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GPS Receiver Noise Can Be Used To Detect Snow Depth

timothy posted more than 4 years ago | from the for-the-journal-of-sensors-and-transducers dept.

Earth 51

cremeglace writes "Scientists at the University of Colorado at Boulder have found a use for GPS besides finding restaurants or the occasional road-that-doesn't-exist: it can be used to measure snow depth. The new technique, which takes advantage of distortions of the GPS signal after it reflects off the snowpack, may potentially improve weather forecasts by allowing meteorologists to track snowfall patterns. ScienceNOW has the story, which one geophysicist describes as 'a classical case of one person's noise becoming another person's signal.'"

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It's... (3, Funny)

SunSaw (700981) | more than 4 years ago | (#29596767)

snow joke!

But you have to have the... (2, Funny)

hawk16zz (960734) | more than 4 years ago | (#29597821)

snow how!

Re:But you have to have the... (2, Funny)

Kratisto (1080113) | more than 4 years ago | (#29598383)

It's ice to see another impending pun thread on Slashdot.

Simpler tool (3, Funny)

rossdee (243626) | more than 4 years ago | (#29596913)

There already exists a tool for measuring snow depth. Its called a ruler. There are imperial (yardstick) and metric varieties.

Another useful thing is a shovel, you can dig yourself out, and cut a path to the part of the road that has been plowed.

A cellphone is very useful too, you can call work and tell them you are stuck in a snowdrift and won't be in today. Don't forget to get out of the car before calling though, since in some places its illegal to use a cellphone in a car.

Re:Simpler tool (1)

Icegryphon (715550) | more than 4 years ago | (#29596963)

There already exists a tool for measuring snow depth. Its called a ruler. There are imperial (yardstick) and metric varieties.

But how what will I use my $250 GPS depth gauge with?
Is it going to sit in the corner with my $250 Bedazzler? [slashdot.org]

Re:Simpler tool (0, Offtopic)

drseuk (824707) | more than 4 years ago | (#29596965)

iPhones reflect off snow quite well when they explode (I'm told).

Re:Simpler tool (1)

Ingcuervo (1349561) | more than 4 years ago | (#29596973)

A cellphone is very useful too, you can call work and tell them you are stuck in a snowdrift and won't be in today. Don't forget to get out of the car before calling though, since in some places its illegal to use a cellphone in a car.

and this is a clear case of hearing bells and not knowing where!!

Re:Simpler tool (4, Informative)

Thornburg (264444) | more than 4 years ago | (#29597019)

TFA is talking about using an existing network of 1100 GPS receivers currently tracking plate tectonics to also track snowfall, without any additional equipment and without interfering with their current operation.

This not about using your Garmin to find out how much snow is in your front yard.

Re:Simpler tool (0, Redundant)

oodaloop (1229816) | more than 4 years ago | (#29597461)

Now why would you ruin a perfectly argument by reading TFA? You're not new here, are you?

Re:Simpler tool (0)

Anonymous Coward | more than 4 years ago | (#29597559)

Pro-tip: You don't get to make "you must be new here" comments if your uid is over 1,000,000.

Re:Simpler tool (4, Funny)

Anonymous Coward | more than 4 years ago | (#29597713)

Pro-tip: You don't get to decide who gets to do what based on their uid if you are posting anonymously.
* Note irony in this response.

Re:Simpler tool (1)

adamziegler (1082701) | more than 4 years ago | (#29598821)

Pro-tip: You don't get to make ironic posts if you plan to point out that your post was ironic.

Re:Simpler tool (0)

Anonymous Coward | more than 4 years ago | (#29597931)

And why not? I fail to see how it makes the joke less funny.

Re:Simpler tool (0)

Anonymous Coward | more than 4 years ago | (#29598083)

If I had signed up when I first started reading /., I would have been at ~450,000.

Unfortunately I just signed up recently, so I'm "officially" new here. Ain't that a bitch.

Here's the white paper [tinyurl.com] .

Yeah, made that argument about being new myself... (1)

autocracy (192714) | more than 4 years ago | (#29598159)

Thankfully there's enough unwashed masses behind me that I'm starting to look good by comparison.

Re:Yeah, made that argument about being new myself (1)

dgatwood (11270) | more than 4 years ago | (#29598311)

Eh, sonny?

Re:Yeah, made that argument about being new myself (1)

RockDoctor (15477) | more than 4 years ago | (#29603481)

Eh, sonny?

Speak up, Boy!
And Speak English while you're at it.

