This Small Business Innovation Research Phase I project will examine the feasibility of developing a balloon-based instrument that can measure water vapor and methane at high precision and accuracy. Water vapor and methane play critical roles in the chemistry, dynamics, and radiative budget of the atmosphere, but their concentrations are quite poorly characterized near the tropopause and in the stratosphere. Commercial hygrometers are unreliable in these regions, and no existing instrumentation can measure methane onboard standard weather balloons. Key innovations for this project are a low power vertical cavity surface emitting laser (VCSEL) to measure methane, newly developed compact optical cells to minimize space and weight requirements, singular valued decomposition algorithms to increase long-term precision, and the addition of another VCSEL at 1854 nm to probe water vapor. <br/><br/>Development of a combined water vapor and methane instrument for standard weather balloons will significantly advance the understanding of global climate change by providing researchers with valuable measurements that cannot be accomplished currently. More accurate measurements of these gases in the upper troposphere and stratosphere will enable scientists to more accurately predict changes to the ozone layer and climate change. More accurate levels of water vapor in the upper troposphere will yield more accurate forecasts.