Over 30% of Earth’s land surface has seasonal snow. On average, 60% of Northern Hemisphere has snow cover in midwinter. About 10% of Earth’s land surface is covered permanently by snow and ice. Terrestrial snow cover

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.

Sierra Nevada:67% Colorado:63% Utah:60% Arizona/New Mexico:39% OctNovDecJanFebMarAprMayJunJulAugSep Month Average Monthly Flow (1000AF) Average Monthly SWE(in) SWE Flow Snow contributions to annual precipitation Serreze et al., 1999 Most runoff & recharge comes from snowmelt

FUNDAMENTALS OF REMOTE SENSING A.Energy source B.Atmospheric interactions C.Target interactions D.Sensor records energy E.Transmission to receiving station F.Interpretation G.Application Snow measurements Space-borne 4

Microwave satellite data SensorResolutionDomainPurpose AMSR-E ASAR RadarSAT QuickSCAT SSM/I High Low Partial Full Snow wetness Dry snow cover Dry snow sover SWE correlation 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, , 37.0, & 85.5 GHz. Spatial resolution: 15 km at 85.5 GHz & 69 km at MHz Near-circular, sun-synchronous, & near- polar orbit, with an altitude of 860 km

Northern Hemisphere Snow Extent from SSM/I

SensorResolutionDomainPurpose MODIS LANDSAT IKONOS ASTER MISR AVHRR Very High High Moderate Partial Full Snow Cover Grain Size Snow Cover Grain Size BRDF - Solar Snow Cover Optical satellite data

MODIS snow cover, western U.S. Image Color Legend: whitesnow pinkcloud greyno data / night greensnow/cloud free land bluewater 500 m spatial resolution 36 bands, m

Airborne data NASA DC-8NASA P3NOAA AC690 AIRSAR PSR GAMMA Snow water equivalent Snow extent Snow depth Snow wetness Freeze/thaw Snow water equivalent Snow extent Snow wetness Freeze/thaw 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.Typical flight line is 16 km long, measuring a ground swath 3000 m wide. –Measures average SWE over area of ~5 km flight lines throughout coterminous U.S.1800 flight lines throughout coterminous U.S. Two twin-engine aircraft fly ~900 lines/year.Two twin-engine aircraft fly ~900 lines/year.

Snow Measurement Airborne Snow Survey Program

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.Typical flight line is 16 km long, measuring a ground swath 3000 m wide. –Measures average SWE over area of ~5 km flight lines throughout coterminous U.S.1800 flight lines throughout coterminous U.S. Two twin-engine aircraft fly ~900 lines/year.Two twin-engine aircraft fly ~900 lines/year.

Snow Measurement Airborne Snow Survey Program

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