1. Kenny Matsuoka, Charles Raymond, Howard Conway, and Shuji Fujita
Detection of in-situ ice fabric anisotropy near the WAIS divide using polarimetric radar
Kenny Matsuoka, Charles Raymond,
Howard Conway, and Shuji Fujita

2. Acknowledgements On-ice crews for 2005-6 field season
NSF – OPP # ; PI: Raymond
RPSC
WAIS camp
Science Construction
Comm shop Larry Homen
National Institute of Polar Research, Tokyo
UW Space Grant Pavan Vaswani
Joe
Donovan
Ryan
Peter

3. Ice-crystal alignments (ice fabric)
Two common fabric patterns found in ice cores
Projection to the horizontal plane
Past Current Future
strain history  preferred fabric  deformation

4. Anisotropy in ice permittivity induces anisotropic radio echo
Anisotropic reflectivity
e||c = 1.01e_|_c
Permittivity e: A B
Reflectivity R:
RA >> RB
RA - RB = 10 ~ 20 dB
Horizontal plane
Birefringence (a path effect) A
Two principal polarization components A and B travel at different speeds, and can arrive at the receiver with different phase. B

5. Polarimetric radar method
Frankensled II
Starburst
measurements
60-MHz and 179-MHz
pulse-modulated radars
30 m
12 azimuths (15o intervals)

6. Azimuthal variations in the echo
180o-periodic echoes
 Anisotropic (uniaxial) reflectivity
Rmax - Rmin
179 MHz is more sensitive to fabric-based reflection.
Echo drop
90o-periodic echoes
 Birefrigence (or biaxial reflectivity)
When the azimuth of the polarization plane is altered, we can see two typical features. …
Apparent echo features can be complex, if both effects happen together.

7. Study Area: WAIS divide
19 circles:
Sites for polarimetric radar measurements
Contour:
Surface topography
Color image:
Bed topography (SOAR, BEDMAP)

8. Uniaxial echo found at 179 MHz
Data taken with different pulse widths show the same feature
Echo intensity (dBm)
Site: Adivide

9. High vs. Low radar frequencies
(179 M)
(60 M)
Apparent uniaxial echo only at 179 MHz suggests that anisotropic reflectivity is induced by ice fabric.
Site: Adivide

10. Depth dependence of echo-drop orientation
179 MHz; Site: BW30

11. Biaxial, orthogonal, signal drops
60 MHz
60 MHz
179 MHz
Site: AE30

12. Azimuth of biaxial echo drops in 60 MHz data (preliminary results)
Azimuths of the drops: 45o off principal axes of the ice fabric
19 circles:
Radar measurements
Contour:
Surface topography
Color image:
Bed topography (SOAR, BEDMAP)

13. Summary
Features of the ice fabric can be measured by polarimetric radar over large areas.
In some locations, principal axes of the ice fabric are aligned with surface slope.
In some locations, more complex features are found that could arise from spatial or temporal complexity in ice flow.
Coming field season: - Polarimetric radar measurements of shallower ice
- Strain grid measurements

14. Take-home messages
For ice core scientists: Measure ice fabric of the Divide Core at high vertical intervals from shallow depths.
For ice core drillers: Measure azimuth of each ice core.
For ice-flow modelers: Radar measurements may provide a proxy of fabric-induced enhancement factor in ice flow.
For radar nuts: Let’s develop state-of-the-art polarimetric radar.

15. Thank you!
Kenny Matsuoka

16. Radio-wave propagation within ice
Glaciological
characteristics
Mechanisms
Attenuation
Chemistry + temperature
Birefringence
Polarization dep.
Ice crystal alignments
Reflection
Polarization dep.
Ice crystal alignments
Density
Chemistry + temperature

17. Radio echoes are frequency, polarization-plane dependent
60 MHz
Frequency-dependent
179 MHz
Polarization dependent
First of all, I would like to show radar data from Antarctica that shows frequency, and polarization-plane dependent features.
90o difference in the polarization plane azimuth
Matsuoka et al. (2003)
179 MHz

19. Strong fabric at deeper depths induces azimuthal variations to 60 MHz as well.

20. Birefringence effects estimated with a Greenland summit ice core
Crystal-alignment data from the GISP2 ice core were used
Crystal alignments data courtesy: Larry Wilen (Ohio Univ.)
Birefringence is significant almost everywhere in the ice sheets

21. Spatial variation of the fabric suggested by the radar
Matsuoka et al. (2004)

22. Anisotropic high-scattering zone
Matsuoka et al. (2004)
Only in the region with significant horizontal strain
Only when the polarization plane is aligned to the horizontal compression axis.
Fast-flowing ice distorts the scattering zone

23. What can we learn from the radio-echo intensity?
Pr : echo intensity
R : reflectivity
B : birefringence
L : loss (attenuation)
z : depth (e: permittivity)
S : radar system parameters
Matsuoka et al. (2003)
Frequency f and polarization-plane b dependences
of the echo intensity can be caused by
reflectivity and birefringence