Tributaries of West Antarctic ice streams revealed by RADARSAT interferometry

Science

Volumn 286, Issue 5438, 1999, Pages 283-286

  Joughin, Ian ^a   Gray, Laurence ^a   Bindschadler, Robert ^a   Price, Stephen ^a   Morse, David ^a   Hulbe, Christina ^a   Mattar, Karim ^a   Werner, Charles ^a  

^a NONE

Author keywords

[No Author keywords available]

Indexed keywords

ICE;

ICE MOVEMENT; ICE SHEET; RADARSAT; REMOTE SENSING;

ANTARCTICA; ARTICLE; GEOLOGY; INTERFEROMETRY; PRIORITY JOURNAL; TELECOMMUNICATION; VELOCITY;

ANTARCTICA;

EID: 0033536643     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.286.5438.283     Document Type: Article

References (42)

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17. A technique for determining two-dimensional ice motion from one pair of coherent images was presented by K. H. Thiel, A. Wehr, X. Wu, paper presented at the Workshop on Glaciological Applications of Satellite Radar Interferometry, Pasadena, CA, 28 to 29 March 1996. Rignot (5) also used a related correlation technique for two-dimensional motion and refers to R. Michel (thesis, University of Paris XI, 1997). Independently, we have developed the speckle-tracking approach (A. L. Gray et al., paper presented at IGARSS '98, Seattle, WA, 6 to 10 July 1998), which takes advantage of its ability to coregister members of an interferometric pair with subpixel accuracy to quantify two-dimensional motion.
18. Interferometric phase data were used to obtain velocities at which the phase data could be unwrapped (for example, <125 m/year). Phase unwrapping refers to the process by which the modulo-2 ambiguity in the phase data is removed. Where crossing swaths were available, both horizontal vector components were derived from the phase data [I. Joughin, R. Kwok, M. Fahnestock, IEEE Trans. Geosci. Remote Sensing 36, 25 (1998)]. In regions with only single-track coverage, speckle tracking was used for the along-track component. Speckle tracking was used for both components where displacements were too large to allow phase unwrapping. A small gap in the RADARSAT coverage was filled with the data from the survey grid in Fig. 1 (16). Velocity measurements (see Fig. 1) (15) were used to solve for the interferometric baseline parameters. The residual difference between control points and estimated velocity is 5 m/year, indicative of the random component of the velocity error. Systematic errors may be higher in areas that are not well constrained by the control velocities.
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33. -3 are similar to the measured velocity.
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37. Our velocity data and the ice thickness data from the University of Wisconsin are on a 5-km grid. The change in ice thickness at grid center points is calculated as the residual flux into each grid cell divided by the area of the grid cell, plus a uniform accumulation rate of 0.09 m/year [E. R. Venteris and I. M. Whillans, Ann. Glaciol. 27, 227 (1998)]. Error propagation gives 1σ uncertainties in the rates of thickness change between 0.35 and 0.67 m/year. The 1σ uncertainty in the mean rate of thickness change is smaller (0.02 m/year). Additional uncertainty arises from the assumption that surface velocity is equal to the depth-averaged velocity. For nonsliding regions (speeds less than ∼15 m/year), this can overestimate the thickness change by up to 20%. Measured surface velocities suggest substantial sliding for most of the calculation area, in which case depth-averaged and surface velocities are equal, and the overestimation in thickness change is negligible.
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42. I.J. and C.W. performed this work at the Jet Propulsion Laboratory under contract with NASA; K.M. is under contract from Intermap Technologies (Calgary, Alberta, Canada). R.B. and S.P were supported by NASA grant NRA-98-OES-03, D.M. was supported by NSF grant OPP-9319369, C.H. was supported by a NRC Resident Research Associateship, and L.G. and K.M. were supported by the Canada Centre for Remote Sensing. RADARSAT data are copyrighted by the Canadian Space Agency. We thank J. Bamber, C. Bentley, and D. Blankenship for the surface and bed elevation data; P. Vornberger for the digitized ice stream boundaries shown in Fig. 1; and C. Bentley and R. Alley for comments that led to substantial improvements to this report.