Active Microwave Physics and Basics
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Active Microwave Physics and Basics
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Simon YuehJPL, Pasadena, CA
August 14, 2014
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How Deep Can the Radio Waves Penetrate• 10 to17 GHz microwave can penetrate dry
snowpack with a broad range of depth (1 to 5 m)
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• Experiment, Radio Laboratory, Helsinki University of Technology in 1987• Theoretical simulations from bicontinuous medium/NMM3D, Xu et al, 2012
Frequency Penetration Depth
10 GHz (X) ~5 m14 GHz (Ku)
~1 m
18 GHz (K) ~0.5 m37 GHz (Ka)
~0.1 m
0.01m
0.1m
1m
10m
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Radar Sounding of SnowSurface Scattering
• Surface scattering dominates at near nadir looking• Early demonstration by late Prof. Hal Boyne (CSU)
• Current Status – A well-developed tool for probing the snow stratigraphy– Marsahll et al., ground-based FMCW Radar – Gogineni et al., aircraft-based Snow Radar
Courtesy of Boyne
• What is the resolution?– ΔR=Range resolution=C/2B– ΔH=H(1/cosθ-1) for rough interface
• Beamwidth (2θ) and height (H)– Horizontal resolution=2Hθ – limited by
beamwidth ΔRΔH
B ΔR
1 GHz 15 cm
5 GHz 3 cm
H ΔH
1000 m, 10deg 3.8m
10 m, 5 deg 1 cm
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Off-nadir Looking RadarVolume Scattering
SAR processing can achieve horizontal resolution of a few meters from space
Backscatter contributions:Volume, surface, and interaction terms.Observed backscatter coefficient σ° :
asgvvg '0
At off-nadir angles (30-50 degrees incidence angles)Volume scattering starts to dominateSurface scattering diminishes
Main parameters for snow backscatter:Dry snow• Snow water equivalent • Grain size (d)• Density (ρ)• Soil background signalWet snow• Liquid water content (radar signal does not
penetrate)
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One example of data and theoryMore data acquired through CLPX2, SnowScat and SnowSAR campaigns
• Snow
50 60 70 80 90 100 110 120-20
-18
-16
-14
-12
-10
-8
-6
SWE (mm)
VV
(dB
)
SnowSCAT backscatter against SWE, 40 , 16.7GHz
10.2GHz13.3GHz16.7GHz
03/01/201112/28/2010
SnowSCAT backscatter time series σvv with 40∘ incidence angle against SWE. Data taken from at Sodankylä between 12/28 /2010 and 03/01/2011.
Simulated radar backscatter using the DMRT/QCA for snow volume scattering at three frequencies. All three frequencies show response to snow water equivalent for moderate and large grain size.
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SAR Snow TomographySide-looking radar with multiple baselines
• Snow stratigraphy - Metamorphism and environmental factors create complex layering structures in the snow pack
• SAR Tomography will provide insight into snow and ice – Lack of comprehensive theoretical
development and experimental testing for snow
• SAR Tomography – Tested for 3-D forest canopy mapping– Coherence and multiple baselines– Demosntrated by GB-SAR, K Morrison of Cranfield U.
Measurements at Reynolds Creek study site, 200 meters from tower - 116 manual probe depth measurements. (Marshall et al. of BSU)
Leln
r
dr
Hei
ght (
m)
Sla
nt R
ange
(m)
Polarimetric tomographic profile over a forested area using DLR’s E-SAR system at L-band [Moreira et al., IEEE GRS magazine, 2013].
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Recent campaigns covering main snow regimes
Churchill, Canada, Tundra
(Near-)Coincident Ku-band and X-band scatterometers and SAR used
Sodankylä, Finland, Taiga
Innsbruck, Austria, Alpine
Colorado, USA Alpine/Tundra/ Taiga/Prairie
Inuvik, Canada, Tundra
Kuparuk, Alaska, Tundra
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Radar backscatter versus SWE – from Sodankylä, Finland, Taiga
Backscatter versus observed SWE, Sodankylä, Finland , SnowScat measurements for winter I , for winter II radiative transfer model calculation for 3 different values of grain size
SnowScat measurements at 40° for two winters
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Radar backscatter versus SWE – from Rocky Mountain, Colorado
Backscatter for VV, HH, and VH polarizations shows sensitivity to SWE for three sampling sitesYueh et al., Airborne Ku-band Polarimetric Radar Remote Sensing of Terrestrial Snow Cover, IEEE TGRS, Vol. 47, No. 10, 3347-3364, 2009.
NASA/JPL POLSCAT measurements