A self‐adjusting positioner has been developed for allowing a sensor to measure instantaneous flow properties at a fixed distance from a moving water surface. It thus permits measuring the flow field in the troughs of progressive wind waves, which is essential information for understanding air‐water interaction. With the aid of a special statistical technique to sample and average simultaneous recordings of water surface displacements and instantaneous flow properties, such as velocity, pressure, temperature, and humidity, a more complete description of both air and water flows near the interface can be obtained. The probe positioner works on the principle of the classical position servosystem. A capacitance gauge provides the actuating signal which is proportional to the depth of the water below the probe. The dynamic characteristics of the system, as expressed by its transfer function, indicate its applicability for wind waves generated both in laboratories and oceans.