## 1 Introduction  
Ice shelf calving in Greenland can trigger and/or enhance ice flow acceleration and glacier front retreat [1], which is becoming a crucial factor affecting Greenland's ice sheet stability [2]. In particular, loss of an ice shelf can reduce resistance to ice flow from a grounded glacier [3, 4, 5], leading to increased discharge from the ice-sheet interior into the oceans [6, 7]. Ice shelf calving is an important component of dynamic ice sheet changes, representing the greatest source of uncertainty in projections of sea level rise. Although some observation and modeling investigations suggest that tidewater glaciers are sensitive to both atmospheric and oceanic forcing [8, 9, 10], the physical processes of the frontal collapse and their responses to warming air and sea temperatures are not fully understood [2]. The frontal collapse of floating ice shelf is a complex process, which is mainly driven by several hydrological and kinematic forces, including tributary glacier inflow, sea ice buttressing and supraglacial pond drainage. During the past decades, ocean warming [11, 12] and increased air temperature [13] reduced sea ice concentration in the fjords and intensified glacier surface melt, influencing the vulnerability of marine-terminating glaciers [14, 15, 16]. Some studies suggested that an increase of surface melting induced instability of the outlet of the glacier, leading to hydro-fracturing or even collapse due to melt ponds filling some crevasses in Northeast Greenland [17; 18]. Additionally, sea-ice concentration controlled the seasonal dynamics of the ice velocity response to buttressing fluctuations in the Totten Ice Shelf of Antarctica [19]. In addition, the tributary glacier inflow destabilized ice structural heterogeneity and intensified the vulnerability of the Larsen C ice shelf [20; 21]. The dynamic characteristics of the hydrological and kinematic precursors and underlying response mechanisms, which control the development of ice calving, remain poorly understood. Thus, it is crucial when investigating a frontal collapse process to capture the spatial-temporal variability of these hydrological and kinematic precursors. Satellite remote sensing has proven to be a useful tool to observe ice velocity change [22], supraglacial lakes [23; 24; 25; 26] and sea ice evolution [19; 27; 28]. Optical and microwave remote sensing images (e.g., Landsat-8 and Sentinel-1) have been widely applied to extract annual and seasonal ice velocity of outlet glaciers in Greenland [29; 30; 31]. Very long-term remote sensing observations have recorded the multi-decadal evolution of supraglacial lakes on the Larsen B ice shelf before it collapsed in 2002 [32; 33]. However, ice flow speed-up, terminus calving and lake drainage usually occur at daily to weekly timescales. Limited by the spatial-temporal resolution of the available remote sensing images, it is a challenge to acquire dense and abundant observations to characterize such short-lived dynamic process [34; 31]. In recent years, the focus in optical remote sensing has shifted from the use of a few scenes from individual satellites to utilizing data from multiple satellites. Twin satellites or constellations of satellites can shorten the revisit time and meet continuous coverage. The advantages of the short-temporal sampling rate and increasing spatial resolution recently have been exploited to capture rapid changes in glacier flow [35], indicating a huge potential to acquire the high spatial-temporal characteristics of hydrological and kinematic precursors of ice calving. The Petermann Glacier (PG), located in the outermost northwest corner of Greenland, is one of only three glaciers in Greenland with a floating ice tongue. Two major calving events occurred in PG between 2010 and 2012, which dramatically reduced the ice tongue length from approximately 85 km in 2010 to around 50 km in 2012 [36].