USE OF ALASKA HIGH ALTITUDE PROGRAM (AHAP) IMAGERY TO DETERMINE CHANGES IN ALASKA'S GLACIERS

Studies that investigate volume changes of Alaska’s glaciers rely heavily on comparing recent elevation data (taken from various sources such as Lidar profiles and SRTM DEMs) with National Elevation Dataset (NED) DEMs. Since the NED DEMs are derived from aerial images acquired in the early 1950s, this comparison gives a very good estimate of total change in the last 40 to 60 years, but does not show the trajectory of change within this period.

Alaska’s High Altitude Program (AHAP) that acquired airborne data from the 1970s and 1980s provides a valuable source of information during a period when we have a general paucity of satellite remote sensing data over the Alaskan glaciers. Though AHAP images are available for almost all Alaskan glaciers, they have been rarely exploited by the glaciology community.

We applied established stereo-photogrammetric techniques on selected AHAP images of the Western Chugach Mountains to derive DEMs for several glaciers. For the photogrammetric processing we used different sources of Ground Control Points (GCPs). In one study area, we retrieved GCPs from a high resolution laser scan, in other areas, the GCPs solely based upon satellite imagery and topographic maps.

We carried out a quality analysis by comparing the DEMs we generated to all other available DEMs.

Results show that accurate GCPs derived from laserscans or field measurements allow for creating high quality AHAP DEMs.

The availability of increasing number of high resolution laser scans in the near future will allow for deriving a rich set of AHAP DEMs. This development is very timely and exciting since these DEMs are one of the very few elevation sources available for the late 70s.