LiDAR Acquisition1. Introduction

1. Laser capturing unit2. Signals

2. Aerial LiDAR1. Objective and general setup2. Scanning process3. Characteristic properties – further information

3. Terrestrial LiDAR1. Objective and general setup2. static vs. mobile3. Registration

4. Bathymetric/Hydrographic LiDAR1. Objectives and general setup2. Characteristics – further information

5. Atmospheric LiDAR

Introduction

• LiDAR = Light Detection and Ranging• Laser-based scanning – terrain– bathymetry– atmospheric properties

• Collection of point set („point cloud“) data

Introduction

• Common setup to all scanners: transmitter and detector

• Detectors varies betweenscanners

𝑠 (𝑡 )=𝑐 ∗𝑡𝐿2

Introduction

• signals: pulse-ranging or continuous wave• Both create discrete measurements• Final data: single/multi-return range

measurements or (full) waveform

Images taken from: Conservation Applications of LiDAR Data, Joel Nelson, University of Minesota;

Further information on signals:Airbone laser scanning – an introduction and overview, A. Wehr and U. Lohr, ISPRS Journal of Photogrammetry and Remote Sensing, Volume 54, Number 2, July 1999, pp. 68-82(15)

Single-return Mutli-return Waveform return

Aerial LiDAR

• Objective: – earth observation of large areas (municipalities or

bigger)– 2.5D data

Aerial LiDAR

• Scanning process

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α

β

Δz

Δy

s(t)

plane pos. F

p

Aerial LiDAR

• Swath scanning -> line scan patternImage from: A guide to LiDAR data acquisition and processing for the forest of the Pacific Northwest, D. Gatziolis and H.-E. Andersen, Gen. Tech. Rep. PNW-GTR-768. Portland, Oregon, U.S. Department of Agriculture, 2008

Aerial LiDAR

• Characteristics and Properties:– Scanning angle– Scanning frequency– Pulse length -> vertical resolution– Footprint diameter– Footprint spacing (non-uniformal horizontal resolution)– Returns per pulse

• Beam frequency for topographic scan: 1040 – 1064 nm

Aerial LiDAR

• further information– continuous wave: “Introduction to continuous-wave Doppler

lidar”, C. Slinger and M. Harris, TechReport– full-waveform lidar: “From single-pulse to full-waveform

airborne laser scanners: Potential and Practical Challenges”, W. Wagner et al., Int. Archives of Photogrammertry and Remote Sensing, Vol. 35, No. Part B, 2004, pp. 201-206

– full-waveform lidar: “Empirical Comparison of Full-Waveform Lidar Algorithms: Range Extraction and Discrimination Performance”, C.E. Parrish et al., Photogrammetric Engineering & Remote Sensing, Vol. 77, No. 8, August 2011, pp. 825-838

Terrestrial LiDAR

• capture smaller-scale landscape phenomena in full 3D (steep coast segments, yardrangs)

• Time-series captures• 360° capture

Image courtesy:Using Terrestrial Light Detection and Ranging (Lidar) Technology for Land-surface Analysis in the Southwest, Soulard, C.E. and Bogle, R.C. and Western Geographic Science Center and Geological Survey (U.S.), Fact Sheet, 2011

Terrestrial LiDAR

• static LiDAR: fixed position; semi-automatic registration; standard in geological field survey

• mobile LiDAR: vehicle-mounted; easier large-scale survey; restricted to drivable (urban) regions

Terrestrial LiDAR

• reference of scans:– aerial & mobile terrestrial LiDAR: semi-automatic– static terrestrial LiDAR demands registration

ÞComputer Vision: – control points in view– inertia sensors– shape fitting– image-guided registration

Image:Terrestrial laser scanning in geology: data acquisition, processing and accuracy considerations, Buckley, S.J. et al., Journal of the Geological Society, May 2008, Volume 165, pp. 625-638

Bathymetric LiDAR

• Objective: scan shallow water areas (harbor, rivers and deltas)

• setup very similar to aerial LiDAR• 2 lasers: 532 nmand 1064 nm

Image source:Meeting the Accuracy Challenge in Airborne LiDAR Bathymetry, Guenther, G.C et al., Proceedings of EARSeL-SIG-Workshop LIDAR, 2000

Bathymetric LiDAR

• further literature:– Meeting the Accuracy Challenge in Airborne LiDAR

Bathymetry, Guenther, G.C et al., Proceedings of EARSeL-SIG-Workshop LIDAR, 2000

– Green, waveform lidar in topo-bathy mapping – Principles and Applications, Nayegandhi, A., USGS St. Petersburg/Florida

Atmospheric LiDAR

• surveying atmospheric properties (temperature, aerosols, etc.)

• usually telescope at detector• observable particles and properties depend on

beam wavelength (1064 nm or 532 nm) and backscatter type

Atmospheric LiDAR

Image courtesy of: Xinzhao Chu, CU-Boulder, Lecture “Fundamentals of LiDAR Remote Sensing”, 2011