Measuring Snow Water Equivalent
Using a Non-contact Method
Brian Day, CEO
Campbell Scientific (Canada)
Measuring Snow Water
Equivalent (SWE)
SWE is the measurement of how much
water is present within a snowpack
Value of Measurement:
Flood Forecasting
Reservoir Storage for Hydro Electric
Generation, Drinking Water and Irrigation
Snow Loading on Structures
Present Methods
Snow Courses
Cost Per
Week
Cost Per
Season
Helicopter
Labour
Travel
$ 10,000.00 $ 40,000.00
$ 6,000.00 $ 24,000.00
$ 1,000.00 $ 4,000.00
Total
$17,000.00 $68,000.00
Inaccuracies
– Incorrect Sampling
– Dry 10% - Wet 40%
Not Real Time
Snow Scales and Pillows
Snow Scale
Inexpensive
Prevent infiltration into ground
Subject to Ice Bridging (critical at
melt)
Snow Pillow
Expensive Infrastructure
Subject to Ice Bridging (critical at
melt)
Measurement Challenges
Current methods have several related drawbacks:
Repetitive costs (some can only be
reached by helicopter)
Inaccuracies, especially during the snowmelt period
Sensor changes the measurement
conditions
Non-contact Method
CS725 Non-contact SWE Sensor
Principle:
Measures the absorption of
natural ground gamma
radiation through snow
cover.
Originally concept developed
by the Institute of Research
and Development of Hydro
Quebec in 2003
Theory
100000
Number of Counts
10000
Without Snow Cover
With Snow Cover
K
Difference between the 2 signals
is used to calculate SWE
TL
1000
100
Signal attenuated due to snow cover
10
1
Energy Spectrum
How it works
CS725 SWE
Sensor
Bursts of light are
converted to electrical
signals. Counts are
accumulated over a 6
hour period.
Gamma Spectrometer
(thallium-doped sodium iodide)
Photo Multiplier Tube
Naturally occurring gamma radiation
from ground
Test Results
Field Trials & Deployments
1. 3 years in Canadian Rockies;
Sunshine Ski Resort in Banff, AB
2. 2007-2010 – Utah; SNOTEL site
3. Hydro-Quebec; 9 CS725 sites
4. Environment Canada; 2010 –
Present
5. NVE Norway – 2010 to present
6. NY Dept. ENV – 2013 to present
7. NFLD Hydro – 2011 to present
8. Italy – 2013/2014
Catskill Water Shed,
New York State
CS725 test site
(2012/2013)
Installation in New York State
CS725
Snow Scale
DATE
Snow Core
29-May
30-Mar
29-Jan
30-Nov
1-Oct
2-Aug
3-Jun
4-Apr
3-Feb
5-Dec
6-Oct
7-Aug
8-Jun
9-Apr
9-Feb
11-Dec
12-Oct
13-Aug
14-Jun
15-Apr
14-Feb
16-Dec
17-Oct
18-Aug
19-Jun
20-Apr
19-Feb
21-Dec
22-Oct
23-Aug
24-Jun
25-Apr
24-Feb
26-Dec
27-Oct
28-Aug
29-Jun
30-Apr
1-Mar
1-Jan
SWE (mm)
Winter 2012/2013 New York State
CS725/Snow Scale Comparison New York State
110
100
90
80
70
60
50
40
30
20
10
0
Sunshine Village
CS725 test site
(2008-2011)
Installation Sunshine Site
Jul-11
Jun-11
Jun-11
May-11
May-11
Apr-11
Apr-11
Mar-11
Mar-11
Feb-11
Feb-11
Jan-11
Jan-11
Jan-11
Dec-10
1000
Precipitation Gauge
600
500
400
1
200
100
0
0
Snow Depth (m)
800
Dec-10
900
Nov-10
Nov-10
Oct-10
SWE (mm)
Sunshine 2010/2011Data
2.5
CS725 K
GMON3
Snow Pillow
Snow Depth
2
700
1.5
300
0.5
Closing Comments
Advantages of Non-contact
Measurement
Performance not affected by adverse
conditions
Effective in any type of snow or ice
Easy installation (mount ~3 m above snow)
Measurement covers a large area of
~50 – 100 m2
Maintenance free for 7 years
Ensuring Measurement Accuracy
Install prior to snowfall
• Reference count over bare ground (i.e. high in
K/Tl)
• Soil water content needs to be known as it
attenuates gamma radiation just prior to
freeze up
Soil moisture content is used in the CS725
self calibration sequence to determine
“noSnow”
Thank you!
Questions?