"LiDAR (Light Detection And Ranging) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses. Like the similar RADAR technology, which uses radio waves, the range (i.e., distance) to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signal. LiDAR technology has application in Geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, remote sensing and atmospheric physics." (Wikipedia)

Although LiDAR and RADAR share similarities (both are DAR systems), they operate very differently and are used in very different applications. The first LiDAR was developed in the late 1930's using searchlights in experiments to measure stratospheric aerosols. However, it wasn't until the invention of ruby lasers in 1960 that LiDAR, as we now know it, came into being. Since then, the application areas in which LiDAR is used has expanded considerably, and , as mentioned in the Wiki article cited above, the technology is now used by archaeologists, geographers, foresters and physicists.

An article on LiDAR and 3D imaging. A good overview of LiDAR and forest applications. LiDAR magazine. A Dummies Guide to LiDAR.

A video showing a gyroscope mounted on a car's roof. The Alberta Geological Survey's report on LiDAR on Turtle Mountain. The London LiDAR video.

Answers to the questions in class:

Why is the IR laser used for bathyrmetry? Absorption is a problem, as described here:

“The infrared band is quickly absorbed and is therefore used to detect the water surface, while the green band is used as the optimum color to achieve maximum penetration in shallow water. Lidar bathymetry systems operate at a much slower rate, currently around 1000 soundings per second, due to the need to generate a much longer laser pulse and higher power requirements.” (Source) None-the-less, it does seem strange that bathymetric LiDAR systems use the IR laser to identify the top-of-the-water values (that is, given "the infrared band is quickly absorbed" why does it follow that it "is therefore used"?).

How far can the laser penetrate the water column?

“Measurement depths for the system range from 0.3, to about 3 times the secchi depth.” (Source) Based on various sites I visitied, it appears as though the depth can be up to 60 m in very clear water, but as the sediment load increases the maximum depth rapidly decreases.

Text: Chapter 10.3: Laser Scanning