I n s t r u m e n t s

a n d

M e t h o d s

Figure 2. Daily snow depth data from Agassiz Ice Cap, Ellesmere Island, N.W.T. 1991 to 1995.

cable.Thisisthe onlyexistingdata setforsnow depth
measurement from an Arctic Ice Cap.Itispart of a col-
laborative project between CSCC and the Glaciology Divi-
sion of Natural Resources Canada.It is the first time that
theglaciologistshaveknowledgeofthedistributionof
snowfallforthe entire year,insteadofonce a yearmass
balance determination.In the summerof 1992,the snow
depth measurements show a "negativedepth" indicatinga
short period of summermelt.

SR50 SENSOR

The next and most recentversion of the sensor is the SR50.
The SR50 is capable of picking up small targets ortargets
thatare highlyabsorptivetosoundsuchaslowdensity
snow.The SR50 can measure multiple targets andit makes
use of a unique echo processing algorithm to help ensure
measurement reliability.If desired, the SR50 can output
measurementqualitynumbersalongwiththedistance
measurement. The qualitynumbers have no unitsof meas-
ure but canvary from 162 to 600.Numbers lower than 210
areconsideredtobemeasurementsofgoodquality.
Numbers greaterthan 300,indicate that there is a degree
of uncertainty in the measurement.A furthermodi-
fication in the SR50has given it the capabilityof having

an SDI (Serial Device Interface) output.
In Figure 4, thegraphshows the distribution of SR50 qual-
ity numbers for this past winter at a test site at the Edmon-
ton International Airport.Therewereonly 14 occurrences
of quality numbers with values greater than 300.Forthe
period from November 1995 to May 1996, this is only .3%
of all the hourly readings. Figure5 is the actualsnow depth
data for the same site.Hourly readings from the SR50 are
shownaswellasmanualreadingsfromthenearby
AtmosphericEnvironmentServicesweather station.Snow
depth distribution at the site is not uniform whichexplains
the discrepancy between the two readings.
Figure5 also reminds us of the dynamic nature of snow
depth, especially in areas with dry snow conditions.In-
variably, eachsnow fall event is followed by a decreasein
snow depth due to either settling of the snow or scouring
and erosion by the wind.
Hourly snow depth data fora third site, BeaverMoun-
tain,isshowninFigure 6.BeaverMountainislocated
approximately 43 km.northeast of Logan, Utah.The sta-
tion is located close to the 2200 meterlevel.The manual
readingswere takenat the very same site and thetwo read-
ingscompare favourably.Thesnowdepth dataforthis
site ismuch smootherthan the previous site.The snow

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