NAEVA Successfully Deploys Underwater DGM Array

In cooperation with 3D Geophysics, NAEVA performed DGM in support of a Site Inspection at four underwater ranges associated with NAS Oceana, Virginia Beach, Virginia. The Underwater UXO Towed Array (UUTA) utilized the Geonics High Power EM61-Flex3 electromagnetic metal detector, Trimble 5700 RTK GPS, and a Trimble AgGPS FmX navigation system. The EM61-Flex3 system is based on the standard Geonics EM61HP with four 1.0 x 0.2 meter air-cored receiver coils arranged side by side and enclosed by a transmitter coil. The UUTA includes an EM coil support platform (whale tail) and a rigid down-rigging system. The downrigger is equipped with a control surface (hydrofoil or ‘elevator’), which allows the system operator to control the height of the coil above the sea bottom during data acquisition. The UUTA uses two RTK receivers to accurately measure the exact position and heading of the boat and combined with the rigid downrigger provides accurate geolocation of the platform.

Underwater Data Collection

The MLFXMarine (Geomar Software, Inc.) acquisition program captures the GPS, pressure transducer, inclinometer, and sonar bottom depth data and then calculates the position of the sensor platform. The system operator adjusts the sensor height by using a control wheel, allowing the sensor to maintain an average height of 2.6 feet above the seafloor. The survey covered approximately 319 linear miles in depths ranging from 3 to 32 ft. This extremely challenging project was completed on schedule and within budget.

3D Geophysics Boat