LIDAR Intro

7/31/2019 LIDAR Intro

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Brief Introduction


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Visualization

Segmentation

Classification

Filtering

Transformations

Gridding

Mathematical operations

Typical operations performed on LIDAR

point cloud data


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The simplest visualization will plot all the points with a single color and size, and the

operations of Zoom, Rotate, and Navigate will be available.

More advanced software will render each LIDAR point according to other characteristics, it can

be brightness coded according to the laser return intensity.

Other Software will render a Triangulated Irregular Network (TIN) or Digital Elevation Model

(DEM)

Visualization

Visualization of LIDAR data: A) As a point cloud. B) As a DEM.


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Primitive fitting is the application of the least square methodology to compute the spatial

parameters that define simple geometric figures or volumes such as lines, circles, planes, spheres,

cones and cylinders.

Primitive Fitting

Primitive fitting process illustrated: A) Point cloud. B) Picking points from the sphere surface. C)

Fitted sphere based on the picked points.


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An important visualization tool is the selection of a particular baseline and the generation of a

cross sectional view of the point cloud at the baseline.

Generating Cross Sections

Cross section generation from the point cloud


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Merging is performed by setting one point cloud as the base reference frame, and then

common points or common primitives are identified between the base and the source

point cloud. From the common points a 3D rotation and translation transformation is

computed using least squares adjustment.

Merging

Illustrates a merging operation between two point clouds color coded as white and pink that were obtained from different scan

angles, using the common points method the pink point cloud was rotated to the white coordinate system to produce a single

coherent data set.


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Allows the user to manually do single point selection. This is to navigate through the

point cloud using the zoom and rotate controls to pick out single points from the cloud.

Single Point Selection

MeasurementsThe ability to precisely select points from the clouds allows the analyst to make measurements

such as distances between points, and angles between lines connecting the points.

SegmentationThe operation that will segment or segregate points into different groups based on characteristics

without knowledge of what they really are. An example of segmentation could be the separation of

points, based on intensity values, into low intensity, medium intensity and high intensity.


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Implies the separation of points into different groups or classes defined by an intrinsic

or natural characteristic.

Classification

FilteringIs the removal of a set of points from the clouds based on either a segmentation or classification

scheme. A classification filter could be one that removes vegetation from an urban scene

TransformationsSuch as: Cropping, rotations and translations


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How LIDAR works

Pulses of laser light are produced. Light scatters from molecules and aerosols in the atmosphere.

Scattered light intensity is measured.

From the back-scattered power detected water vapor density,temperature, direction and velocity can be inferred.

This is an schematic example of howLIDAR is used to measure the watervapor density by comparing 2

different wavelength pulses with thesame intensity. The back-scatteredintensity is then analyzed andcompared to calculate the waterabsorption or water density.


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Typical LIDAR Methods

Type of LIDAR Measurement Principle ApplicationMie Scattering LIDAR Mie scattering of laser light caused by

aerosols, etc. Measurement of aerosols in the loweratmosphereRayleigh Scattering LIDAR

Rayleigh scattering of laser lightcaused by molecules, etc. Measurement of the density andtemperature of the air in the middle

atmosphere

Raman Scattering LIDARRaman scattering (a kind of inelasticscattering) of the laser light caused bymolecules

Measurement of water vapor, highdensity air pollutant from exhaust.

Fluorescent LIDARFluorescent measurement fromexcited gas molecules Identification and densitymeasurement of middle atmospheric

molecules

Differential Absorption LIDARAbsorption of laser light caused bymolecule The identification and measurementof molecular density

Doppler LIDARMeasurement of the wavelength shiftscaused by the Doppler effect of Miescattered light

Measurement of direction and velocityof wind


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Observation of Asian Dust

On this particular day, an Asian dust was observed even in Chiba area, Japan (in

the vicinity of 4 km)


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Aerosol Fallout

An example of observation of vigorous downward aerosol motion due to

descending air flow.


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Observation of Rain Clouds

Rain clouds descend gradually from a height of around 2 km, with the

circumstances from the onset to the cessation of precipitation being observed..


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Doppler LIDAR is an instrument in which pulses of light from a laser aretransmitted to the atmosphere to be reflected from aerosols suspended inthe atmosphere.

Then this weakly reflected signal is collected by a telescope. The distancefrom which the reflection occurs is calculated by relating the speed of light

to the timing of the transmitted and received pulses.Since the reflection of the light pulses comes from small particles entrainedin the wind, the Doppler shift from these particles provides a tracer for thewind field.

Doppler LIDAR


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An Overview of Lidar Point Cloud Processing Software GEM Center ReportNo. Rep_2007-12001 by J.C. Fernandez, A. Singhania, J. Caceres, K.C.Slatton, M Starek, R.Kumar

Doppler Lidar Observations of an Atmospheric Thermal Providing Lift toSoaring Ospreys by Grady J. Koch

http://www.physics.adelaide.edu.au/optics/res/water1.htm

http://jp.hamamatsu.com/en/rd/technology/energy/lidar.html

http://www.teramobile.org/teramobile.html

http://smsc.cnes.fr/CALIPSO/GP_mission.htm

References
http://www.physics.adelaide.edu.au/optics/res/water1.htmhttp://jp.hamamatsu.com/en/rd/technology/energy/lidar.htmlhttp://www.teramobile.org/teramobile.htmlhttp://smsc.cnes.fr/CALIPSO/GP_mission.htmhttp://smsc.cnes.fr/CALIPSO/GP_mission.htmhttp://www.teramobile.org/teramobile.htmlhttp://www.teramobile.org/teramobile.htmlhttp://jp.hamamatsu.com/en/rd/technology/energy/lidar.htmlhttp://jp.hamamatsu.com/en/rd/technology/energy/lidar.htmlhttp://jp.hamamatsu.com/en/rd/technology/energy/lidar.htmlhttp://www.physics.adelaide.edu.au/optics/res/water1.htm

LIDAR Intro

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