Saturday, 24 December 2016

Vegetation mapping using LiDAR

Introduction

LIght Detection And Ranging (LiDAR) technology is capable of making spatially located point elevation measurements to generate precise and high resolution Digital Elevation Model (DEM) of a chosen canopy or particular structure. Vegetation and trees mapping can be expertly done using LiDAR technology. LiDAR’s fast, dense, and systematic dataset permits mapping of land-use classification, vegetation canopy, ground elevations in dense vegetation covers, areas of minute textural differences, areas of minute elevation differences, and point and line features i.e. trees, water lines etc.         

Why vegetation mapping is important?
Natural resources when managed for a positive reason of saving the ecosystem in an optimistic way, can offer benefits for longer time period without getting deteriorated. Natural resources management is not comprehensive unless vegetation is properly identified with its characteristics, uses and impacts on the environment. Such vegetation mapping is sure to be efficiently done using LiDAR for determining species and groups of vegetation, measuring vegetation in three dimensions, and mapping vegetation spectrally, spatially, and temporally. If and when vegetation mapping is done in a resourceful and well-organized manner, it can solve widespread concerns during forest inventories, ecological studies, environmental modeling, hazards control, risk mapping, and wildlife safety. LiDAR data can be used to identify distinct structures in any canopy such as trees in parks, fruit orchards or forests. Distinct 3D models of trees can be created using LiDAR data. LiDAR can also acquire data on leaves’ characteristics, diversity of microhabitat, and transpiration.



Factors that effect LiDAR data
The accuracy of LiDAR data depends upon the factors like alignment of the coordinate system, quality of point data, point density, vegetation height thresholds, vegetation density in the canopy, wind that affects the leaves, leaf-on and leaf-off seasons, forest cover effects, complex vegetation cover, size of individual trees, undergrowth of herbs, shrubs’ areas, wood quality, birds in the vicinity, slope and elevation of the terrain, terrains with high and low reliefs, data recruitment times and dates, aircraft fluctuations, the distance between LiDAR sensor and trees, pulse mode, site conditions, weather, interpolation of points, stitching accuracy, and the LiDAR sensor itself. The task of creating a well-defined 3D model of tree is accomplished when the modeling of leaves, twigs, branches, tree height, tree crown, and crown diameter are incorporated into it.    

The DEM
When LiDAR data is achieved, generation of DEM can be done flawlessly after filtering of errors and outliers removal from LiDAR points, interpolating and reorganization of the points, and separation of ground points i.e. ground filtering. DEM which is representation of the landscape along with its vegetation quantitatively can be used to assess the terrain, vegetation, and trees conditions and their effects on the surroundings. DEM provides a broad vision and is used to get the spatial information about processes occurring within the forest canopy. After evaluation of DEM, the decision can be made for the management and control of vegetation areas for the betterment of neighboring flora and fauna, wildlife, water bodies, human settlement, and the vegetation itself.

Conclusion
LiDAR technology acquires accurate and workable 3D data swiftly and competently. The use of LiDAR technology in forest environments can speedily attain precise spatial data of trees and vegetation temporally. When LiDAR data is presented in form of DEM, it enables researchers to visualize the canopies’ physical, chemical, and biological scenarios through an unprecedented visualization for the quantitative analysis of the forest’s canopy.     

References

Analysis of the factors affecting LiDAR DTM accuracy in a steep shrub area

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Wednesday, 24 August 2016

LiDAR – The Technological Glaze

LiDAR is a remote sensing technology which is used to measure elevation of objects from a specified level. This technology uses laser to detect the objects. LiDAR can be used from ground, air or space. When collecting LiDAR data from an aircraft, the system mounted in the aircraft scans the ground or any required surface. A GPS (Global Positioning System) is also integrated with LiDAR that keeps track of aircraft’s location and attaches the locational parameter with the collected data. Since the elevation and position of the aircraft changes during the flight, the system calculates precise location of aircraft and with respect to it, locates the rest of the data. This information is continuously recorded in the computer automatically.


What are pulse and return?
When the light is emitted towards the ground from an airborne LiDAR system, one single dispatch of light is called a pulse. When the light hits the respective object, it reflects back towards the LiDAR system, that reflected light when it reaches and detected by the system is called a return.


What is LiDAR output?
High-resolution maps are the output of LiDAR procedure. LiDAR technology provides fine-scale and spatially defined three-dimensional landscape information and map structural components like elevation, dimension and density of the structures. At the start, LiDAR data is stored as a series of points. LiDAR data can also be stored in the form of contours lines. The most fascinating form of output of LiDAR is DEM or digital elevation model. DEM is made when the scanned surface is represented with continuous elevation values in 3D format along with the values’ co-ordinates.      

DEM

How the height of the object is calculated?
When the light is emitted from the LiDAR system, the time is recorded. The time is again recorded when the light reaches back after hitting the object below. Using the speed of light and the time difference between pulse & return, the distance between the LiDAR system and the top of that object is calculated. Then the distance between the aircraft and the ground surface is determined. The ground elevation is also calculated using GPS.

Is LiDAR data accurate?
The turbulence of the aircraft during flight and its tilt are incorporated into the system so that accurate data can be recorded. The angular measurements of pulse & return are taken into account as well when calculating the elevation that gives precise elevations of the objects and ground surface.

Where are applications of LiDAR?
LiDAR is used to monitor, record, store, quantify, classify, predict, and manage data in the fields of surveying, construction site selection & evaluation, large scale land use planning, terrestrial elevation modeling, flood modeling, hydrographic models, power lines management, piping networks, forestry, archeology, agriculture, urban modeling, transport planning, environmental monitoring & modeling, climate change, atmospheric physics, geosciences, geography, geology, tectonic activity mapping, and glacial data recording etc.

What are the benefits of using LiDAR technology?
LiDAR increases humans’ capability to gather data, represent data, and to respond to that data.
Greater efficiency, faster results.
Automatic 3D modeling.  
Automatic locational tag.
Large scale topographic maps are achievable.
Making night time data collection possible.
Urban and even rural areas are quicker to survey.
Cost effective.

References:
Into the Third Dimension: Benefits of Incorporating LiDAR Data in Wildlife Habitat Models. (WWW)

LiDAR applications in surveying and engineering. (WWW)

A meta-analysis of terrestrial aboveground biomass estimation using lidar remote sensing. (WWW)


A review of the role of active remote sensing and data fusion for characterizing forest in wildlife habitat models. (WWW)

What is LIDAR? (WWW)

Lidar remote sensing of laser-induced incandescence on light absorbing particles in the atmosphere. (WWW)

Assessing the transferability of statistical predictive models for leaf area index between two airborne discrete return LiDAR sensor designs within multiple intensely managed Loblolly pine forest locations in the south-eastern USA. (WWW)


By LiDAR geek: