Now that the Promark2's have been around for a while . . .

I have noticed that my MAP330 receives sats that my other hand-helds receive in woods, AND, gets a much better lock than my Promark Xcm's.

I wonder if the Promark2 users have noticed a lot of good lock in places(like trees) that one wouldn't really expect.

What type of trees are you dealing with John?

Shawn

Well, basically Oaks(pin) and Maples(sugar).

I don't really expect much in heavy foilage, but hell, this is Ohio. That means there is about as much time of the year with no leaves(and low moisture) as opposed to the time with leaves.

Anyway, my question comes about because I take my MAP330 into HEAVY woods and always get a good lock(5-7 sats). I don't know if that kind of lock autonomously relates to that kind of lock for differential.

If it does, well then I'd park my butt in the back of a property for an hour or two(to attempt resolution of multi-path).

I've had so-so results with my Promark Xcm's, but sometimes they'd work pretty good, even though they'll drops sats on a dare.

Reason I ask it that conifers seem to be more adverse than the hardwood trees. I have suspected that this is because pine needles grow to varying lengths and that somewhere in that variety of lengths the needles match the quarter or half wavelength of the GPS signal. It could just be that the clusters of needles are more dense.

As to your question, you can absolutely get good results under tree canopy with the promark2. Thales likely won't say it because you have to work outside the box. First you want to be as far away from tree trunks as possible since they obstruct signal reception. Second you have to forget about your normal processing times. Experiment a little, but we have found that 2 hours seems to do nicely. Third, use mission planning and wait until those sv's are stacked. Fourth, keep an eye on the solar weather. This actually winds up explaining many seemingly mysterious loose solutions.

Basically, because you are pushing the system in one very important aspect (signal multipath/obstruction) you need to give it every possible boost in the other areas of importance.

The PM2 does seem to do a great job of tracking the sv's under canopy but remember, it is receiving bounced signals.

Shawn

What do you mean by 'lock'?

A handheld can be receiving and using satellites and even applying WAAS corrections, but this does not tell you if the solution isn't being degraded by the vegetation.

I find that the statistics are less reliable under canopy and the positions are much worse.

A good test is to take a few positions and go back an hour later and do a few more, or do a series every 10 minutes on the same point. I find that instead of being spread error of about 2 meters that one often finds in the clear, it gets to be more like 10 under canopy. Of course that will vary.

Point being this same degradation will affect static sessions also and possibly even the ability to get fixed solutions.

- jlw

and redundancy should be considered when repeating redundant measurements for additional verification of vaildated data

i.e., a second session in those canopy conditions is warranted

jd

Set up a short baseline. Even 20 feet is long enough. Do it where you have a nice clear view of the sky.

Measure that baseline with your GPS gear just to get something for comparison.

Measure it again with a large dry sponge set on top of each GPS antenna. You might have to tie it on to keep it from blowing off.

Measure it once more but this time with the sponges soaking wet. Keep them wet for the duration of the session.

Compare raw data and residual plots from each session. Use the repeat vectors tab to compare the vectors.

Water in trees is like the water in the sponge.

Brings new meaning to "soaking up all this stuff" huh.
Modified By Dave Huff on 10/8/2003 at 11:33 PM