Degrove Surveyors recently completed a multibeam hydrographic survey for the NAVFAC Underwater Electro-Magnetic Measurement System (UEMMS) Type VI Upgrade Project at Naval Station Mayport in Mayport, Florida. This project upgraded an existing Type V magnetic measurement range.
Degrove completed the post-construction survey of the one-half square mile project area, located on the river bottom of the Naval Station Mayport ship channel in the St. Johns River. The survey was used to detect any small shoals, lumps, or areas above the navigation channel limit of -50 feet MLLW that may require the contractor to send down additional divers to rake the area.
Due to the high accuracy requirement of this survey, Degrove utilized the state-of-the-art R2Sonic 2024 multibeam system, along with dual-antenna RTK GPS for positioning and a CODA Octopus F175 Inertial Measurement Unit (IMU) for motion detection. We employed this system on our 26’ SeaArk survey vessel with twin 150 horsepower engines. Patch tests and performance tests were completed within days of the survey to ensure that all offsets and calibrations were correct. A sound velocity probe was mounted at the multibeam transducer to account for real time changes in sound velocity, and full sound velocity profiles were taken every two hours. Accurate measurement of the sound velocity was especially critical on this project due to the dynamic water conditions near the mouth of the river, as well as the water depth.
Maps were produced showing one foot contour intervals and dense spot elevations. Degrove delivered hard copy maps as well as electronic CAD files.