4a. Appendix I. Description of the imaging vehicle HabCam

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The imaging vehicle, HabCam, consists of stereo high resolution color CCD cameras and four 25 Ws strobe lights mounted on a steel frame (Fig. 8; Howland et al 2006). The strobes are place 0.5 m from the camera for an overall vehicle length of 3 m. The strobes are fitted with an fresnel lens to provide a structured light beam intersecting the bottom at an angle of about 20 degrees at a vehicle altitude of 2 m. This intersection angle minimizes illumination of water column particulates thereby maximizing image contrast. The field of view (FOV) of the camera depends on the altitude off the bottom: at 2 m FOV ~ 1.5 m while at 3 m FOV ~ 2.2 m square. Altitude from an onboard pencil bean sonar is used to calibrate the FOV in real-time. The cameras and strobes are synchronized to fire at 15 Hz while images are transmitted on the fiber optic tow cable over Gigabit Ethernet.
Ancillary sensors on the towed vehicle include a Benthos altimeter for precise positioning above the bottom, an Imagenics 881a scanning imaging sonar mounted on the front of the vehicle for obstacle avoidance and sea floor roughness, a SeaBird SBE37 CTD, a WetLabs wetstar chlorophyll fluorometer, and a digital, color Video Plankton Recorder (Gallager et al, 2004). The cameras, strobes, and all sensors interface through fiberoptic interface unit which includes 2 Ethernet to fiber optic transceiver channels (1000 BaseT), a 16 port RS232 to Ethernet server, and appropriate power supplies
All data are transmitted to the surface through a 0.68 inch triple armor, 3 fiber, 3 conductor tow cable. A single fiber optic, 8 conductor slip ring is mounted on a winch. The 1000BaseT Ethernet is transmitted through the single fiber optic pass-through to a Ethernet switch via CAT6 cable.
The vehicle is towed from the A-frame on the F/V Kathy Marie between 1 and 5 kts at an altitude of 2-3 m depending on water clarity. Altitude is adjusted manually by observing a real-time data stream of critical navigational data (altitude, vehicle depth, roll, pitch, yaw, bottom depth, etc.). At 5 kts and a frame rate of 6 fps, more than 60% overlap between images provides the necessary information for construction of mosaics (see below) and 3D topography. Stereo image pairs are used to obtain precise measurements of benthic targets. Currently, we have built one stereo imaging vehicle which we will operate off the F/V Kathy Marie for this project.