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Ian Joughin

Senior Principal Engineer

Affiliate Professor, Earth and Space Sciences

Email

ian@apl.washington.edu

Phone

206-221-3177

Biosketch

Ian Joughin continues his pioneering research into the use of differential SAR interferometry for the estimation of surface motion and topography of ice sheets. He combines the remote sensing with field work and modeling to solve ice dynamics problems. Solving the problems helps him understand the mass balance of the Greenland and Antarctic Ice Sheets in response to climate change.

In addition to polar research, he also contributed to the development of algorithms that were used to mosaic data for the near-global map of topography from the Shuttle Radar Topography Mission (SRTM).

Department Affiliation

Polar Science Center

Education

B.S. Electrical Engineering, University of Vermont, 1986

M.S. Electrical Engineering, University of Vermont, 1990

Ph.D. Electrical Engineering, University of Washington, 1995

Publications

2000-present and while at APL-UW

Ice velocity of Jakobshavn Isbrae, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariae Isstrøm, 2015–2017, from Sentinel 1-a/b SAR imagery

Lemos, A., A. Shepherd, M. McMillan, A.E. Hogg, E. Hatton, and I Joughin, "Ice velocity of Jakobshavn Isbrae, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariae Isstrøm, 2015–2017, from Sentinel 1-a/b SAR imagery," The Cryosphere, 12, 2087-2097, doi:10.5194/tc-12-2087-2018, 2018.

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18 Jun 2018

Systematically monitoring Greenland's outlet glaciers is central to understanding the timescales over which their flow and sea level contributions evolve. In this study we use data from the new Sentinel-1a/b satellite constellation to generate 187 velocity maps, covering four key outlet glaciers in Greenland: Jakobshavn Isbrae, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariae Isstrøm. These data provide a new high temporal resolution record (6-day averaged solutions) of each glacier's evolution since 2014, and resolve recent seasonal speedup periods and inter-annual changes in Greenland outlet glacier speed with an estimated certainty of 10%. We find that since 2012, Jakobshavn Isbrae has been decelerating, and now flows approximately 1250 m yr-1 (10%), slower than 5 years previously, thus reversing an increasing trend in ice velocity that has persisted during the last decade. Despite this, we show that seasonal variability in ice velocity remains significant: up to 750 m yr-1 (14%) at a distance of 12 km inland of the terminus. We also use our new dataset to estimate the duration of speedup periods (80–95 days) and to demonstrate a strong relationship between ice front position and ice flow at Jakobshavn Isbrae, with increases in speed of  ~ 1800 m yr-1 in response to 1 km of retreat. Elsewhere, we record significant seasonal changes in flow of up to 25% (2015) and 18% (2016) at Petermann Glacier and Zachariae Isstrøm, respectively. This study provides a first demonstration of the capacity of a new era of operational radar satellites to provide frequent and timely monitoring of ice sheet flow, and to better resolve the timescales over which glacier dynamics evolve.

Intercomparison and validation of SAR-based ice velocity measurement techniques within the Greenland Ice Sheet CCI project

Boncori, J.P.M., and 19 others including I. Joughin, "Intercomparison and validation of SAR-based ice velocity measurement techniques within the Greenland Ice Sheet CCI project," Remote Sens., 10, 929, doi:10.3390/rs10060929, 2018

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12 Jun 2018

Ice velocity is one of the products associated with the Ice Sheets Essential Climate Variable. This paper describes the intercomparison and validation of ice-velocity measurements carried out by several international research groups within the European Space Agency Greenland Ice Sheet Climate Change Initiative project, based on space-borne Synthetic Aperture Radar (SAR) data. The goal of this activity was to survey the best SAR-based measurement and error characterization approaches currently in practice. To this end, four experiments were carried out, related to different processing techniques and scenarios, namely differential SAR interferometry, multi aperture SAR interferometry and offset-tracking of incoherent as well as of partially-coherent data. For each task, participants were provided with common datasets covering areas located on the Greenland ice-sheet margin and asked to provide mean velocity maps, quality characterization and a description of processing algorithms and parameters. The results were then intercompared and validated against GPS data, revealing in several cases significant differences in terms of coverage and accuracy. The algorithmic steps and parameters influencing the coverage, accuracy and spatial resolution of the measurements are discussed in detail for each technique, as well as the consistency between quality parameters and validation results. This allows several recommendations to be formulated, in particular concerning procedures which can reduce the impact of analyst decisions, and which are often found to be the cause of sub-optimal algorithm performance.

Ionospheric correction of InSAR data for accurate ice velocity measurement at polar regions

Liao, H., F.J. Meyer, B. Scheuchl, J. Mouginot, I. Joughin, and E. Rignot, "Ionospheric correction of InSAR data for accurate ice velocity measurement at polar regions," Remote Sens. Environ., 209, 166-180, doi:10.1016/j.rse.2018.02.048, 2018.

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1 May 2018

Interferometric synthetic aperture radar (InSAR) has become an essential tool for measuring ice sheet velocity in the Polar Regions. At low radar frequencies, e.g. L-band (1.2 GHz) but also at higher frequency, e.g. C-band (5.6 GHz), the ionosphere has been documented to be an important source of noise in these data. In this paper, we employ a split-spectrum technique and investigate its performance for correcting ionospheric effects in InSAR-based ice velocity measurements in Greenland and Antarctica. Three case studies using ALOS PALSAR data are used to assess the performance of the split spectrum technique for ionosphere correction over a range of environmental parameters. We employ several approaches to evaluate the results, including visual inspection, profile analysis, comparison of experimental and theoretic errors, comparison with reference data from other sources, generation of double difference interferograms, and analysis of time series of multi-temporal data. Our experiments show that ionospheric distortions are observed regularly, and in our analyzed Greenland dataset and Antarctic dataset the ionospheric noise reaches 14 m/yr and 10 m/yr, respectively, which exceeds the signal associated with ice motion. Our analysis using several different approaches demonstrates that the split-spectrum technique provides an effective correction. The split spectrum technique is also found to be superior to currently used approaches such as baseline fitting and multi-temporal averaging. The noise level is reduced by a factor of 70% in Greenland test areas and 90% in Antarctic test areas.

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In The News

Antarctic'as ice sheet is melting 3 times faster than before

Associate Press, Seth Borenstein

The melting of Antarctica is accelerating at an alarming rate, with about 3 trillion tons of ice disappearing since 1992, an international team of ice experts said in a new study.

14 Jun 2018

Hidden lakes drain below West Antarctica's Thwaites Glacier

UW News and Information, Hannah Hickey

Thwaites Glacier on the edge of West Antarctica is one of the planet’s fastest-moving glaciers. Research shows that it is sliding unstoppably into the ocean, mainly due to warmer seawater lapping at its underside.

8 Feb 2017

Satellite system tracks glaciers' flow in real time

Nature News, Jeff Tollefson

The Global Land Ice Velocity Extraction project (GoLIVE) is the first to provide scientists with regular, semi-automated measurements of ice movement across the entire world. The Landsat 8 satellite covers the planet every 16 days.

16 Dec 2016

More News Items

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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