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szeptember 24.
2021
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Lóczy Dénes
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Cryosphere research is an important mission nowadays because the change of present ice shields strongly influences global climatic processes. The use of remote sensing methods in this field of research is becoming more widespread, as we can study temporally and spatially different phenomena. The surface velocity of glaciers responds quickly to changes in any climatic parameter. By examining glaciers’s speed, we can estimate the extent of environmental change. Using object-tracking algorithms, we can study the surface velocity of glaciers based on the cross-correlation of satellite images. This method finds the same features on two images and calculates their possible displacement relative to each other. Then it assigns direction and speed to the movement. Feature and Speckle Tracking are two ways of this method. While Feature Tracking uses objects tracked by landmarks, in the case of Speckle Tracking, the algorithm can detect different physical parameters calculated from the radar images. We use a recently developed method that uses the Feature and Speckle Tracking methods simultaneously to investigate the velocity of glaciers in the Southern Patagonian Ice Field (SPI) based on Sentinel-1 SAR radar images. The method has not been used in these areas before. Our aim is to monitorize the condition of the glaciers as accurately as possible to get insight into the environmental change in the area.
In the studied area 946 of one kilometer square regions were selected along the flow line of the glaciers, from their fronts to the accumulation areas. We have documented the surface velocity of glaciers from 2019 to 2021. Based on the 30 meter resolution SRTM data, the statistical values of the slope, aspect, height and curvature parameters of the topography were calculated. Based on gravity and radar measurements, statistical values of the ice thickness and glacier bed elevation data were also determined. While glacier speed is analyzed in a determined time frame, other parameters are used for correlation analysis.
The surface velocity in the SPI shows an acceleration compared to previous results. At the front of the glaciers velocity values of thousands of meters/year are common, suggesting that a significant change in the environment is present. As the temperature of the air increases, the amount of meltwater generated on the surface of the glaciers increases, which leaks to the bottom of the glaciers, causing their faster movement. Furthermore, as the air temperature rises, so does the sea temperature, which also causes fast velocity at the front of tidewater glaciers. The relationship between the velocity and the increase in air temperature is well illustrated by the fact that the fastest surface velocities are experienced during the summer periods. This characteristic seasonal fluctuation in velocity is especially true of the northernmost Jorge Montt Glacier (highest speed around 4700m/yr). In contrast, on the largest Pio XI glacier, we can observe rapid but constant movement throughout the year (maximum around 2000 m/yr). In addition to the climatic parameters, the different velocity is most probably the result of different topographic features as well, that are also examined thoroughly.
