comparison of methods for ice bottom mapping

Comparison of Methods for Ice Bottom Mapping

• Sahana Raghunandan, John Paden, Shannon Blunt, Carl Leuschen

• Ken Jezek, Xiaoqing Wu, John Paden, Carl Leuschen

Current Platforms

GPR

DC-8

Twin Otter

P-3

Methods• Interferometric SAR (INSAR)

– Beam forming followed by absolute phase estimation where phase is related to the angle of arrival

• SAR Tomography• MUSIC• MLE• RISR

Tomographic Concept

MLE 1

MLE 2

MUSIC

RISR

Simulation

MLE/MUSIC Comparison

558 559 560 561 562 563 564

7462

7462.5

7463

7463.5

7464

350

400

450

500

558 559 560 561 562 563 564

7462

7462.5

7463

7463.5

7464

350

400

450

500

MLE/MUSIC Comparison

562 562.5 563 563.5 564

7459

7460

7461

7462

7463

7464

7465 200

250

300

350

400

450

500

562 562.5 563 563.5 564

7459

7460

7461

7462

7463

7464

7465 200

250

300

350

400

450

500

Cross Over Analysis

562 562.5 563 563.5

7462

7462.2

7462.4

7462.6

7462.8

7463

7463.2

7463.4

7463.6

7463.8

7464

-60

-40

-20

0

20

40

562 562.5 563 563.5

7462

7462.2

7462.4

7462.6

7462.8

7463

7463.2

7463.4

7463.6

7463.8

7464

-30

-20

-10

0

10

20

30

40

50

Basal Topography – Tomography and Interpolated Nadir Data

Basal Topography estimate of Isunguata Sermia Glacier computed by subtracting tomographic ice thickness from ATM surface elevation model (upper). Basal topography estimated by interpolating nadir ice thickness data and subtracting from surface elevation model (lower).

Data Comparisons

Basal topography constructed from tomography (red), nadir data (blue) and interpolated nadir-data (black) along the northerly (upper left), central (upper right) and southernly (lower left) profile lines. ATM derived surface elevation along the deglaciated terrain forward of the glacier (lower right) illustrates the similarity of the glaciated and deglaciated basal topography.

Proglacial and Subglacial Terrain

Hill-shaded model of the tomography-derived basal topography (dark blue) overlaid on a hill-shaded model of the interpolated nadir-data topography (gray). These are overlaid on a hill-shaded model of the ice-sheet, exposed-rock surface (light blue). The vertical exaggeration of each model is 10x. Similarity between proglacial and subglacial terrain suggests that erorsion processes largely unchanged as glacier has retreated.