I'm using a Promark XCM primarily for static work, and computing baselines to base stations whose sampling rate is set at 15 seconds (and out of my control). It seems to me that logging data at anything greater than 15 seconds on the Promark is simply logging redundant data. My Promark however won't accept a raw data sampling rate of greater than 3 seconds.

Can anyone comment on whether there is any advantage to logging this 'redundant' data, and if not, how do I change the Promark to log at 15 seconds? At present if I enter a value greater than 3 it responds with 'Reset data sampling rate' and won't proceed.

Secondly, has anyone had any experience of observing at night to decrease ionospheric effects? Does it significantly increase the length of baselines which can be successfully 'fixed'? We have had some problems with longer baselines and wonder whether night obs would improve this.

Many thanks.

Jon

I have no experience with the Promark XCM so I won't venture a guess. As far as redundant data, I figure the more you can store and analyze via software, the better.

As for night time gps'n, I have run several "yard sessions" to experiment with Locus units. For the most part, the data does seem cleaner. Faster lock, faster positions. I too would like expert opinion on the viability of "longer baselines" at night. But, not to make a pun (o.k. a pun intended), stretching L1 at night may just be a "shot in the dark".

J.D. Billings

First, I need to get Jon together with Angie at the office. She knows more about that ProMarkX than any of the rest of us and may be able to help. Since it is DGPS my first suggestion would be to just interpolate that base station data from 15 to 3 seconds and not fight what you can't change but Angie will know if there is a way to change it. Just so none of our readers get confused, the ProMarkX has been around longer than the ProMark2 and the X is intended for GIS and mapping work rather than surveying.

Now, J.D. I can tell you from my experience that working at night does make it easier to get those long lines with L1 to come together. What is in the manual is the official company policy but I can tell you as a long time user of Ashtech Dimensions (does anybody remember them?) I was able to measure some very long lines and that night time work was better than daytime work. For one project our work day started at 10PM and ended when we got ten sessions done. Ten sessions was all the Dimensions would hold.

How long is "very long"? Is 52 miles with L1 receivers long enough to suit you. I just wanted to see how well I could match the NGS on a line between two HARN stations 52 miles apart. My slope distance between their coordinates and ellipsoid height and my measured position was 0.052 meters.

Is that good enough to suit you?

I spent nearly three hours on that session to get those results.

Phil

Phillip and JD...Greetings from the UK...and thanks for the replies...they are very interesting and helpful.

Night obs...this is encouraging...I think our survey crews may be less than enthusiastic, but I think we may try some long baseline night observations and see how it turns out. 52 miles...wow, thats one heck of a baseline for L1!

We look like getting a couple of Promark2's in the next couple of weeks, it will be interesting to compare them with the X-CM.

As to the data sampling query, the only problem with observing at 3 secs instead of 15 secs is that you obviously log 5 times more data than is strictly necessary and it takes 5 times longer to download...now, if this improves accuracy so be it, but if not it would be nice to work out how to avoid it.

Thanks once again..

For those of you with ProMark X-CM units, here's a cool revelation.....Your data collected with firmware rev. 5.03 in the old promark cm is usable in the Ashtech Solutions software...Just convert to rinex using the converter on the Ashtech website and Solutions sucks it right in....You can get real cm level work AND , more importantly, get least squares adjustment analysis of your data instead of having to use Ray Hintz's Hector the Vector or Ron Sawyer's Starnet....Older versions of the Promark CP will have to be upgraded to the CM level model for this to work.....As to the data collection interval, I have not tried logging at 15 seconds yet since I figured out Solutions would process the stuff, so that will be my next trick.....b

Phillip

Thanks for the input. Like I said to Jon, I know nothing about the PM X. Some days I think I know less and less about everything. I was curious to hear experiences of longer L1 base lines at night. You are that experience, so now you are a target for a whole lot of questions (lol).

How do you determine at what time after local sundown that the ionosphere has settled to allow you maximum capability on those longer lines? Being a night person, and having many needs to get quality resuts of 20+ miles, I am very interested in your experiences. I know it's not the "manual". We have tried, and successfully done a few other things that aren't in the manual as well. And i would also think it's a "user beware" situation as far as the manufacturer is concerned when one steps out of bounds of the published specs and recommended procedures. But, if it can be made to work, and the results can be truly verified by the software, I want to use it. I'd lots rather spend 3 hours watching the lights blink at midnight to run a 20 mile beseline than have to deal with noisy data on two sessions of 1.5 hours during the day.
Tell us more....

Thanks

J.D.

P.S. I'm trying to learn all I can about solar influences on gps, so bear with me

J.D.,

I used to do this from 2 hrs. after susnet until 2 hrs. before sunrise. Take a pillow and an alarm clock.

