Lidar (Light Detection and Ranging) measures back scattered light from particles & molecules in meters per steradian and parts per million (ppm). It uses a pulsed laser, telescope and fast detectors and electronics. The Nd: YAG lidar emits light at 532nm and 1064nm. Fast detectors and electronics beneath a telescope measure laser light scattered by atmospheric constituents of multiple wavelengths.
Lidar is used for long term monitoring of the stratospheric aerosol layer. This layer effects solar radiation and ozone. Stratospheric aerosols cool the earth by reflecting light back into space.
The plot above shows the Total Integrated Aerosol Backscatter (IABS) measurements from Mauna Loa since 1980. The eruptions of El Chichon and Mt. Pinatubo are evident. No clear trends are seen in background stratospheric aerosols.
The lidar measures backscatter from volcanic particles and other aerosols high in the atmosphere (15.8-33km). The volcanic particles are composed mainly of water and sulfuric acid and persist for up to a decade following major eruptions such as occurred in 1982 and 1991. These particles influence the ozone layer, and as illustrated in the graph below of apparent solar transmission, reduce the amount of sunlight reaching the earth.
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GMD Lidar: Mauna Loa, Hawaii