A new video survey method of microtopographic laser scanning (MiLS) to measure small-scale seafloor bottom roughness

A novel video survey method measures small-scale seafloor bottom roughness in fragile and deep-sea habitats called microtopographic laser scanning (MiLS). Using a controlled submersible platform, an attached downward-facing video camera with a single optical laser can return imagery to detail the bottom profile at a resolution of similar to 1-2 cm. The method compares the position of the underlying substratum and laser dot between successive video frames to determine distance traveled in the forward direction and substratum height. The video imagery is processed using photogrammetry to calculate small-scale topography (horizontal and vertical axes). MiLS is adaptable for most aquatic habitats as it can be executed using any platform that can move forward with a constant slope over the desired transect. Traditional techniques of measuring small-scale roughness are largely restricted to easily accessible habitats and often yield measurements that are relative and not comparable among different habitats and studies. Quantifying roughness in ways that permit comparisons is critical to understanding effects of bottom roughness and would benefit many fields of aquatic science. With its versatility, ability to access remote locations and output of quantified measurements, MiLS has the potential to fill this need. It is also likely this method will be useful in subaerial habitats such as wetlands. Here, we describe the MiLS equipment, theory, and method in detail, and then demonstrate its application in a lab trial and in a field study in a deep-sea (<= 450 m depth) sponge and coral habitat where its high resolution, accuracy, and precision is made evident.