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Abstract
Many fundamental questions about planetary evolution require monitoring of the atmosphere with unprecedented accuracy at both high and low latitudes, over both day and night and all seasons. Each planetary atmosphere presents its own unique challenges. For the planets/moons that have relatively low surface pressure and low trace gas concentrations, such as Mars or Europa, the challenge is to have enough sensitivity to measure the trace gas of interest.
Trace gases and isotopic ratios in planetary atmospheres offer important but subtle clues as to the origins of the planet's atmosphere, hydrology, geology, and potential for biology. An orbiting laser remote sensing instrument is capable of measuring trace gases on a global scale with unprecedented accuracy, and higher spatial resolution that can be obtained by passive instruments. For Mars our proposed measurement technique uses Differential Absorption Lidar (DIAL) in the 3-4 um spectral range to map various trace gas concentrations from orbit on a global scale. For earth, we can use the same technique at 1.65 um to measure methane concentrations, a strong greenhouse gas. The instrument uses Optical Parametric Amplifiers (OPA) and Optical Parametric Oscillators (OPO) for the transmitter along with photon counting detectors to achieve the necessary sensitivity. Preliminary results demonstrating CH4 detection in a cell using the present OPO/OPA configuration will be presented.