1 evaluation of radar measurements hans-peter marshall, boise state university and crrel snow...
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![Page 1: 1 Evaluation of radar measurements Hans-Peter Marshall, Boise State University and CRREL Snow Characterization Workshop, April 13-15, 2009](https://reader035.vdocuments.site/reader035/viewer/2022062423/56649d0e5503460f949e42af/html5/thumbnails/1.jpg)
1
Evaluation of radar measurements
Hans-Peter Marshall, Boise State University and CRRELSnow Characterization Workshop, April 13-15, 2009
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Locate instrumentation-related signals…
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And get rid of them!
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Locate causes of major reflections
• Metal reflectors placed at known depths, to determine cause of reflections in original signal
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Metal reflector experiment
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Metal reflector experiment
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Metal reflector experiment
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Metal reflector experiment
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Accuracy of using mean dielectric properties to estimate velocity: < 2%
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Comparing FMCW signal to in-situ electrical measurements
• radar => in-situ dielectric properties (Finish snowfork)
[e.g. Harper and Bradford, 03]• In-situ properties => physical
properties(e.g. Sihvola et al, 1985; Schneebeli et
al, 1998; Matzler, 1996)
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In-situ Density and Wetness
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In-situ Reflectivity
12
12
situinR
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Radar Snow Water Equivalent Estimates
1 2 ( )
s
g
z
z
SWE z dz( ) /s gTWT z z c
rmsSWE (TWT ,) 2%
rmsSWE (TWT ,d) 9%
rmsSWE (TWT , 250kg / m3) 10%
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Comparison of radar with SMP at Swiss Federal Institute for Snow and Avalanche Research
=> Small diameter rod driven through snow at constant velocity, pressure measured at tip
250 measurements/mm
Measures rupture force of grain bonds
SnowMicroPenetrometer
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Snowpit comparison, SLF, Feb 19, 2004
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Multi-Layer Model
2 2( , ) ( , )E r t E r t ��������������������������������������������������������
2 22
2 2
( )
( )
0
( , )( )
( , )
y
R i
i
I i
Ex z
E w tR
E w t
( 1)
( 1)
2( 1)
2( 1)
( )( )
1 ( )
i i
i i
i i
i
i i
j di i
i j di i
r
r R eR
r R e
(e.g. Ulaby et al, 1981)
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3-layer model – complicated for thin layers
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Depths of major reflections automatically picked
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Comparison of FMCW radar and SnowMicroPen
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Chuckchi Sea, BarrowMarch, 2006
• 300 meter profile on 1st year sea ice
• 601 MagnaProbe measurements
• >3000 FMCW radar snow depths
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Static comparison
1) Expected error = velocity uncertainty (1.5 cm) + radar resolution (1.5 cm) + difference in horizontal support (2cm) = 5cm
2) Mean values within 1.5 cm
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Density/Velocity distribution from SWE cores
+/- 5% uncertainty in depth estimate due to density variability
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FMCW radar profile
Mean measured density used to estimate depth from radar TWT
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FMCW radar / Magnaprobe comparison
1) Similar variability, good agreement
2) Differences mainly due to different support and coregistering of measurements
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Comparing point depths to radar measurements
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1.7 km profile, x=10 cm, z=1.5 cm
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1.7 km profile, x=10 cm, z=1.5 cm
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1.7 km profile, x=10 cm, z=1.5 cm
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Conclusions - limitations
• Signal attenuated in very wet snow
• Magnitude information from reflections difficult to interpret for thin layers
• No mechanical / microstructural information
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Conclusions - advantages
• Rapid (50 Hz) estimates of snow depth, SWE, major stratigraphic boundaries
• Basin-scale areas can be covered
• Slab geometry can be measured
• Simulate active microwave remote sensors