Infrared Techniques for Measuring Ocean Surface Processes

Ocean surface processes, and air–sea interaction in general, have recently received increased attention because it is now accepted that small-scale surface phenomena can play a crucial role in the air–sea fluxes of heat, mass, and momentum, with important implications for weather and climate studies. Yet, despite good progress in recent years, the air–sea interface and the adjacent atmospheric and marine boundary layers have proven to be difficult to measure in all but the most benign conditions. This has led to the need for novel measurement techniques to quantify processes of air–sea interaction. Here the authors present infrared techniques aimed at simultaneously studying multiple aspects of the air–sea interface and air–sea fluxes. The instrumentation was tested and deployed during several field experiments from Research Platform (R/P) FLIP and Scripps pier. It is shown that these techniques permit the detailed study of the ocean surface temperature and velocity fields. In particular, it is shown that cross-correlation techniques typically used in particle image velocimetry can be used to infer the ocean surface velocity field from passive infrared temperature images. In addition, when conditions make cross-correlation techniques less effective, an active infrared marking and tracking technique [which will be called thermal marker velocimetry (TMV)] can be successfully used to measure the surface velocity and its spatial and temporal derivatives. The thermal marker velocimetry technique also provides estimates of the heat transfer velocity and surface renewal frequencies. Finally, infrared altimetry is used to complement the temperature and kinematic data obtained from passive imagery and active marking. The data obtained during the testing and deployment of this instrumentation provide a novel description of the kinematics of the surface of the ocean.