Explanation of LIDAR
LIght Detection And Ranging (LIDAR)
is analogous to RADAR except that light waves are used instead of radio
waves. Optical radiation is emitted by a laser and sent out in a
particular direction through the atmosphere. This radiation can cover
wavelengths from the ultra-violet (0.3-0.45 um), visible (0.45-0.70 um)
to the infrared (1-15 um) depending on the type of laser selected. When
the beam encounters aerosol particles or air molecules in the
atmosphere, laser radiation is scattered in all directions including
some in the direction from which the radiation came from. Hence, the
term backscatter is used to define the radiation returned to a receiver
mounted adjacent to the laser transmitter. With very short pulses of
radiation sent out, timing how long it takes for pulses to be returned
allows the backscattered radiation to be determined at a number of
range intervals from the lidar system. If the lidar system has been
calibrated backscatter is defined in units of /meter/steradian. Since
backscatter can vary over a wide range of values (up to five orders of
magnitude depending on the type of scatterer and its concentration), the
logarithm of the backscatter is often used to allow plots of the
backscatter data to be made.
Responsible Official: Dr. James E. Arnold (jim.arnold@msfc.nasa.gov)
Page Curator: Paul J. Meyer (paul.meyer@msfc.nasa.gov)
Last Updated: May 15, 1995