the answer to many of them is that there is no perfect solution.

1. Hardware: others are much more aware of the weaknesses and strengths of various hardware packages out there, so I'll leave them to comment. It may be that what is required is some best practice advice.

2. Hardware user interface: again, I'll defer to others.

3. Software for data analysis: yes, you are definitely right in this regard. Commercial software is not well tuned for many glaciological applications, except may be in the case of very short (<5km) baselines.

Commercial software presumes that motion is either nothing (static) or could be anything up to 1000m/s, so there is information lost as we know glacier motion is normally quite steady (or at least <1m/epoch). That's why I've found that the best analysis is done in scientific software, typically making use of a Kalman Filter at the data analysis stage. This allows some constraints to be placed on the site motion, but also allows control over all sorts of data editing and analysis options. This has an unfortunate overhead as it requires training, but several courses have been run in Europe and the US and these have been well attended by glaciologists who are now publishing work based on their own analysis. Software of interest includes Track (within the GAMIT/GLOBK package which you can google). Others are making use of free online access points to "scientific" software. Several of these can process kinematic positions (see http://gge.unb.ca/Resources/PPP/Purpose.html for a sum
 mary). I urge caution, though, especially when interpreting small signal, as it's not always clear what models (ie, ocean tide loading) etc have been applied. Never treat it as a black box delivering perfect results.

One can get all sorts of spurious signals by processing glacier data as "static" as I've shown in a few papers I can forward on if interested. Unless the glacier is moving at tectonic rates, then I'd strongly recommend *never* using static processing. The one strong point of commercial software is single frequency GPS analysis, where no widely available (and hence viable) scientific solution exists as far as I know, but baseline lengths here are very limited.

PS, your use of "dGPS" is, in my opinion, ambiguous as in many sectors it refers to differential pseudorange positioning (ie, decimetres to metres accuracy). I'd recommend use of the phrase differential carrier phase positioning.
cheers

Matt King
[hidden email]


----------------------------------------------------------------------

Message: 1
Date: Sat, 27 Nov 2010 18:06:38 +0100
From: Andrew Mercer <[hidden email]>
To: [hidden email]
Subject: [CRYOLIST] GPS Discussion
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=us-ascii

I would like to start a discussion on the relative merits of different dGPS receivers and their associated software.
During discussions with colleagues it has become apparent that dGPS is a common source of frustration and irritation. Expensive cable and cable port breakages are frequent and the post processing software and the survey control software seem to lack user friendliness that might encourage a more positive view of GPS work. The cold conditions inevitable on glaciers and ice sheets are not conducive good battery performance.

Here in Stockholm we have used Trimble products for several years and the above problems have applied to all the units.

It should be noted that this discussion is about geodetic GPS (kinematic and static) and not about the small, handheld "Garmin" type units.


Andrew Mercer

Room X433
Department of Physical Geography & Quaternary Geology
Stockholm University
SE-10691
Stockholm

Telephone: 08 164959
e-mail: [hidden email]
Skype: andrewpmercer
AIM: mercergeoinfo

http://people.su.se/~anme4406/








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Re: GPS Discussion

Bjorn Johns
Andrew,
UNAVCO manages a pool of nearly 300 survey grade GPS systems (Trimble
5700, R7, NetRS, NetR9) that are applied to a variety of polar research
applications. I agree with you - it is a special challenge taking
commercial GPS survey receivers and deploying them in the polar regions
and not ending up with frustrated users.  Custom add-ons and training
are often necessary to make things work smoothly. Equipment obsolescence
often introduces a new set of complications. Commercial survey software
can be excellent for some applications and lacking for others. As a
facility we try to keep up with these challenges to support a broad user
base. Individual users often settle into their own project-specific best
practices. For an overview of UNAVCO's polar-specific support, see
www.unavco.org/polar. Let me know if I can provide further, or specific,
information.
Best,
Bjorn

Bjorn Johns
Polar Services Manager, UNAVCO
[hidden email]
+1 (303) 381-7470  (720) 320-7531 cell


On 11/29/10 3:18 AM, Matt King wrote:

> Hi Andrew
>
> Your email poses some useful questions, although I suspect the answer to many of them is that there is no perfect solution.
>
> 1. Hardware: others are much more aware of the weaknesses and strengths of various hardware packages out there, so I'll leave them to comment. It may be that what is required is some best practice advice.
>
> 2. Hardware user interface: again, I'll defer to others.
>
> 3. Software for data analysis: yes, you are definitely right in this regard. Commercial software is not well tuned for many glaciological applications, except may be in the case of very short (<5km) baselines.
>
> Commercial software presumes that motion is either nothing (static) or could be anything up to 1000m/s, so there is information lost as we know glacier motion is normally quite steady (or at least<1m/epoch). That's why I've found that the best analysis is done in scientific software, typically making use of a Kalman Filter at the data analysis stage. This allows some constraints to be placed on the site motion, but also allows control over all sorts of data editing and analysis options. This has an unfortunate overhead as it requires training, but several courses have been run in Europe and the US and these have been well attended by glaciologists who are now publishing work based on their own analysis. Software of interest includes Track (within the GAMIT/GLOBK package which you can google). Others are making use of free online access points to "scientific" software. Several of these can process kinematic positions (see http://gge.unb.ca/Resources/PPP/Purpose.html for a su
 m

