Terrestrial snow cover
On average, 60% of Northern Hemisphere has snow cover in midwinter.
Over 30% of Earth’s land surface has seasonal snow.
About 10% of Earth’s land surface is covered permanently by snow and ice.
Snow & water resources
Wide areas of the mid-latitudes depend on
snowmelt runoff from seasonally snow-covered
alpine areas for urban & agricultural supplies, and
to maintain healthy ecosystems
About 85% of the streamflow in the Colorado river
originates as snow
Snowmelt accounts for the major source of
groundwater recharge in the semi-arid western U.S.
140
6
120
5
Average Monthly Flow (1000AF)
100
4
SWE
Flow
80
3
60
2
40
1
20
Average Monthly SWE(in)
Snow contributions to annual
precipitation
Arizona/New Mexico:
39%
Utah:
60%
Colorado:
63%
Sierra Nevada:
67%
0
-1
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Month
Most runoff & recharge comes from snowmelt
Serreze et al., 1999
Snow measurements
Space-borne
FUNDAMENTALS OF REMOTE SENSING
A. Energy
source
B. Atmospheric
interactions
C. Target
interactions
D. Sensor
records
4
Microwave satellite data
Sensor
Resolution
Domain
Purpose
RadarSAT
High
Partial
Snow wetness
ASAR
High
Partial
Dry snow cover
QuickSCAT
Low
Full
Dry snow cover
SSM/I
Low
Full
Dry snow sover
SWE correlation
AMSR-E
Low
Full
Dry snow cover
SWE correlation
Radarsat
5.3 GHz
HH polarization
Standard Mode: 100 km swath width, 25 m resolution
Radarsat:
Antarctica
ERS-1:
Greenland
Special Sensor Microwave
Imager (SSM/I)
SSM/I is a 7-channel, 4-frequency,
linearly polarized, passive microwave
radiometric that measures atmospheric,
ocean and terrain microwave brightness
temperatures at 19.35, 22.235, 37.0, &
85.5 GHz.
Spatial resolution: 15 km at 85.5 GHz &
69 km at 19.35 MHz
Near-circular, sun-synchronous, & nearpolar orbit, with an altitude of 860 km
Northern Hemisphere Snow
Extent from SSM/I
Optical satellite data
Sensor
Resolution
Domain
Purpose
IKONOS
Very High
Partial
Snow Cover
LANDSAT
High
Partial
Snow Cover
Grain Size
ASTER
High
Partial
Snow Cover
Grain Size
MISR
High
Partial
BRDF - Solar
MODIS
Moderate
Full
Snow Cover
AVHRR
Moderate
Full
Snow Cover
MODIS snow
cover, western
U.S.
Image Color Legend:
white
snow
pink
cloud
grey
no data / night
green
snow/cloud free land
blue
water
500 m spatial resolution
36 bands, 0.620-14.385 m
Airborne data
NASA DC-8
NASA P3
AIRSAR
Snow extent
Snow depth
Snow water equivalent
Snow wetness
Freeze/thaw
NOAA AC690
PSR
Snow extent
Snow water equivalent
Snow wetness
Freeze/thaw
GAMMA
Snow water equivalent
Soil moisture
Snow Measurement
Airborne Snow Survey Program
– Snow Water Equivalent (SWE) estimated from
attenuation of naturally occurring terrestrial
gamma radiation.
• Typical flight line is 16 km long, measuring a
ground swath 3000 m wide.
– Measures average SWE over area of ~5 km2
• 1800 flight lines throughout coterminous U.S.
• Two twin-engine aircraft fly ~900 lines/year.
Snow Measurement
Airborne Snow Survey Program
Atmosphere
Cosmic Rays
Radon Daughters
in Atmosphere
Gamma Radiation
reaches
Detector in Aircraft
Uncollided
Scattering
Gamma Radiation
Absorbed by Water
in the Snow Pack
Natural Gamma Sources
238
U Series,
232
Th Series, 40K Series
Snow
Soil
Snow Measurement
Airborne SWE: Accuracy and Bias
Airborne measurements include ice
and standing water that ground
measurements generally miss.
RMS Agricultural Areas: 0.81 cm
RMS Forested Areas: 2.31 cm
Snow Measurement
Airborne Snow Survey Program
– Snow Water Equivalent (SWE) estimated from
attenuation of naturally occurring terrestrial
gamma radiation.
• Typical flight line is 16 km long, measuring a
ground swath 3000 m wide.
– Measures average SWE over area of ~5 km2
• 1800 flight lines throughout coterminous U.S.
• Two twin-engine aircraft fly ~900 lines/year.
Snow Measurement
Airborne Snow Survey Program
Atmosphere
Cosmic Rays
Radon Daughters
in Atmosphere
Gamma Radiation
reaches
Detector in Aircraft
Uncollided
Scattering
Gamma Radiation
Absorbed by Water
in the Snow Pack
Natural Gamma Sources
238
U Series,
232
Th Series, 40K Series
Snow
Soil
Snow Measurement
Airborne SWE: Accuracy and Bias
Airborne measurements include ice
and standing water that ground
measurements generally miss.
RMS Agricultural Areas: 0.81 cm
RMS Forested Areas: 2.31 cm