Playing in the Sandbox

Prosilica GC2450C in USGS Ocean Sedimentation Study.

The US Geological Survey (USGS) is renowned worldwide for its studies on the environment. The organization aims to provide reliable scientific information to describe and understand the Earth.

One of its divisions, the USGS Coastal & Marine Geology Program (CMGP) focuses on research on the coastal and marine environment such as river and ocean sedimentation. The program has three field centers in the US, Wood’s Hole - Massachusetts, St Petersburg - Florida and Menlo Park / Santa Cruz - California where this current project is based.

Sand grains study
One of the project’s objectives is to capture close-up color images of sand grains in order to study their coarseness and how their size influences re-suspension of sediments by waves and currents. The team will be looking to develop a theoretical model to predict how the sea-bed morphology off the Californian coast line might change over time and, in the longer term, study changes in ocean behavior.

The USGS has undertaken similar projects in the past (e.g. Grand Canyon Monitoring and Research Center’s study of sediments in the Colorado river), however this is the first time that the organization has used a camera with Gigabit Ethernet technology.

System set-up
The Prosilica camera used in this system is the 5- Megapixel GC2450C (color model) with Gigabit Ethernet output. The camera, which features the high-quality Sony ICX-625 CCD image sensor, was selected by the team at the CMGP for its excellent image quality, high sensitivity, low noise, high resolution (2448 x 2050) and ultra-compact size (33x46x43mm).

The GC2450C is set-up inside a 30.5cm (12”) long and 9cm (3.5”) outside diameter stainless steel pressure housing with 5mm (.2”) thick acrylic windows fitted with a light ring to ensure even lighting around the main target area. The pressure housing itself is mounted on a custom-made tripod which is operated (i.e. raised and lowered into the ocean) by a hydraulic system. The system is linked to a PC located off the Santa Cruz wharf via a 100 meter (300ft) long Cat-6 cable. The GC2450C is fitted with a macro-lens.

Technical challenges

After being tested at the marine facility in Santa Cruz, where technicians were working on camera focusing, a crucial matter for this project as the team will be studying sand grain particles measuring approximately a few tenth of a millimeter, the system has now been moved to the ocean just off the coast of Santa Cruz, California where it will be lowered at the bottom of the ocean every hour or two depending on conditions to capture aerial view images of sand grains. In the event of a storm the camera will be set to image more frequently to observe the higher activity. Other sensors will monitor other factors such as turbidity, solidity, concentration and grain size of particles and wave pressure to further study all the elements influencing sedimentation.