| 03 Nov 2025
Glacier surge activity over Svalbard from 1992 to 2025 interpreted using heritage satellite radar missions and Sentinel-1
Abstract. Based on massive processing of heritage radar data from the satellite missions ERS-1/2, JERS-1, ENVISAT ASAR, ALOS PALSAR and Radarsat-2, and in combination with data from the current Sentinel-1 and ALOS-2 PALSAR-2 missions, we compiled a ~30-year time series of radar backscatter over Svalbard. We exploited this data to detect glacier surges by using changes in backscatter as an indicator of increased or decreased surge-related crevassing. In this way, we reconstructed an as consistent as possible time series of surge activity on Svalbard for 1992 to 2025. We recorded 24 surge-type events during the pre Sentinel-1 period 1992–2014 (23 years) and 34 surge-type events during the post Sentinel-1 period 2015–2025 (11 years). This time series shows an approximately threefold increase in surges since 2015, from an average of about one surge per year to more than three surges per year. We show that this increase is unlikely to be explained alone by the better resolution, coverage and quality of the Sentinel-1 data compared to the data from the earlier SAR heritage missions. Simulation results indicate that the observed increase is extremely unlikely to be attributed to random perturbations in surge cyclicity, and instead suggest the influence of an external forcing mechanism. The number of surges during the recent decade seems high, but due to uncertainties in historical records, it remains unclear whether this frequency is exceptional or if earlier decades were unusually quiet. The cause of the observed threefold increase in surge activity also remains uncertain, given our incomplete understanding of surge initiation in relation to climate variability and non-climatic surge controls.
Firstly, I want to thank the authors for completing the work for the community. It can be challenging and time-consuming to work with multiple historical satellite missions. As outlined in the manuscript, each dataset typically has distinct characteristics, and special considerations or care are often needed to ensure high-quality analysis results. I acknowledge such a huge effort associated with this work.
In this study, the authors examine five heritage satellite radar datasets and Sentinel-1 data to identify surge onset and termination in Svalbard using methods from Leclercq et al. (2021) and Kääb et al. (2023). The results agree well with existing records and have updated our knowledge of surging glaciers in Svalbard by adding a few more events and clarifying previous identifications. The study also shows that both C-band and L-band can be used to identify surge events based on radar backscatter changes, which could be useful information for future radar missions. The manuscript is well prepared, with detailed descriptions, and the discussion offers interesting validations and perspectives on surge frequency and external forcings. I enjoyed reading it.
The manuscript is ready to be accepted by TC, in my opinion, but if the authors have time, the following comments may be considered before publication.