On 23 Mar, 13:30, "Martin Rowley"
wrote:
"Iain Thornton" wrote ...



A recent *Euro News TV report called - "Mapping Out The Future of
Alpine Glaciers" features a Campbell Scientific weather station in
use
in Northern Italy. When you see the challenging environments the
station endures and the journey required to access it one can see
why
reliability and low power are so important in these solar powered,
autonomous systems.
The camera shows a number of sensors including the SR50A sonic snow
depth sensor; all sensors are measured by the CR3000 datalogger in
the
enclosure which also processes and stores the data onboard and
controls the telecommunications to transmit data back to the control
centre.
See the report herehttp://bit.ly/adCTnB- I hope you all find it of
interest.

... Thanks! indeed it was: I would have liked to see more of the
'innards' of the system, i.e., a demonstration of how the snow
depth/thickness is actually measured, some idea of how accurate these
particular sensors are & how they cope when high-altitude weather is
'extreme' and the snow levels are fluctuating dramatically - but I
realise this was for a general audience.

Martin.

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

Hi Martin,

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. An air temperature measurement is also required to
correct for variance in the speed of sound, this can either be taken
from a seperate temperature sensor (usually available on the AWS) or
on variant SR50AT a built-in sensor provides the reading. Measurement
range is 0.5-10m with a resolution of 0.25mm and an accuracy of ±1.0cm
or ±0.4% of target distance whichever is greatest. The sensor will
operate within specification between -45°C and +50°. Some idea of the
likely snow height is useful before positioning the sensor so that it
doesn't end up buried. I am hoping to feature an application story on
this sensor in our next newsletter.

Interestingly there has been some discussion about the surface beneath
the sensor - clearly if it is grass then regular mowing is required to
prevent erroneous snow readings in summer so artificial surfaces are
sometimes used. I am positive that I once read a report that rabbits
and other small animals liked to sit beneath the sensors also causing
false readings but I can't for the life of me track it down - if
anything you would imagine the ultrasonic pulses to scare animals
away.

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. A leaflet and manual
for the sensor is also available on our website at
http://www.campbellsci.co.uk/index.cfm?id=233.

Hope that helps.