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Seasonal Glacier Surface Velocity Fluctuation and Contribution of the Eastern and Western Tributary Glaciers in Amery Ice Shelf, East Antarctica

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Seasonal Glacier Surface Velocity Fluctuation and Contribution of the Eastern and Western Tributary Glaciers in Amery Ice Shelf, East Antarctica CZECH POLAR REPORTS 9 (1): 49-60, 2019 Seasonal glacier surface velocity fluctuation and contribution of the Eastern and Western Tributary Glaciers in Amery Ice Shelf, East Antarctica Shridhar Digambar Jawak1,2, Shubhang Kumar3, Alvarinho Joaozinho Luis1, Prashant Hemendra Pandit4*, Sagar Filipe Wankhede1 1Earth System Science Organization (ESSO), National Centre for Polar and Ocean Research (NCPOR), Ministry of Earth Sciences (MoES), Headland Sada, Goa 403804, India 2Svalbard Integrated Arctic Earth Observing System (SIOS), SIOS Knowledge Centre, Svalbard Science Park, P.O. Box 156, N-9171, Longyearbyen, Svalbard, Norway 3Centre for Land Resource Management, Central University of Jharkhand, Ranchi 835205, India 4National Bureau of Soil Survey and Land Use planning (NBSS & LUP) - Indian Agriculture Research Institute (IARI), New Delhi 110012, India Abstract Glaciers play a crucial role in the study of the climate change pattern of the Earth. Re- mote sensing with access to large archives of data has the ability to monitor glaciers frequently throughout the year. Therefore, remote sensing is the most beneficial tool for the study of glacier dynamics. Fed by many tributaries from different sides, the Amery Ice Shelf (AIS) is one of the largest ice shelves that drains ice from the Antarctic ice sheet into the Southern Ocean. This study focuses on the eastern and the western tribu- taries of the AIS. The primary objective of the study was to derive the velocity of the tributary glaciers and the secondary objective was to compare variations in their velocities between the summer and winter season. This study was carried on using the European Space Agency’s (ESA) Sentinel-1 satellite’s Synthetic Aperture Radar (SAR) data acquired from the Sentinel data portal. Offset tracking method was applied to the Ground Range Detected (GRD) product of the Sentinel-1 interferometric wide (IW) swath acquisition mode. The maximum velocity in summer was observed to be around 610 m/yr in the eastern tributary glacier meeting the ice shelf near the Pickering Nuna- tak, and around 345 m/yr in the Charybdis Glacier Basin from the western side. The maximum velocity in the winter was observed to be 553 m/yr in the eastern side near the Pickering Nunatak whereas 323 m/yr from the western side in the Charybdis Glacier Basin. The accuracy of the derived glacier velocities was computed using bias and root mean square (RMS) error. For the analysis, the publicly available velocity datasets were used. The accuracy based on RMS error was observed to be 85-90% for both seasons with bias values up to 25 m/yr and root mean square error values up to 30 m/yr. Key words: Antarctic, glacier velocity, offset tracking, synthetic aperture radar DOI: 10.5817/CPR2019-1-5 ——— Received May 7, 2019, accepted June 3, 2019. *Corresponding author: P. H. Pandit <[email protected]>; <[email protected]> Acknowledgements: The authors would like to thank European Space Agency (ESA) for providing Sentinel-1 images available online. We would like to acknowledge Dr. M. Ravichandran, Director, ESSO-NCPOR for his encouragement to carry out the work. The whole study was carried out at the Polar Remote Sensing Division of NCPOR, Goa. 49 S. D. JAWAK et al. Abbreviations: AIS – Amery Ice Shelf, CGB – Charybdis Glacier Basin, CM – Clemence Massif, ESA – European Space Agency, PN – Pickering Nunatak, SAR – Synthetic Aperture Radar, GRD – Ground Range Detected, IW – Interferometric Wide, POD – Pre- cise Orbit Determination Introduction The cryosphere is one of the most im- in ice dynamics but also to estimate and portant parts of the Earth’s ecosystem. The map the ice motion. interest in the study of glaciers has in- Glacier velocity has been estimated creased rapidly in the past decades as gla- from space using sequential images cap- cier dynamics are affected due to the tured by multiple satellites, by either opti- change in the climatic patterns (Schellen- cal technology or the synthetic aperture berger et al. 2016). Recent advancement in radar (SAR). Although this work was ini- the studies has increased our understand- tially started with the launch of optical ing of the mass balance of the ice sheets, sensor satellite Landsat, the SAR sensor their contribution to the sea level rise, and has been the method of choice to map ice the flow dynamics (Rignot 2006, Schellen- velocity. The reason was its ability to op- berger et al. 2016). Regular monitoring and erate in all weather conditions, higher tem- understanding the glacier flow dynamics poral and spatial correlation compared to helps in the assessment of the changes that optical sensors, winter and summer