A new method for estimating the area of the seafloor from oblique images taken by deep-sea submersible survey platforms

Abstract

In order to extract quantitative information on deep-sea benthic animals (no. individuals or biomass in an area) using oblique video/photo images taken by deep-sea submersible survey platforms, a new method was established to estimate the imaged area of the seafloor from the oblique images. The trapezoidal area appearing on the lower half of the screen was calculated using underwater horizontal and vertical aperture angles of the camera, the angle of incidence of the camera, and the camera-to-seafloor distance. The incidence angle of the camera was obtained using the angles of vehicle pitch and camera tilt, while the camera-to-seafloor distance was calculated from the lens-to-vehicle bottom distance, horizontal distance of lens-to-altimeter, and vehicle altitude. The areas estimated by the present method from images taken by some submersible survey platforms were comparable to those that were actually measured. With the above parameters, and by focusing on the lower half of an image, our method can be used for estimating the seafloor area from any oblique video/photo images taken by any submersible survey platform. Thus, this method is useful for the extraction of quantitative data on benthic animals from legacy oblique video/photographs acquired by submersible survey platforms.