Detailed comparison of glaciological and geodetic mass balances for Urumqi Glacier No.1, eastern Tien Shan, China, from 1981 to 2015

The mass balance of Urumqi Glacier No.1, eastern Tien Shan, has been monitored since 1959, using the direct glaciological method. This study presents a detailed comparison of the glaciological mass balance with a high-quality product of geodetic surveys in the overlapping period from 1981 to 2015. We analyzed the generic differences between glaciological and geodetic mass-balance measurements, including in-depth uncertainties assessments. The statistical comparison shows that the reduced discrepancy (delta = 0.53) between the geodetic mass balance ( - 0.53 +/- 0.14 m w.e. a(-1)) and corrected annul glaciological mass balances ( - 0.46 +/- 0.14 m w.e. a(-1)) falls within the 95% confidence interval and reveals that no statistical significant bias between the two datasets is detectable over the period. Thanks to the good agreement, calibration of the glaciological to the geodetic data series is currently not required. The more negative geodetic mass balance is probably relevant to the glacier surface characteristics. The uncertainty of our results measured with geodetic method was close to the majority of similar studies, but bigger than those derived from multi-temporal high-quality DEMs. Further studies should continue using a long-range terrestrial laser scanning (TLS) system to derive high-resolution and -precision digital elevation models (DEMs) of the glacier surface at the monthly time-scale, which will provide a powerful complement to the glaciological measurements.