Abstract: A high-altitude atmospheric sensor may include a frame configured to attach to a body of an aircraft, where the frame defines an open measurement cavity for air to travel through during flight of the aircraft. The sensor may further include one or more light sources providing input light such as mid-infrared quantum cascade lasers, a beamsplitter to separate the input light into measurement light propagating along a measurement path and reference light propagating along a reference path, one or more measurement cells providing optical paths for the measurement light in the open measurement cavity of the frame, one or more detectors to capture the measurement light from the one or more measurement cells and the reference light, and a controller to generate one or more spectroscopy measurements of air passing through the open measurement cavity during the flight of the aircraft.