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Portable Underwater Photographic Tripod for Coral-Reef Studies
A newly designed underwater tripod was developed to more easily photograph and study the movement of sediment in coral-reef habitats, regardless of sea-floor roughness or slope. The basic design parameters were portability, light weight, and easily adjustable arms and legs for onsite configuration. These qualities give coral-reef scientists freedom to move the tripod or adjust the housing components for optimum results over a wide variety of bottom morphologies. The tripod also had to be robust, so as to withstand long-term deployments during large storm events and precarious positioning on the seabed. The framework of the new tripod is composed predominantly of anodized aluminum plate and tubing to resist corrosion by seawater, off-the-shelf Speed-Rail fittings to enable a wide variety of configurations, and customized adjustable brackets. The Speed-Rail fittings and customized brackets allow the camera and strobe housings to be shifted up and down and side to side and rotated in vertical and horizontal planes to capture exactly the desired view. Pad eyes (metal pads with holes through which a shackle can be put) are welded at numerous spots on the frame so that it can be secured firmly to the seabed with sand anchors—large metal spirals that are screwed 3 to 4 ft down into the sea-floor sediment. Guy lines are connected to the electronic housings to minimize vibrations caused by underwater currents and wave surge. The tripod was first deployed last summer for 3 months near the Hanalei River outlet on the Island of Kauai in Hawaiʻi. Divers positioned the tripod near a coral colony at a water depth of about 10 m. A concrete block painted with gridlines, used both for scale and for detecting evidence of sedimentation, was positioned almost vertically within the camera's view. The system's electronics included a Canon 20D high-resolution digital still camera with intervalometer (for time-lapse photography), electronic strobe, and battery pack. The camera was set to take a photograph every 4 hours. The system operated successfully for the entire 3-month deployment, collecting more than 575 images. An image obtained early in the study shows the water as calm and clear, with no accumulated sediment on the block or turbidity in the water column. A second image taken 1 week later, however, shows turbid water and an accumulation of sediment on the block. A photograph taken by a diver just before recovery of the instrument shows biofouling by algae and other organisms that have accumulated on the system's components.
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in this issue:
Underwater Photographic Tripod for Coral-Reef Studies
New Web site: Topics in Coastal and Marine Sciences New Directions in Geographic Visualization of Scientific Data
USGS Ridge-to-Reef Team Honored for Work in Hawaiian Islands
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U. S. Department of the Interior | U.S. Geological Survey
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