Measuring snow depth
MJHanagan
Posts: 189
in Accessories
The snow will be flying up here in New England in the not to distant future and this year I want to try building a snow depth sensor. I have found a commercial sensor based on ultrasound for around $150 and a few internet posts using the relatively inexpensive Parallax Ping sensor.
Has anyone tried using the Parallax 28044 laser range finder to measure snow depth? This sensor has a 2 meter range which would work quite well for measuring normal snow fall amounts around here. However, snow being what it is I wonder if the laser would reflect consistently off the surface so it could be measured accurately, say +/- 1-2 mm. At $100 it is a bit too pricey to buy just to see if it might work.
Has anyone tried using the Parallax 28044 laser range finder to measure snow depth? This sensor has a 2 meter range which would work quite well for measuring normal snow fall amounts around here. However, snow being what it is I wonder if the laser would reflect consistently off the surface so it could be measured accurately, say +/- 1-2 mm. At $100 it is a bit too pricey to buy just to see if it might work.
Comments
A really low tech solution would be to just bungy some cheap yardsticks to several trees or other fixed objects and observe with a pair of binoculars and average the readings.
I have a nice copper snow depth gauge that I normally use but it's hard to see when I'm away from home :-))
Wireless security camera linked to WiFi?
http://www.walmart.com/ip/Disney-Peel-Stick-Growth-Chart-Winnie-the-Pooh/15676326?action=product_interest&action_type=title&item_id=15676326&p
Of course, making your own would be even cheaper. It seems everyone uses a stick which can be as much as 60 feet long. http://www.tripadvisor.it/LocationPhotoDirectLink-g143020-d144747-i43765188-Crater_Lake-Crater_Lake_National_Park_Oregon.html
https://en.wikipedia.org/wiki/Snow_gauge
Snow should show up very well. I would be willing to bet that it would work quite well.
I have one I'd be willing to let you borrow if you want to try it. Send me a PM if you are interested.
Bean
I'm liking the Pooh gauge idea and a web cam!!
Got any snow where you are yet?
I was thinking about making some type of "snow simulator" then trying the Ping sensor to see how it might respond. Perhaps something like a fluffy blanket lightly stretched over some type of wooden frame might mimic the soft acoustic properties of snow. If the Ping works then I have a really inexpensive sensor.
But using a laser would be way cooler! I may take you up on your kind offer once we have snow on the ground to test it with. Alternatively, I could try to behave over the next several weeks in hopes Santa would leave a 28044 under the tree this year ;-)
If I needed A 60 foot stick to measure snow depth I think I might be looking for some other real estate!
You've probably already run across it, but just in case, have you looked at Chris Nafis' site, http://howmuchsnow.com/? He has prototypes based on both ultrasonic and infrared triangulation, along with proof data and background.
Here is an old thread from the BASIC Stamp forum from when Chris started work on the ultrasonic method.
That's a relief... I thought you might be offended.
Personally, I rather have a typhoon any day than a winter in New England.
But there is a reason you don't see typhoon scenery featured on many holiday greeting cards!
A good coating of the white stuff covers up some otherwise bleak brown colored scenery.
When a typhoon hits, we get a day off. The other days are T-shirt weather and travel by motor scooter.
Digging out the car and the driveway just adds to one's toil.
Amanda
A good snow depth gage for me would be the number of lost postal workers or paper delivery persons.
One can always determine the weather is not fit to go outside by asking for a pizza delivery. A refusal indicates one should remain where they are.
I'm not so sure that sensor would work well. It has a hard time outside in the sunlight.
I have one myself and I think we're due for some snow soon. I just looked out the window and it's snowing now. It's not deep enough to really measure yet but once there's a bit more snow, I'll test a couple sensors on it.
I personally think an ultrasound sensor would work. I'm not sure why I think this but snow just doesn't seem the same as soft fabric. I think it would reflect the ultrasound. I'll test this out too.
Speaking of snow, I think I owe erco a figure 8 in the snow.
They say the Parallax 28044 laser range finder doesn't work so well in direct sun, and I thinkit would work less well in snow.
The SF02 on the other hand https://www.parallax.com/product/28043 works very well in direct sun to its full 50 meter range, although I haven't tried it on snow in full day light. I should try this next time it snows.
So a big question is where will you be measuring, will it be in full sun light; and how much snow do you intend to measure, will it be under two meters or will it be over four meters?
This will tell you which will do the job.
Then just buy the most expensive one, because that will be the most fun to play with.
Snow has a nominal bulk density somewhere in the 0.07 to 0.12 g/cm³ range (4.4 to 7.5 lbs/ft³). Compare this to acoustical foam which has a nominal density of around 0.03 g/cm³ (1.7 lbs/ft³) and one can see this might be a bit of a challenge. Added to the low density difficulty is the random orientation of the snow surface. A flat surface perpendicular to the direction of the PING beam should reflect enough sound back to the sensor but any significant undulation of the snow surface will send the incident sound scattering off to la la land.
