SnowSAR in Canada: An evaluation of basin scale dual-frequency (17.2 and 9.6 GHz) snow property retrieval in a tundra environment

Joshua King and Chris DerksenClimate Research DivisionEnvironment CanadaToronto, Ontario, Canada

Thanks to: Nick Rutter, Tom Watts and all participants in the field campaign

Motivation

• Radar as an emerging technology for observation of snow properties

• ESA Earth Explorer CoReH2O

• Dual frequency 17.2 and 9.6 GHz (Ku- and X-band) synthetic aperture radar (SAR)

• Few studies have investigated seasonal/spatial Ku- and X-band radar response and no previous study in a tundra environments

Ku

VV

VH

Research Gaps

1. Soil/Vegetation properties• Uncertainties related to variation

in soil and vegetation dielectrics

2. Snow grain properties• Unbiased measurements may

allow the role of large depth hoar to be evaluated

3. Scaling of observations• Are small scale variations in

snow and soil properties influential at the airborne and/or satellite level?

SnowSAR in Canada• Airborne radar operating at the

proposed CoReH2O frequencies

• 17.2 and 9.6 GHz

• Dual-polarization (VV, VH)

• 2 x 2 m spatial resolution

• Three observation campaigns in Trail Valley Creek near Inuvik, NWT (December 2012 , March 2013, April 2013)

• Trench stratigraphy experiments

• Improved snow grain characterization (IRIS)

• Seasonal soil permittivity in multiple locations

Study area and plan

Flight data summary

December - 0/27March – 24/27April - 23/27

Incidence angles between 38 and 55 degrees

Local incidence angles between 26 and 62 degrees

Swath generally < 400 m

All 4 channels (Ku and X VV, VH) available with all completed flight lines

Snow Measurement Campaign

Snow Pit (< 1 m)

Snow Trench (5 to 50 m)

Snow Transect (> 100 m)

Lidar (Basin scale)

Sic Sic Creek Basin

Sic Sic Creek - Snow Pit Locations

Upland Tundra

River Valley

Forest Transition

Pit Locations

December

March

April

March

Sic Sic Creek - Seasonal

UplandPlateau

Valley

Foresttransition

Pit Locations

Sic Sic Creek - Backscatter

UplandPlateau

Valley

Foresttransition

April 2013, 50 m, 45-50 deg elevation

MEMLS Workflow – Pit

MEMLSActive

SurfaceRoughness

SnowPits

SSA to Pc

From IRIS2-Layer

Snowpack

SnowInput 1

Wegmüller & Mätzler (1999)

Mironov (2010)

MET TowerData

ObservedData

DerivedData

SimulatedData

M = 0.05Q = 0.1Sccho = 13

Sic Sic Creek - MEMLS Active

• 10 m average of observed radar backscatter

• Small range of depth suggest grains may be an important in sic sic creek

• Can we compare single pits against radar pixels?

Sic Sic Valley - 5 m Trench

• IR photography completed in 5 to 50 m trench excavations by Watts & Rutter• Stratigraphy extracted from stitched IR imagery to create 2D map

Sic Sic Valley - 5 m Trench

• Topography produces a range of depth over short distances

• Also tends to drive DH fraction

• Distribution of grain properties built from snow pits within +-3 days

• Due to the nature of tundra snow, the slab distribution includes solid facets

MEMLS Workflow – Distribution

MEMLSActive

TrenchExcavation

SurfaceRoughness

StratigraphyDistribution

SnowPits

GrainDistribution

2-LayerSnowpack

SnowInput 1 Snow

Input 2 SnowInput n

Wegmüller & Mätzler (1999

Mironov (2010)

MET TowerData

Field Data

DerivedData

SimulatedData

Valley Trench – MEMLS Active

Summary/Moving forward

• Relating backscatter to physical snow properties is a complex process

– Improved understanding of horizontal variation in grain properties and stratigraphy is needed

• Model advancement and inversion possible but requires community effort to assist in validation

– Physically based justification for tuning possible with known distributions

• Additional uncertainties including soil contribution must be resolved in the near future

Snow texture

Vegetation

• Backscatter appears influenced by local vegetation

• Methods needed to decompose contributions from vegetation and snow to develop retrieval

Upland Tundra – Soil Permittivity

Snow Measurement Campaign

Snow Pit (< 1 m)

Snow Trench (5 to 50 m)

• Manual Stratigraphy• Density (100 cc cutter)• Temperature Profile (4 cm)• IRIS SSA (5 cm)

• IR Stratigraphy• Multiple snow pits• IRIS SSA (5 cm)

Snow pits in local context