>   mary). I urge caution, though, especially when interpreting small signal, as it's not always clear what models (ie, ocean tide loading) etc have been applied. Never treat it as a black box delivering perfect results.
>
> One can get all sorts of spurious signals by processing glacier data as "static" as I've shown in a few papers I can forward on if interested. Unless the glacier is moving at tectonic rates, then I'd strongly recommend *never* using static processing. The one strong point of commercial software is single frequency GPS analysis, where no widely available (and hence viable) scientific solution exists as far as I know, but baseline lengths here are very limited.
>
> PS, your use of "dGPS" is, in my opinion, ambiguous as in many sectors it refers to differential pseudorange positioning (ie, decimetres to metres accuracy). I'd recommend use of the phrase differential carrier phase positioning.
> cheers
>
> Matt King
> [hidden email]
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 27 Nov 2010 18:06:38 +0100
> From: Andrew Mercer<[hidden email]>
> To: [hidden email]
> Subject: [CRYOLIST] GPS Discussion
> Message-ID:<[hidden email]>
> Content-Type: text/plain; charset=us-ascii
>
> I would like to start a discussion on the relative merits of different dGPS receivers and their associated software.
> During discussions with colleagues it has become apparent that dGPS is a common source of frustration and irritation. Expensive cable and cable port breakages are frequent and the post processing software and the survey control software seem to lack user friendliness that might encourage a more positive view of GPS work. The cold conditions inevitable on glaciers and ice sheets are not conducive good battery performance.
>
> Here in Stockholm we have used Trimble products for several years and the above problems have applied to all the units.
>
> It should be noted that this discussion is about geodetic GPS (kinematic and static) and not about the small, handheld "Garmin" type units.
>
>
> Andrew Mercer
>
> Room X433
> Department of Physical Geography&  Quaternary Geology
> Stockholm University
> SE-10691
> Stockholm
>
> Telephone: 08 164959
> e-mail: [hidden email]
> Skype: andrewpmercer
> AIM: mercergeoinfo
>
> http://people.su.se/~anme4406/
>
>
>
>
>
>
>
>
> ------------------------------
>
> _______________________________________________
> You're subscribed to the CRYOLIST mailing list
> To change your subscription options, visit http://cryolist.org/member
> To send a message to the list, email [hidden email]
>
> End of CRYOLIST Digest, Vol 9, Issue 22
> ***************************************
> _______________________________________________
> You're subscribed to the CRYOLIST mailing list
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> To send a message to the list, email [hidden email]
>
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Re: GPS Discussion

Andrew Mercer
In reply to this post by Andrew Mercer-2
To recap the discussion: user interfaces seem to be the greatest hurdle,
something that is not unique to GPS. There has been little feedback on
component failure, perhaps Stockholm has been unlucky (or careless).
The user interface issue is not really anything we can affect directly
as discussion so far with various retailers and manufacturers has
resulted in much listening and no action. We have our own guides and
cheat sheets to help the less tech savvy glaciologist but these always
need improving.

Andrew Mercer

Stockholm University
INK
tel: +46 (0)8 164959



On 11/27/2010 06:06 PM, Andrew Mercer wrote:

> I would like to start a discussion on the relative merits of different dGPS receivers and their associated software.
> During discussions with colleagues it has become apparent that dGPS is a common source of frustration and irritation. Expensive cable and cable port breakages are frequent and the post processing software and the survey control software seem to lack user friendliness that might encourage a more positive view of GPS work. The cold conditions inevitable on glaciers and ice sheets are not conducive good battery performance.
>
> Here in Stockholm we have used Trimble products for several years and the above problems have applied to all the units.
>
> It should be noted that this discussion is about geodetic GPS (kinematic and static) and not about the small, handheld "Garmin" type units.
>
>
> Andrew Mercer
>
> Room X433
> Department of Physical Geography&  Quaternary Geology
> Stockholm University
> SE-10691
> Stockholm
>
> Telephone: 08 164959
> e-mail: [hidden email]
> Skype: andrewpmercer
> AIM: mercergeoinfo
>
> http://people.su.se/~anme4406/
>
>
>
>
>
>
> _______________________________________________
> You're subscribed to the CRYOLIST mailing list
> To change your subscription options, visit http://cryolist.org/
> To send a message to the list, email [hidden email]
_______________________________________________
You're subscribed to the CRYOLIST mailing list
To change your subscription options, visit http://cryolist.org/
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