High Wavenumber Ocean Wave Spectra Determined through Polarimetric Imaging
Two intensive field experiments using R/P FLIP were staged within the ONR Radiance in a Dynamic Ocean (RaDyO) field program in the Santa Barbara Channel and in the central Pacific Ocean south of Hawaii. As part of this program, our team gathered and analyzed a comprehensive suite of sea surface roughness measurements designed to provide optimal coverage of fundamental optical distortion processes associated with the air-sea interface. This contribution highlights exciting new sea surface roughness measurement capabilities that underpin a number of the scientific advances resulting from the RaDyO program.
The observations gathered comprised standard marine environmental variables (winds, waves and fluxes). Our roughness measurements were highlighted by the first field deployment of our polarimeter for detecting wave fields down to 1.5 mm wavelengths at sample rates up to 60 Hz. These high resolution measurements were complemented by co-located scanning and fixed lidars. In addition, co-located video and infrared imagery gave an unprecedented coverage of the sea surface microstructure including breaking waves, over a range of wind speeds and underlying sea states.
We present open ocean wavenumber spectra for wavelengths from 3 mm to 1,000 mm obtained from our polarimetric imaging camera for a range of sea state conditions. We present results on the mean wavenumber spectrum and the modulation properties of the short-wave spectrum by the dominant waves.
These results highlight the complex interplay of wind and surface currents in shaping the small-scale roughness of the sea surface that suggests the traditional Cox-Munk framework may not be sufficient. These small-scale slope observations demonstrate the possible oversimplification of the classic Cox-Munk view that mss increases linearly with wind speed. The small-scale slope observations suggest the potential importance of upper-ocean currents in addition to the wind. These results are timely considering issues raised in the recent review article on the conundrums of capillary-gravity waves [Munk, 2009]. These field results demonstrate that the polarimetric camera gives a robust characterization of the fine-scale surface wave features intrinsic to wind-driven air-sea interaction processes.