Lidar is an acronym from Light Detection and Ranging. It is similar to radar as it transmits electromagnetic energy. Lidar uses lasers to determine the characteristics of a target such as distance and the component of its speed toward or away from the Lidar. The laser transmits electromagnetic energy and a telescope receives whatever energy is reflected to the Lidar. Calipso will carry lidars that transmit with wavelengths of .532 micrometers and 1.064 micrometers. These wavelengths are in the visible and near infrared portions of the electromagnetic spectrum. (A micrometer is one-millionth of a meter.) When lidars of different wavelengths are used and one is centered on a wavelength that is absorbed by a substance being studied and the other lidar is not, the temperature of the sensed particles may be determined.

Lidars are similar to radars, but are primarily different in the wavelength employed. Precipitation detection radars transmit at wavelengths from about 3 to 10 centimeters. At these much longer wavelengths, precipitation is easy to detect, but small aerosols are not. Cloud radars generally transmit at wavelengths between 3 and 8.6 millimeters enabling the study of the structure of clouds and the relatively small components of clouds. Wavelengths near 3 and 8.6 millimeters are frequently used because absorption by oxygen and water vapor is minimized. So, the wavelengths employed by lidars are much shorter than those used by radars.

Ground-based Lidars have been used in research to study wind, aerosol properties, and ozone.

URLs: LIDAR

http://www.ghcc.msfc.nasa.gov/sparcle/sparcle_tutorial.html

http://users.aber.ac.uk/ozone/lidar.html

http://www.photonics.com/spectra/tech/XQ/ASP/techid.21/QX/read.htm

http://oea.larc.nasa.gov/PAIS/LaserSensing.html

http://aesd.larc.nasa.gov/GL/tutorial/lidar/lidar_mn.htm

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