Advances in predicting spatial deformations in imagery acquired by viewing through the sea surface

The image-based airborne detection of submerged threats and obstructions is frequently confounded by interfacial refraction and in-water scattering, which reduce image contrast and resolution. In particular, refractive effects spatially dissociate the received image, often to the extent that target shape is obscured. In the late 1980s, Schippnick addressed the problem of predicting deformations in trans-interfacial imagery. Over the past six years, we have developed models that simulate image degradation by trans-interfacial viewing. Additionally, our models can approximately reconstruct a submerged target given partial knowledge of sea surface topography and ocean optical properties. In this paper, we summarize recent advances in our simulation techniques that render our models more realistic physically, as well as amenable to processing SIMD-parallel architectures. We emphasize the simulation of image deformations, which facilitates algorithm development in support of image clarification or automated target recognition. In particular, we discuss requirements for the simulation of receiver noise, electronic effects (e.g., automatic gain control, saturation, and thermal noise), as well as spatial noise such as pixel blooming and point-spread effects resulting from image intensifier tubes. Additional emphasis is given to techniques for simulating caustic effects within the water column, including backscattering of intense irradiance from turbid water. The ability of our models to accommodate layered media is also considered. Analyses pertain to practical simulation issues such as computational cost, numerical error in predicting the spatial location of target features, and approximate computation of simulation operations. Our models are structured in terms of functional modules that correspond to individual physical processes and are coded in standard computer languages. Thus, our models are easily maintained and are portable to a wide variety of computers.