Obtaining experimental air flow data for validating computational models of ship air wakes is critical to addressing current challenges associated with recovering maritime aircraft using naval vessels. Small unmanned aircraft are desirable for this task due to their maneuverability and minimal invasiveness in terms of installation and usage. This paper presents a small, tethered, unmanned aircraft system capable of providing high-resolution air wake measurements behind a moving maritime vessel under a wide variety of wind conditions. The air wake measurement task is accomplished by having the aircraft autonomously sweep behind the moving vessel at various altitudes while collecting both air flow data from an omnidirectional probe and relative state measurements. Relative state measurements are obtained through a sensor fusion scheme involving differential GPS and vision-based pose measurements from an infrared beacon array mounted on the ship deck. The proposed system is able to deduce both the steady-state and turbulent components of the air wake stream as a function of position relative to the ship without the need for rigorous sensor calibration. Results demonstrating the robustness of the tethered flight and relative state estimation schemes to a relative wind speed of up to 10 m/s are obtained with motion-capture-validated simulation testing as well as indoor testing in hardware. Near-term future work will include conducting outdoor field experiments to show the effectiveness of the platform as a high-resolution in-situ air wake measurement system.