"Iain Thornton" wrote ...

The SR50A snow depth sensor is manufactured by Campbell Scientifc
Canada and is designed specifically to withstand harsh Canadian
conditions. Mounted horizontally at a known height pointing at the
ground, the sensor emits ultrasonic pulses and measures the elapsed
time between the emission and return of the pulse to determine any
change in height.
snip

These sensors are used by many of the world's national met services
and quite extensively in mountainous regions such as the Alps - if
interested there is an independent paper entitled EVALUATION OF
ULTRASONIC SNOW DEPTH SENSORS FOR AUTOMATED SURFACE OBSERVING SYSTEMS
(ASOS) which can be found by Googling the title.
snip

Hope that helps.

.... Indeed it does! Many thanks for that very full answer, and also
for indicating the appropriate paper: I managed to locate it, and for
others, the abbreviated url is he-

http://tinyurl.com/ydl8fbm

It's a long read, but well worth it as it is an important subject. The
photographs of typical installations are worth looking at, and the
introduction & conclusions/recommendations would provide a useful
summary if you're not inclined to plough through the entire paper,
though looking at Section 3 would also be appropriate.

As a life-long member of the 'we used to do it better with a ruler'
brigade, I was *very* impressed, and, as long as some of the
limitations were taken into account (high winds/heavy snow/snow
character etc.), which seem to be detectable relatively easily, the
system, particularly the Campbell units, returned creditable
performances. I suppose that, as with rainfall measurement, there will
always be problems with power supply fluctuation/failure and data
transfer loss - but the rigs themselves seem to be very rugged and
give a decently low mean error and small s.d.

There's probably a continuing problem with *small* amounts of snow
(and patchy but 50% cover) given the fixed nature of the sensor, but
this was recognized by the recommendation that multiple sensors should
be employed.

I shall look at these data with much more understanding in the future.
Once again, a most useful post.

All the best,

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023