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GROUNDING LINE VALIDATION TEAM

Team Members: Michael Jefferson (Senior)

Joyce Bevins (Junior)Robyn Evans (Junior)Ryan Lawerence (Sophmore)

Mentor:Dr. Malcolm LeCompte

2+ OVERVIEW

Abstract Introduction Determining the Grounding Line Results Future Works Conclusion

3+ ABSTRACT

Dynamics and mass balance of an ice sheet can be derived from an accurate measurement of its area. To measure the area of a continental ice sheet, the grounding line must first be accurately determined. The grounding line is the boundary between the ‘grounded’ ice resting on land and any associated floating ice comprising a retaining ice shelf. 

During a project entitled Antarctic Surface Accumulation and Ice Discharge or ASAID, Dr. Robert Bindschadler, lead an international team of glaciologists and computer scientists, including ECSU students, in an effort to obtain a more accurate measure of the area of the Antarctic ice sheet and determine its mass balance. That is, whether the amount of ice is growing or diminishing over long time intervals. Bindschadler’s team determined the grounding line using methods of photoclinometry with LANDSAT Enhanced Thematic Mapper (ETM) image brightness and surface elevation data from the Geoscience Laser Altimeter System (GLAS) aboard NASA’s Ice, Land and Cloud Elevation Satellite (ICESat). The ASAID grounding line (GL) was established using LANDSAT 7 and GLAS data obtained in 2003. However its accuracy and utility had not been tested.  

With the current ASAID 2003 Grounding Line (GL), the CERSER GL Validation Team was tasked by Dr. Bindschadler with determining its accuracy in two coastal regions and whether changes have occurred over long time intervals.  The team over-laid the 2003 GL on LANDSAT Seven ETM imagery temporally proximate to 2003. This modified image was then compared to decades older LANDSAT 4 & 5 Thematic  

4+ ABSTRACT CONT’DMapper (TM) imagery. GL validation and change determination were planned for two geographic areas known to exhibit rapid changes potentially due to climate warming: Pine Island Glacier (PIG) and Larsen Ice Shelf. However, due to time constraints, the team only examined a limited portion of the PIG.

The GL was tested along a portion of the Antarctic coast near the PIG. To accomplish the validation, LANDSAT 7 images from 2003 used in creating the GL, were obtained from the USGS archive (lima.usgs.gov).  Other LANDSAT images were obtained from the USGS GLOVIS on-line archive (glovis.usgs.gov). The oldest possible, cloud-free LANDSAT 4 and 5 TM images were obtained for the regions of interest. To facilitate data manipulation and image comparisons, the extremely large GL vector file, obtained from Dr. Bindschadler. was truncated to include only the geographic regions of interest. Truncation and image comparisons were accomplished using ITT Visualization System’s ENVI image processing software. Any departure from perfect geographic pixel registration was corrected by using the 2003 image as a reference and then warping the older image to conform to the common fixed control points visible on both images. The grounding line overlying the 2003 image was then examined and compared to the older image. The geographic coordinates and extent of any departures from coincidence were recorded and reported.

A possible deviation in the GL was found while comparing a 2001 LANDSAT 7 image to a 1986 LANDSAT 5 image, near a small glacier feeding into Pine Island Bay.  Comparison with a 2003 image of the same area revealed no GL inaccuracy; however a small ice shelf appeared to have progressively diminished over time until it disappeared in 2003.

5+ KEY TERMS

Landsat 7 ETM+ (Enhanced Thematic Mapper Plus) – multispectral scanner instrument on the Landsat 7 satellite used to collect the image data used in GL validation research

GloVis (Global Visualization Viewer)- USGS online archive used to store Landsat imagery

LIMA (Landsat Image Mosaic of the Antarctic) - provided 2003 images used to define the GL

PIG (Pine Island Glacier) the area of interest for the grounding line investigation

Grounding Line - the last portion of an ice sheet that is supported by land before it becomes a floating ice shelf

Hinge Point - the inflection point between ice shelf and ice sheet Ground Control Points - a system of distinct geographic features that is

recognizable on images and used to facilitate image to image pixel registration

6+ OBJECTIVES

Overlay the GL vector file on the 2003 Landsat image used to create it and check for topographic consistency Is it landward or seaward of an apparent coastline?

