Glacier mass loss during the 1960s and 1970s in the Ak-Shirak range (Kyrgyzstan) from multiple stereoscopic Corona and Hexagon imagery

Comprehensive research on glacier changes in the Tian Shan is available for the current decade; however, there is limited information about glacier investigations of previous decades and especially before the mid 1970s. The earliest stereo images from the Corona missions were acquired in the 1960s but existing studies dealing with these images focus on single glaciers or small areas only. We developed a workflow to generate digital terrain models (DTMs) and orthophotos from 1964 Corona KH-4 for an entire mountain range (Ak-Shirak) located in the Central Tian Shan. From these DTMs and orthoimages, we calculated geodetic mass balances and length changes in comparison to 1973 and 1980 Hexagon KH-9 data. We found mass budgets between -0.4 ± 0.1 m·w.e.a^-1 (1964-1980) and -0.9 ± 0.4 m·w.e.a^-1 (1973-1980) for the whole region and individual glaciers. The length changes, on the other hand, vary heterogeneously between +624 ± 18 m (+39.0 ± 1.1 m.a^-1) and -923 ± 18 m (-57.7 ± 1.1 m·a^-1) for 1964-1980. An automation of the processing line can successively lead to region-wide Corona data processing allowing the analysis and interpretation of glacier changes on a larger scale and supporting a refinement of glacier modelling.