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Collecting Static data in the rain
Posted by jimmy-cleveland on February 20, 2018 at 7:50 pmI have a small topo project that I need to set some control for. It is a very small (1/2 mile) road project where we are building a road between two existing roads. Pretty simple for the most part. My plan is to set two pairs of control points on each end of the job, and start out on one pair, and traverse trough to the second pair, and adjust.
It is supposed to rain the next three days. No thunderstorms that I am aware of, but rain. I have (4) receivers available to collect static. I have an NGS benchmark within about a mile or so from the site. It is both a horizontal and vertical point.
I have read on here before about using shower caps on the GPS heads when it is raining. I have some very thin garbage bags here at the office that I am thinking would work well, and should really cover the receivers. Has anyone done this, and does it affect the quality of the data you are collecting? It would be a great use of time for the guys since we cannot work in the field with total stations and digital levels.
Any advice is greatly appreciated.
Thanks!
Jimmy
(@mark-silver), (@lrday),
(@john-hamilton)john-hamilton replied 6 years, 2 months ago 13 Members · 15 Replies- 15 Replies
I think I read somewhere, probably here, a similar question and someone pointed out that satellite GNSS signals are microwave, so anything that heats up in your microwave oven, like vegetables (leaves on trees), is going to block GNSS. Plastic doesn’t heat up, but water does. Presumably the covers on the receivers is for added protection. We don’t cover ours, but we do pack up if there is lightning around.
Thunderstorms or not, I would think that rain would hinder positional accuracy from satellite signals. I am not a meteorologist nor a physicist, but it would seem to me that rain would act as a conductor for energy on the ground to energy in the clouds. Maybe not enough to cause a lightning strike, but possibly enough to interfere with a GPS/GNSS signal.
I can’t wrap my head around the shower cap thing. My receivers are all submersible to 1-meter. I would be more concerned about optical plummets and wooden tripods. No real harm. Just a pain to dry out.In regard to lightning, we pack up in fear of a fry-up, not because of signal concerns (or maybe we should be concerned).
I personally don’t think that the rain makes any appreciable difference from a processing standpoint. If it did, I would be able to take a CORS site like St George (SGU1) where it rains three times a year and see the elevation jump when it rains. (I see the elevations jump, but I have never been able to correlate it with weather, BP, temperature or actually anything short of a crow building a nest on the antenna.)
Gavin might have additional information because he runs several check receivers in his network and it is rumored to rain a lot in his area.
I suspect that if there is a rain bias, it is worse for RTK than for static.
Depending on the receiver there are varying chances of getting water in them. All of the (CHC and iG) receivers that we currently sell and have sold are submersible, even with the battery door removed. It is better if you don’t do that because the battery connectors will plate, but water won’t get into the head’s main electronics.
The Ashtech receivers absolutely were not waterproof (like PM500 / PM800) and I personally always put a plastic bag on the top with the bottom wide open. At one semi-permanent site, I actually used a large plastic ice-cream pail upside down with the wire handle duct-taped to the mount. There are some other receivers (I won’t name them because I don’t want to get sued) that are currently sold that absolutely are not waterproof and have horrible battery doors. One would be crazy to not bag them.
I have customers who coat the domes with RAIN-X so that water does not pool on top. I don’t think that would hurt anything, I am not sure if it is needed.
UNAVCO prefers to have modeled choke-ring antenna without domes, however if I walk outside here this morning and look at my un-domed choke-ring here at the office or at home there is over 1′ of snow sitting on rings that are nearly full of ice-rings (literally rings of ice, right?.) But even with 1′ of snow on top, I can’t see that any RTK results change. However, I prefer to deploy choke-rings in this area with domes (assuming there are robotic type-mean IGS calibrations for the antenna with the dome.)
So, I guess my general opinion is ‘no need to worry about it.’ But, if Gavin (@gschrock) says otherwise, then I agree with him.
Don’t turn the receiver upside down and you should be good. We’ve never covered ours during light rain but don’t stick around if there is the slightest chance of lightning.
T. Nelson – SAM, LLCFor the small area you’re describing I wouldn’t expect there to be a significant enough difference in the tropospheric delay to create a perceptible error in the data. As all have said, avoid lightning, otherwise go for it. As far as plastic bags, I wouldn’t do it; every receiver I’ve ever used was water resistant enough to survive a heavy rainfall as long as the ports and battery door were either downward facing or securely covered. We know a little bit about rain here in South Louisiana, and I’ve never had a problem from it unless it was sunny at the base and storming at the rover, or vice versa, but that would be more with RTK than static, and on longer baselines. I have had people describe noticeable problems with VRS when conditions varied between the CORS stations as well as the rover, but even that was several years and a lot of software revisions ago.
