Lecture 12 Content LIDAR 4/15/2017 GEM 3366

The LIDAR instrument transmits light out to a target The transmitted light interacts with and its direction is changed by the target Some of this light is reflected / scattered back to the instrument where it is analyzed The change in the properties of the light enables some property of the target to be determined. The time for the light to travel out to the target and back to the LIDAR is used to determine the range to the target 4/15/2017 GEM 3366

LIDAR is an acronym for Light Detection And Ranging LIDAR sensors measure elevation by bouncing laser light off of a surface and measuring the time the light pulse takes to return. 4/15/2017 GEM 3366

What can you do with LIDAR? Measure distance Measure speed Measure rotation Measure chemical composition and concentration of a remote target where the target can be a clearly defined object, such as a vehicle, or a diffuse object such as a smoke plume or clouds 4/15/2017 GEM 3366

A lidar sensor transmits and receives electromagnetic radiation, but at a higher frequency. Lidars operate in the ultraviolet, visible and infrared region of the electromagnetic spectrum. 4/15/2017 GEM 3366

LIDAR transmits and receives electromagnetic radiation, but at a higher frequency LIDAR operate in the ultraviolet, visible and infrared region of the electromagnetic spectrum LIDAR’s transmitter is a laser, while its receiver is an optical telescope 4/15/2017 GEM 3366

For some LIDAR applications more than one kind of laser is used Different kinds of lasers are used depending on the power and wavelength required The lasers may be both cw (continuous wave, on continuous like a light bulb) or pulsed (like a strobe light) For some LIDAR applications more than one kind of laser is used 4/15/2017 GEM 3366

The receiving system records the scattered light received by the receiver at fixed time intervals LIDARS typically use extremely sensitive detectors called photomultiplier tubes to detect the backscattered light photocounts are received and recorded for fixed time intervals during the return pulse 4/15/2017 GEM 3366

where c is the speed of light, 3 x 108 m/s The times are then converted to heights called  range bins since the speed of light is well known range bins from time:  where c is the speed of light, 3 x 108 m/s if each range bin is 160 ns long the height of each bin is 24 m (note: 1 ns = 1 x 10-9s) 4/15/2017 GEM 3366

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LITE stands for LIdar Technology Experiment LITE flew on shuttle mission STS-64 in September, 1994 LITE  was the first successful demonstration of operating a LIDAR from space 4/15/2017 GEM 3366

LITE was designed to measure clouds and aerosols, the small particles of "stuff" in the air that includes cloud droplets. Operating a LIDAR from space allows large regions of the atmosphere to be rapidly sampled. 4/15/2017 GEM 3366

5 minutes of LITE observations over the Sahara on September 18, 1994. The Atlas Mountain range to the  right of the thin black line at 31oN separates air masses thick in aerosols (left) and low in aerosols (clear air, right). A complex aerosol structure exists over the desert, with aerosol plumes reaching over 5 km in altitude 4/15/2017 GEM 3366

LIDAR systems There are three basic generic types of lidar: Range finders DIAL Doppler lidars 4/15/2017 GEM 3366

Range finder LIDARS are the simplest LIDARS Range finder LIDARS are the simplest LIDARS. They are used to measure the distance from the LIDAR instrument to a solid or hard target. 4/15/2017 GEM 3366

Differential Absorption LIDAR (DIAL) is used to measure chemical concentrations (such as ozone, water vapor, pollutants) in the atmosphere. A DIAL LIDAR uses two different laser wavelengths which are selected so that one of the wavelengths is absorbed by the molecule of interest whilst the other wavelength is not. The difference in intensity of the two return signals can be used to deduce the concentration of the molecule being investigated. 4/15/2017 GEM 3366

Doppler LIDAR is used to measure the velocity of a target Doppler LIDAR is used to measure the velocity of a target. When the light transmitted from the LIDAR hits a target moving towards or away from the LIDAR , the wavelength of the light reflected/scattered off the target will be changed slightly. This is known as a Doppler shift - hence Doppler LIDAR. The true wind velocity and thus a remote measurement of the wind velocity is computed 4/15/2017 GEM 3366

Basic LIDAR airborne components Consists of: Airborne vehicles LIDAR An inertial navigation system- records aircraft’s pitch, roll, etc.) GPS receiver – records x,y,z positions of the LIDAR system Computer – performs the computations to transform positions in the air to unknown positions on the ground 4/15/2017 GEM 3366

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Current LIDAR accuracies range between 10-15cm The final result from the LIDAR system is the coordinates of a dense pattern of ground points and an image of the ground points Current LIDAR accuracies range between 10-15cm 4/15/2017 GEM 3366

LIDAR data examples LIDAR light intensity map 4/15/2017 GEM 3366

LIDAR intensity data Willapa Bay,Washington 4/15/2017 GEM 3366

Forested area LIDAR image 4/15/2017 GEM 3366

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