Airborne Circumnavigation of the Great Ice Sheets for Mass Balance and Dynamics Studies
1. Measurement Objective
The core measurement goal is to create 3-dimensional image maps of portions of Greenland and
Antarctica as they would appear were the ice sheets stripped away. An airborne campaign is envisioned that could deliver the first, continuous measurements of ice thickness around the Greenland and Antarctic Ice Sheets. To measure basal topography and reflectivity, HF/VHF tomographic radars form the fundamental instrument suite. Achieving the goal means completing the
first airborne circumnavigation of the Antarctic Ice Sheet for scientific research.
2. Instrument Feasibility
The measurement goal mandates swath-mapping capabilities not provided by current profiling
sounders. Proven tomographic techniques achieve this capability by: 1) separating basal returns
from symmetric points to the right and left of the flight path that arrive at the same time to the
nadir; 2) rejecting surface clutter from rough surfaces; 3) overcoming ice attenuation, especially
for warm ice. Figure 1 summarizes performance differences that can result from upgrades to a
previously proven system (GISMO) where the result is an increased swath that meets the posting
and height accuracy requirements.
Figure 1. GISMO vs TomAS performance comparison. For this case, GISMO would achieve a 4
Km swath compared to a 7 Km TomAS swath.
3. Observation coverage
Ideally, measurements are needed over a 50km wide ribbon upstream of the grounding
lines/ice margins for both Greenland and Antarctica. Figure 2.1-2 (left) shows an approximate
route about the Antarctic grounding/terminus line and for Greenland (right) shows a route about
the 1000 m elevation contour (red line). This contour is indicated because much of the Greenland
Ice Sheet terminates on land. In addition, to improve our knowledge of subglacial processes
along the ice flow, our observation will focus on specific glacier drainages initially identified to
be Whillans I.S., Peterman Glacier and the North East Ice Stream (NEIS).
3-1
Use or disclosure of information contained on this sheet is subject to the restriction on the cover page of this proposal.
Figure 2: Left graphic shows
the Antarctic Grounding line
(blue line) and the Whillans
Ice Sheet study area. Yellow
dots show Antarctic bases.
The right graphic shows the
1000 m contour (blue line) of
the Greenland Ice Sheet and
the North East Ice Sheet and
Peterman Basin regions.
4. Flight Requirements
Detailed later in Section 6, we selected the DC3 Basler conversion BT-67 aircraft which has a
3200km range, a cruise speed of 380 km/h and a 7.6 km operating ceiling. Using these flight
characteristics, Table 1 summarizes the flight-hour requirements for our science missions. These
calculations included transit times to/from stations or fuel sites, a margin of 15% on aircraft efficiency and a turn-time of 5min/turn. Our analyses have revealed that until the ice-thickness exceeds 2.2km, it is best to fly at or near the aircraft ceiling to be 5 to 6km above the surface,
which is also advantageous for fuel efficiency. This reduces the maximum basal incidence angle
for a given swath and as such the surface cross section is improved over a lower altitude geometry covering the same swath. For flight planning we assume aircraft operations at 6km altitude.
Based on a priori knowledge of approximate ice thickness and ice conditions and referring to
Figure 1, we assume an 8km swath for the grounding lines in Antarctica and Greenland (where
the ice less than 1.5km). For the basins we assume a 7km swath due to the presence of potentially thicker ice (but with generally lower attenuation). The circumnavigations each require 7 racetracks in a series of piece-wise linear segments flown with a 10% overlap.
For Antarctica the science collections will take just over 840 hours. This translates to 84
flight-days which are distributed over 270 deployment days. Therefore we have a weather/contingency margin of 69%. In Greenland total flight hours are 376 hours over two 60 day
flight seasons translating to a margin of 69% also.
Science
Transit
Turns
Total
Greenland 1000m contour
152.6
54.6
6.3
213.5
Antarctic grounding line
435.4
189.7
8.4
633.5
Greenland basins
71.6
40.8
16.5
128.9
Antarctica basin
83.3
37.9
9.3
130.6
Totals
742.9
323.0
40.5
1106.5
Table 1: BIIR coverage and flight hours including 7 complete race
tracks about the Greenland 1000 m contour and the Antarctic
Grounding line. One circumnavigation of Antarctic is about 100
hours.
4-2
Use or disclosure of information contained on this sheet is subject to the restriction on the cover page of this proposal.
5. Operational time lines
Optimal operations are early April to late May for Greenland and from November to February
for Antarctica before significant melting or surface water occurs in Greenland, but also when logistical access is reasonable in Antarctica. Two field campaigns are planned for Greenland
Spring 2012 and 2013 and three field campaigns are planned for Antarctica each fall (Southern
hemisphere Spring) from 2012 to 2014. Should there be delay in meeting the first deployment in
Greenland, there is a second opportunity in Spring 2014 to recoup with no scientific sacrifice.
6. Measurement Platform System Capabilities
Due to the harsh environment and remoteness of Greenland and Antarctica, selection of a suitable platform is critical. We conducted a comprehensive aircraft survey covering multiple agencies and commercial operators. With a strong desire to use one platform for both Greenland and
Antarctica, the primary drivers in selecting an aircraft and operator were the following: 1) ceiling
exceeding 6 km barometric altitude, 2) range exceeding 2800 km, 3) operating costs and aircraft
availability, 4) ability to transit to and land at most Antarctic bases, 5) instrument accommodation in terms of weight, power and operators, 6) wing-span of ~20m with wing hard mount points
for the dipole array.
We have concluded that the DC-3 Basler Turbo conversion (BT-67) aircraft operated by Kenn
Borek Air (KBA) is best suited for our purposes. The BT-67 is a versatile, long-range (3700 km)
aircraft capable of ski or wheel operation with a ceiling of over 7.6 km. KBA has extensive experience in flying scientific missions in both Greenland and Antarctica. The KBA BT-67 has been
proven in several polar geophysical campaigns and has flown antenna arrays similar to the BIIR
configuration. Compatibility with instrument power, weight, operating frequencies and wingspan requirements have been established with KBA. The BT-67 was the only available aircraft
identified that fits all of our criteria and has significant performance margin.
Figure 3 depicts the BT-67 with the BIIR150 MHz dipole arrays mounted beneath its wings. A
contract for installation, aircraft modifications (additional hard mount points) and operations will
guarantee access and exclusive use of the aircraft during the scheduled deployments. KBA currently owns two BT-67 aircraft and will soon acquire three more. Although only one will be configured for our operation, the others serve as backup if absolutely necessary. KBA operates a
large fleet of aircraft and has full in-house maintenance, repair and modification expertise. This
reduces risk by having a single organization responsible for BIIR’s aviation operations. However, if a BT-67 is unavailable, there are a number of aircraft with multiple agencies that are compatible with BIIR for Greenland operations.
Government agency aircraft were considered for BIIR and those agencies contacted. NASA
does not appear to have any aircraft that currently land in Antarctica. The P-3 is the most likely
candidate, but is not currently configured for Antarctic operation and we are unaware of any
plans to do so. The P-3 does, however, provide a good backup for Greenland. The NSF was contacted regarding C-130 operations, but they are unable to modify or commit a single aircraft for
our purposes. Furthermore, the C-130’s are limited to large bases for landing which makes some
regions inaccessible for data collection.
Figure 3. BT-67 configured with tomographic radar array
6-3
Use or disclosure of information contained on this sheet is subject to the restriction on the cover page of this proposal.