A new ice thickness and bed data set for the Greenland ice sheet 1. Measurement, data reduction, and errors

Ice thickness data collected between 1993 and 1999 using a coherent ice-penetrating radar system developed at the University of Kansas have been combined with data collected by the Technical University of Denmark in the 1970s to produce a new ice thickness grid for Greenland. Crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5-km spacing grid using a kriging interpolation procedure. A high-resolution land-ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where, in the past, the relative errors have been largest. The ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of Greenland. The ice thickness grid was compared with the currently available data set. Differences in the center of the ice sheet, where the ice is thickest, were of the order of a few percent. Near the margins, however, large differences, of as much as a factor of 10, were found. The total volume of ice contained in the ice sheet was reestimated and found to have a value of 2.93 x 10(6) km(3). The ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet. Anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow.