Thermal Infrared Multipath Reflection from Breaking Waves Observed at Large Incidence Angles

The infrared signature of breaking waves at large incidence angles was investigated using laboratory experiments and a radiometric model. Infrared imagery of the water surface at incidence angles greater than 70 ^° shows multipath reflections for both spilling and plunging waves generated using a programmable wave maker. For the spilling breakers, the multipath signature was initially distinct from the breaking wave front roller signature but then merged to create a single large bright distributed target. For the plunging breakers, the roller and multipath signatures overlapped from the inception of breaking. The radiance of the multipath reflection was higher than the surrounding water for simulated cold sky conditions and lower for a simulated warm sky. A specular double-reflection model successfully predicted the presence of multipath reflection but the magnitude was sensitive to small uncertainties in geometry, wave slope, and input temperatures. The results show that multipath reflection from breaking waves is characteristic of large incidence angle infrared measurements and increases the area and magnitude of the infrared signature of breaking waves compared to the background.