Determining sea ice thickness with an airborne scanning laser
Sea ice is regarded by many as the 'canary in the coal mine' for climate researchers. Model climate predictions show that an expected increase in air temperature will be most dramatic in the polar regions and that summer Arctic sea ice extent will decline further in the next 10 to 20 years. While Antarctic sea ice extent and concentration is routinely monitored from space, it is currently unknown whether changes are occurring in its thickness distribution, and therefore its mass balance, in response to environmental change.
Photo: Image by Jan L Lieser, ACE CRC, helicopter courtesy www.3Dkitbuilder.com and TheyerGFX Pty Ltd.
- a scanning laser system (a recent acquisition of the Australian Antarctic Division) in combination with radar, to determine sea ice and snow cover properties (ultimately thickness);
- a digital camera to take aerial photographs for sea ice classification and concentration estimates; and
- a pyrometer for measuring surface temperature.
The latter helps to identify sea ice type, particularly for thin (new) ice. An inertial navigation system (INS) also provided precise information on the helicopter's location and attitude during operation. All together the aircraft was named 'RAPPLS', which stands for Radar-Aerial Photography-Pyrometer-Laser Scanner.
Photo: Tony Worby
the airborne data were calibrated for the long range surveys.
The laser scanner produces an across-track scanning pattern of the underlying surface (see image above). This pattern can be adapted to different applications, flying altitudes and speed. During SIPEX, we used a setup which allowed us to scan with a swath width of about 450 m. We successfully used the laser system on 28 flights for over 50 hours. The data are currently being processed at the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC) in close cooperation with the Australian Antarctic Division.
Photo: ACE CRC
This example demonstrates the great potential for sea ice monitoring and validation of space-borne sea ice thickness estimates (such as those from NASA's ICESat - a laser altimeter satellite - or ESA's upcoming CryoSat-II - a dedicated cryosphere radar mission). It also demonstrates the capabilities of high precision range measurements for digital elevation mapping of glaciers, ice shelves, icebergs, and islands. In combination with the simultaneously taken digital aerial photographs, we will produce high resolution 3-D digital elevation models. This work represents the first in a series of airborne sea ice monitoring efforts to be carried out by the Australian Antarctic Division, and will make an important contribution to improving our understanding of the thickness of East Antarctic sea ice and its spatio-temporal variability.
JAN L. LIESER
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