alike, occur in the glacier throughout the year and finer spatial resolution available at the (Joughin 2002). Unfortunately, regular as- time (Mouginot et al. 2017a). The continu- sessment of glaciers through field visits is ous acquisition and the free distribution limited in remote regions of the Earth such of the datasets of Landsat satellite series as Antarctica and Himalayas, due to vari- along with Sentinel satellite programme ous factors including harsh weather and have offered a novel opportunity to study high logistical costs, etc. (e.g. Tong et al. the velocity of polar and Alpine glaciers 2018). The remote location of Antarctica and the ice sheets motions. makes remote sensing the best available One of the significant parameters for technology that could be used for regular examining the variations in the dynamics monitoring and assessment of glaciers and of glaciers and ice streams is the glacier its parameters (Pandit et al. 2018a, Jawak surface velocity, which facilitates mass et al. 2018a). transport from ice sheets to the oceans During the last decades, the progress in (Hanna et al. 2013, Mouginot and Rignot the remote sensing technology has allowed 2015, Wuite et al. 2015). The mass bal- major advancement in the cryosphere study ance of the East Antarctic ice sheet over by providing complete and precise obser- the past two decades remains unclear (Liu vation of the complex pattern of the ice et al. 2017). A study conducted by Gol- sheets and has significantly improved our ledge and Levy (2011) suggests that the understanding of the science of ice flow. ice velocity of outlet glaciers of East Ant- The glacier velocity mapping has been ac- arctica have a dynamic response to en- curately estimated (Fan et al. 2019, Pandit vironmental changes. Thus, the study of et al. 2018b, Jawak et al. 2018a, b; Liu et surface ice flow velocity and its seasonal al. 2017, Jawak et al. 2017). Remote sens- changes needs to be conducted (Liu et al. ing-based observations, in particular, have 2017). made it possible not only to detect changes 50 AIS TRIBUTARY GLACIER VELOCITY The Amery Ice Shelf (AIS), East Ant- InSAR (Tong et al. 2018), speckle tracking arctica is among the largest ice shelves of (Tong et al. 2018, Gray et al. 2001) and off- Antarctica. Various studies (Joughin 2002, set tracking (Sánchez-Gámez and Navarro Tong et al. 2018, Manson et al. 2000, 2017, Strozzi et al. 2002) on SAR data, Pittard et al. 2015, King et al. 2007) have feature tracking (Fukuda et al. 2014) on been performed to estimate the annual ve- optical data, and many more. Of these locity of the AIS and the tributary glaciers methods, velocity estimation using offset contributing to its flow from the western tracking has been previously carried out in and eastern side, as well as the head of the various regions including mountain gla- glacier. Unfortunately, very few studies ciers such as the Andes (Riveros et al. have focused on the estimation of seasonal 2013), the Himalayas (Satyabala 2016) and glacier velocity variations in the AIS and continental glacier of Antarctica (Gomez its surrounding glaciers. Since outlet gla- et al. 2019). The study conducted by Sán- ciers are more susceptible to variations in chez-Gámez and Navarro (2017) in Cana- climatic patterns than the inland glaciers dian Arctic included both offset tracking (Scambos et al. 2004, Zhou et al. 2014), as well as DInSAR method and concluded understanding the seasonal variations in that both the techniques resulted in good surface velocity of these outlet glaciers accuracy and complemented each other. helps in better assessment of the changes The objectives of the current study that occur in the glaciers as inland glaciers were (1) to estimate the ice flow velocity are less affected by the climate change as of the eastern and western tributary gla- compared to outlet glaciers. ciers of the AIS, East Antarctica and (2) to Several methods have been used in the compare the variation in the summer and past to estimate glacier velocity such as winter season velocity of the tributary gla- e.g. Interferometric SAR (Joughin 2002, ciers using offset tracking method on SAR Tong et al. 2018) (InSAR), Differential data. Material and Methods Study Area The AIS represents one of the fastest al. 2001). The current study (Fig. 1) was glaciers in Antarctica. The glacier is typi- conducted on the four major tributary gla- cal by high surface velocities and drains cier that contributes to the flow of the AIS 16% of the mass from the interior of Ant- both from the eastern and the western side arctica (Gray et al. 2001, Jawak et al. 2019). of the ice shelf. The two major glaciers The temperature variation ranges between from the eastern side meet the AIS near 0°C to 10°C within single a day during sum- the Clemence Massif (CM) region and the mer. In winter, the daytime temperature Pickering Nunatak (PN). The other two gla- varies between -15°C and -18°C (Jawak et ciers meet the AIS from the western side al.
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