DEM Control in Arctic Alaska Using ICESat Laser Altimetry
by Craig Lingle
Dedicated researchers are known for doing whatever it takes in the field to get the data they need. In this case, dedication meant traveling to Barrow, Alaska, in March 2004 and setting out on snow machines with an Inuit guide who kept watch for polar bears.
Reginald Muskett, a UAF Geophysical Institute (GI) doctoral candidate in geophysics, and ASF Remote Sensing Service Center Manager Don Atwood took Global Positioning System (GPS) measurements of geographical position and elevation on five frozen tundra lakes within 50 miles of Barrow.
Their GPS data collection is part of a project investigating the suitability of ICESat laser altimeter data for control of digital elevation models (DEMs) in arctic Alaska. Accurate control is essential for DEMs.
On-ground differential GPS measurements, such as those made by the researchers, have excellent accuracy. The Barrow GPS measurements taken in March were compared to elevation measurements on the same tundra lakes derived from data acquired in fall 2003 by NASA’s Geoscience Laser Altimeter System (GLAS), which is carried onboard the ICESat satellite.
GLAS instrumentation is a nextgeneration space lidar that combines a precision surface lidar with a sensitive cloud and aerosol lidar. ICESat is a NASA Earth Observing System (EOS) satellite mission, launched in January 2003.
The 2003 ICESat/GLAS-derived elevations on the tundra lakes compare closely to the ground differential GPS elevations measured on those same lakes. ICESat altimetry will therefore provide high quality DEM control in this region.
More recent ICESat/GLAS elevations, derived from data acquired during February and March 2004, will also be included in the analysis after these data are processed and made available by the National Snow and Ice Data Center in Boulder, Colorado.
Comparing datasets taken over the flat, relatively uniform terrain of the Alaska North Slope is an important first step in this project. Additional verification will involve comparisons to accurate high-resolution DEMs derived from STAR3i (airborne) interferometric SAR data provided by Intermap Technologies, Inc.
In the next, more challenging phase of the project, comparisons will be made over some of Alaska’s more rugged and varied terrain. Analogous comparisons will be carried out among ICESat-derived elevations, ground GPS measurements, and airborne interferometric SAR-derived DEMs in suitable areas.
The preliminary results in this project indicate that ICESat/GLAS-derived elevations on frozen tundra ponds have accuracies of about 3-30 cm relative to ground GPS measurements. ICESat altimetry will thus be an excellent source of control for digital elevation models in this region, which may include DEMs derived from ASF SAR data.
In addition to Muskett and Atwood, others at the GI carrying out this National Geospatial Intelligence Agencyfunded project include Research Professor Craig Lingle (principal investigator) and co-investigators from ASF: Nettie La Belle-Hamer (director), Rudi Gens (remote sensing scientist) and Rick Guritz (special projects manager). GI Research Professor Jeffrey Freymueller is carrying out precision differential reduction of the GPS data, and Britton Kerin from ASF is software engineer for the project.
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