Matthew Kowalczyk, Eng., CEO of Ocean Floor Geophysics will be presenting at UMC 2016 being held in Incheon, Korea from October 9th through 13th, 2016.
A Self-Compensating Magnetometer (SCM) System for High-Resolution Mapping on AUVs Matthew Kowalczyk, Ocean Floor Geophysics, Canada
Initial Tests of an AUV-borne Controlled Source Electromagnetic (CSEM) System Matthew Kowalczyk, Ocean Floor Geophysics, Canada; Scripps Institution of Oceanography and Fukada Salvage and Marine Works Co. Ltd.
More information on the conference can be found at the website http://www.underwatermining.org
A Self-Compensating Magnetometer (SCM) System for High-Resolution Mapping on AUVs
Ocean Floor Geophysics Inc.
In June this year OFG released a new Self-Compensating Magnetometer (SCM) system, designed specifically for AUVs, to the subsea industry. In 2014, Ocean Floor Geophysics developed a method to compensate raw survey magnetic data collected inside an the AUV using data collected during a calibration maneuver prior to the survey. Correction coefficients were calculated from the calibration maneuver data to account for the magnetization of the AUV itself, its motion through the Earth’s magnetic field, and for variable currents related to the AUV’s propulsion and maneuvering. The process was not automatic and required operator supervision at all stages.
This has led to the further development to the only Self-Compensating Magnetometer (SCM) system on the market. The system is a combination subsea magnetometer sensor (up to 6000m rated), a processor/data logger, mechanical calibration procedure, and a proprietary software algorithm that computes a series of correction coefficients and applies them to calculate compensated and corrected magnetic data in real time.
Potential high-resolution mapping applications for this system that require the use of AUVs include geologic mapping, engineering applications for pipeline and cable mapping and tracking, mine countermeasures, mapping of unexploded ordinance (UXO), and archeological applications for mapping ship wrecks. Examples of maps of the compensated magnetic data that were collected on surveys for some of these various applications will be shown.
Initial tests of an AUV-borne controlled source electromagnetic (CSEM) system
Ocean Floor Geophysics Inc.
Scripps Institution of Oceanography
Fukada Salvage and Marine Works Co. Ltd.
Controlled source electromagnetic systems (CSEM) are used to map subsurface resistivity structure. In 2014 and 2015, OFG used a towed CSEM system developed by the Scripps Institution of Oceanography to map gas hydrate deposits to depths of several 100 metres below the seafloor. We would like to be able to perform CSEM surveys over submarine massive sulfide (SMS) deposits. However, towing the system at a constant depth in terrain with steep bathymetric gradients, such as in the vicinity of hydrothermal chimneys associated with SMS deposits, would prove difficult. Other difficulties with a towed system include requiring a large ship to deploy and power the system, and long, time consuming, turns for high resolution surveys with tight line spacing because the receivers extend well behind the ship.
A novel approach to overcome these difficulties would be to mount electrodes on an AUV with the transmitter towed in the ocean by a ship or emplaced on the seafloor. It would require a smaller ship to launch an AUV than to launch and power a long source/receiver array, and the AUV is capable of tight turns, saving ship time when little useful data is collected. In addition to deployment considerations, the largest potential benefit is the ability to simultaneously collect high-resolution multibeam, sidescan, subbottom profiler, magnetometer, and chemical sensor data.
The largest uncertainty regarding an AUV-borne CSEM system is whether the signal (of the received electric field) to noise (related to the vehicle propulsion plus payload) ratio is sufficiently high. OFG, Scripps, and Fukada Salvage and Marine Works Co. Ltd. (Fukada) devised an experiment was to record the ambient electric field noise on CSEM electrodes mounted to an operating AUV graciously provided by Fukada. A series of tests were designed and run to investigate how the ambient noise levels on the electrodes changed with the vehicle operating while (1) turning off the payload devices one by one; (2) varying the heading of the vehicle; and (3) varying the speed of the vehicle. Data were analyzed together by OFG and Scripps and results are presented. As well, EM modelling results using these preliminary test results are presented here to show the sensitivity of the electric field response over typical massive sulfide deposits