A 3-D laser line scanner for outcrop scale studies of seafloor features

Manned submersibles and remotely operated vehicles make it possible to use many of the techniques of land geology on the seafloor. A fundamental aspect of geological maps is the documentation of the orientation of various planes and lines in space. Strike and dip typically characterize planes, and trend and plunge characterize lines. Sedimentary bedding, lava flow tops, dike margins, igneous layering, metamorphic foliations, joints and faults, etc. Land geologists determine the orientation of outcrop-scale features with various types of hand-held compasses and inclinometers. However, this type of instrument is not appropriate for use on the seafloor and different approaches are required to obtain orientation data. A 3D laser scanning system currently being developed by the Harbor Branch Oceanographic Institution Engineering Division, under National Science Foundation and Duke University sponsorship, affords a method of collecting orientation data. Similar to previously designed HBOI systems, surfaces of interest are rapidly scanned to produce high-resolution digital maps. The 3D map coordinates combined with the measured roll and pitch angles of the instrument are used to accurately determine orientation of the scanned geologically relevant planes and lines on seafloor outcrops. Unlike other techniques currently in use, this instrument does not need to be carefully positioned or placed on the rock surface and is not affected by magnetic fields. Furthermore, due to the high scan rate, the instrument need not be held stationary while scanning. During a single seafloor traverse of several hours, thousands of measurements can potentially be made.