REQ: Help with GPS devices to store coordinates for sampling points in remote areas

[Bob Marshall]

My main interest is water quality monitoring of streams and rivers,
especially sediments. However, I was wondering if anyone has been using
GPS (Global Positioning Systems) devices, like a "MAGELLAN GPS Tracker", to
locate their sampling points in remote locations?

What level of success can these devices be used for reproducing coordinates
for returning to the same sampling point on several different occasions?
Awhile back I had heard there were limitations with processing a decent
signal through forest canopy or rough terrain, and these conditions are
pretty normal for streambanks in our area. Do these factors still affect
the performance of newer devices with 12 channel receivers? Also some
models will display elevations. What degree of accuracy is realistic?

If anyone has experience monitoring water quality with more professional
systems like Trimble's "GPS Pathfinder Pro XR/XRS", I would be interested
in learning about your use of these instruments as well.

Please share your comments, successes, failures, pitfalls, recommendations,
etc... .

Thank you, Bob M.

[Michael Hagen]

You might try posting this on sci.geo.satelite-nav too.
I've been using a Trimble geoexplorer for quite some time and it works
adequately. Flag your sample point and you will be within sight distance
(by GPS standards) when you return. Otherwise practice lower tech field
navigation skills: map and compass.
Mike H

[Kimikaze]

Bob Marshall <ma...@intrepid.net> wrote in message
news:01be4f9e$651a44c0$99a3bed1@cloverleaf-01...

>My main interest is water quality monitoring of streams and rivers,
>especially sediments. However, I was wondering if anyone has been using
>GPS (Global Positioning Systems) devices, like a "MAGELLAN GPS Tracker", to
>locate their sampling points in remote locations?

>If anyone has experience monitoring water quality with more professional

>systems like Trimble's "GPS Pathfinder Pro XR/XRS", I would be interested
>in learning about your use of these instruments as well.
>
>Please share your comments, successes, failures, pitfalls, recommendations,
>etc... .
>Thank you, Bob M.

I have some experience with GPS during fieldwork (see below).

I think GPS can be a useful tool but a single station will not give you more
accurate results than approx. 30 meters. For accurate results (differential
correction) you need a basestation (satellite antenna+station+PC), a handset
(with a memory) and a good postprocessing software package.
Maybe for other purposes a lesser degree of positional accuracy is needed
and a handset alone will do.

My Story...
During my study in Physical Geography I used a Trimble GPS system during
fieldwork in the French Allier river.
We did some profiling and bank-mapping using simple theodolites. It was
necessary to map our field data in standardized coordinates (so-called
georeferencing), in order to be able to calculate bank erosion /
sedimentation using geo-referenced aerophoto's. Additionally, by using
georeferenced data, future users would be able to calculate differences
comparing our data with theirs.

Since there were no accurate maps of the present channel forms (the Allier
is a dynamic mixed sand-gravel river with a highly variable bed-topography)
we couldn't link our measured positions to e.g. standard coordinates of
French topographic maps. That's where the GPS came in.....

We used a system with a basestation (located at a fixed position) and a
handset.
The basestation continuously (during fieldhours) measured its known position
(every 3 seconds), yielding the errors of the GPS-satellite at any given
time.
The handset ('Rover') was used to measure some key positions of our
measurement areas, using a tripod, and measuring a single position for five
minutes (every 3 seconds).
The handset was operational within a radius of 50 km around the basestation
wich fitted our needs because
we visited 6 research-areas along an 80-kilometer-long stretch of the river.

'Back at the office' we postprocessed (using differential correction) the
data of both basestation and handset and we were able to determine the
coordinates of our key postions with an accuracy of 10-20 centimetres.
Converting the GPS positions to our French topo-coordinates was a piece of
cake using a built-in function in the processing software (Pathfinder
Office).

Kimikaze
please remove ".ditniet" from my email adress before replying

[Bob Marshall]

Appreciated everyone's input on GPS devices. The suggestion to post in
(sci.geo.satelite-nav) looks like a good one, although I've already picked
up a good deal from reading the other messages in that news group.

My project's not as ambitious as contending with French Geography and the
Allier River, but the story was interesting reading and very appropriate
for the reasons I'd like to work out a sound GPS strategy. As for variable
topography, I've had to do follow-up work on sites where "permanent"
monuments were placed less than two years ago only find an empty sand bar
or similar.

Again, thanks for your thoughtful responses.
Bob M.

Bob Marshall <ma...@intrepid.net> wrote in article
<01be4f9e$651a44c0$99a3bed1@cloverleaf-01>...

> My main interest is water quality monitoring of streams and rivers,
> especially sediments. However, I was wondering if anyone has been using
> GPS (Global Positioning Systems) devices, like a "MAGELLAN GPS Tracker",
to
> locate their sampling points in remote locations?
>

> <SNIP>

[Rob Blomquist]

In article <01be4f9e$651a44c0$99a3bed1@cloverleaf-01>,
ma...@intrepid.net says...

> If anyone has experience monitoring water quality with more professional
> systems like Trimble's "GPS Pathfinder Pro XR/XRS", I would be interested
> in learning about your use of these instruments as well.

I manage GPS equipment for King County Water and Land Resources,
Seattle, Washington (splash.metrokc.gov).

In the PNW streamside vegetation is the most difficult problem
that we have to encounter. Forests don't have to be that dense
to block GPS signals from getting to the receiver.

I recently upgraded all our equipment to Trimble Pro XR, and it
works far better than our GeoExplorer II, and far better than
Pro XL, but it is not the Cat's Meow.

I also got 2 Lasertech Impulse 200 XR lasers, and Mapstar
digital compasses for 2 of our units. They can extend our
mappable area under canopies that we could not home to map with
GPS.

If you wish to contact me further about this, try my work email:
rob.bl...@metrokc.gov.
--
Rob Blomquist aka TriDog
Seattle, WA
tri...@jps.net
http://www2.jps.net/~robbo

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