Regards,
Brian

One should expect to, in general, get better answers at night on longer lines because the ionosphere is less noise at night and has less horizontal variability. To get a feel for the difference between night and day go the NGS web site
www.ngs.noaa.gov
then click on the research lab.

They have "movies" of the variation of the ionosphere during 24 hour periods.

OK, you were right. I shot off my mouth and said it could be done. Go with the flow guys. Listen to Mr. Geodesist. Read all you can and do experiments. There are two ways to know you have succeeded:

1. Measure something where you already know the answer.

2. Duplicate what you did before.

If you are going to push the envelope you have your work cut out for you but the rewards are in less moving around to get to where you want to go.

I visited with one of the guys at the NGS one day. I asked him how far I should go to pick up a bench mark to put some balance in my vertical positions. His answer was a question: How far do you need to go?

For most of my night time work I have started at 10 PM and worked until some time before noon when I saw the signal to noise ratios going to pot on me. That cut off time would vary with the day. In general terms I would work long lines in the middle of the night and try to be working on short stuff when the sun came up.

You would be amazed at what kinds of strange questions you can get asked when you are sitting there with your little flashlight in some of the loneliest country you ever saw in northwest Kansas or southeast Arkansas or even right there in beautiful downtown Lawton, Oklahoma, America.

One night I did not need my light on for a while and I sat there on my little camp stool on a levy on the west side of the Mississippi. After a while I felt like I had company. When I turned on my flashlight I saw more deer in one place than I have ever seen in my life. I think I was a bigger surprise to them than they were to me.

Have you ever had a deer stand there and bark at you like a dog?

Modified By Phillip Stevenson on 10/20/2001 at 4:42 AM

Can I have my Junior Geodesist Secret Decoder Ring now?

Static- No improvement if you log 3 secs, but the CORS logs 15-30..Set yours for the same..The rest of the data cannot be used..It's not in sync'..
Just makes your files bigger and longer to download...This goes for unit-unit static also..No reason to set the base for 1 sec and the rover for 10 sec..The software will only produces results for the common 'time tag', which in this case would be 10 secs..No static solution should 'interpolate' to determine the integer..


Sub-Meter- This is a little different beast..If your base and rover are both set to 5 second intervals then you can get more data quicker..Sub-meter software/hardware will interpolate between common 'time tags', which leads to some degradation in the final data solution.I've found (and this is through years of experience), that the best sub-meter is 'longer epoch sync'ing', such as 10 seconds or more..This take longer to get data, but seems to produce more consistent results...We use the Omnistar (John Chance) corrections and have seen much better results than using the coast guard beacons...Omnistar is calculating the correction from several different base stations at one time (much like OPUS) and providing a 'smoothed' correction for the rover...
TM

PS- Phil...It's in the mail...I had a spare.

two notes...tell local law enforcement what you're up to...don't wear aluminum foil on your head, no matter how much it helps...

three notes, i guess...if there are bootleggers or "experimental" farmers in your area, put up with what you get for data during hours of daylight and don't survey near them at night...

four notes, i guess...explain it to your wife...take her with you a couple of times...she'll soon lose her suspicious inclinations...

I tried takin' her with me one night. She bitched incessantly about the bad a.m. radio reception. Could barely keep up with the Rangers base ball game. At least they won that one anyway.

my wife has decided that going with me when i'm surveying is more aerobics than she normally wants in a week...we do hike sometimes, but only when the dog is with us...he drags me around and she can daisy-pick or whatever it is wimmins do when afield...

she tells her friends that one should not hike with men who walk for a living...

as far as night surveying goes, there's a HARN point at the SE corner of my place...she can see me from the porch and that's fine with her...

My solution was to just put Sharon to work. I bought her a GPS handheld, a GPS receiver, a fixed height tripod, and made her a copy of the map, SV chart, and the session list and gave her a kiss when we headed for our first set up. She's a better navigator than I am and has kept us in the field 'til the sun came up. "Come on, Phillip, just a couple of more sessions and we can go home tomorrow!" She calls me on the phone and wakes me up to ask me if I'm awake.

my wife turns into either a pumpkin or a witch if she's not asleep by 10pm...she has a lousy sense of direction...if i'm lucky, she'll bake some cookies for me and leave them on the counter top with a note telling me not to wake her up when i come home...

my wife insisted on going out with me this a.m. for an early session. I'm the night owl, she's the morning person, so it should have been pleasant. We were on the job site before sun rise and she sat in the truck shivering in the "severe" 40-50° East Texas fall weather for a couple of hours. Ever noticed how they want to talk about "us stuff" or something other than the project at hand. She's stayin home next time, but probably not bakin' cookies.

yeah, i get that a lot...gratefully, she has decided that home is where her heart is at when she's not at work...when we do preliminaries, i call it hiking, make sure i take her out to lunch, bring the dog and accidentally encounter monuments...