GEOLOGIC MAPPING WITH LIDAR

Topography is a key resource for geologic and geomorphic mapping. High-resolution digital elevation models (DEMs) derived from lidar are revolutionizing our art and science. Nearly a decade of experience working with lidar DEMs suggests the following: (1) Data quality makes a difference. Some surveys are better than others. I recommend a minimum data density of 1 pulse/m², coupled with best-possible ground return identification. Absolute vertical error is not the most useful measure of data quality. (2) Know your artifacts. Some lidar calibration errors look like fault scarps. Common classification and interpolation artifacts reduce slopes and mislocate slope breaks. (3) Make the right image. Shaded-relief images are not optimal. Try shade-by-slope, color-by-elevation, and other possibilities. What aspects of topography are key to your mapping problem? (4) Interpret on-screen in a GIS. It's much more efficient than mapping on hard copy and subsequent digitizing. Interpretations are better when you can easily change image backdrops and viewing scales. (5) Try geomorphic mapping. Focusing on the evolution of surface morphology alone allows a stronger set of interpretive constraints than is possible if one attempts to map substrate directly.

The most significant downside to mapping with lidar is that one's final product commonly no longer fits the available publication-quality base maps. The upside is that our maps can be more detailed, can have greater spatial accuracy, and can reflect a much subtler understanding of surface processes and recent earth history.