EP0087271A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Electromagnetic geophysical surveying apparatus and system
Assignee: Geonics Ltd
•
Filing: 1983-02-17
•
Granted: —
•
Expires: 2003-02-17
Abstract
Abstract A frequency domain geophysical electromagnetic surveying system is provided in which intermittent primary fields having sharp terminations are generated in a cycle having a fundamental frequency by a transmitter (8), and a receiver (14) includes a gate (22) passing only secondary signals received during interruptions of the primary field, the gated signal being applied to filters (24, 25) turned to harmonics of the predetermined frequency. The filter outputs are synchronously demodulated (261, 26Q, 281, 28Q) to provide signals corresponding to at least the in-phase component of the secondary signal at the fundamental frequency, and preferably in-phase and quadrature components at at least two harmonics. The system can provide improved resolution particularly of the characteristics of inphase secondary signals received from terrain being surveyed.
Inventors
- 👤 James Duncan Mcneill
- 👤 Alexander Arkadievich Kaufman
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-31 00:22
CPC Classifications
G; G01; G01V; G01V3/00; G01V3/08; G01V3/10; G01V3/104
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
206 words
1 . apparatus for processing signals from a geophysical electromagnetic survey of the type in which terrain to be surveyed is subjected to a primary magnetic field by a transmitter energized by a cyclical current waveform such that the field is subject to abruptly commencing interruptions at regular intervals, and a receiver produces.secondary signals corresponding to current induced at the receiver during the interruptions by transient secondary fields induced in the terrain by the abrupt commencement of the interruptions, characterised in that the apparatus is configured to process only such secondary signals as occur during regular predetermined intervals within the interruptions, together with a reference signal in synchronism with said cyclical current waveform, and to apply such secondary signals to a narrow band filter (24) tuned to accept the fundamental frequency of the cyclical current waveform, the output of the filter together with said reference signal being applied to at least a first synchronous detector (26I) which detects the filter output in relation to the phase of the primary current waveform on a detection axis adjusted to provide any phase compensation necessary for the periods.in which the secondary signal is not processed, whereby to recover the in-phase component of the secondary signal at said fundamental frequency.
Claim 2
Dependent Claim
206 words
1 . apparatus for processing signals from a geophysical electromagnetic survey of the type in which terrain to be surveyed is subjected to a primary magnetic field by a transmitter energized by a cyclical current waveform such that the field is subject to abruptly commencing interruptions at regular intervals, and a receiver produces.secondary signals corresponding to current induced at the receiver during the interruptions by transient secondary fields induced in the terrain by the abrupt commencement of the interruptions, characterised in that the apparatus is configured to process only such secondary signals as occur during regular predetermined intervals within the interruptions, together with a reference signal in synchronism with said cyclical current waveform, and to apply such secondary signals to a narrow band filter (24) tuned to accept the fundamental frequency of the cyclical current waveform, the output of the filter together with said reference signal being applied to at least a first synchronous detector (26I) which detects the filter output in relation to the phase of the primary current waveform on a detection axis adjusted to provide any phase compensation necessary for the periods.in which the secondary signal is not processed, whereby to recover the in-phase component of the secondary signal at said fundamental frequency.
Claim 3
Dependent Claim
53 words
Apparatus according to claim 1, characterised in that it includes a second synchronous detector (26Q) receiving said filter output and said reference signal and which has a detection axis in quadrature with that of the first synchronous detector whereby to receive the quadrature phase component of the secondary signal at said fundamental frequency.
Claim 4
Dependent Claim
75 words
Apparatus according to claim 1, further including one or more additional narrow band filters (25) each tuned to a different higher harmonic of said fundamental frequency, and each associated with in-phase or in-phase and quadrature synchronous detectors (281, 28Q) receiving reference signals at frequencies which are multiples of the fundamental frequency appropriate to the harmonic to be detected, whereby to recover at'least in-phase components of at least two different harmonic components of said secondary signal.
Claim 5
Dependent Claim
42 words
Apparatus according to claim 3, characterised in that it includes means (32) to determine the amplitude difference of similarly phased outputs of detectors associated with filters tuned to different harmonic components, after compensation of said outputs to eliminate frequency dependent amplitude differences.
Claim 6
Dependent Claim
36 words
Apparatus according to any of claims 1 to 4 for processing signals which are prerecorded, characterised in that the apparatus further includes means (32) for recovering secondary and reference signals from a record of such signals.
Claim 7
Dependent Claim
78 words
A frequency domain geophysical electromagnetic surveying system comprising a transmitter adapted to submit terrain being surveyed to successive abruptly terminated magnetic fields by application of a cyclical current waveform at the fundamental frequency with interruptions following the termination of each field, and a receiver gated to respond to secondary magnetic fields generated by the terrain only during predetermined intervals wholly within the interruptions, characterised in that the receiver includes apparatus according to any of claims 1 to 5..
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.