I am interested in measuring moisture of snow, in other words, its water content.
Any recommmendations? Would it be possible with a typical soil moisture sensor? In theory it sounds possible.
Explain what you mean by "water content". Snow IS water.
As an aside, the commonly available, cheap soil moisture sensors work very poorly, if at all, and most people give up on them after a while.
Obviously, yes. Snow can however ”hold” different amounts of water which determine its characteristics.
Any experiences with a bit more expensive sensors?
According to this Ski and Snowboard Waxing How-to and http://www.dartmouth.edu/~jaydavis/fssc/features/Galaneswax2.html and other similar websites...
...for ski wax planning, you need to measure the humidity of the air, not the moisture content of the snow.
So, find out how it is done "manually" and exactly what is being measured. Then you may be in a better position to figure out how to do it with a similar or other device.
For what it is worth, hydrologists are very interested in the water content of the snowpack, since that allows them to predict springtime floods. The metric of choice is "snow water equivalent," which is the water content of the entire snowpack at a particular location.
It can be measured in a variety of simple mechanical ways (snow pillows and sampling tubes), but the most interesting are by the use of microwaves and gamma ray emissions.
Since you probably want the water content of the uppermost few millimeters, those sorts of techniques may not be applicable. And probably beyond your budget. Just food for thought...
Snow can however "hold" different amounts of water which determine its characteristics.
You are confusing volume of snow with mass of snow.
The volume of snow is determined largely by air content, which is in turn mostly dependent on the temperature when snow is formed, and aging processes after being deposited.
If the point of all this is just to determine which ski wax to use, ask the local experts. Conditions change hourly.
simpjr:
It is a common practice (at least where I am from) to study the moisture content of the snow, in addition to the air humidity. A common test is to simply weigh the mass of snow/water before and after melting.
Interesting. I expect that the weight would not change, except for the weight of the tiny amount of water vapor in the pore spaces of the snow, which presumably would be driven off by melting...and that small change may be confounded by other processes during melting of the snow crystals...such as evaporation and, possibly, sublimation.
What volume of snow is melted? What is the resolution and accuracy of the weigh scale? How is the difference in weight (if there is any...I'm skeptical) used to determine the snow "moisture content"?
Ignore the earlier post. The tests are probably based on volume rather than mass, as you have pointed out. I do not know any details about it, sadly. I will return after more research.
Thank you for the feedback!
weigh the mass of snow/water before and after melting.
The weights will be the same, of course, for any practical measurement.
This is a useful guide to volume/water content relationships in snow pack.
simpjr:
The tests are probably based on volume rather than mass
I suspect this is not true, either.
However, the goal may be density, which is related to snow "water content" and (obviously) a combination of mass and volume. If that is the case, melting is not required. And I'm interested in how it could be used for ski waxing (I ski, both XC and downhill), because all reasonable references that I am aware of refer to air humidity, not snow moisture content (or density, or snow water equivalent), for wax selection (as well as air temperature, snow temperature, snow texture...)
Snow is made of interlocking ice crystals. All ice crystals, even very cold, will have mobile water molecules on the surface which you
might think of as a bit like liquid water. Pressurizing ice locally melts it, which is why its so slippery (due to water being
denser than ice). That makes a real water film that's more than a few molecules.
When snow is at 0 degrees C some of it may be melt water absorbed over the surface of the ice crystals, and
held in place by surface tension.
So there are many ways to think about the water content of snow, but to a first approximations its 100% ice
below 0C, and a mixture of ice and water at 0C. Partially melted snow will eventually drip out the excess water, this is when its called slush.
Due to the mobile water molecules on the surface, and sublimation, even cold snow changes structure over time,
becoming rougher in texture and compacting under its own weight.
To measure the percentage of water and ice in a sample of snow you can use calorimetry to determine the latent heat of fusion and compare this to the total mass. You measure the heat energy needed to bring the snow upto 0.1C (ie make sure its all just melted). That's going to be basically the latent heat of fusion of the ice only.
From 'simple' physics, wouldn't some electrical properties of the snow depend on:
- How compacted the snow is
- How 'wet' it is
- Temperature
For any 'sensical' data, I would measure the temperature with some other electrical quantity such as conductivity, or else.
Snow is basically a mix of ice and air (disregarding contamination from sticks, rocks, etc) - so take a scoop of snow with a known volume, measure it's weight, and you can calculate the density of the snow and with it the water content of the snow.