Quantifying Surface Fluctuations using Optical Flow Techniques and Multi-Temporal LiDAR

D.C. Finnegan, H. Farid, D.E. Lawson and W. Krabill

Transactions of the American Geophysical Union, San Francisco, CA, 2006

In recent decades scientific communities have seen a significant increase in technological innovations and applications using airborne and spaceborne remote sensing. In particular, airborne laser altimetry has provided the opportunity to characterize large-scale terrain and geologic processes such as glaciers and ice sheets at fine-scale resolutions. Although, processing and deriving information from these data can still pose significant challenges. To this end, we describe a novel approach that combines the use of a multi-temporal LiDAR (Light Detection and Ranging) topographic dataset and optical flow techniques, adapted from the computer vision community, to quantify ice flow dynamics of the Hubbard glacier. Using NASA's Airborne Topographic Mapper (ATM-IV) LiDAR as a source of high-resolution (~5cm) topographic data, repeat airborne surveys of the Hubbard Glacier terminus were acquired on August 22nd and 26th, 2005. From the resulting Digital Elevation Model (DEM) we seek to measure a dense motion field that describe both the shift and change in elevation of the glacier. The change in the DEM is modeled spatially as locally affine but globally smooth. The model also explicitly accounts for changes in elevation, and for missing data. This approach is built upon a differential multi-scale framework, allowing for the measurement of both large and small scale motions. The resulting measurement yields a dense 2-D motion vector field for each point in the DEM. On the Hubbard Glacier, we achieve an average accuracy within 8% as compared with manual measurements. These results are encouraging and show that repeat high-resolution elevation data that LiDAR provides allows us to quantify surface processes in a precise yet timely manner. These results may then be incorporated as essential boundary conditions into models that seek to predict geologic behavior such as glacier and ice sheet flow.