LiDAR – An Emerging Tool for Geological Applications

Title: LiDAR – An Emerging Tool for Geological Applications

Author: Jason Stoker

Publication: The OUtcrop, October 2012, p. 6-10

Over the past five to ten years the use and applicability of light detection and ranging (LiDAR) technology has increased dramatically. As a result, more and more LiDAR data now are being collected across the country for a wide range of applications, and LiDAR currently is the technology of choice for high resolution terrain model creation, 3-D city and infrastructure modeling, forestry, and a wide range of scientific applications. LiDAR is a key technology for geological applications both within and outside the U.S. Geological Survey, and efforts are underway to try to collect high resolution LiDAR data for the entire United States (http://pubs.usgs.gov/fs/2012/3089/pdf/fs2012-3089.pdf).

What is LiDAR?

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Figure 1. Diagram of an airborne LiDAR instrument.

LiDAR is a category of active remote sensing instruments that can produce 3-D data useful in producing highly accurate, geo-referenced 3-D information. LiDAR applies a combination o f three mature technologies to calculate 3-D information: compact laser rangefinders, highly accurate inertial measurement units, and the global positioning satellite system (GPS). Integrating these technologies into a single system and mounting it into an aircraft (similar to what is done for aerial photography) allows for the collection of high-resolution elevation information from the air (Fig. 1). An advantage of airborne LiDAR is that these laser pulses can penetrate through gaps in the vegetative canopy to help identify geologic features not detectible by optical systems, while collecting information from the vegetation canopy, which is important for all kinds of ecological applications. The absolute accuracy of elevation data acquired from airborne LiDAR can be centimeters per LiDAR return. The data today can be collected at rates of up to 400,000 points per second, which can be translated into extremely high-resolution elevation information. One hour of data collection can result in billions of individually
georeferenced 3-D points.

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Figure 2. An RGB colorized point cloud of approximately 1 km2 before classification for the Arkansas Valley in Colorado.

How Do LiDAR Data Appear?
The source LiDAR data that come from the instruments typically are referred to as a ‘point cloud’ – that is, a cloud of XYZ coordinates with various attributes associated with each point (Fig. 2). For geological applications these point clouds are processed with filtering routines and manual techniques to identify the points that correspond with the bare ground versus the points that represent other objects, such as water, buildings,
or vegetation. Following this processing, the data are referred to as a “classified point cloud,” a common LiDAR deliverable.

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Figure 3. The same area as Figure 2, with data converted to a bare-earth surface.

Once points are classified they are converted to a more user- and computationally-friendly format, such as a surface model (Fig. 3). For geological applications, a Digital Elevation Model (DEM) usually is the desired product, which represents the surface form of bare-earth features. To generate this, points that were classified as bare earth are interpolated horizontally (and there are many ways to do this) into either of two main types of surface models, a raster grid or a triangulated irregular network.

It is these bare-earth DEMs that geologists predominantly use to help identify and map features such as faults, alluvium, and historic landslides. These features often cannot be seen with other remote sensing technology, and some features have gone undetected by
geologists even during field visits (Fig. 4).

Where can I get LiDAR data products?
There are several avenues for acquiring LiDAR data for particular areas of interest. Many commercial companies will collect LiDAR data for individualized specifications and areas. The costs associated with these customized acquisitions will vary based on the extent of the area, desired density of points (related to spatial resolution), accuracy, and turnaround time. There usually are economies of scale, so the larger the area collected, the less the cost per square mile. A simple internet search of “LiDAR vendor” will provide an extensive list of companies. Organizations, such as The Management Association for Private Photogrammetric Surveyors (MAPPS) (http://www.mapps.org),
also have extensive lists of their member companies that collect LiDAR data.

For users who do not need specific, customized data, there may be data already available in the public sector resulting from prior acquisitions that could suffice for certain  applications. A recent study of federal agencies estimates that almost one-third of the conterminous United States has been flown at least once with LiDAR, and a coordinated effort is underway to try to acquire LiDAR coverage for the entire United States (except
for Alaska, which will be handled differently). There are many federal, state, and local agencies paying for collections of LiDAR data that will be made available in many formats for public download. Following are a few portals for downloadable LiDAR
data.

The USGS Center for LiDAR Information Coordination and Knowledge
(http://LiDAR.cr.usgs.gov)

In 2006, the USGS initiated CLICK as a virtual center designed to provide LiDAR point cloud data via download. There currently are over 30 TB of LiDAR point cloud data
available through the link below, with over 1.1 trillion points represented, and more data are added all the time.

USGS Earth Explorer
(http://earthexplorer.usgs.gov)

LiDAR data also can also be downloaded via another USGS portal called Earth Explorer. Earth Explorer accesses the same datasets available through the link below.

National Science Foundation (NSF) OpenTopography
(http://www.opentopography.org)

OpenTopography provides data from NSF and other sources, mainly for the geosciences. The OpenTopography Facility is based at the San Diego Supercomputer Center at the University of California–San Diego, and is operated in collaboration with the School of Earth and Space Exploration at Arizona State University. Core operational support for OpenTopography comes from the NSF Earth Sciences: Instrumentation and Facilities Program and the Office of Cyberinfrastructure. OpenTopography was initiated as a proof-of-concept cyberinfrastructure in the Earth Sciences project of the NSF  Information and Technology Research (ITR) program funded through the Geoscience Network (GEON) project. Opentopography provides access not only to point-cloud data, but allows users to create customized derivatives from those data.

National Oceanic and Atmospheric Administration (NOAA) Digital Coast (http://www.csc.noaa.gov/digitalcoast)

Digital Coast was developed by NOAA to provide information needed by those who want to conserve and protect coastal communities and natural resources. Digital Coast also supplies the associated tools, training, and information to turn data into information capable of making a difference in coastal management. The NOAA Coastal Services Center built the prototype for this portal in 2008 and reached out to potential users to provide feedback to guide the refinement of the site. Digital Coast provides LiDAR and other data, as well as extents of data from CLICK.

Others

There are many state, local, or application specific LiDAR portals, and the number is increasing every year. If you are interested in areas not currently offered by the portals above, you also can ask your state’s Department of Natural Resources, County GIS  Coordinator, or city planner about available LiDAR data or future planned acquisitions. If none exist, a good strategy is to build a consortium of people interested in acquiring LiDAR data for the same area. Some good examples of this approach are the Puget Sound LiDAR Consortium (http://pugetsoundLiDAR.ess.washington.edu), the Oregon Statewide LiDAR Consortium (http://www.oregongeology.org/sub/projects/olc/default.htm), and the International Water Institute’s consortium for the Red River Basin (http://www.iwinst.org/LiDAR). The beauty of LiDAR data is they can be used for such a wide range of applications, many unrelated interest groups can benefit from a single
LiDAR collection.