A compact system to extract topography information from scenes viewed by a miniaturized submersible explorer

In images taken underwater, it is generally difficult to correctly extract distances and geometric information of objects. Different techniques, collectively referred to as photogrammetry, exist to measure features in images. One of these is to project a reference pattern onto an object in a scene viewed by a camera, and register the distortion of this pattern, to calculate the shape of, and distance to, that object. This method is implemented here on a miniaturized submersible explorer equipped with, among many other instruments, a camera. Diffractive optical elements (DOEs) have been designed and manufactured using microsystems technology, to, together with a laser diode, camera, and in-house developed software, provide a compact system for projecting reference patterns and analyzing their deformations. The system has been characterized by measuring the distances and angles of objects in a water tank, and attempting to reproduce their shapes. The range of operation of the system, verified to be at least one meter, is limited by the compact mounting in the small submersible and the cameras’ performance. The system was found to work well under turbid conditions as well as in water containing larger particles. Together with a vehicle-mounted camera, the compact and low-power DOE laser projection system enables topographical measurement.