Errors and Improvements in Lagrangian Tracking of Sea Ice

The Lagrangian Ice Tracking System (LITS) uses the NSIDC's Polar Pathfinder sea ice drift data set to calculate the motion of individual points in the ice pack forward or backward in time. (In its offline version, LITS also integrates climate model output to extend scenarios into the future, for planning and policy applications.) The underlying gridded ice motion vectors are based on ice-buoy drifts, satellite-derived motions, and surface-stress estimates from reanalysis winds. LITS has a wide range of applications, as a research tool as well as for environmental stewardship and planning. But its applicability to any specific problem depends on how accurate the drift-estimates, and resulting ice tracks, are. We present a detailed error analysis of the current (V3) Polar Pathfinder data and how these errors propagate through LITS. The errors are time-dependent, as the underlying inputs have changed over time, and the analysis provides guidance about applicability of different periods. Some of the errors uncovered in the construction and testing of LITS are being addressed in a new PPF gridded product (V4); we extend our error analysis to V4, comparing with V3, and suggesting next steps toward continued error reduction.