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The Effects of Reflector Geometry on Radar Data Acquisition
International Symposium on Radioglaciology 9/09/2013
Nicholas Holschuh, Sridhar Anandakrishnan, Knut Christianson
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Objectives of RESC
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Historic Objectives
•Determine the depth to (and geometry of) the basal reflector
•Describe the internal structure of the ice sheets using the internal reflecting horizons (IRHs)
Modern Objectives
•Use return powers from basal reflectors to determine dielectric properties of the ice-bed interface
•Analyze the spectral quality of reflectors to uniquely identify layers through space
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MotivationC
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MotivationC
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The brightest reflectors are sometimes traceable through the lossy region …but at other times, are completely lost in the noise…
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MotivationC
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What is the source of the data loss?
- Affects deeper reflectors more than shallow ones- Appears to be related to reflector slope- More prevalent in the High Frequency Airborne Data
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Assumptions - Specularity
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Internal Reflectors: Specular(Obey the Law of
Reflection)
Basal Reflectors: Diffuse
Reflection Coefficient
Reflection Coefficient +
Angular Distribution
Refr
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Beam FocusingC
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Ground Survey
Airborne Survey
n = 1 + 0.851ρ
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Beam FocusingC
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Ground Survey Airborne Survey
Refraction Limits:
Ground Survey – 49ºAirborne Survey – 34º
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StackingIn
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Com
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Tra
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Sup
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C
om
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Sta
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(N
orm
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Ideal S
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(Norm
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StackingIn
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Sta
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Com
ponent
Tra
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Sup
eri
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C
om
ponents
Sta
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race
(N
orm
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Ideal S
tack
(Norm
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Stacking Controls
1) Radar Frequency2) Reflector Dip3) Stacking Distance
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Stacking – 1m Posting Interval
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Stacking – 1m Posting Interval
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Stacking – 10m Posting Interval
Intr
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R. Pa
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Sta
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g 0.018
Concl
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Stacking – 10m Posting Interval
Intr
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Sta
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Stacking – 20m Posting Interval
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Sta
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Stacking – 10m Posting Interval
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Sta
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0.00090.00210.01790.01950.04681
0.00260.02240.02950.03020.08211
0.01180.02520.03020.04790.09851
0.02250.04050.07090.09850.20271
0.94620.96190.97680.98910.9971
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Stacking Amplitude LossIn
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Radiation PatternIn
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Describes the angular distribution of the gain for a given radar antenna (Typically optimized for Nadir)
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Radiation PatternIn
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Caveats - SpecularityIn
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Offsets 0 – 1400m (100m)
Transmitter
Receiver
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ConclusionsIn
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Areas of intense deformation (and therefore glaciological interest) are prone to internal data loss
Amplitude loss due to reflector geometry should be corrected for if dipping beds are used in amplitude analysis.
Loss is ultimately a function of radar design and data collection methods. Choosing appropriate radars (frequency), platform, and stacking
distances can minimize data loss.
Nicholas Holschuh – [email protected]
Advisors: Sridhar Anandakrishnan
Richard Alley
Collaborator: Knut Christianson
Questions?
This material is based upon work supported by the National Science Foundation Graduate
Research Fellowship Program under Grant No. DGE1255832.
We would like to acknowledge the use of data products from CReSIS generated with support from NSF grant ANT-0424589 and NASA grant NNX10AT68G.
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