Laser-based underwater imaging sensors have been developed and matured in the last decade that provide high resolution optical imagery of the sea floor. Laser Line Scan (LLS) and Streak Tube Imaging Lidar (STIL) have been particularly successful. A prototype Fluorescence Imaging Laser Line Scan (FILLS) sensor has been deployed in several underwater environments, yielding highresolution (~1 cm pixel size) imagery of the associated benthic habitats. The prototype FILLS sensor illuminates the sea floor with 488 nm laser light, and constructs four independent images from light collected at 488 nm, 520 nm, 580 nm, and 685 nm, respectively. The 488 nm image is formed from elastically scattered light (i.e., light scattered with no change in photon energy), while the other images are formed by inelastically scattered light. (The FILLS sensor is routinely operated during nighttime hours so that ambient illumination is negligible). Fluorescence is the primary physical mechanism giving rise to the inelastically scattered light sensed by FILLS. Coral reef environments produce particularly strong (and spectacular!) fluorescence imagery. FILLS was developed primarily for the detection, classification, and identification of man-made objects in underwater environments. In addition it can serve admirably for the characterization of underwater habitats. Examples of FILLS imagery relevant to fish habitat evaluation will be presented.
Characterization of soft-bottom benthic habitats of the Åland Islands, northern Baltic Sea