By John R. Hughes, editor, Earth Imaging Journal, Denver.
In late 2009, a $14.3 million allocation from the American Recovery and Reinvestment Act for new light detection and ranging (lidar) elevation data prompted the U.S. Geological Survey (USGS) National Geospatial Program (NGP) to develop a common base specification for all lidar data acquired for The National Map. Released as a draft in 2010 and formally published in 2012, the USGS–NGP Lidar Base Specification Version 1.0 was quickly embraced as the foundation for numerous state, county and foreign country lidar specifications.
Prompted by a growing appreciation for the wide applicability and inherent value of lidar, a USGS-led consortium of federal agencies commissioned a National Enhanced Elevation Assessment (NEEA) study in 2010 to quantify the costs and benefits of a national lidar program. A 2012 NEEA report documented a substantial return on such an investment, defined five Quality Levels for elevation data and recommended an eight-year collection cycle of Quality Level 2 lidar data as the optimum balance of benefit and affordability.
In response to the study, the USGS–NGP established the 3D Elevation Program (3DEP) in 2013 as the interagency vehicle through which the NEEA recommendations could be realized. Overall movement throughout the industry toward more consistent practices in collecting, handling, processing, documenting and delivering lidar point cloud data will allow the technology and data to become more useful to a broader user base, and thereby benefit the nation as a whole.
Although lidar data have been used in research and commercial mapping applications for more than a decade, lidar is still a relatively new technology. Advancements and improvements in instrumentation, software, processes, applications and understanding are constantly refined or developed.
The most recent Lidar Base Specification is based on the experience and research of the USGS–NGP pertaining to the lidar technology being used in the industry. Furthermore, the USGS–NGP acknowledges that a common set of best practices hasn’t been developed or adopted by the industry for numerous processes and technical assessments (for example, measurement of density and distribution, classification accuracy and calibration quality). USGS encourages the development of such best practices with industry partners, other government agencies and appropriate professional organizations.
Unlike most other lidar data procurement specifications, which largely focus on the products derived from lidar point cloud data, such as the bare-earth digital elevation model (DEM), the Lidar Base Specification places particular emphasis on the handling of the source lidar point cloud data.
The specification is intended to ensure that the complete source dataset remains intact and viable to support the wide variety of DEM and non-DEM science and mapping applications that can benefit from lidar technology. The source dataset includes the data, metadata, descriptive documentation, quality information and ancillary data collected in accordance with the minimum parameters described within the specification.
Adherence to the specifications of the NEEA Quality Level 2 and Quality Level 1 lidar data ensures that point cloud and derivative products are suitable for the 3DEP. The 3DEP’s goal to fully realize the benefits documented in the NEEA report depends on the ability to manage, analyze and exploit a lidar dataset spanning the nation. The vast quantity of lidar data requires these functions to be handled through computerized, machine-driven processes that will require uniformly formatted and organized data.
Presidential Executive Order 13642, “Making Open and Machine Readable the New Default for Government Information,” requires federal agencies to implement an Open Data Policy, which makes government data easily accessible and usable. Adherence to the Lidar Base Specification ensures that the point cloud source data are handled in a uniform manner by all data providers and are consistently delivered to the USGS in clearly defined formats.
Lidar is a fast-evolving technology, and much has changed in the industry since the final draft of the “Lidar Base Specification Version 1.0” was written. Lidar data have improved in accuracy and spatial resolution, geospatial accuracy standards have been revised by the American Society for Photogrammetry and Remote Sensing, industry standard file formats have been expanded, additional lidar applications have become accepted and the need for interoperable data across collections has been recognized. To download the updated “Lidar Base Specification Version 1.2” publication, which addresses recent changes and provides continued guidance toward a nationally consistent lidar dataset, visit the USGS website at http://pubs.usgs.gov/tm/11b4.