Abstract
Abstract. Antarctica and Greenland are two major Earth’s continental ice shelves which play an important role in influencing Earth’s energy balance through their high albedo. The ice sheets comprise of grounded ice or the continental glaciers and their associated ice shelves. Surface velocity is an important parameter that needs to be monitored to understand the glacier dynamics. Marine terminating glaciers have higher velocity than land terminating glaciers. Therefore, ice shelves are generally observed to have higher velocity as compared to continental glaciers. The focus of this study is Amery ice shelf (AIS) which is the third largest ice shelf located in east Antarctica terminating into the Prydz Bay on the eastern Antarctica. The surface ice-flow velocity of AIS is very high compared to its surrounding glaciers which flows at a rate of 1400 m a−1 and drains about 8% of the Antarctic ice sheet. AIS is fed by different glaciers and ice streams at the head, as well as from the western and eastern side of the ice shelf before it terminates into the ocean. The primary objective of this study was to compute velocity of the eastern tributary glaciers of AIS using SAR from Sentinel-1 data. The secondary objective was to compare the winter and summer velocities of the glaciers for 2017–2018. The offset tracking method has been applied to the ground range detected (GRD) product obtained from Sentinel-1 satellite. This method is suitable for regions with higher glacier velocity where interferometry is generally affected by the loss of coherence. The offset tracking method works by tracking the features on the basis of another feature and calculates the offset between the two features in the images. Two tributary glaciers near the Clemence massif and another glacier near the Pickering Nunatak feed into this ice shelf from the eastern glacial basin region that drains ice from the American Highland, east Antarctica. The glaciers near the Clemence massif showed low annual velocity which ranged from 100 m a−1 at the head to ∼300 m a−1 near the end of the glacier, where it merges with AIS. The glaciers flowing near the Pickering Nunatak exhibited moderate velocity ranging from 150 m a−1 at its head and reaching up to 450 m a−1 near the tongue. The summer velocity (March 2018) was observed to be higher than the velocity in winter (July 2017) and the difference between the summer and the winter velocities was found to be between 50 m a−1 and 130 m a−1. The results for the velocity were obtained at 120 m resolution and were compared with the previous MEaSUREs (Making Earth System Data Records for Use in Research Environments) yearly velocity at 450 m and 1 km resolution provided by National Snow and Ice Data Center portal. The results were evaluated using statistical measure- bias and the accuracy was derived using the root mean square error. The bias did not exceed 20 m a−1 for the three glaciers and the accuracy was observed to be more than 85% for most of the regions. The accuracy of the results suggests that the offset tracking technique is useful for future velocity estimation in the regions of high glacier velocity.
Highlights
The ice and snow in the Polar Regions play a crucial role in Earth’s radiation budget as the cryosphere reflects about 90% of the incoming solar radiation (Jawak and Luis, 2014)
On account of the high surface flow velocity of the Amery ice shelf (AIS) and its tributary glaciers, the estimation of velocity considering unwrapped phase Synthetic Aperture Radar (SAR) using interferometric techniques is less reliable due to the lack of coherence needed for precise calculations, and due to unavailability of ground control points for phase calibration in areas that are enveloped by ice (Lugli and Vittuari, 2017)
The interferometric technique measures the movement along the line of sight efficiently (Tong et al, 2018; Joughin et al, 2010), which acts as a limitation in most of the regions of the AIS as the ice shelf flows along the azimuthal direction
Summary
The ice and snow in the Polar Regions play a crucial role in Earth’s radiation budget as the cryosphere reflects about 90% of the incoming solar radiation (Jawak and Luis, 2014). The continental shelves of Antarctica and Greenland are almost completely covered by ice (Jawak et al, 2018). In the southern hemisphere Antarctica hosts larger ice mass and in the northern hemisphere Greenland contains relatively less ice mass, both of which could contribute to sea level rise of 66 m, if completely melted. The availability of satellite remote sensing technology and its progress in recent decades has enhanced our capability to monitor these regions at regular time intervals over a long period of time (Jawak and Luis, 2014)
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