I have been playing with a PING sensor using various pillows and plush blankets as proxies for freshly fallen fluffy snow. Depending on which blanket and its flatness I can sense its location with decent accuracy and fairly good reproducibility. However, a slightly rumpled surface can often result in no reflection back to the sensor. A very fluffy throw blanket is particularly troublesome for the PING sensor. A couch pillow with noticeable curvature seems to be OK, presumably because it has a relatively dense fabric surface (the fluffy poly fill doesn't get a chance to come into play).
I haven't come across many documented uses of lasers for snow depth measurements. I imagine the spectral reflectivity of snow is quite intense since it is made up of very fine ice crystals. This might preclude the use of simple laser proximity sensors.
Perhaps the only way to combat the high spectral reflectivity of light and the low acoustic reflectivity is to throw a high level of energy at the surface in hopes of seeing something reflect back. I have a feeling this is what the $150 ultrasound detectors are doing.
No snow in my forecast in the next week so I will continue with the blankets.
I would certain appreciate any feedback from anyone fortunate, or unfortunate, to have snow already!
PS - I hope a 2 meter sensing range will be sufficient. We had lots of snow last year here in central Massachusetts but the average accumulated depth never got much greater than about 3 feet.
I helped with instrumentation for the USFS Sierra zone observatory, and that used the Judd ultrasonic snow depth sensor. ($$$) The sensor does in fact have trouble during active snowfall, especially when windy. Sloping terrain is to be avoided. Even so, the data set forms a very nice dotted line during periods of relative calm. There is a photo of the hardware and a description at http://criticalzone.org/sierra/infrastructure/sensors-field-instruments-sierra/. The system pictured is based on a BASIC Stamp (long live it!) and a custom sensor interface board and a vDrive USB flash interface, and a Dust Networks mote. Recently a couple of the principals involved involved in the project started their own company and replaced the Stamp logger with their own, Metronome Systems, which integrates the latest Linear Tech/Dust motes along with a fancy Cypress PSoC.
Does anyone at Parallax know the output power of the 40 kHz sound pulse from the PING sensor? I cannot find it in the online documentation.
http://www.circuitsgallery.com/2012/05/numeric-water-level-indicator-liquid.html
There are plenty of small ready-made versions of this, but I expect you'd need to make something custom for 2m depths.
Edit: as an alternative, you might also be able to use a capacitive approach. Place two long strips of copper next to each other, with one connected to ground and the other connected to the Propeller. Then, using the same pulse-then-sample technique I used with the Propeller Badge pads, you should be able to measure how much charge us leaking to ground, which should be proportional to hire deep the snow is. I'm sure there are still some technical challenges to this approach, but the party I described above would be dirt cheap to implement.
So why not have a pole climbing sensor that recalibrates as it climbs the pole? With an ultrasonic sensor having a range of about 4 feet, one suddenly has the ablity to vastly increase its range.
That's an interesting idea. One could then trigger all four sensors at the same time and measure the response time for each individual sensor. If the snow is cooperative then you would see four very similar response times and report the average value. If on the other hand the snow is being particularly uncooperative you might "sense" one of the outgoing pings on at least one of the other sensors. If you receive two or more dissimilar responses then you could average them or develop an algorithm to determine the most probable value.
I got a price from Judd of $700 for their snow depth sensor. The MaxBotix HRXL-MaxSonar-WRS Series sensor is about $150 and comes ready to mount. A set of four PING sensors would be $120 plus the cost of a suitable enclosure. From a pure economical standpoint the MaxBotix sensor seem the better option so far.
If I have to move the sensor up that's my signal to move to another climate!
http://www.senscomp.com/ultrasonic-sensors/complete-ultrasonic-ranging-solutions.php
Check out the ICs available there too if you are interested to DIY. It is not out of the question. The Propeller by itself would be great for the pulse generation and return echo timing functions.
Many ultrasonic transducers like the PING have open frame construction that does not lend it to outdoor environs. There are other transducers that are sealed and more environmentally protected. (e.g., Prowave 400EP250) I recall that Parallax had an outdoor version in progress, but I'm not sure what became of that.
http://www.ebay.com/itm/331685483931
The TSL1401 line scanner is capable of detecting a brightly colored stick poked in the ground and producing an output proportional to the length. I am assuming it would be capable of measuring snow depth by subtracting current length from calibrated full length. I havent tried this and it would require a light source for night readings but it might be an inexpensive method to try.
That is an interesting approach. One might opt for a black stick and look for white snow edge. The photodetector has maximum sensitivity around 800 nm (just beyond visible red) so some type of IR LED might provide the necessary illumination at night.