This Small Business Innovation Research (SBIR) Phase I project proposes to support the development of a compact, rugged instrument for field measurements of methane flux. The instrument is based on a new technology called Off-Axis Integrated Cavity Output Spectroscopy (Off-Axis ICOS) combined with established eddy covariance techniques. This novel instrument will measure methane flux with high sensitivity, accuracy and specificity in real time. The instrument combines inexpensive, robust telecommunications-grade near-infrared diode lasers with Off-Axis ICOS, a patented innovative technology that provides extremely long optical paths (several kilometers typical) to yield an instrument capable of continuously recording data in the field with state-of-the-art precision (better than 0.2% uncertainty at a 10-Hz rate). By significantly increasing the accuracy of methane flux measurements in the field, the instrument will significantly enhance studies of global warming and facilitate multi-year studies and comparisons between geographically distant sites. These studies (which could involve using the instruments aboard airplanes to enable wide coverage and to correlate with satellite images) will help quantify the global carbon cycle on small and large spatial scales, and enable scientists to generate more reliable models of climate change and to determine environmental impact.<br/><br/>The proposed instrument is hoped to exceed current performance levels in accuracy, sensitivity, speed and reliability and thus compete favorably against existing technology (gas chromatographs, flame ionization detectors). As a result, the proposed novel instrument has several commercial applications including industrial process control, vehicle engine testing, and atmospheric and environmental monitoring. For industrial process control, the instrument may be applied to real-time measurements of multiple pollutants in petrochemical and chemical production plants and in vehicle test facilities, and for on-site mud gas analyses in oil and gas exploration, where existing technology is too slow, expensive or insensitive. In engine testing, for example, the proposed instrument should provide measurements with a faster response and a sensitivity that is three orders of magnitude better than current techniques. In addition, the low cost, portability, and reliability of the instrument should enable researchers in atmospheric chemistry, geology, biology and ecology to more accurately monitor, and determine the sources and sinks of, greenhouse gases and pollutants in the field and on board aircraft.