Re:Simpler tool (0)

Anonymous Coward | more than 4 years ago | (#29597033)

Of course, and here's how to use it: Mount the ruler where snow will fall. Then mount your cellphone with the camera pointing to the ruler, and install an app to periodically take photos and send them to a flickr stream.

A classical case? (2, Insightful)

roothog (635998) | more than 4 years ago | (#29597001)

Seems like a pretty modern example, unless, say, the Romans had GPS.

Re:A classical case? (1)

vertinox (846076) | more than 4 years ago | (#29599271)

Seems like a pretty modern example, unless, say, the Romans had GPS.

They did, but the clay tablets kept breaking when the trebuchet launched slaves returned from low earth orbit

This must be a ... (2, Funny)

CannonballHead (842625) | more than 4 years ago | (#29597011)

snow news day.

Re:This must be a ... (0)

Anonymous Coward | more than 4 years ago | (#29597107)

hey, i thought it was funny.

Re:This must be a ... (1)

ChefInnocent (667809) | more than 4 years ago | (#29597297)

I thought it was funny too, but we're getting our first snow [weather.gov] of the season today.

Re:This must be a ... (-1, Troll)

Anonymous Coward | more than 4 years ago | (#29597901)

Who modded this offtopic? I think you're a dumbass.

Re:This must be a ... (1)

CannonballHead (842625) | more than 4 years ago | (#29598671)

Humor is off topic on a geek site, you know. ;)

Re:This must be a ... (0)

Anonymous Coward | more than 4 years ago | (#29598989)

I suppose it does decrease one's efficiency.

So, we've discovered (3, Insightful)

idontgno (624372) | more than 4 years ago | (#29597051)

satellite radar altimetry. [altimetry.info]

Of course, it's accidental radar altimetry, rather than a dedicated instrument. Neat hack.

Re:So, we've discovered (1)

TooMuchToDo (882796) | more than 4 years ago | (#29597159)

Data is data =)

Re:So, we've discovered (2, Informative)

Wolvenhaven (1521217) | more than 4 years ago | (#29597241)

You can't stop the signal Mal, you can never stop the signal

Re:So, we've discovered (1)

spoonist (32012) | more than 4 years ago | (#29598043)

What's the frequency, Kenneth?

Re:So, we've discovered (1)

mhajicek (1582795) | more than 4 years ago | (#29600131)

Until the system has a snow-crash.

Re:So, we've discovered (4, Informative)

PeterBrett (780946) | more than 4 years ago | (#29598233)

satellite radar altimetry. [altimetry.info]

Of course, it's accidental radar altimetry, rather than a dedicated instrument. Neat hack.

Um, no. It's not like SRA, apart from the use of a satellite, RF radiation, and the measurement of a distance.

Main differences:

  • This system is bistatic; SRA is monostatic.
  • This system uses an (almost) isotropic antenna to collect radiation from pretty much everywhere; SRA uses a high gain antenna to survey only a very narrow target swathe.
  • This system measures the effective speed of light in a multipath environment, assuming the multipath reflectors are at fixed distances; SRA measures the distance of multipath reflectors, assuming the effective speed of light is fixed.

Disclaimer: I work on satellite synthetic aperture radar, which is different again, and my knowledge of SRA isn't comprehensive.

Re:So, we've discovered (1)

deglr6328 (150198) | more than 4 years ago | (#29598297)

not really, no. Satellite radar altimetry is just simple time domain reflectometry. Send a pulse of light, microwaves, whatever and use the elapsed time (along with knowledge of the speed of light) until hearing the echo to determine distance, subtract ephemeris data describing the satellite's orbit and get alitmetry out. Done. That is not at all what is being done here. So far as I know, there is no way of directly measuring snow depth from a satellite. If you're in orbit at 400 miles up trying to measure snowpack with even a ridiculously huge +/-1 foot accuracy, you're going to need less than 0.5ppm precision measurements on your reflectometry time - I have to think that the atmospheric-transit pulse broadening alone would smear that type of precision to hell, even with LIDAR. No, this technique uses a very clever, much more nuanced method to detect snow depth. They're modeling multi-path reflections of GPS signals off the ground using knowledge of the dielectric constant and surface roughness of the material being reflected off of, and the satellite elevation angle and antenna gain profile of the receiver, among other things, to model the effects of snow cover on signal to noise ratio, which is directly measurable by the GPS reciever. It's really a very solid piece of work http://www.agu.org/pubs/crossref/2009/2009GL039430.shtml [agu.org] . We already have the SNOTEL [wikipedia.org] network of meteorology and snow depth detection stations in the western US, which is made up of several hundred individual sites. However, while SNOTEL is a large system (really a gorgeously designed piece of parsimonious engineering if you ask me - small solar powered stations sitting out in the middle of nowhere patiently listen for reflections of radio waves off of meteors in the upper atmosphere, and upon hearing them, send a quick burst of the day's collected data out, which reflects off of the few-second-lived plasma tail of the burnt-up meteoroid, which is then detected by a central ground station in Boise. fantastic!) but the US is BIG, and getting more accurate detailed maps of snow cover over larger areas using already in place equipment is a very cute trick that could have important implications for monitoring, for instance, global warming effects over long periods of time.

