Author: Shawn Henderson, P.E.
Underwater tactile inspection in turbid water by an experienced Professional Engineer adds more resolution to SONAR scanning.
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We recently inspected structural damage 110 feet beneath the waterline on a dam in turbid water. Seasoned project managers were responsible for assembling a qualified team to a remote location within a limited time. Professional commercial divers rigged equipment across to the site and then down to depth and prepared the confined space area for inspection in zero visibility. The location and extent of the damage was assessed by a Professional Engineer/commercial diver conducting tactile inspection and the use of a post-processed point cloud created from multiple scans of a 3D multibeam SONAR (BlueView 5000) launched on a tripod.
LIGHT IN TURBID WATER
The scattering of visible light in turbid water makes visual inspections impractical. Visible light waves that penetrate ocean water are absorbed or scatter. Blue light (λ 475 nm) penetrates the deepest in clear ocean water. Clear water boxes can aid with inspection techniques that use light.
SOUND IN TURBID WATER
A SONAR wave frequency pf 3.0 MHz (λ 500 µm) has a wave length more than 1000x longer than visible blue light minimizing wave scattering and allowing clearer imaging in turbid water. Rougher surfaces (damage) scatter diffusely more acoustic energy. Resolution is dependent on many variables including: range; frequency; noise; target geometry; reflectivity; onscreen pixels; and sampling characteristics.
TACTILE INSPECTION (Professional Engineer) IN TURBID WATER
Tactile inspection can be performed by a Professional Engineer to determine gross damage and boundary conditions. From many years of experience a flaw resolution of ¼” is practical over a complete area in zero visibility, although tactile inspection cannot determine flatness across an expanse.
An experienced Professional Engineer onsite can interpret data and quantify locations and the extent of damage. The data from both the 3D SONAR scans and tactile inspection can be used cumulatively. Henderson & Associates, PLLC integrates professional engineering with technically managing skilled trades from sometimes complex sets of requirements.
Please contact us for more information or to set up a consultation.
Shawn Henderson, P.E.