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Over the past 20 years, active sensor techniques have emerged as crucial airborne and ground-based measurement techniques, providing the Earth sciences community with unique measurements for scientific disciplines in atmospheric chemistry, dynamics, studies of the Earth radiation budget, climate, meteorology, altimetry and crystal dynamics.' Two techniques, Lidar (Light Detection and Ranging) and DIAL (Differential Absorption and Lidar) have demonstrated the ability to conduct range resolved measurements of aerosols, cloud dynamics, height of the planetary boundary layer, humidity, trace species, and atmospheric winds. Experiments are routinely conducted from scientific aircraft in national and international campaigns. Additionally, airborne measurements have been conducted to demonstrate centimeter accuracy in Lidar ranging experiments. New applications are also emerging in aviation meteorology and in chemical agent, stand-off detection.2 To date, an active sensor experiment at optical frequencies (i.e. lasers) has not been conducted from space for Earth sciences experiments. However, under sponsorship from NASA's Office of Aeronautics and Space Technology, OAST, an experiment is planned for 1992 to conduct a technological Lidar experiment from the Space Shuttle with a Nd:YAG laser, at the fundamental, first and second harmonic wavelengths (1064 nm, 532 nm, 355 nm). Experimental plans and details of the instrumentation have been previously published.3 In this conference, a status of the Laser Transmitter Module [LTM] for the Space Shuttle experiment has been presented.4 A second laser experiment to measure the vertical profiles of water vapor in the lower atmosphere is also under development for a scientific experiment from the NASA U-2.5 The laser transmitters being developed for this experiment are using alexandrite technology. Experimental designs and concepts for this experiment have also been presented in this conference.6 From a technological perspective, this experiment is important since the DIAL experiment must be configured to be totally autonomous, and will develop systems technology in associated E/O systems technology including a laser wavemeter/spectrometer, detectors and information systems.
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