Investigate whether the GL can be used as a tool to investigate long term changes in coastal topography. Compare 2003 GL and Imagery with older Landsat images

Image from: www.google.com

7+ DIAGRAM OF THE GL

Illustration shows grounding line, ice shelf

In the teams research, the inflection point would be between the glacier and the ice shelf

The ice shelf is subject to tides and waves

8+ ENVI The ENVI product family provides a variety of software

solution for processing and analyzing geospatial imagery used by scientists, researchers, image analysts, and GIS professionals around the world.

Envi was used to display, georectify, and compare images in order to determine if there were variations in the grounding line

9+OVERLAYING GROUNDING LINE ON LANDSAT IMAGE Obtained grounding line vector file from Dr. Robert

Bindshadler working at NASA Goddard in Greenbelt, Maryland

The grounding line was created using LIMA images from 2003

The specific image for PIG was obtained from the LIMA dataset

ASAID grounding line

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Pine Island GlacierLat:-74, Long: -101Path: 001 Row: 113

11+ZOOM ON AREA OF

INTEREST

12+DOES THE GROUNDING LINE FIT?

Before continuing the research, validation of the grounding line was needed to see if it was a correct match

After the comparison, the grounding line fit the image perfectly

+ 13GROUNDING LINE OVERLAID ON 2003 IMAGE

14+ OBJECTIVE TWO:

Can the GL be used as a tool to determine temporal changes to

coastline?

15+ INVESTIGATION OF THE GROUNDING LINE

LIMA website had no single image that covered the entire area of interest PIG a mosaic of path/row (Latitude delimiter/ Longitude

delimiter) : 233/113 and 233/114

Those LIMA images did not have early Landsat counterparts

GloVis was used to obtain Landsat images (001/113)from 2001 possessing older counterparts

Since grounding line was georeferenced with its LIMA imagery, image to image registration was required

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IMAGE TO IMAGE REGISTRATION

2001 image was chosen as the geographic reference for registration

Common geographic points (five) were selected in both the reference image and the one to be registered

ENVI provides the image to image registration process that co-registers image pixels at common geographic points in each image

17+ TRUNCATION OF THE GROUNDING LINE

After completing the validation of the grounding line and warping the 1986 image, problems started occurring

The grounding line was a very large file Took a while to load Frequently caused freezes and crashes Slowed image to image comparisons

The solution to this problem was to truncate the GL to the area containing Pine Island Glacier

18+TRUNCATING THE GROUNDING

LINE Used an ENVI tutorial detailing creating a new polygon

file Wanted to get as accurate as possible to the grounding

line Opened the original grounding line and and overlayed

it on the area of interest Tediously picked points on the line and created a new

file that was smaller and could be opened in a timely manner

19+ MAKING THE COMPARISON

ENVI was used to display the GL as a vector overlay on the 2003 and 1986 satellite images

The images were linked allowing an overlapped display of one co-registered image upon another

With this utility changes over time could be readily viewed

+ 202001 VS. 1986

This shows a comparison between the 2001 vs. the 1986 warped image

These are the ground control points that allow the image to be georeferenced

21+ 2003 VS. 2001

This shows a comparison between the 2003 vs. the 2001 image

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RESULTS GL was an accurate depiction of the 2003 coastline From 1986 -1989 - 2001 there was an ice shelf retreat until its

dissipation in 2003 Confirmation from Dr. Robert Bindshadler shows that our

research uncovered a retreating ice shelf

23+ FUTURE WORKS/CONCLUSIONS

Due to time constraints we only investigate a small section of Pine Island Glacier

Further investigation of unexamined portion of the Pine Island Glacier coastline might show variations in the retaining ice shelf or changes in the grounding line itself

Larson Ice Shelf remains to be investigated Implement new software beta test

New NASA Goddard software to investigate GL

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REFERENCES/ACKNOWLEDGEMENTS

GloVis: Glovis.usgs.gov LIMA: lima.usgs.gov ENVI:

http://www.ittvis.com/language/en-us/productsservices/envi.aspx

Dr. Robert Bindshadler, Glaciologist at NASA Goddard