What is a 3-D laser scanner?

      A 3-D laser scanner is a ground-based LIDAR (LIght Detection And Ranging) instrument. It is set up on a tripod and sweeps the surrounding environment with optical rays. The rays produce reflections when they encounter solid objects. The instrument determines the XYZ coordinate of each reflection point relative to the scanner position by measuring the azimuth and the two-way travel time of each ray with accuracy better than 1 cm. Reflection points can be spaced within 1 cm of each other on the scanned objects. Using this technology, researchers can scan a solid object from several different directions and later merge the reflection points into a single continuous data set using a common 3-D coordinate system. Spatial interpolation of the reflection points yields a 3-D surface model of the object.

1. Simultaneous Digital Mapping of Outcrop Topography and Stratigraphy - Caprock Canyons, Texas

     The 3-D scanner measures the brightness of the light beam reflected off the ground as well as its XYZ-coordinate.  Different types of rocks reflect the light in different strengths.  Using some image enhancement techniques, in some cases, it is possible to identify stratigraphic boundaries in the 3-D topographic model produced from the scan data.  The example shown here was obtained at a bend of a dry river gorge (see the photo above) in the Caprock Canyon State Park near Quitaque, Texas.  Compare the photographic image below with the processed scan data image.  Alternate bedding of red sandstone and white gypsum layers is clearly visible.

       The 3-D scanning technology is also useful in capturing the complex geometry of speleothems and the internal architecture of caverns.  Examples below were obtained in the Big Room of the Carlsbad Cavern, New Mexico.

Map view of a portion of the Big Room, Carlsbad Cavern.

Flowstone feature with elevation color-coding

     By repeating 3-D surveys of a dune, it is possible to document in detail how it is migrating and changing its shape over time.  Example below compares the cross section of a barchan dune in the White Sands National Monument cbetween January 2003 and May 2003.

Nagihara, S., K. R. Mulligan, and W. Xiong, 2004, Use of a three-dimensional laser scanner to digitally capture the topography of sand dunes in high spatial resolution: Earth Surface Processes and Landforms, v. 29, p. 391-398.

Nagihara, S., J. Hargis, R. Goss, J. Wright, and G. Hill, 2002, Sub-centimeter-resolution digital topography and surface lithology models obtained from a 3-D laser scanner survey in the South Prong Canyon, Texas Panhandle: Proceedings of the ASPRS-ACSM Annual Convention, 12 pages in the CD-ROM conference proceeding volume.

Nagihara, S., R. Goss, B. Musgrave, J. Gamel, G. Hill, and T. Bemis, 2002, Three-dimensional laser scanning of speleothems in the Carlsbad Caverns: West Texas Geological Society Fall Symposium, p. 35-42.