I do tell all of our field personnel to keep the instrument cases closed and dry, and not to put the receivers back in them until they’re thoroughly dried.
I would have answered you sooner but I was out in the rain surveying. A fairly heavy mix of rain and snow today, in fact. As I’ve said before, we work in the rain in the PNW all winter long and don’t really give it a thought. Just dry it thoroughly at the end of the day and leave it in the open in a well ventilated heated room overnight.
The very first GPS job I did in 1986 was during a thunderstorm. This was when we had LARGE macrometer antennas (3′ by 3′ if I recall correctly) sitting on tripods with the thick cable running into the vehicle to the (also LARGE) receiver, and a generator sitting outside the vehicle to power it. No cell phones back then, so of course I was wondering if I should bring it in or not. I did. And someone was killed nearby at a little league game.
I never worry about rain, but lightning is another story.
Quick story-I was processing data for a client, and one station had a lot of cycle slips, very noisy, would not process. I asked him what was wrong with that station, he said it was wide open, on a highway overpass. Then he called back and said the office guy they recruited to run that receiver held an umbrella over it because he was worried about the rain ruining the receiver.
I bought a couple of inline lightning bypass or arrester gizmos, with the intention of installing in the radio antenna cable, the theory being that lightning would hit the highest part of the base setup, i.e. the external radio antenna, travel down, hit the bypass, and go to ground, thus saving the day for all the equipment. Ran out of minerals to install it. But I can see it would be wise, to cover the case that you can’t get back to the base in time to pack it up.
Raindrops on antennae are not a real problem because they are small, random and not fixed in any one location. A plastic bag over an antenna could actually cause more problems because it could create locations where raindrops would puddle and essentially remain fixed for the duration of the observation. I have not covered an antenna in the last 15 years, but receivers are much more susceptible to rain damage.
Snow, ice, birds and squirrels require much greater attention if you must observe.
Lightning storms should be associated with the possibility of rapid local atmospheric changes and cause you to pay attention.
Paul in PA
I’ve never had rain to interfere with the collecting of static data.
A thunderstorm cell will disrupt reception and the receiver may be interrupted or it may end collection of data from the unit(s) affected.
I’ve never had issues with rain and static, RTK I sure have, it’s dangerous sometimes even if there isn’t visible electrical disturbances. Had a radio ruined during a rain storm, lightning didn’t hit it, but the static electricity build-up fried it.
For stand alone static receivers it usually isn’t an issue but it wouldn’t surprise me to see one get damaged. I’ve never seen processing issues from rain, snow is a different issue, it can really mess up an antenna getting signals. Probably best to use wooden legs and take any external antennas off.
For a 1/2 mile job, I would static each control point, I don’t mean 4 hours for OPUS, but 10 minute sessions on points with 4 receivers would walk through that job really quickly. Is there too much canopy to do that?
In the 25 years I’ve been using GNSS I’ve never worried about or been affected by rain during observations. And like Gavin and Mr. OK, I live in the Pacific North Wet. If I recall correctly, neither NGS or USACE GPS instructions discourage observations taken in rain.
As for the hardware, every receiver I have used has been physically capable of operating in wet conditions. Just dry it off when you get back to the office. I would propose that the plastic bag will add more error into you fix than the rain. Antennas specs are significantly different with and without a ray-dome.
So go ahead and embrace the liquid sunshine. Just pack it in when you hear thunder in the distant.
This post kind of makes me want to be surveying somewhere that rain would keep me from working outside.
We have used shower caps for the last 20 years here in Alaska to protect GPS units and controllers.
Don??t use them unless it??s a downpour or on base station when it??s raining and blowing over 20 mph.
We also use large chains around the tripod legs to keep them from blowing over.
If we couldn??t do static in the rain we would have to stop using GPS for surveying.
We have had many more issues with total stations. It used to be normal for us to push the bad weather until the equipment stopped or numbers started running down the screen. Standard equipment for the truck and office is rubbing alcohol to pour over electronics to displace water and dry quicker.
A recent addition to our rain gear is CorrosionX to repel water.
The only problem I have had with a receiver in the rain is with an old R8. These have a hole on the bottom labeled “VENT”. This has a “membrane” that is supposed to not let water through. Apparently the membrane developed a small hole, and let water in. Ruined the board inside. I note that my newer R10 does not this vent.
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