SYSTEMS AND METHODS FOR CALIBRATING AN ELECTROMAGNETIC RECEIVER
An electromagnetic receiver includes at least one sensor for measuring electromagnetic signals, and a calibration antenna configured to generate an electromagnetic signal at a first frequency.
1 . An electromagnetic receiver, comprising:
at least one sensor for measuring electromagnetic signals; and
a calibration antenna configured to generate an electromagnetic signal at a first frequency.
2 . (canceled)
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4 . The receiver of claim 1 , further comprising a power source coupled to the calibration antenna.
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6 . The system of claim 1 , wherein the calibration antenna is an electric dipole.
7 . The receiver of claim 1 , wherein the calibration antenna is a magnetic dipole.
8 . The system of claim 1 , wherein the calibration antenna is configured to generate an electromagnetic field at a second frequency.
9 . The method of claim 8 , wherein the first frequency is about 0.06 Hz and the second frequency is about 10 Hz.
10 . The system of claim 8 , wherein the calibration antenna is configured to generate the electromagnetic field that sweeps from the first frequency to the second frequency.
11 . The system of claim 1 , wherein the receiver comprises a pair of electrodes separated by a selected distance and connected via a circuitry for measuring a current flowing through the pair of electrodes.
12 . The system of claim 11 , wherein the circuitry connecting the pair of electrodes comprises a control for adjusting an impedance between the pair of electrodes.
13 . The system of claim 1 , further comprising a memory for recording signals measured by the at least one sensor.
14 . The receiver of claim 1 , wherein the at least one sensor comprises at least one of 1) a pair of electrodes; 2) three pairs of electrodes arranged in mutually orthogonal directions; 3) a magnetometer and 4) three magnetometers.
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18 . A method for calibrating an electromagnetic receiver, comprising:
energizing a calibration antenna disposed within the receiver to generate an electromagnetic signal; and
detecting the electromagnetic signal using at least one sensor disposed within the receiver.
19 . The method of claim 18 , further comprising deploying the receiver to a seafloor position.
20 . (canceled)
21 . The method of claim 18 , further comprising storing data collected by the at least one sensor when detecting the electromagnetic signal.
22 . The method of claim 21 , further comprising:
collecting survey data using the at least one sensor, and
analyzing the calibration data collected by the at least one sensor to correct the survey data.
23 . The method of claim 18 , further comprising adjusting at least one parameter of the receiver based on the detected data.
24 . The method of claim 23 , wherein the parameter comprises at least one of 1) at least one selected from an impedance between at least one pair of electrodes, a position of the receiver, and an orientation of the receiver; 2) the impedance between at least one pair of electrodes, and wherein the impedance is adjusted to match that of surrounding seawater; 3) the impedance between at least one pair of electrodes and wherein the impedance is adjusted to be below that that of surrounding seawater; and 4) the position of the receiver, and wherein adjusting the position of the receiver comprises using an ROV to reposition the receiver.
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28 . The method of claim 18 , further comprising determining the electromagnetic field generated by energizing the calibration antenna; wherein determining the electromagnetic field comprises pre-computing the electromagnetic field.
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32 . The method of claim 18 , wherein the at least one sensor comprise a vertical electric field sensor, and further comprising using the detected electromagnetic field to adjust for movement of the vertical electric field sensor.
33 . A method for making an electromagnetic survey, comprising:
deploying a plurality of electromagnetic receivers on a seafloor;
for each receiver:
energizing a calibration antenna in receiver to generate a calibration electromagnetic signal; and
detecting the calibration electromagnetic signal using one or more sensors in the receiver,
generating a controlled source electromagnetic signal external from the receiver;
detecting the controlled source electromagnetic signal with one or more of the receivers; and
for each receiver, correcting the detected controlled source electromagnetic signal using the detected calibration electromagnetic signal.
34 . The method of claim 33 , wherein energizing the calibration antenna is done at a plurality of frequencies.
35 . The method of claim 33 , wherein the generating the controlled source electromagnetic signal is done at a plurality of frequencies.
36 . The method of claim 33 , further comprising, adjusting a parameter for at least one receiver based on the detected calibration electromagnetic signal.
37 . (canceled)