great (1)

mikey177 (1426171) | more than 4 years ago | (#29597119)

all we need it to do now is find all the money, car key, credit cards that people lose skiing and then i might go out and buy one

Re:great (0)

Anonymous Coward | more than 4 years ago | (#29598007)

Not one of those things will still be useful by the time you recover them.

First post ? (0, Offtopic)

oqaqiq (1636635) | more than 4 years ago | (#29597205)

First snow.

Snow compactness? (1, Interesting)

Anonymous Coward | more than 4 years ago | (#29597451)

Does it account for the fact that almost-melting snow will layer more compactly then sub-30C snow which is extremely crystalline and less likely to make compact layers?

Re:Snow compactness? (2, Informative)

PeterBrett (780946) | more than 4 years ago | (#29598489)

Does it account for the fact that almost-melting snow will layer more compactly then sub-30C snow which is extremely crystalline and less likely to make compact layers?

Disclaimer: I haven't RTFPaper. I'll do that tomorrow, since it's of professional interest. What follows is guesswork.

Imagine you've got an RF antenna on a flat surface. Above the flat surface is a layer of snow of constant thickness h. Now place at least three point RF sources at different angles theta and distances r from the antenna. Assume that all the sources lie above the snow.

Now, the distance that each RF signal must travel through the snow, x, will depend on d and theta, but not on r. You'll find that x is linearly dependent on d. Let t = alpha * x be the increase in signal flight time due to the snow. alpha will be a function of the dielectric properties of the snow.

So, basically, I don't think you can tell the difference between an increase in d and an increase in alpha, and ergo, the answer to your question is, "No." On the other hand, IIRC there's actually very difference in terms of dielectric properties between different types of snow, so it could be that the effect is dominated by the snow depth.

Re:Snow compactness? (2, Informative)

PeterBrett (780946) | more than 4 years ago | (#29598699)

Heh. Having read the paper [agu.org] , it seems that it's not that simple, unfortunately. However, they seem to have assumed a standard model for snow:

We assumed density of 240 kg m3 for the new snow and a snow temperature of 2C ( = 1.48 i2.76 × 104), after Jacobson [2008].

Re:Snow compactness? (0)

Anonymous Coward | more than 4 years ago | (#29607873)

The paper just shows they are using multipath to measure the reflected signal off the snow and we able to correlate the signal with snow depth. Personally I think in most situations there will be too many unknowns for the technique to be useful. The article is well written and mentions these problems. If you have any wind when the snow falls, you're going to have drifting which makes such measurements useless. It reminds me of the time someone at JPL showed me they could measure the time delay of cause by a tree next to a GPS antenna and map out the shape/density of the tree. This was in the direct path, but it's still similar.

Re:Snow compactness? (1)

PeterBrett (780946) | more than 4 years ago | (#29611323)

If you have any wind when the snow falls, you're going to have drifting which makes such measurements useless.

I take great exception to this statement and your dismissive attitude towards their results. Drifting will introduce uncertainty into the measurements, and that uncertainty can be estimated and accounted for. It by no means makes the measurements 'useless.' Scientific experiments are never carried out in ideal environments, and the mathematical methods that have been developed to extract information from poor-quality data are truly amazing.

For example, in my field of satellite synthetic aperture radar, all of our data contains high-power speckle noise, thermal noise and heavy multipath and shadowing artefacts. Nevertheless, there is always useful information to be extracted from even the most heavily-corrupted areas -- it's "just" a matter of creating probabilistic models of how the errors occur and use that to extract as much information as possible. We never say, "Oh, this area has some layover, it's useless."

