1. Global Ice Sheet Mapping Orbiter Understand the polar ice sheets sufficiently to predict their response to global climate change and their contribution global sea level rise What is the mass balance of the polar ice sheets? How will the mass balance change in the future?

2. Mass Balance Ice sheet mass balance is described by the mass continuity equation Altimeters InSAR Passive Microwave No spaceborne Technique currently available Consistency between evaluations of the left and right hand sides of the equation will yield a far more reliable result

3. Ice Dynamics and Prediction Terms related to gradients in ice velocity (InSAR) integrated over thickness Altimetry Understanding dynamics coupled with the continuity equations yields predictions on future changes in mass balance Force Balance Equations Basal Drag (inferred)

4. Global Ice Thickness Mission Goal: Measure glacier ice thickness from pole to pole to: –Determine total global volume of glaciers and ice sheets –Estimate mass balance using ice thickness and interferometrically derived ice velocity. –Determine basal boundary conditions from radar reflectivity –Use ice thickness and other glaciologic data to map derived stresses and stress gradients that are components of the force balance equations. –Map internal structures (layers, bottom crevasses, buried moraine bands, brine infiltration layers) –Use spaceborne measurements of ice thickness and other key glaciologic variables to predict response of glaciers and ice sheets to changing climate –Contribute technologies to planetary studies; understanding the phenomenology of radar sounding

5. Prioritized Science Requirements Measure ice thickness to an accuracy of 20 m or better Measure ice thickness every 1x1 km (airborne < 250 m) Measure ice thickness ranging from 100 m to 5 km Measure radar reflectivity from basal interfaces (rel. 2 dB) Obtain swath data for full 3-d mapping Measure internal layers to about 20 m elevation accuracy Pole to pole observations; ice divides to ice terminus One time only measurement of ice thickness Repeat every 5-10 years for changes in basal properties