Autonomous marine robots for geotechnical surveying at sea: the WiMUST experience

Geotechnical surveying consists of acquiring "images" of the geophysical structures underground, by "illuminating" the area with powerful acoustic waves and measuring with sensors the signals reflected back. The process can be done at different scales with different resolutions: oil and gas exploration (also known as geophysical exploration) usually requires to cover large areas of deep water (up to hundreds of square kilometres) to be covered at a relatively small resolution (the larger the oil field, the better!). Civil engineering applications, such as the installation of pillars, wind farms, submerged pipes or cables, and port infrastructure, often requires higher imaging resolution of smaller areas (hundreds of square metres) in shallower waters. This is what we call geotechnical characterization. Whatever the scale, traditional methods for "imaging" the sea bottom with acoustic signals are based on towed equipment: a boat tows one or more acoustic sources, such as air guns, which explode very powerful "air bubbles" in the water, or "sparkers" firing electrical pulses underwater making a thunderbolt-like sound.