Assessing EO image degradation from underwater optical turbulence in natural waters

It is a well-known fact that the major degradation source on EO imaging underwater is from scattering by the medium itself and the constituents within, namely particles of various origins and sizes. Recent research indicates that under certain conditions, such degradations could be caused mainly by the variations of index of refraction associated with temperature and salinity micro-structures in the ocean. These would inherently affect the optical signal transmission underwater, which is of vital interest to both civilian and military applications, as they could include diver visibility, search and rescue, mine detection and identification, and optical communication. The impacts from the optical turbulence are yet fully understood, in part due to the challenges associated with parameterization of individual factors. This study presents the initial attempts in quantifying the level of EO image degradation due to optical turbulence in natural waters, in terms of modulation transfer functions, and enhancements using the lucky patch approaches derived from optical flow techniques. Image data collected from natural environments during SOTEX (Skaneateles Optical Turbulence Exercise, July 22-31, 2010) using the Image Measurement Assembly for Subsurface Turbulence (IMAST) are presented. Optical properties of the water column were measured using WETLab's ac-9 and LISST (Laser In Situ Scattering and Transmissiometry), in coordination with temperature, conductivity and depth. Turbulence conditions were measured by two different approaches, namely a 3D Doppler based velocimeter with Conductivity/Temperature combo, and a shear based Vertical Microstructure Profiler.