What is LIDAR? What are its applications in GIS?
LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. These light pulses—combined with other data recorded by the airborne system— generate precise, three-dimensional information about the shape of the Earth and its surface characteristics.
A LIDAR instrument principally consists of a laser, a scanner, and a specialized GPS receiver. Airplanes and helicopters are the most commonly used platforms for acquiring LIDAR data over broad areas. Two types of LIDAR are topographic and bathymetric. Topographic LIDAR typically uses a near-infrared laser to map the land, while bathymetric lidar uses water-penetrating green light to also measure seafloor and riverbed elevations.
LIDAR systems allow scientists and mapping professionals to examine both natural and manmade environments with accuracy, precision, and flexibility. NOAA scientists are using LIDAR to produce more accurate shoreline maps, make digital elevation models for use in geographic information systems, to assist in emergency response operations, and in many other applications.
Applications of LIDAR
Archaeology -
LIDAR has many applications in the field of archaeology including aiding in the planning of field campaigns, mapping features beneath forest canopy, and providing an overview of broad, continuous features that may be indistinguishable on the ground. LIDAR can also provide archaeologists with the ability to create high-resolution digital elevation models (DEMs) of archaeological sites that can reveal micro-topography that are otherwise hidden by vegetation. LIDAR-derived products can be easily integrated into a Geographic Information System (GIS) for analysis and interpretation. Beyond efficiency, its ability to penetrate forest canopy has led to the discovery of features that were not distinguishable through traditional geo-spatial methods and are difficult to reach through field surveys. An April 2009 flyover of the Maya city of Caracol used LIDAR equipment to help scientists construct a 3-D map of the settlement in western Belize. The survey revealed previously unknown buildings, roads, and other features in just four days, scientists announced at the International Symposium on Archaeometry in Tampa, Florida.
Atmospheric Studies -
NASA plans to test a laser-based sensor (Fall, 2010) in space that will help scientists better understand global climate and how it might be changing. The instrument, called LITE (LIDAR In-Space Technology Experiment), will orbit the Earth while positioned inside the payload bay of Space Shuttle Discovery. During this nine-day mission, LITE will measure the Earth's cloud cover and track various kind of particles in the atmosphere. Designed and built at the NASA Langley Research Center, LITE is the first use of a LIDAR system for atmospheric studies from space. LIDAR is similar to the radar commonly used to track everything from airplanes in flight to thunderstorms. But instead of bouncing radio waves off its target, LIDAR uses short pulses of laser light. Some of that light reflects off of tiny particles in the atmosphere and back to a telescope aligned with the laser. By precisely timing the LIDAR "echo," and by measuring how much laser light is received by the telescope, scientists can accurately determine the location, distribution and nature of the particles. The result is a revolutionary new tool for studying constituents in the atmosphere, from cloud droplets to industrial pollutants, that are difficult to detect by other means.
Bathymetry -
Although it is still beyond our reach to acquire precise and high-resolution seafloor depths from space, LIDAR bathymeters on fixed wing and rotary aircraft can penetrate the water column to collect seafloor data at depths of up to approximately 230 feet (70 meters). Bathymetric LIDAR uses a high powered laser to transmit electromagnetic energy, specifically in near-infrared and green wavelengths, from the aircraft platform through the water column and make a time difference measurement to calculate the seafloor depth. Most modern units today use a frequency between 200 and 4,000 Hz, which can result in upwards of 14 million measurements per hour and a horizontal spacing of approximately 0.5 to 6 meters on the seabed. While airborne, a laser altimeter mounted in the aircraft pulses both of these wavelengths to the surface of the water and measures the time it takes for the energy to return. The infrared light is reflected back to the aircraft from the water surface while the green light travels through the water column. Energy from the green light reflects off the seafloor and is captured by the airborne sensor. The water depth is obtained by determining the time difference between the infrared and green laser reflections using a simple calculation that incorporates the properties of the water column along with system and environmental factors.
Contour Mapping -
LIDAR Contour Mapping is a rapid, cost-effective source of high-accuracy, high-density elevation data for many traditional topographic mapping applications. The technology allows large area topographic surveys to be completed significantly faster and at a reduced cost compared to traditional survey methods.
Meteorology -
The first LIDARs were used for studies of atmospheric composition, structure, clouds, and aerosols. Initially based on ruby lasers, LIDARs for meteorological applications were constructed shortly after the invention of the laser and represent one of the first applications of laser technology. Elastic backscatter LIDAR is the simplest type of LIDAR and is typically used for studies of aerosols and clouds. Differential Absorption LIDAR (DIAL) is used for range-resolved measurements of a particular gas in the atmosphere, such as ozone, carbon dioxide, or water vapor. Raman LIDAR is also used for measuring the concentration of atmospheric gases, but can also be used to retrieve aerosol parameters as well. Doppler LIDAR is used to measure wind speed along the beam by measuring the frequency shift of the backscattered light. Scanning LIDARs, such as NASA's HARLIE LIDAR, have been used to measure atmospheric wind velocity in a large three-dimensional cone. Synthetic Array LIDAR allows imaging LIDAR without the need for an array detector.
Geology -
In geology and seismology a combination of aircraft-based LIDAR and GPS have evolved into an important tool for detecting faults and measuring uplift. The output of the two technologies can produce extremely accurate elevation models for terrain that can even measure ground elevation through trees. Airborne LIDAR systems monitor glaciers and have the ability to detect subtle amounts of growth or decline.
Biology and conservation -
LIDAR has also found many applications in forestry. Canopy heights, biomass measurements, and leaf area can all be studied using airborne LIDAR systems. Similarly, LIDAR is also used by many industries, including Energy and Railroad, and the Department of Transportation as a faster way of surveying. Topographic maps can also be generated readily from LIDAR, including for recreational use such as in the production of orienteering maps.
Imaging -
3-D imaging is done with both scanning and non-scanning systems. "3-D gated viewing laser radar" is a non-scanning laser radar system that applies the so-called gated viewing technique. The gated viewing technique applies a pulsed laser and a fast-gated camera. Coherent Imaging LIDAR is possible using Synthetic array heterodyne detection which is a form of Optical heterodyne detection that enables a staring single element receiver to act as though it were an imaging array. 3D mapping Airborne LIDAR sensors are used by companies in the Remote Sensing area to create point clouds of the earth ground for further processing (e.g. used in forestry). A common format for saving these points (with parameters like x, y, return, intensity, elevation) is the LAS file format.
Law Enforcement -
LIDAR devices have been developed that can pinpoint oncoming cars in traffic and determine their rate of speed with a great degree of accuracy.
Oceanic Studies -
LIDAR imaging has been used to analyze oil contamination in the Gulf of Mexico resulting from the 2010 BP oil rig disaster.
Source : WikiGIS
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