Grounding line mapping in Antarctica using 15 years of DInSAR data

Transcription

1 Grounding line mapping in Antarctica using 15 years of DInSAR data Jérémie Mouginot 1 Eric Rignot 1,2, Bernd Scheuchl 1 1 University of California, Irvine 2 Jet Propulsion Laboratory

2 Introduction Outline Definition Why grounding lines delineation is important? DinSAR mapping Methodology Datasets Results Comparisons & Discussion

3 Grounding Lines - Definition Grounding lines (GL) are the boundary between grounded and floating ice. Different flow regimes of grounded and floating ice are coupled across the GL. Huybrechts (2009) InSAR is making an immense contribution, with its ability to map and monitor GL location on a large scale and to unprecedented horizontal accuracy.

4 Grounding lines dynamic The ice sheet ice shelf transition zone are a key parameter for marine ice sheet dynamics. It may allow especially rapid response if the ice sheet to changes in climate Van der Veen, Fundamental of Glacier Dynamics

5 Methodology Same time interval with the exact same imaging geometry, i.e. same satellite track. To form the interferogram, we migrate image pixels by calculating the motion field using a speckle tracking technique [Michel and Rignot, 1999] Interferogram = range displacements surface topography + imaging geometry + glacier flow + tidal flexure of floating ice ALOS 2007 Track171

6 Methodology Differencing interferogram removes the glacier flow signal Surface topography (or short differential baseline) is used to remove topography. Tidal motion has a distinct signature of elastic bending GL are mapped in range domain with a horizontal precision of 100 m.

7 Methodology - Mapping limit of tidal flexing (F) grounding line (G) line of first hydrostatic equilibrium (J) break in surface slope (I) maximum extent of the flexure zone (H)

8 Data ERS-1 & -2 Earth Remote Sensing Satellite 1 and 2 (ERS 1/2): years 1992, 1994, and 1996 Antarctic Peninsula, West Antarctica north of 81 S, Victoria Land and Wilkes Land in East Antarctica: 1 day repeat cycle Best for GL mapping strong tidal signal compared to ice motion Spaatz Island English Coast

9 RADARSAT-1 Data - RADARSAT 1 Year : 2000 East Antarctica 24 day repeat cycle. Decorrelation is a bit bigger that with ERS

10 RADARSAT-2 Data - RADARSAT areas south of 81 S 24 day repeat cycle. Siple Coast

11 Data - ALOS ALOS PALSAR select areas north of 77.6 S 46 days L-band ; good correlation even if the repeat cycle is large

12 Results Green : ALOS Blue : R2 Pink : R1 Red : ERS We mapped 1.4 million grounding line points experiencing tidal flexure. Ice reaches the ocean at over 28,600 km of the coastline, or 76% of Antarctica, of which 22,600 km experiences tidal flexure. Currently working with NSIDC to make this dataset available.

13 Comparison - Region1 Siple Coast Excellent agreement between DInSAR and ICESat Same detection principle, but : ICESat noise of cm [Brunt et al., 2010] vs 1 cm with DInSAR. On Mercer Ice Stream, DInSAR GL extends 50 km farther south than delineated by MOA break in slope is not a reliable indicator of GL.

14 Comparison -Region 2 Victoria Land Disparity between DInSAR and MOA exceeds 50 km on many glaciers: seaward on Aviator, Borchgrevink, and Tucker glaciers; landward on Lille, Rennick and Matusevitch glaciers. On Rennick Glacier, ICESat & MOA detects grounding in the middle of the ice shelf. DInSAR however reveals that this is only an ice rise.

15 Comparison -Region 3 On Pine Island Glacier, MOA places G at the inner edge of an already identified ice plain, 20 km upstream of the 1996 DInSAR position, in a region where no tidal motion is detected. On Slessor Glacier, the ICESat delineation agrees with DInSAR, while MOA s is km too far inland.

16 Grounding Lines retreat Strong evidence that GL is moving (Rignot, 1998) and that melting is related to inland thinning (Shepherd et al, 2004) PIG 2011 from ERS-2 ice phase

17 Conclusion First, complete, high precision, uniform sampling, seamless mapping of GL around Antarctica based on 15 years of DInSAR data. MOA delineation is in large disagreement with tidal motion recorded by DInSAR in areas of fast flow. A single interferogram yields errors in GL mapping of several km on fastmoving ice DInSAR method is essential. Errors yield large biases : in calculated ice fluxes. in the set up of numerical ice flow models. in the analysis of ice ocean interactions or simply the selection of a drill site near an ice stream grounding zone We detected the rapid GL retreat of several major glaciers that drive a large part of the ice sheet mass budget (e.g., Pine Island, Thwaites, Smith gl.) DinSAR based Grounding Line will be soon available at NSIDC for the science community

18 Recommendation Acquisition of 3 consecutive cycles is critical for grounding line mapping. Routinely observations over super-sites are recommend to follow the evolution of major sea level contributor (Pine Island, Thwaites, Jakobshavn gl., )

19 THANK YOU! Jeremie Mouginot Department of Earth System Science University of California, Irvine Croul Hall Irvine, CA