C.J. van der Veen, V.I. Lytle and S. Gogineni
Center for Remote Sensing of Ice Sheets, The University of Kansas,
2335 Irving Hill Road, Lawrence, KS 66045, email@example.com
Together, the ice sheets in Greenland and Antarctica contain enough freshwater to raise global sea level by more than 60 m if they were to melt entirely and transfer to the world’s oceans. A complete collapse of these vast reservoirs of ice is unlikely in the near future. However, recent observations have raised the real possibility that the contribution of great ice sheets to global sea level rise over the next century may be greater than the models employed by the Intergovernmental Panel on Climate Change (IPCC) predict. This realization has come primarily from new and innovative observations from both airborne- and spaceborne-sensors.
|Figure 1. Top: Drawing of the Meridian UAV with Vivaldi
antenna-array for sounding, imaging and mapping of polar
ice sheets. Bottom: Fuselage fabrication is nearing
completion, and final assembly is beginning (left) and wing
assembly has begun.
Air- and spaceborne remote sensing is revolutionizing our understanding of ice sheets. The launch of the ERS-1 satellite in July 1991 heralded a new era in glaciology and the way the polar ice sheets are observed. This platform carried a variety of instruments including a radar altimeter (RA) and a synthetic aperture radar (SAR) that have proven to be invaluable for detecting changes in Greenland and Antarctica. Since then, other satellites have provided information on surface elevation changes, ice-surface velocities and melt extent [Jezek 2002; Joughin et al.,1998, Krabill et al., 2000; Rignot, 2002; Rignot and Thomas, 2002; Thomas, 2001; and Zwally et al., 2002]. These data illuminated unpredicted dynamics and have forced the glaciological community to reevaluate reigning paradigms on the flow of large ice sheets. Until recently, the prevailing view was that these large ice masses move sluggishly, discharging ice from the interior to the world’s oceans at a slow, orderly, and predictable rate. This view was increasingly challenged as observations of rapidly changing outlet glaciers and ice streams became available. For example, Jakobshavn Isbræ, in western Greenland, more than doubled its speed from around 6 km/yr in 1992, to nearly 14 km/yr in 2003 [Joughin et al., 2004]. In the Antarctic Peninsula, collapse of floating peripheral ice shelves following regional warming has led to increased discharge from glaciers previously buttressed by these ice shelves [Shephard and Wingham, 2002]. Some of the speed-up events appear to have been of short duration, with two east Greenland glaciers decelerating and apparently stabilizing – perhaps temporarily [Howat et al., 2007]. Thus, it is vital to sustain these observations in the future to distinguish short-term events from changes that are sustained over longer periods, so we can provide improved estimates of sea level for use by society.
The current generation of prognostic ice-sheet models were developed before these observations of rapid change became available. Consequently, these models are likely underestimating the rate of disappearance of the ice sheets, and under-predicting future sea level rise, as acknowledged in the IPCC Fourth Assessment Report issued in 2007 [IPCC, 2007]. To improve these models, an increased understanding of the processes contributing to rapid changes is urgently required. Acquiring such understanding requires imaging the polar ice sheets from top to bottom. Satellite remote-sensing is able to map the ice surface elevation and morphology, and surface-flow fields from which information about the glacier bed can be inferred by modeling. Surface-based seismic studies, while logistically intensive, yield a three-dimensional view of the ice sheets locally, along with providing unique information about the presence or absence of water. Airborne radar sounding enables regional characterization of the internal ice structure, the ice thickness, and conditions at the ice-bed interface. Innovative, coordinated applications of all three approaches are required to resolve the issue of why the flow of the great ice sheets is increasing.
The University of Kansas has been conducting airborne mapping of the Greenland Ice Sheet using ice-penetrating radar since 1993. Primary products from these surveys resulted in the first-ever Greenland bed topography map published in 2001 [Bamber et al., 2001], and mapping of internal layers, notably in areas where deep ice cores have been retrieved, to characterize the internal flow structure of the ice. As our ability to measure important characteristics of the Greenland Ice Sheet increased, it became apparent that improved understanding of its flow dynamics required an expanded, interdisciplinary approach aimed at combining targeted observations (using remote sensing systems and field-based sensors) with modeling efforts. To enable this critical need, the National Science Foundation, with additional funding provided by the respective core university partners and in-kind support from industry and collaborating institutions, established the Center for Remote Sensing of Ice Sheets (CReSIS) in July, 2005.
CReSIS is a Science and Technology Center involving six US Universities and several affiliated institutions around the world. Led by the University of Kansas (Lawrence, KS); partner universities are The Ohio State University (Columbus, OH), The Pennsylvania State University (State College, PA), the University of Maine (Orono, ME), Elizabeth City State College (Elizabeth City, NC), and Haskell Indian Nations University (Lawrence, KS). The latter two are minority-serving universities, reflecting the strong commitment of CReSIS to involve traditionally underrepresented groups in this research. CReSIS has also established fruitful collaborations with institutions in Denmark, Norway, Australia, United Kingdom, and Iceland. Technology developed at CReSIS is applied in collaborative projects such as the international effort to explore the Gamburtsev Subglacial Mountains in East Antarctica, and conducting airborne proof-of-concept experiments for the Global Ice Sheet Mapping Orbiter (GISMO) whose long-range science goal is to perform pole-to-pole measurements of glacier and ice-sheet thickness, basal topography, and physical properties of the glacier bed [Jezek et al., subm.].
