, CA, 9-11 Nov. 1999 
> contributions of ablation and 
iss balance. By quantifying their 
arer picture of the large-scale 
1anging climate will be obtained. 
xpected to provide useful insight 
' Greenland, and those from 
for the interpretation of the 
of smaller glaciers, the ATM 
e potential, with the capability of 
nn the tracking of the movement 
this measurement of detailed 
posed to just visible features, that 
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f passes up an down a glacier 
scription of velocity fields and 
e tensor. In this way, the surface 
ire glacier could be quickly 
of the ATM beach mapping 
orm suggest that such a program 
uite feasible. 
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wal of Remote Sensing. 67, 194- 
Calculation of ice 
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*.F. Martin, R.N. Swift, and E.B. 
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W. Wright, and J. Yungel, 1999. 
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International Archives of Photogrammetry and Remote Sensing, Vol. 32, Part 3W14, La Jolla, CA, 9-11 Nov. 1999 
AIRBORNE LASER ALTIMETRY OVER THE CENTRAL WEST ANTARCTIC ICE SHEET 
D.D. Blankenship, S.D. Kempf, D.L. Morse, M.E. Peters 
Institute for Geophysics, University of Texas, Austin TX, USA 
(blank, scottk, morse, mattp)®@ig.utexas.edu 
R.E. Bell, R.B. Arko 
Lamont Doherty Earth Observatory, Columbia University, Palisades NY, USA 
(robinb, arko)@ldeo.columbia.edu 
KEY WORDS: Airborne Laser Altimetry, West Antarctica 
The portion of the West Antarctic ice sheet (WAIS) encom- 
passing the ice divide separating the Pine Island and Ross 
Embayments and ice stream D within the Ross Embayment 
is a particular focus for WAIS research. Proposed activities 
include both deep ice coring and shallow coring traverses near 
the divide as well as a seismological traverses of the ice stream 
onset. Here we report on results of the laser altimetry com- 
ponent of a 100,000 line-km aerogeophysical survey (on a 5.3 
km grid) collected by the Support Office for Aerogeophysical 
Research (SOAR) covering ice stream D from the ice divide 
to the grounding line (Figure 1). 
This survey utilized a 16 uJ (total energy) pulsed laser (23 
nsec pulse at 1064 nm) with a 1.8 to 3.5 m footprint (for a 
typical flight elevations of 500-1000 m). The average range 
from the aircraft to the ice surface was determined every 
eight to nine meters along the flight path by summing the 
travel-times for 64 laser returns. These averaged laser ranges 
were ultimately projected to a position on the ice surface 
using aircraft attitude information from an on-board laser 
gyroscope. The aircraft position was determined kinemati- 
cally using differential carrier phase GPS observations made 
at one-second intervals with multiple receivers. Surface ele- 
vations determined with this system have single-season un- 
corrected mean deviations for observations made at points of 
intersecting flight paths ranging from 0.13 to 0.39 meters. 
These mean deviations are reduced to 0.07 m to 0.28 m after 
correcting profiles for a linear drift in the vertical position of 
the aircraft (Table 1). 
These new surface elevation data provide a calibration surface 
for space-based altimetry measurements and are a benchmark 
for future ice sheet volume change detection. Augmented by 
satellite imagery, these data also should be sufficient for re- 
solving the position of the topographic ice divide and bound- 
aries of ice stream initiation with the sub-kilometer precision 
necessary for modeling WAIS dynamics. 
REFERENCES 
[Blankenship et al., 1999] Blankenship D.D., Morse, D.L., 
Finn, C.A., Bell, R.E., Peters, M.E., Kempf, S.D., Hodge, 
S.M., Studinger, M. Behrendt, J.C. and Brozena, J.M., 1999. 
Geologic controls on the inititation of rapid basal motion for 
West Antarctic ice streams; a geophysical perspective includ- 
ing new airborne radar sounding and laser altimetry results. 
In: The West Antarctic Ice Sheet, R.B. Alley, ed., in press. 
  
  
    
  
4 co 
<> 1000 kmn— 
Figure 1: Coverage of CASERTZ/IRE, SOAR/BSB and 
SOAR/TKD aerogeophysical surveys conducted in West 
Antarctica. 
Table 1: Summary of laser altimetry statistics. 
  
  
  
Season Survey Line km  Deviation! 
post(pre) leveling 
1991/92 IRE? 25k 0.37 m 
1992/93 IRE? 25k 0.09 m 
1994/95  BSB 18k 0.07 (0.13) m 
1994/96 BSB 26k 0.13 (0.22) m 
TKD. 24k 0.10 (0.19) m 
1996/97  TKD? 33k 0.28 (0.39) m 
  
! RMS of half the observation discrepancy at the 
“crossover” locations. 
? from [Blankenship et al., 1999] 
? including a region with ice motion exceeding 1 m/day 
ACKNOWLEDGEMENT 
The authors thank the SOAR technical staff for collecting 
these data and Ken Borek Air Ltd. for operating the survey 
aircraft. This work was supported by NSF-OPP 9319379 
and 9319369.