Surface wave processes play an important role in the coupled ocean-atmosphere system. Measurements and models of the drag of the sea surface at moderate to high wind speeds suggest that essentially all the momentum transfer at the surface is supported by the form drag over surface waves. In situ measurements have been supplemented at times with intensive airborne measurements from manned aircraft flying at low altitudes, but the limited availability of suitable aircraft, accidents, and in-flight events in recent years have limited the capabilities of manned aircraft to address the broader needs for air-sea interaction research. Space-borne sensors do not have the resolution to be the primary instruments in air-sea interaction studies at the scale of the surface waves.
A UAV system to measure air-sea fluxes of momentum and other variables in the marine atmospheric boundary layer (MABL) along with simultaneous surface wave measurements is being developed. This technology will lead to an improved understanding of the dependence of air-sea fluxes on the surface wave field, it will permit rapid measurements of parameters for input into coupled atmosphere-ocean models, it will lead to greater geographical and environmental diversity of the air-sea flux data bases, and most importantly it will permit measurements at low altitudes that are too dangerous for human flight. This low altitude (O(10) m) capability will result from the use of laser altimetry, differential GPS (DGPS) and inertial motion units (IMUs) to provide input to the controls for low altitude flight. This combination of instrumentation will also measure the surface wave field under the aircraft track. The combined data set from the two aircraft will permit coherent measurements of wave-induced effects on the air-sea fluxes. It will also have the payload capacity to add interferometric SAR at a later time to measure ocean surface currents.