Lidar (Light Detection And Ranging)
Lidar (Light Detection And Ranging) is a remote sensing method used to examine the surface of the Earth. It is uses eye-safe laser beams to see the world in 3D, providing machines and computers an accurate representation of the surveyed environment.
Lidar is an optical means of measuring reflected light from distant objects to determine range, and to determine position. The Lidar uses 1.064 nanometer wavelength laser light pulses to measure distances by recording the time delay from the transmitted pulse and light reflected back from objects.
Lidar Sensor Types
Lidar systems can be divided into 2 major types: i)Airborne ii)Terrestrial
- Airborne Lidar Systems focuses on the processing and management of airborne Lider data in such Geospatial applications. This is mounted in an aircraft, scanning in one direction perpendicular to the flight of the aircraft in a push broom fashion. The data can be thought of as a long strip representing the surface of the underlying terrain. The application of this data is more oriented toward direct measurement of the earth’s surface used in conjunction with GIS, Remote Sensing or Photogrammetric applications, such as land cover mapping, hydrology analysis, site selection, etc. There are two types of airborne sensors: Topographic and Bathymetric.
- Terrestrial Lidar Systems are operated at ground level scanning in a vertical direction while rotating about a vertical axis. There are two main types of terrestrial lidar: Mobile and Static.
Application/ Uses for Radar Data
Lidar is commonly used to make high-resolution maps, with applications in;
- Atmospheric physics
- Laser guidance
- Laser altimetry
- Autonomous cars
- Helicopter Ingenuity
Advantages of using Lidar in GIS
- Lidar uses an active illumination sensor and can be collected day or night when compared to traditional photogrammetric techniques.
- Data can be collected quickly with very high accuracy.
- Surface data has a higher sample density. The high sample density improves results for certain applications such as floodplain delineation.
- Collect elevation data in a dense forest, where photogrammetry fails to reveal the accurate terrain surface due to dense canopy cover.
- Lidar does not have any geometric distortions like a side-looking radar.
- Lidar can be integrated with other data sources.
Using Lidar in ArcGIS
ArcGIS supports lidar data provided as LAS or ASCII files. There are 3 different formats datasets that can be used to manage and work with your lidar data in ArcGIS. The datasets are LAS dataset, Terrain dataset, and Mosaic dataset.
ArcGIS datasets that uses for Lidar data
|Parameters||LAS Dataset||Mosaic Dataset||Terrain Dataset|
|ArcGIS applications||ArcCatalog, ArcScene, ArcMap||ArcCatalog, ArcGlobe, ArcMap||ArcCatalog, ArcGlobe, ArcMap|
|Storage locations||File system||Geodatabase||Geodatabase|
|Relationship to LAS source files||Points to||Points to||None|
|Size limitation||Limited by space on disk||Limited by size allowed by geodatabase||Limited by size allowed by geodatabase|
|Surface constraints||Supported||Not supported directly(supported if present in LAS dataset or terrain dataset)||Supported|
|Lidar inputs||LAS files||LAS files, terrain datasets, LAS datasets||Multipoint feature class|
|Types of lidar||Airborne and terrestrial||Airborne||Airborne|
|Rendering||Points, triangulated surface viewed in 2D and 3D||Raster||Triangulated surface|
|Analysis||Tools that can ingest point clouds or TINs Use with 3D Analyst tools Use with LAS dataset tools||Use with tools that can ingest raster data Use with Spatial Analyst tools and other raster dataset tools||Tools that can ingest TINs or raster datasets Use with 3D Analyst tools Use with Spatial Analyst tools and other raster dataset tools|
|Display||Thinned points Can change display by choosing different class types or data types Display is modified using the LAS dataset toolbar or the layer properties dialog box||Uses cache for faster display Can change display by choosing different class types or data types Display is modified using the layer properties dialog box or the Image Analysis window||Thinned points based on pyramids Can change display by choosing different class types or data types Display is modified using the layer properties dialog box|
|Editing points||Can edit the points residing in the LAS files||Cannot edit points||Can edit the LAS points as multipoints referenced by the terrain dataset|
|Combining with data||Supports LAS files, feature classes, and shapefiles||Supports LAS files, LAS datasets, terrain datasets, and other raster formats||Supports LAS and feature classes|