Apparatus and method for determining earth's near-surface properties with on-time measurements from airborne time-domain electromagnetic data
A device and method for calculating electrical properties of a surveyed underground formation. The method includes selecting a waveform having multiple current transition rates; placing a time-domain electromagnetic (TEM) system above the underground formation while generating with a transmitter a transient primary magnetic field during an on-time period and no magnetic field during a following off-time period, due to the waveform; and recording with a receiver magnetic related data generated by the earth as a result of the transient primary magnetic field. The receiver records the magnetic related data during the on-time period using plural on-time gates sampling.
1. A method for calculating electrical properties of a surveyed underground formation, the method comprising:
selecting a waveform having multiple current transition rates;
placing a time-domain electromagnetic (TEM) system above the underground formation while generating with a transmitter a transient primary magnetic field during an on-time period and no magnetic field during a following off-time period, due to the waveform; and
recording with a receiver magnetic related data generated by the earth as a result of the transient primary magnetic field,
wherein the receiver records the magnetic related data during the on-time period using plural on-time gates sampling.
2. The method of claim 1 , wherein the waveform has continuously varying current transition rates.
3. The method of claim 1 , wherein the waveform has multiple different current transition rates.
4. The method of claim 1 , wherein the gates are placed in time to more densely sample the magnetic related data near changes in a slope of the multiple different current transitions.
5. The method of claim 1 , wherein the waveform is part of a sine function.
6. The method of claim 1 , wherein the waveform has a continuously varying slope.
7. The method of claim 1 , wherein the on-time gates have a width that varies in time.
8. The method of claim 7 , wherein the width of the on-time gates increases in time.
9. The method of claim 1 , further comprising:
recording with the receiver the magnetic related data during the off-time period.
10. The method of claim 1 , wherein the off-time period is followed by another on-time period.
11. The method of claim 1 , further comprising:
generating an image of the surveyed underground formation based on the recorded magnetic related data.
12. A time-domain electromagnetic (TEM) system for calculating electrical properties of a surveyed underground formation, the TEM system comprising:
a controller for receiving a waveform having multiple current transition rates;
a transmitter for generating a transient primary magnetic field during an on-time period and no magnetic field during a following off-time period, when the waveform is applied to the transmitter; and
a receiver for recording magnetic related data generated by the earth as a result of the transient primary magnetic field,
wherein the receiver records the magnetic related data during the on-time period using plural on-time gates sampling.
13. The TEM system of claim 12 , wherein the waveform has continuously varying current transition rates.
14. The TEM system of claim 12 , wherein the waveform has multiple different current transition rates.
15. The TEM system of claim 12 , wherein the waveform is part of a sine function.
16. The TEM system of claim 12 , wherein the waveform has a continuously varying slope.
17. The TEM system of claim 12 , wherein the on-time gates have a width that varies in time.
18. The TEM system of claim 12 , wherein the receiver also records the magnetic related data during the off-time period.
19. The TEM system of claim 12 , wherein the controller is further configured to generate an image of the surveyed underground formation based on the recorded magnetic related data.
20. A non-transitory computer readable medium including computer executable instructions, wherein the instructions, when executed by a processor, implement instructions for calculating electrical properties of a surveyed underground formation, the instructions comprising:
selecting a waveform having multiple current transition rates;
instructing a time-domain electromagnetic (TEM) system to generate, with a transmitter, a transient primary magnetic field during an on-time period and no magnetic field during a following off-time period, due to the waveform; and
recording with a receiver magnetic related data generated by the earth as a result of the transient primary magnetic field,
wherein the receiver records the magnetic related data during the on-time period using plural on-time gates sampling.