The Self-Compensating Magnetometer (SCM) System Test Results from a Remus 600 AUV Survey in Yellowstone Lake. Matthew Kowalczyk Feb 15, 2017

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1 The Self-Compensating Magnetometer (SCM) System Test Results from a Remus 600 AUV Survey in Yellowstone Lake Matthew Kowalczyk Feb 15, 2017

2 Company History OFG was formed in 2007 to develop and deploy advanced sensors for use in seafloor mineral exploration Business lines: (a) AUV operations and technical support, and (b) development of new geophysical seafloor exploration systems (primarily EM and magnetic) 2008: Agreement with Canadian Microgravity for AUV borne gravity surveys, ROV borne EM Mark II and magnetometers deployed in commercial survey 2009: EM Mark III and magnetometers deployed in commercial SMS survey 2010 Present: Continued commercial ROV borne survey and exploration services Operations support, geophysics and hydrography services 2014 Present: Vulcan CSEM towed 2012 Present: array AUV Operations 3D Vertical Cable Geophysical, Seismic (VCS) geochemical and Towed Array Marine hydrography services. Induced Polarization System Improved AUV Magnetics 2015 Present: AUV with Synthetic Aperture Sonar and pipeline inspection technology Release of OFG Self- Compensating Magnetometer for AUVs AUV CSEM Production and sale of low impedance Ag/AgCl marine electrodes 2007: First commercial mapping of SMS deposit by OFG patented EM system 2

3 Magnetic Surveying Well established in land based mineral exploration Often done from an airplane, also by foot Produces maps with resolutions suitable for mapping geological structure and potential ore bodies prior to test drilling For marine applications, AUVs and ROVS can fly close to seafloor to produce high resolution maps of narrow or small targets for: Mapping of hydrothermal vent systems and associated massive sulfide deposits Naval mine hunting and UXO Pipeline and cable inspections 3

4 Challenges of Magnetic Surveying with AUVs Main difficulty: High static and dynamic magnetic fields in vehicle corrupt the ambient magnetic data Some (poor) possible solutions are: Proton precession or Overhauser magnetometers - Very sensitive, but won t function near AUV body due to high magnetic gradients present within the body of the AUV. Degaussing of the AUV - Difficult and eventually wears off. Towed bodies or pole mounts - Specialized mounting apparatus complicates operations and adds risk to vehicle safety. Obscured Anomalies 4

5 The OFG Solution Mount a simple, robust, small, 3- axis fluxgate magnetometer INSIDE the AUV to minimize effect on vehicle dynamics and efficiency. Run AUV through a short physical calibration maneuver to measure heading, attitude, variable motor effects. Apply OFG proprietary algorithm for the calculation of magnetic correction coefficients to the magnetic measurements. 5

6 Magnetic Compensation Results Magnetic Map Before Compensation Magnetic Map After Compensation Anomalies are revealed 6

7 The Self-compensating Magnetometer System The success of magnetic compensation in an ISE Explorer AUV has led to the development of a self-compensating magnetometer (SCM) system. In 2016, product testing began with installation of magnetometers on several under water vehicles (AUVs and ROVs): Ocean Server Iver3 Kongsberg Hugin 1000 MBARI Mapper REMUS 600 ROPOS ROV Results from 3 of these installations are presented here 7

8 Example 1: Ocean Server IVER3 Installed the SCM on an IVER3 for a survey of Flemming Bay in Victoria, B.C. Mounted the sensor externally on the vehicle Used external charge port for power and communication. Magnetometer 8

9 Example 1: Ocean Server IVER3 Raw data had heading error on the order of 2500nT Compensated data revealed a 30nT anomaly in the survey area. 9

10 Example 2: ROPOS ROV Installed SCM on ROPOS ROV for a survey off the coast of British Columbia Careful placement of sensor to avoid areas of the vehicle with varying DC electrical currents that aren t being recorded Utilized an ROV specific calibration maneuver Magnetometer 10

11 Example 2: ROPOS ROV No correction for ROV tether or thrusters was required Good spatial contiguity between lines Comparison to visual observations showed SCM correctly detected magnetic features at each vent site 11

12 Example 3: REMUS 600 Installed the SCM on a REMUS 600 for a survey of Yellowstone Lake Magnetometer Photograph courtesy of Rob Sohn, Woods Hole Oceanographic Institution 12

13 Raw Total Field (nt) Example 3: REMUS 600 Unexpected noise in the raw data required additional filtering to obtain an acceptable signal sec median filtered for spike removal Time (sec) 13

14 Example 3: REMUS 600 Excellent results were obtained Four survey areas combined Magnetic calibration manoeuver was run on one site and applied to all four surveys Levelling between surveys was not required Magnetic lows correspond to seeps and pockmarks on lake bottom 14

15 Example 3: REMUS 600 Comparison between aerial magnetic data and data collected with the AUV 15

16 Acknowledgements OFG would like to acknowledge the following for their cooperation and assistance in collecting and providing data : Greg Packard and Rob Sohn of Woods Hole Oceanographic Institution John Jamieson of Memorial University The crew of the ROPOS ROV 16