The NASA Rapid OZone Experiment (ROZE) is an in situ instrument capable of measuring ozone (O3) throughout the troposphere and lower stratosphere on airborne platforms. The instrument uses cavity-enhanced absorption to measure the amount of ozone in a sampled volume flowing through an optical cell. The high-sensitivity of the cavity-enhanced detection scheme and the small sample volume enable high precision measurements in short integration times, making this instrument suitable for measuring O₃ fluxes (the exchange between the Earth's surface and atmosphere) with the eddy covariance technique. The instrument is designed for autonomous operation and requires minimal support (and no gases or dry ice) in the field. An inlet mounted in the free stream is needed to sample ambient air.