Apparatus for orienting an electromagnetic field sensor, and related receiver unit and method

1. Apparatus for orienting at least one electromagnetic field sensor of a receiver unit configured to be deployed on the seabed in a marine electromagnetic survey or on the ground in land electromagnetic survey, the apparatus comprising:

at least one orientation detector having an output which is dependent upon an orientation of the at least one electromagnetic field sensor, the at least one orientation detector and the at least one electromagnetic field sensor being mounted on a shaft suspended pivotably from an upper end of the apparatus;

at least one positioning device comprising at least one rod being located above a lower end of the shaft and configured to move laterally; each of the at least one rod comprising an actuator;

at least one controller which is arranged in communication with the at least one orientation detector and the at least one rod actuator;

the at least one controller being configured to be operable to generate at least one instruction for operating the positioning device to laterally move the at least one rod against the shaft and the at least one electromagnetic field sensor into a predefined orientation within an electro-magnetic field, in dependence upon the output from the at least one orientation detector.

2. Apparatus as claimed in claim 1 , wherein the at least one rod actuator comprises a motor.

3. Apparatus as claimed in claim 1 , being operable underwater.

4. Apparatus as claimed in claim 1 , wherein the at least one electromagnetic field sensor comprises an electric dipole.

5. Apparatus as claimed in claim 4 , wherein the at least one actuator is configured to operate to move the electric dipole having an axis such that the dipole axis is vertical.

6. Apparatus as claimed in claim 1 , having an exterior which is electrically non-conductive.

7. Apparatus as claimed in claim 1 , wherein the at least one electromagnetic sensor comprises at least two sensing elements and, in the predefined orientation within an electro-magnetic field, the two sensing elements are aligned on an axis having a predefined, desired orientation.

8. Apparatus as claimed in claim 1 , wherein the at least one electromagnetic field sensor is configured for detecting either or both of a vertical field component and a horizontal field component of an electromagnetic field.

9. Apparatus as claimed in claim 1 , further comprising a support structure for coupling the at least one electromagnetic field sensor thereto for supporting the at least one electromagnetic field sensor.

10. Apparatus as claimed in claim 9 , wherein the at least one positioning device being connected between the support structure and the at least one electromagnetic field sensor for moving the shaft and the at least one electromagnetic field sensor relative to the support structure for arranging the at least one electromagnetic field sensor in the predefined orientation within an electro-magnetic field.

11. A method of performing an electromagnetic survey, the method comprising:

(a) deploying at least one receiver unit on the ground or on a seabed;

(b) transmitting an electromagnetic field; and

(c) detecting at least one component of the electromagnetic field using an electromagnetic field sensor;

the electromagnetic field sensor being mounted on a shaft suspended pivotably from an upper end of the apparatus and arranged in a predefined orientation within an electromagnetic field through operation of at least one actuator to move a rod laterally against said shaft and thus moving the sensor into the predefined orientation within an electro-magnetic field by at least one instruction from a controller in dependence upon output of an orientation detector.