LIDARLight Detection and Ranging

Kate Whalen

PHY 3903

Nov. 25, 2005

Outline

• Some applications• How lidar works• Examples of current

lidar projects– Purple Crow Lidar

– Dalhousie Raman Lidar

Applications

• Distance measurements

• Atmospheric composition

• Weather

• Mapping

• Speed measurements

Lidar Basics

• Active remote sensing• Light is emitted,

scattered, and detected.

• Since we know the speed of light, we can measure the distance travelled!

Details• 3 main parts

• Transmitter– Example: Pulsed Nd:YAG

laser (532 nm)• Low beam divergence

• Narrow spectral width

• Receiver– Optical telescope

• Detector– PMT

– Chopper• Eliminates near-field returns

Purple Crow Lidar (UWO)• Detector consists of a 2.65 m

mercury mirror, rotating at 10 rpm– Parabolic mirror

• 532 nm Nd:YAG laser used for Rayleigh scattering– Elastic scattering at 30-90 km

• Obtain T(z) from density profile– Assumptions

• Hydrostatic equilibrium

• Ideal gas

(z) z2N(z)

P RT

P gz

PCL Projects

Dalhousie Raman Lidar• CABOT Observatory

– Canadian Atmosphere-Biosphere Observations Trailer

• 607 nm Nd:YAG laser• Raman scattering

– Inelastic scattering (change in rotational or vibrational energy)

– Frequency of scattered photon depends on temperature, type of molecule

• Investigates atmospheric aerosols & clouds– Transboundary pollution

transport

CABOT Projects

In Conclusion…

• Lidar is an example of physics for the benefit of the planet!

References• Thanks to Dr. Bob Sica and the PCL group at UWO!

• Argall, P. S. & R. J. Sica, Lidar (Laser Radar). In The Encyclopedia of Optics, Vol. 2, Ed. T. G. Brown et al., Wiley-VCH, Weinheim, 2005.

• Duck, T. J. et al., Lidar measurements of atmospheres. Physics in Canada 61 (5) 247-252, 2005.

• Sica, R. J. et al., Lidar measurements taken with a large-aperture liquid mirror. 1. Rayleigh-scatter system. Applied Optics 34 (30) 6925-6936, 1995.

• Environment Canada: Air Quality Processes Research Division [Online]. http://www.msc.ec.gc.ca/arqp/index_e.cfm [Nov. 24, 2005].

• Purple Crow Lidar [Online]. http://pcl.physics.uwo.ca/ [Nov. 24, 2005].• REALM: Regional East Atmospheric Lidar Mesonet [Online]. http://

alg.umbc.edu/REALM/ [Nov. 24, 2005].• The Atmospheric Optics Laboratory [Online]. http://aolab.phys.dal.ca [Nov.

24, 2005].