Oscillator Drift Correction for Long-Term Seismic Timing
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Solution Overview
Problem
Current time source systems for ocean bottom seismic data acquisition face challenges in maintaining accurate timing due to frequency drift from aging, temperature, pressure, and acceleration, leading to inaccurate seismic data sampling and high power consumption, especially in GPS-denied environments where traditional oscillators fail to provide low enough time error for long-term deployments.
Innovation Solution
A system comprising a local oscillator, phase meter, processor, counter circuit, and temperature sensor that generates dual-linear time-dependent or temperature-dependent time error estimations, allowing for accurate time corrections by synchronizing and calibrating periodic signals with reference time signals, even in the absence of external reference sources, thereby correcting time errors and maintaining accurate seismic data sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a Temperature Compensated Crystal Oscillator (TCXO) is used for marine seismic surveys, then power consumption is low, but time error accumulates excessively during long term deployments
Solution Approach 1:
The system performs preliminary characterization of the oscillator's frequency drift behavior during calibration phases when reference signals are available. By pre-determining drift coefficients and storing them for later use, the system prepares correction data in advance that can be applied during deployment without requiring continuous reference signals or excessive power consumption.
Solution Approach 2:
The system implements feedback by continuously monitoring the oscillator's frequency drift and using the characterized drift model to generate real-time correction values. The correction module feeds back adjusted timing signals that compensate for the predicted drift, creating a closed-loop system that maintains accuracy despite the oscillator's inherent instability.
2Measurement precision
If an Oven Controlled Crystal Oscillator (OCXO) is used to reduce time error, then time error is reduced, but power consumption exceeds one watt which is unsustainable for long term operations
Solution Approach 1:
The system changes the operational parameters of the crystal oscillator by carefully controlling its temperature environment and applying voltage adjustments to optimize the frequency-stability-to-power-consumption ratio. By operating the oscillator at specific temperature points and voltage levels, the system achieves acceptable stability without requiring the full power of a traditional OCXO.
Solution Approach 2:
The system replaces the mechanical thermal mass and heating elements of a traditional OCXO with an electronic drift compensation system. Instead of physically heating and isolating the oscillator, the system uses electronic algorithms to predict and correct frequency drift, substituting a low-power electronic solution for a high-power mechanical one.
3Measurement precision
If GPS timing signals are used for real time ADC clock accuracy correction, then clock accuracy is improved, but the system cannot operate in GPS denied environments
Solution Approach 1:
The system performs self-characterization of its oscillator's drift behavior during calibration phases when reference signals are available. By building an internal model of its own drift characteristics, the system becomes self-sufficient and can operate autonomously in GPS-denied environments, using its own historical performance data to correct its timing without external assistance.
Solution Approach 2:
The system performs preliminary drift characterization and correction model development during deployment phases when reference signals are available. This advance preparation creates a correction algorithm that can be executed independently later, allowing the system to transition from reference-dependent operation to autonomous operation in challenging environments.
4Measurement precision
If higher power OCXOs are used to sustain long time seismic survey operation, then time error is reduced, but operational costs and power source requirements increase
Solution Approach 1:
The system applies partial correction by characterizing and compensating for the dominant drift components (temperature-dependent and time-dependent) while accepting residual higher-order drift effects. This partial approach achieves sufficient accuracy for seismic survey applications without requiring the full power and complexity of a high-precision OCXO, optimizing the trade-off between correction thoroughness and power consumption.
Data Source
AI summary
A system and method for making time error estimations and time corrections for substantially long deployment times are provided. The system has a low power local oscillator, a power source, a processor, a computer-readable storage medium, a phase meter, a counter circuit, a temperature sensor, and a communication port. Time signal measurements and frequency signal measurements are made at a first time and at a second time, and time-dependent or both time and temperature-dependent time error estimations are generated for interval times between the first time and the second time using a dual-linear estimation technique. A corrected time-tag data set having highly accurate time-tags may then be generated from the time-dependent time error estimation or both the time and the temperature-dependent time error estimation.