The central mission of CReSIS is “to understand and predict the role of polar ice sheets in global sea level change. To achieve this mission, CReSIS is developing sensors and platforms to probe the polar ice sheets. Radar systems are continually being improved to refine observations, particularly in challenging areas such as fast-moving outlet glaciers with heavily fractured and wet surfaces, both of which decrease the useful radar energy, and image the ice-bed interface through two to three kilometers of ice. We have successfully demonstrated radar imaging of the ice-bed interface through 3-km thick ice [Gogineni et al., 2007] and used radar return characteristics to detect meltwater at the base of north-central Greenland [Oswald and Gogineni, 2008] where numerical ice-sheet models incorrectly predicted the basal ice to be frozen to the bed. The Center is also developing autonomous vehicles to support airborne- and surface-based observations. The uncrewed aerial vehicle (UAV), with a wing-span of 8 m that can carry a payload of 55 kg and has a flying range of 1750 km, is being developed for deployment in Antarctica during the 2008-2009 field season [Donovan and Hale, 2007]. Figure 1 shows the prototype UAV, called Meridian. It has a large wing-span to accommodate an eight-element ultra-wideband antenna array needed to sound, map, and image the ice. The design of the UAV is optimized to accommodate the radar weight, volume, and power, and the antenna-array size. CReSIS is also investigating new approaches to field-based measurements including the development of a ”streamer-based” seismic array for rapid data collection, and a firn-penetrating probe to obtain fine-resolution density data needed to model and interpret near-surface internal layers mapped with an ultra-wideband radar.
Within its first three years, CReSIS has achieved a number of glaciological firsts. After more than a decade of attempts, the current generation of radars successfully imaged the deep trench under Jakobshavn Isbræ. Mapping this trench has proven to be a major challenge because of its narrow width (around 6 km) and great depth (1500 m, with approximately 1 km of overlying ice). This trench impacts the flow of Jakobshavn in important ways, funneling drainage to the coast and focusing geothermal heat supplied to the deep ice. Figure 2 shows a radar echogram of data collected across the Jakobshavn channel and represents the first successful radar sounding of this channel. The radar used to collect these data can simultaneously sound ice, map internal layers, and image the ice-bed interface. In central Greenland, we have produced the first ever truly two-dimensional map of bed topography at an unprecedented 30-m spatial resolution. By analyzing the shape and characteristic of radar return from the bed, we have shown that it is possible to map locations under the ice sheet where meltwater is present at the glacier base [Oswald and Gogineni, 2008]. These data are vital to understand the state and dynamics of the ice sheets and to validate prognostic numerical ice-flow models.
|Figure 3. Spencer Johnson, a Topeka middle
school student, is explaining regelation to guests at
a Family Science Night, a topic he learned while
participating in “Ice, Ice, Baby” activities at his school.
Science and technology development are a large thrust within CReSIS. At the same time, the Center has a strong commitment to education and outreach, with the primary objective to use polar science to increase student interest in STEM-related fields of study. Educational efforts span from K-12 through undergraduate to the graduate level. The University of Kansas has entered a formal agreement with the nearby Topeka school district and developed a series of popular classroom activities – called “Ice Ice Baby” – to make polar science understandable and interesting for K-12 levels. These activities and related educational materials are freely available from the CReSIS website. Figure 3 shows an example of this activity at a school in Topeka. Summer Schools for Teachers have been organized in Ohio and Kansas to increase knowledge about Climate Change, introduce teachers to existing classroom resources, and develop lesson plans for introducing climate change and sea level in the classroom. CReSIS also participates in PolarTREC (http://www.polartrec.com/) which offers teachers an opportunity to participate in polar field research. Research Experience for Undergraduates (REU) is an NSF-sponsored program that allows undergraduate students to spend a summer at one of the CReSIS institutions to engage in scientific research, with the objective to make these students enthusiastic about polar research and pursue graduate studies in this area.
Ice sheet research is inherently interdisciplinary, involving engineers and scientists interested in remote sensing, atmospheric physics, glaciology, geology, geography, numerical modeling, and other fields. The Center provides opportunities to learn and conduct research in an interdisciplinary environment. We developed a graduate curriculum building on the expertise of our faculty and existing courses at partner institutions, and developing new courses. Using the Center’s real-time two-way video conference facility, courses are offered as interactive online classes originating from any of the partner institutions. The courses cover introductory and advanced topics in glaciology, climate change, remote sensing, geophysics, radars and sensors, and business and financial issues of climate change. These courses provide students with an opportunity to explore scientific and technical topics related to climate change research by taking courses outside their area of specialization.
Accurate prediction of sea level is arguably one of the most important societal needs facing the research community. Combining cutting-edge technologies with sustained observations to understand processes and improve numerical models will be required to address this question. Using focused technology development, promotion of sustained observations, and coordination of international modeling efforts, progress is being made to reach this goal.
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