Application of remote sensing and GIS in glacier monitoring: Glacier variability in Central Asia (Tien Shan and Altai) during the last 30--60 years.

摘要

This study aims to estimate glacier changes in the two mountain systems of Central Asia - Tien Shan and Altai, during the last 30-60 years as a consequence of regional climatic changes using remote sensing and GIS methods. To this goal two methodological studies were undertaken demonstrating the potential of Shuttle Radar Topography Mission (SRTM) data and declassified KH-9 Hexagon images for estimation of glacier changes. Glacier area and volume changes were estimated in three pilot basins in Tien Shan and Altai: Akshiirak, Ala-Archa and Aktru using data from historical geodetic surveys, topographic maps, aerial photography, declassified KH-9 Hexagon photographs, ASTER and ALOS/PRISM satellite images, SRTM and IceSAT elevation data and DGPS in situ measurements.;Using SRTM data and a DEM from 1:25,000 topographic map glacier surface changes can be estimated with error about 8.2 m. In spite of SRTM error and the occasional absence of data on steep slopes, major long-term changes on relatively flat ablation and accumulation areas are clearly identifiable. Furthermore, the presence of local areas of rebound on glacier surfaces allowed decoupling of dynamic and climatic components of glacier changes that are not available solely from planimetric data.;The high metric qualities of KH-9 imagery demonstrated a unique opportunity to extend high-resolution land cover/land use change studies to early 70s on regional to global scales. An IDL program was developed for automatic geometric preprocessing of KH-9 images. The distortions of scanned KH-9 film frames were about 6 mum (maximum 47.32 mum) with non uniform local patterns that had to be removed by local interpolation. In bundle triangulation of KH-9 images horizontal accuracies below 8 m were achieved. The KH-9 DEM vertical accuracy over flat terrain was about 6 m and 30 m over high mountains. The triple overlap of the KH-9 images enabled good DEM definition and accuracy on both north and south facing steep mountain slopes.;From 1952 to 2006 the Aktru basin glaciers lost 7.2% of their area. During the last three decades, the rate of area loss accelerated by a factor of 1.8 (from 0.9% to 1.6% per decade). The changes were caused mainly by the increase of summer air temperature by 1.03°C at elevations below 2500 m and 0.83°C at elevations over 2500 m from 1951 to 2000.;The glaciers in Ala-Archa and Tien Shan retreated up to 3 km between the 1860s and 2003, the surface of their ablation areas lowered more than 130 m. The area of the Ala Archa glaciers shrunk by 15.8% over the last 40 yr. The Akshiirak glacierized massif lost about 10 km3 of glacier ice and 12.5% of glacier area between 1943 and 2000. From 1977 to 2003 the rate of volume loss of the Akshiirak glaciers accelerated by a factor of 2.7. Continuous growth of spring and autumn air temperatures in northern Tien Shan and increase of summer air temperature in Central Tien Shan since the middle of 1970's without increase of precipitation may further accelerate glacier recession and intensify desertification processes in the Central Asia and northwestern China.