Seismic Sensor Clock Offset Calibration
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Solution Overview
Problem
Seismic surveys face challenges in accurately determining the time of propagation of seismic signals due to clock drift in seismic sensors, which can lead to inaccuracies in mapping the Earth's subsurface.
Innovation Solution
A method involving the use of two seismic signals propagating in opposing directions between two seismic sensors, allowing for the determination of an offset and scaling factor for the clocks in the sensors, thereby enabling accurate calibration and correction for clock drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high accuracy clocks (such as GPS synchronised clocks) are provided in seismic sensors to ensure sufficient accuracy over the duration of the survey, then measurement precision is improved, but device complexity, size and weight increase
Solution Approach 1:
The patent introduces a master clock as an intermediary reference. Instead of each seismic sensor equipping itself with a complex GPS synchronised clock, the system uses a single master clock with known accurate time to establish reference times. The relationship between the master clock and each sensor's local clock is determined through calibration using seismic signals, allowing all sensors to operate with simpler clocks while maintaining synchronization through the master clock reference.
2Device complexity
If simple clocks are used in seismic sensors to reduce cost and size, then device complexity is reduced, but measurement precision deteriorates due to clock drift
Solution Approach 1:
The patent implements a feedback calibration mechanism. After initial recording with simple clocks, the system uses seismic signals to determine the time relationship between the master clock and each sensor's local clock. This feedback information is then used to correct the recorded times, compensating for the drift in the simple clocks. The calibration process continuously refines the time accuracy without requiring the clocks themselves to be inherently accurate.
3Device complexity
If clock drift correction is performed without a master clock reference, then device complexity is reduced, but measurement precision deteriorates due to inability to accurately determine propagation time
Solution Approach 1:
The patent performs preliminary calibration actions before the main seismic survey. The master clock establishes reference times for multiple calibration events, and the relationship between the master clock and each sensor's local clock is determined in advance using seismic signals. This preliminary establishment of time relationships allows the actual seismic survey to proceed without continuous complex synchronization, as the calibration data is already available to correct propagation time measurements.
Data Source
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AI summary
A method comprises: receiving data indicative of outputs of first and second seismic sensors, said outputs including components corresponding to the detection by the first and second seismic sensors of first and second seismic signals, wherein a direction of propagation of the first seismic signal was from the first seismic sensor towards the second seismic sensor, and a direction of propagation of the second seismic signal was from the second seismic sensor towards the first seismic sensor; identifying, relative to a first clock in the first seismic sensor, a first time associated with a time of arrival of the first seismic signal at the first seismic sensor, and a second time associated with a time of arrival of the second seismic signal at the first seismic sensor; identifying, relative to a second clock in the second seismic sensor, a third time associated with a time of arrival of the first seismic signal at the second seismic sensor, and a fourth time associated with a time of arrival of the second seismic signal at the second seismic sensor; and determining an offset of the first clock relative to the second clock using the first, second, third and fourth times.