Data always has useful information somewhere -- it's just a matter of putting in the work required to get at it. These researchers have demonstrated that the information on snowfall is present. Don't make the mistake of dismissing that result just because there are still some challenges to overcome.

Other method (0)

Anonymous Coward | more than 4 years ago | (#29597501)

I find throwing a cat into a snow drift with a knotted string works good. Not a very good way to find water depth though. Cats tend to glance off water so it's hard to get a good reading.

or (1)

nimbius (983462) | more than 4 years ago | (#29597837)

how deep do we dig before we find the trapped body?

Re:or (1)

spokedoke (1211292) | more than 4 years ago | (#29598395)

This did cross my mind as well, although it should not be a replacement for proper use of an avy probe, more information is never a bad thing. Better yet, it would be great to use the variations in snow-pack density to predict the snow stability. Stupid and/or lazy people are everywhere, even skiing in the backcountry and this could help save their lives.

Your might think it's unimportant. (2, Informative)

plopez (54068) | more than 4 years ago | (#29598369)

All jokes aside, the western US and Canada are completely reliant on snow pack for water supply. No snow, and you have severe drought. Knowing what is happening with snow pack is a huge issue there and in may other places in the world.

http://www.agu.org/pubs/crossref/2007/2006WR005653.shtml [agu.org]

Re:Your might think it's unimportant. (1)

kpainter (901021) | more than 4 years ago | (#29601501)

All jokes aside, the western US and Canada are completely reliant on snow pack for water supply. No snow, and you have severe drought.

Exactly. With this knowledge, you can know you have a severe drought. That is obviously much better than not knowing you have a severe drought.

Re:Your might think it's unimportant. (2, Informative)

dschl (57168) | more than 4 years ago | (#29601839)

We already know, as there are manual snow course surveys and snow pillows all over the place. Here is a list of 400 or so (some are historic and no longer sampled) snow courses [gov.bc.ca] in BC. Many of those get visited every two or four weeks from Jan-Feb through June each year.

I've done the surveys, and you need to measure both snow depth, and moisture content. The process of manual measurement hasn't changed in decades - you drop a metal tube into the ground, pull it up, dig out the soil, measure the weight of the snow that the tube collected, and the depth of the snow. Of the two numbers, the overall moisture content is of greater interest. I hardly even look at snow depth when trying to decide if the water systems I run are facing a drought - the moisture content compared to historic trends is what matters most.

Even then, snow depth is only a guide. If you get high evaporation rates during spring freshet, or lots of wind and moisture loss, what appears to be a healthy snowpack in April can turn into near-record low runoff by June. This year that is exactly what happened in my region. We had a good snowpack, with normal amounts of water equivalent in April, but by June, very little runoff to the reservoirs had taken place. This mostly affected the low and mid elevation watersheds in the Okanagan. The really high elevation watersheds such as Mission Creek had normal runoff, while adjacent watersheds such as Mill and Hydraulic Creeks ended up with varying levels of drought.

More data is always a good thing, but the moisture content matters more than the depth. And even if the data looks promising, that can change in a matter of weeks. You never really know for sure how much water you're going to get until the reservoirs stop filling.

Re:Your might think it's unimportant. (1)

plopez (54068) | more than 4 years ago | (#29640763)

yeah I know. But when I first dropped in on the thread it was all stupid jokes. I just wanted to raise awareness.

Doubtless you are someone who takes snow hydrology seriously as much as I do.

GPS to measure global temperature (1)

Ambitwistor (1041236) | more than 4 years ago | (#29599267)

Interestingly, people have used GPS to measure temperatures in the Earth's atmosphere. The idea is to precisely measure the Doppler shift of the GPS satellite signal. This is modified by the refraction of radio waves through the atmosphere. Atmospheric refraction is governed by the density of air, which in turn depends on its temperature. Thus, radio occultation [wikipedia.org] measurements can be used to infer (a convolved integral of) the air temperature along the line-of-sight. Many such measurements can be used to extract spatial and temporal structure, and also infer information about atmospheric pressure and water vapor content.

Here [nasa.gov] is one early paper, and a review [psu.edu] . This system is gaining increasing attention and may one day be a competitive alternative to existing ground- and satellite-based observation systems.

Ignore, test (0)

Anonymous Coward | more than 4 years ago | (#29600199)

Ignore/-1 Offtopic this.

Well in that case: (0)

Anonymous Coward | more than 4 years ago | (#29607989)

Would this system be capable of acting like a sonar and detecting disruptions in the snow like, say, a trapped skier?

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