Automatic detection of calving events from time-lapse imagery at Tunabreen, Svalbard

Abstract

Abstract. Calving is an important process in glacier systems terminating in the ocean and more observations are needed to improve our understanding of the undergoing processes and be able to parameterise calving in larger scale models. Time-lapse cameras are good tools for monitoring calving fronts of glaciers and they have been used widely where conditions are favourable. However, automatic image analysis to detect and calculate the size of calving events has not been developed so far. Here, we present a method that fills this gap using image analysis tools. First, the calving front is segmented. Second, changes between two images are detected and a mask is produced to delimit the calving event. Third, we calculate the area given the front and camera positions as well as camera characteristics. To illustrate our method, we analyse two image time series from two cameras placed at different locations in 2014 and 2015 and compare the automatic detection results to a manual detection. We find a good match when the weather is favorable but the method fails with dense fog or high illumination conditions. Furthermore, results show that calving events are more likely to occur (i) close to where subglacial melt water plumes have been observed to rise at the front and (ii) close to one another.

Calving controlled by melt-under-cutting: detailed calving styles revealed through time-lapse observations

“…The sequence consists of 34117 images, which has enabled examination of the individual calving styles active at Tunabreen, and identification of the key controls and triggers of calving events. Despite the short data record, our observations are consistent with previous findings at Tunabreen (Åström and others, 2014; Köhler and others, 2015; Vallot and others, 2018b) and allow the mechanisms of failure to be examined in greater detail than hitherto possible.…”

“…sheet collapses, stack topples and subaqueous events). The size-frequency distribution of calving at Tunabreen follows a power law relation (Åström and others, 2014; Vallot and others, 2018b), similar to those observed at other Svalbard glaciers (Chapuis and Tetzlaff, 2014). In these cases, the observed calving frequency distribution is associated with the mutual interplay between calving and instabilities in the local vicinity of the calving region (Schild and others, 2018).…”

“…This possibility will be tested in future work. Automated methods to detect and classify calving events are needed in order to assist in this endeavour, such as from time-lapse imagery (e.g., Vallot and others, 2018b), video (e.g., Bartholomaus and others, 2012), and seismic records (e.g., O'Neel and others, 2007; Köhler and others, 2015; Mei and others, 2017).…”

“…Calving activity at Tunabreen has been documented from time-lapse photography (e.g., Åström and others, 2014; Vallot and others, 2018b), passive seismic monitoring (e.g., Köhler and others, 2015) and satellite data (e.g., Luckman and others, 2015). Luckman and others (2015) found a high correlation between ocean temperature and frontal ablation rates, suggesting that melt-under-cutting is the dominant control on calving losses on seasonal timescales.…”

Monitoring glacier flow in Ny-Ålesund with a high temporal resolution ground-based interferometric-phased array radar

“…If we detect accelerating flow, it might be the onset of a calving event and the antenna can be electronically directed to this area for higher resolution temporal mapping. Machine-learning algorithms or statistical signal processing could help automate the identification of calving onsets by recognizing the behaviour prior to a calving event, similar to what is performed on timelapse imagery (Vallot et al 2018). Steering the antenna towards calving events may be combined with radar monitoring of the whole glacier, but this will cause a trade-off between the temporal rate needed to follow the motion of the calving and the resources needed for continuous monitoring the rest of the glacier.…”