GEOG596A – Proposal for Capstone Project

Creating Ice Drainage Divides of Antarctica using GIS

Matthew Beckley

Advisor: Peter Guth

Senior Scientist: Mario Giovinetto

Table of Contents:

1. Why is this important

2. Review of Past Work

3. Methodology

4. Alternative Method

5. Potential roadblocks

6. Status

The Antarctic ice sheet contains approximately 70% of the world's fresh water, and has been undergoing dramatic changes in recent years.

Image: RADARSAT Mosaic

Why is this important?

• Need to break Ice Sheet into discrete units

• Highlight areas of change

• Ice Sheet vs Ice Shelf

• Grounding line or “zone” in between.

Why is this important?

A A’

B B’

AA’ B’

B

Top Image: Landsat Image Mosaic of Antarctica (LIMA) Bottom images: Scott Polar Research Institute (SPRI)

Why is this important?

Mean Sea Level

• When base of ice is below sea level there is potential for instability

In previous years, drainage basins were created based on surface topography with radar altimetry from the GEOSAT and ERS-1 & 2 satellite missions. This was based on 5 kilometer grids.

Review of Past Work

• Slope vectors colored by magnitude• Arrow direction indicates direction of max slope

Review of Past Work

• ICESat launched in 2004. A lidar altimeter that produced large amounts of data. ICESat DEMs are 500 meter res.

•This required a new approach to produce basins.

Review of Past Work

Methodology

Overview

1. Modify IDL code to create tiled slope vector maps. 2. Assist Senior Scientist in drawing divides in first round of edits. 3. Digitize in using ArcGIS. 4. Concatenate/edit/modify divides in ArcGIS. 5. Translate between IDL and GIS – reading/writing shapefiles in IDL6. Edit divides using imagery and other data7. Iterate the process for each of the tiles working towards a complete file for all of Antarctica. 8. Final products to include:

a) Divide polylinesb) Basin polygons for each of the basinsc) 500m Grid basin maskd) Masks of terrain based on coastlines – designate floating

ice, grounded ice, etc.

Due to increased resolution of Icesat DEM, the maps need to be tiled. Tiled maps were made in IDL.

Methodology: Create tiled slope vector maps

Methodology: Concatenate, edit, & modify divides in GIS

Editing lines and nodes:

Make sure digitized lines are continuous.

Remove extraneous nodes, overshoots, undershoots, etc.

Methodology: Translate between IDL and GIS

Had to learn to read/write shapefiles in IDL to make this possible.

Colleagues work in IDL & UNIX environment. Non-GIS users.

Final product will have to be accessible via UNIX, Fortran, C, & IDL.

The Power of GIS – Layering! Helps assess problem areas. Divides can be corrected based on what high resolution shows.

Methodology: Edit divides using imagery

Coastline, grounding line, and island data were manipulated using xtools to create polygons that were used for masking purposes.

Flowlines on imagery can guide divides. Slope vectors on ice shelves are difficult due to low slope.

Methodology: Edit divides using imagery

Using RADARSAT imagery to clarify positions of divides relative to ice streams

Methodology: Edit divides using imagery

High-res LIMA(15m) also useful for determining divides. Especially for locating rock points. Could be used to fine tune the divides – especially in the valley glacier areas.

Methodology: Edit divides using imagery

The benefits of using a GIS:

• Icesat 500m DEM masked to coastline, layered transparently on a 15m LIMA image

• High-res coastline converted to shapefile.

• Preliminary divides on top ready for editing.

Methodology: Edit divides using imagery

50 Km DEM masked to Radar-based basins 5 Km DEM masked to Radar-based basins

Methodology: Final Products

With new basin polygons I can create a 500m basin mask

Alternative Methods Comparison

Why not use ArcGIS basin toolset to save some work??

Benefits of using GIS for basin creation:1. Ability to layer data from various sources – the core of GIS2. Ability to zoom in and out of problem areas without remaking maps.3. Can provide a good “first-cut” at basin creation allowing time to spend on correcting problem areas along coast and mountain regions.4. As future datasets become larger, it may become a necessity to use automated GIS algorithms and then focus corrections in key areas.

Problems with relying solely on GIS for basin creation:1. Slopes, aspects, and basins can be overly complex for high resolution DEMS.2. For some GIS programs, the algorithms are a “black box” – i.e. how they derive the values are unknown to the user.3. Algorithms are still just a guide, and may not take other variables into account, especially for ice studies. Especially variables such as bedrock topography.

Aspects derived from the hybrid DEM. Divides show agreement for major ridges, but too confusing to use for work near the coast, or in moutainous terrain. GIS basins derived from slopes and aspects are a mess.

Alternative Methods Comparison

GIS-derived aspects from ICESat DEM. Was used as a guide in some regions to determine divides. Mostly for main/obvious ridges.

Have a headache yet??

Need a lot of editing to make the GIS products useful for analysis.

Alternative Methods Comparison

Higher resolution Lidar DEMs - LVIS (Land, Vegetation, and Ice Sensor) High altitude Lidar flown on DC-8 aircraft as part of Operation Ice Bridge. 20 meter DEM draped on Google Earth imagery. No interpolation! Nearest Neighbor gridding – raw data is at 20 meter spacings!

Alternative Methods Comparison

Overview

• Projection issues. • Coastline disagreements. • Conflicting info – give ICESat precedence.• Missing data in the Pole region (south of 86S)• Masking – editing coastlines to form polygons.• ArcGIS Basin Tool – make subset grid. Get realistic basins?

Potential Road Blocks

Potential Road Blocks: Coastline Disagreements

ICESat 500m DEM. Satellite only flew to -86 S, so there is no data to the south pole

Potential Road Blocks: Problem with the “Pole Hole”

RAMP 200 DEM with Pole Data Based on RADARSAT data

Downsample this DEM to 500m, reproject to match ICESat DEM.

Potential Road Blocks: Problem with the “Pole Hole”

ICESat 500m DEM with RAMP data filling in the “pole hole” region.

Potential Road Blocks: Problem with the “Pole Hole”

• Digitizing is 90% completed.

• Some coastline areas need to be examined with imagery.

• Polygons need to be created based on divides. Potential topology issues have not been addressed yet.

• Most roadblocks have been addressed, except for the inevitable basin tool peculiarities.

• Need to create a subset grid and perform ArcGIS basin analysis/comparison.

Status

Questions or Comments??