Ice flow velocity of the Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm, Northeast Greenland, in the 1960s from Historical Satellite Imagery

Abstract. The Northeast Greenland Ice Stream (NEGIS) is experiencing sustained accelerated mass loss due to the combined effects of atmospheric and ocean warming. The Nioghalvfjerdsfjorden glacier (NG) and Zachariae Isstrøm (ZI) are major contributors to the mass balance in NEGIS, draining 12% of the Greenland Ice Sheet (GrIS). Precise measurements of the ice flow velocities of NG and ZI are crucial for estimating the mass balance in NEGIS and predicting future sea level rise. However, the study of early NEGIS is limited by the lack of ice flow velocity before 1985. We proposed a systematic process for orthorectification on CORONA KH-4A imagery, which proved to be efficient and accurate, yielding 25 m precision. Using a hierarchical network densification approach based on ARGON KH-5 and CORONA KH-4A imagery, we successfully generated the ice flow velocity map for NG and ZI from 1963 to 1967. The results showed different changes in ice flow velocity over a 57-year period for NG and ZI. The average ice flow velocity near the grounding line increased by 12.4% for NG and 81.4% for ZI from 1963 to 2020. This paper filled a gap in historical ice flow velocity data for NEGIS and provided early, and valuable information for studying the long-term motion of ice flow. It can also improve the prediction accuracy of future changes in mass balance in this region.