Geodetic glacier mass balance (1975-1999) in the central Pamir using the SRTM DEM and KH-9 imagery

Multiple studies on regional glacier mass balance in the Pamir Mountains have been conducted using the geodetic method, but they were rarely extended to the period before 2000. In this study, we used KH-9 imagery acquired in 1975 to generate the historical DEM for the central Pamir, and then obtained the glacier elevation change by comparing this with the SRTM C-band DEM. The penetration depth of the C-band radar was corrected for different glacier surfaces, i.e. 2.96, 1.68 and 0 m for firn/snow cover, bare ice and debris-covered areas, respectively. The final results suggest that the central Pamir glaciers, overall, experienced a near-zero mass balance of -0.03 ± 0.24 m w.e. a^-1 for 1975-99. Due to glacier surge activity, the elevation change patterns of individual glaciers were highly variable, and their mass balances varied from -0.12 ± 0.26 to 0.63 ± 0.20 m w.e. a^-1. The mean mass budgets of the surge-type glaciers and non-surge-type glaciers were 0.03 ± 0.14 and -0.05 ± 0.28 m w.e. a^-1, respectively. Concurring with previous studies, we conclude that the central Pamir glaciers may have been in a state of approximately balanced mass budget or slight mass deficit from the mid-1970s to the mid-2010s.