Previous posts on data access have focused on general resources for obtaining remote sensing imagery – Getting your hands on all that imagery – and specific resources related to imaging spectrometry – A review of online resources for hyperspectral imagery. To add to this compendium of data resources, the following includes an overview of online archives for lidar data.
Lidar (light detection and ranging), also commonly referred to as LiDAR or LIDAR, is an “active” remote sensing technology, whereby laser pulses are used to illuminate a surface and the reflected return signals from these pulses are used to indicate the range (distance) to that surface. When combined with positional information and other data recorded by the airborne system, lidar produces a three-dimensional representation of the surface and the objects on that surface. Lidar technology can be utilized for terrestrial applications, e.g. topography, vegetation canopy height and infrastructure surveys, as well as aquatic applications, e.g. bathymetry and coastal geomorphology.
Below is an overview of archives that contain lidar data products and resources:
- CLICK (Center for LIDAR Information Coordination and Knowledge) provides links to different publically available USGS lidar resources, including EAARL, the National Elevation Dataset and EarthExplorer. The CLICK website also hosts a searchable database of lidar publications and an extensive list of links to relevant websites for companies and academic institutions using lidar data in their work.
- EAARL (Experimental Advanced Airborne Research Lidar) is an airborne sensor system that has the capacity to seamlessly measure both submerged bathymetric surfaces and adjacent terrestrial topography. By selecting the “Data” tab on the EAARL website, and then following links to specific surveys, users can view acquisition areas using Google Maps and access data as ASCII xyz files, GeoTIFFs and LAS files (a standardized lidar data exchange format).
- NED (National Elevation Dataset) is the USGS seamless elevation data product for the United States and its territorial islands. NED is compiled using the best available data for any given area, where the highest resolution and most accurate of which is derived from lidar data and digital photogrammetry. NED data are available through the National Map Viewer in a variety of formats, including ArcGRID, GeoTIFF, BIL and GridFloat. However, to access the actual lidar data, and not just the resulting integrated products, users need to visit EarthExplorer.
- EarthExplorer is a consolidated data discovery portal for the USGS data archives, which includes airborne and satellite imagery, as well as various derived image products. EarthExplorer allows users to search by geographic area, date range, feature class and data type, and in most cases instantly download selected data. To access lidar data, which are provided as LAS files, simply select the lidar checkbox under the Data Sets tab as part of your search criteria.
- JALBTCX (Joint Airborne Lidar Bathymetry Technical Center of Expertise) performs data collection and processing for the U.S. Army Corps of Engineers, the U.S. Naval Meteorology and Oceanography Command and NOAA. The JALBTCX website includes a list of relevant lidar publications, a description of the National Coastal Mapping Program, and a link to data access via NOAA’s Digital Coast.
- Digital Coast is a service provided by NOAA’s Coastal Services Center that integrates coastal data accessibility with software tools, technology training and success stories. Of the 950 data layers currently listed in the Digital Coast archive, lidar data represents nearly half of the available products. Searching for lidar data can be achieved using the Data Access Viewer and selecting “elevation” as the data type in your search, or by following the “Data” tab on the Digital Coast home page and entering “lidar” for the search criteria. The data is available in a variety of data formats, including ASCII xyz, LAS, LAZ, GeoTIFF and ASCII Grid, among others.
- NCALM (National Center for Airborne Laser Mapping) is a multi-university partnership funded by the U.S. National Science Foundation, whose mission is to provide community access to high quality lidar data and support scientific research in airborne laser mapping. Data is accessible through the OpenTopography portal, either in KML format for display in Google Earth, as pre-processed DEM products, or as lidar point clouds in ASCII and LAS formats.
Lidar can be useful on its own, e.g. topography and bathymetry, and can also be merged with other remote sensing data, such as multispectral and hyperspectral imagery, to provide valuable three-dimensional information as input for further analysis. For example, lidar derived bathymetry can be used as input to improve hyperspectral models of submerged environments in the coastal zone. There has also been more widespread use of full-waveform lidar, which provides increased capacity to discriminate surface characteristics and ground features, as well as increased use of lidar return intensity, which can be used to generate a grayscale image of the surface.
What is readily apparent is that as the technology continues to improve, data acquisition becomes more cost effective, and data availability increases, lidar will play an important role in more and more remote sensing investigations.