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[ACC28-04] Short-term glacier velocity changes in the Southern Patagonian Ice Field detected by the Sentinel-1 satellite
Keywords:Southern Patagonian Ice Field, Sentinel-1 satellite, Glacier
Introduction
The Southern Patagonian Ice Field is the second largest glacier system in the Southern Hemisphere after Antarctica, and like Greenland and other glaciers in the Northern Hemisphere, it is experiencing retreat of its terminus and loss of surface elevation due to glacial outflow (Sakakibara and Sugiyama 2014). Glacier mass loss due to glacier retreat and surface elevation reduction contributes to sea level rise. The amount of glacier discharge is determined by the thickness and flow rate of the glacier, whereas the temporal changes in the flow rates were not precisely known until recently. The seasonal flow rate changes were first detected in the 1980s at mountain glaciers in the Swiss Alps, and have also been observed in Greenland ice sheet and other areas since the 2000s. On the other hand, the flow velocity of glaciers in the Southern Patagonian Ice Field has been studied on the timescale of a half-year to several years (Muto and Furuya 2013), and the flow velocity changes at a higher temporal resolution are not known. In this study, we used Synthetic Aperture Radar (SAR) images from the Sentinel-1B satellite, which has a recurrence period of 12 days, to investigate the temporal changes in flow velocity.
Seasonal changes in glacier flow velocities are generally known to accelerate in spring/summer and decelerate in autumn/winter. However, some surge-type glaciers in Yukon undergo winnter speed-up in their upstream even during their inactive phase of surging (Abe and Furuya, 2015). Moreover, some glaciers in Greenland have been observed to accelerate in winter and spring (Moon et al., 2014). The seasonal change in flow velocity is thought to be dominated by basal water pressure due to temporal changes in the drainage system at the base of the glacier, but the details are not yet clear in the light of those conter-intuitive observations of winter speed-up.
Data and Methods
Sentinel-1B images for approximately three years, January 2018-April 2021, were obtained and the pixel offset method was applied to pairs of 12 days difference in time, assuming that the glaciers are flowing along the gradient of the terrain (parallel flow approximation), and are shown in Figure 1, comparatively We analyzed the spatio-temporal changes in flow rates of seven relatively large glaciers (Occidental, Pio XI, Asia, Tyndall, Viedma, O'Higgins Glacier, and Amalia Glacier) shown in Figure 1. AW3D provided by JAXA was used as the numerical elevation model (DEM).
The pixel offset method was used in an area of about 500m x 600m (412pixel x 42pixel), and the number of steps was set to about 90m x 110m (40 x 8 pixels).
The flow velocity analyzed was less than 10 cm/day when the values were examined in areas considered to have no fluctuation, such as the rocky areas around the glacier. Therefore, the measurement error of the flow velocity is within this range, but the validity of the parallel flow approximation needs to be compared by obtaining the three-dimensional velocity vector.
Results and Discussion
Significant changes were observed in all seven glaciers (Occidental, Pio XI, Asia, Tyndall, Viedma, O'Higgins Glacier, and Amalia Glacier). Among them, Pio XI, Viedma, O'Higgins, and Amalia glaciers showed winter speed-up (Abe and Furuya, 2015) of 400%, 20%, 30%, and 30% acceleration in winter and deceleration in summer, respectively. In the lower reaches of Asia Glacier and Occidental Glacier, the acceleration was found to be 15% in spring.
Moon et al. (2014) and Vijay et al. (2021) have shown that seasonal changes in the flow rate of glaciers in Greenland vary from year to year. We plan to investigate how the glaciers we examined in this study change in other years.
The Southern Patagonian Ice Field is the second largest glacier system in the Southern Hemisphere after Antarctica, and like Greenland and other glaciers in the Northern Hemisphere, it is experiencing retreat of its terminus and loss of surface elevation due to glacial outflow (Sakakibara and Sugiyama 2014). Glacier mass loss due to glacier retreat and surface elevation reduction contributes to sea level rise. The amount of glacier discharge is determined by the thickness and flow rate of the glacier, whereas the temporal changes in the flow rates were not precisely known until recently. The seasonal flow rate changes were first detected in the 1980s at mountain glaciers in the Swiss Alps, and have also been observed in Greenland ice sheet and other areas since the 2000s. On the other hand, the flow velocity of glaciers in the Southern Patagonian Ice Field has been studied on the timescale of a half-year to several years (Muto and Furuya 2013), and the flow velocity changes at a higher temporal resolution are not known. In this study, we used Synthetic Aperture Radar (SAR) images from the Sentinel-1B satellite, which has a recurrence period of 12 days, to investigate the temporal changes in flow velocity.
Seasonal changes in glacier flow velocities are generally known to accelerate in spring/summer and decelerate in autumn/winter. However, some surge-type glaciers in Yukon undergo winnter speed-up in their upstream even during their inactive phase of surging (Abe and Furuya, 2015). Moreover, some glaciers in Greenland have been observed to accelerate in winter and spring (Moon et al., 2014). The seasonal change in flow velocity is thought to be dominated by basal water pressure due to temporal changes in the drainage system at the base of the glacier, but the details are not yet clear in the light of those conter-intuitive observations of winter speed-up.
Data and Methods
Sentinel-1B images for approximately three years, January 2018-April 2021, were obtained and the pixel offset method was applied to pairs of 12 days difference in time, assuming that the glaciers are flowing along the gradient of the terrain (parallel flow approximation), and are shown in Figure 1, comparatively We analyzed the spatio-temporal changes in flow rates of seven relatively large glaciers (Occidental, Pio XI, Asia, Tyndall, Viedma, O'Higgins Glacier, and Amalia Glacier) shown in Figure 1. AW3D provided by JAXA was used as the numerical elevation model (DEM).
The pixel offset method was used in an area of about 500m x 600m (412pixel x 42pixel), and the number of steps was set to about 90m x 110m (40 x 8 pixels).
The flow velocity analyzed was less than 10 cm/day when the values were examined in areas considered to have no fluctuation, such as the rocky areas around the glacier. Therefore, the measurement error of the flow velocity is within this range, but the validity of the parallel flow approximation needs to be compared by obtaining the three-dimensional velocity vector.
Results and Discussion
Significant changes were observed in all seven glaciers (Occidental, Pio XI, Asia, Tyndall, Viedma, O'Higgins Glacier, and Amalia Glacier). Among them, Pio XI, Viedma, O'Higgins, and Amalia glaciers showed winter speed-up (Abe and Furuya, 2015) of 400%, 20%, 30%, and 30% acceleration in winter and deceleration in summer, respectively. In the lower reaches of Asia Glacier and Occidental Glacier, the acceleration was found to be 15% in spring.
Moon et al. (2014) and Vijay et al. (2021) have shown that seasonal changes in the flow rate of glaciers in Greenland vary from year to year. We plan to investigate how the glaciers we examined in this study change in other years.