Development of Instrumentation to Measure Atmospheric Light Extinction and its Scattering and Absorption Components

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In the shortwave optical regions, lack of adequate instrumentation hinders scientific progress across a variety of research areas. The local measurement of light extinction, scattering and absorption in the atmosphere has applications to a number of scientific problems related to:1. Aerosol radiative forcing and its influence on climate change.2. Optical remote sensing using either active or passive systems.3. Atmospheric visibility as needed for regional air quality studies.The Principal Investigators will develop instrumentation capable of measuring total atmospheric light extinction and its scattering and absorption components. The system to be developed includes three specific instruments:(1) An extinction instrument which folds several tens of kilometers of optical path into a one-meter length optical cavity and determines extinction by measuring the exponential decay of the optical power contained in the cavity. (2) A novel scattering instrument concept based on the inverse nephelometer concept which collects virtually all scattered light including the forward scattering from large particles. (3) A light absorption instrument which yields a real time in situ measurement of optical light absorption by utilizing resonant photoacoustic detection of light absorption. The use of an all-solid-state laser makes this instrument much more compact and less power hungry than its predecessors. Innovative acoustic design makes this instrument more than an order of magnitude more sensitive than previous designs. The proposed development of these instruments will result in an instrument cluster which will be far more useful than the three individual instruments used separately. For example, the combination of absorption and scattering measurements can determine the single-scattering aerosol albedo. Addition of the extinction instrument will result in experimental closure on the problem of atmospheric light extinction and its scattering and absorption components. This closure is extremely important for quality assurance purposes, i.e., measurement accuracy can directly be assessed by checking if the sum of measured absorption and scattering extinction equals the measured extinction.