The development of rocket-based and turbine-based combined cycle engines are a high priority for transportation into space. In order to test components and systems, and certify life cycles for these engines, non-intrusive flow diagnostics are required. In particular, high-speed measurements of pressure, velocity, and temperature profiles across both inlet and outlet ducts of these engines would provide a better understanding of engine performance. Southwest Sciences, Inc. proposes to develop a high-speed, non-intrusive monitor to measure such flows. This fiber optic sensor is based on a novel approach derived from wavelength modulation spectroscopy, in which high bandwidth measurements can be acquired and processed with simple electronics. Phase I will focus on validating the proposed technique and in Phase II, a fully operational prototype will be constructed, tested and delivered to NASA.