Global Ice Sheet Mapping Orbiter Understand the polar

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?

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

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

Global Ice Thickness Mission • Goal: Measure glacier ice thickness from 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

Prioritized Science Requirements • • • Measure ice thickness to an accuracy of 20 m or better Measure ice thickness every 1 x 1 km (airborne < 250 m) Measure ice thickness ranging from 100 m to 5 km Measure radar reflectivity from basal interfaces (rel. 2 d. B) 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