MODEL RELEASED. Laser radar. Scientist Dan Walsh at the controls of a laser radar (lidar) which measures atmospheric aerosols, ozone levels & temperatures. The lidar vertically projects 2 beams at different wavelengths. The inten- sity of radiation scattered back (shown on screen) is analysed to determine the stratosphere's composition at altitudes of 15-75 kilometres (km). Stratospheric aerosols come from volcanic erupt- ions, & are mainly comprised of sulphuric acid and water. Ozone gas, mainly found above 19km, blocks harmful ultraviolet rays from the Sun. Photo- graphed at Mauna Loa Observatory on Hawaii, USA.