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<p>Ocean bottom electromagnetic receivers (OBEMs) deployed in freefall from vessels typically reach the seafloor with unknown orientation, posing challenges for Controlled-Source Electromagnetic (CSEM) data interpretation. Accurate knowledge of receiver orientation is essential for reliable estimation of seafloor electrical properties. This study compares four techniques for estimating OBEM orientation based on electromagnetic fields collected during a Time-Domain CSEM survey in the Gulf of Saint Lawrence, Atlantic Canada. The first set of orientations for our comparison was determined from calibrated fluxgate magnetometers in our instruments used as compasses to orient the OBEMs relative to the Earth’s stationary magnetic field. We then compared these to orientations determined by rotating the seafloor horizontal magnetic field time series, such as would be available with coil sensors, to maximize coherence with data from three regional magnetic field observatories (MFO) from the INTERMAGNET network, based on the assumption that the plane wave source field is uniform over those distances. While orientations determined this way showed general agreement with the compass values, consistency was found to vary with distance between the survey area and the MFO locations. To address this, a new approach was tested applying the Spherical Elementary Current System (SECS) method to compute a virtual MFO at the survey site. This approach improved the agreement with compass orientations relative to those determined from any of the remote MFO stations. Finally, we developed a method for orienting OBEMs based on the shape of the electric dipole source field in the DC limit, assuming the transmitter orientation and relative position are known. This method can use estimates from multiple transmitter positions for statistical constraint, providing solutions with standard deviations as low as 4° in our tests. The orientation estimates obtained from all methods show generally good agreement, with the compass-based, SECS, and the electric dipole source field-based method yielding the most consistent results, highlighting their reliability. Moreover, these methods can be readily adapted to processing workflows and span the range of receiver types commonly used in CSEM surveys.</p> Graphical Abstract <p></p>

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Using electromagnetic fields to estimate the orientation of ocean-bottom receivers

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月23日

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  • Fernando Córdoba-Ramírez,
  • Sebastian Hölz,
  • Graeme Cairns,
  • Magnar Gullikstad Johnsen,
  • Mladen Nedimović,
  • Vittorio Maselli,
  • Christian Berndt,
  • Barret Kurylyk,
  • Irena Schulten,
  • Shengchao Yu

摘要

Ocean bottom electromagnetic receivers (OBEMs) deployed in freefall from vessels typically reach the seafloor with unknown orientation, posing challenges for Controlled-Source Electromagnetic (CSEM) data interpretation. Accurate knowledge of receiver orientation is essential for reliable estimation of seafloor electrical properties. This study compares four techniques for estimating OBEM orientation based on electromagnetic fields collected during a Time-Domain CSEM survey in the Gulf of Saint Lawrence, Atlantic Canada. The first set of orientations for our comparison was determined from calibrated fluxgate magnetometers in our instruments used as compasses to orient the OBEMs relative to the Earth’s stationary magnetic field. We then compared these to orientations determined by rotating the seafloor horizontal magnetic field time series, such as would be available with coil sensors, to maximize coherence with data from three regional magnetic field observatories (MFO) from the INTERMAGNET network, based on the assumption that the plane wave source field is uniform over those distances. While orientations determined this way showed general agreement with the compass values, consistency was found to vary with distance between the survey area and the MFO locations. To address this, a new approach was tested applying the Spherical Elementary Current System (SECS) method to compute a virtual MFO at the survey site. This approach improved the agreement with compass orientations relative to those determined from any of the remote MFO stations. Finally, we developed a method for orienting OBEMs based on the shape of the electric dipole source field in the DC limit, assuming the transmitter orientation and relative position are known. This method can use estimates from multiple transmitter positions for statistical constraint, providing solutions with standard deviations as low as 4° in our tests. The orientation estimates obtained from all methods show generally good agreement, with the compass-based, SECS, and the electric dipole source field-based method yielding the most consistent results, highlighting their reliability. Moreover, these methods can be readily adapted to processing workflows and span the range of receiver types commonly used in CSEM surveys.

Graphical Abstract