Land based seismic data acquisition unit
View Patent ↗A wireless seismic data acquisition unit with a wireless receiver providing access to a common remote time reference shared by a plurality of wireless seismic data acquisition units in a seismic system. The receiver is capable of replicating local version of remote time epoch to which a seismic sensor analog-to-digital converter is synchronized. The receiver is capable of replicating local version of remote common time reference for the purpose of time stamping local node events. The receiver is capable of being placed in a low power, non-operational state over periods of time during which the seismic data acquisition unit continues to record seismic data, thus conserving unit battery power. The system implements a method to correct the local time clock based on intermittent access to the common remote time reference. The method corrects the local time clock via a voltage controlled oscillator to account for environmentally induced timing errors. The invention further provides for a more stable method of correcting drift in the local time clock.
1. A method of providing a stable timing signal for a seismic data acquisition unit, comprising:
generating, via a local oscillator of the seismic data acquisition unit, a local timing signal;
receiving, by a wireless receiver of the seismic data acquisition unit, an external time reference;
disciplining, via the wireless receiver, the local oscillator based on the external time reference;
determining a frequency error of the local oscillator by differencing time stamps of the external time reference over a frequency measurement time interval, wherein the frequency measurement time interval corresponds to a frequency accuracy for a variable time stamp uncertainty;
measuring, via at least one environmental sensor, at least one environmental parameter for the seismic data acquisition unit, the at least environmental parameter including an inclination of the seismic data acquisition unit;
storing, in a memory element of the seismic data acquisition unit, a data structure comprising (i) the frequency error, (ii) the time stamps from the external time reference, and (iii) measured environmental parameters encountered over the frequency measurement time interval; and
during a time interval in which the wireless receiver is disabled, adjusting a frequency of the local oscillator to correct for at least one timing error using data stored in the data structure.
2. The method of claim 1 , further comprising:
determining an average of a plurality of measurements of the at least one environmental parameter; and
storing the average in the data structure.
3. The method of claim 1 , further comprising:
enabling the wireless receiver to receive the external time reference during the frequency measurement time interval; and
disabling the wireless receiver at the end of the frequency measurement time interval by entering a low power state.
4. The method of claim 1 , further comprising:
providing historical environmental characteristic data corresponding to the at least timing error; and
storing the historical environmental characteristic data in the data structure.
5. The method of claim 1 , further comprising:
measuring, via the at least one environmental sensor, a temperature of the seismic data acquisition unit; and
storing, in the data structure, measured temperatures encountered over the frequency measurement time interval.
6. The method of claim 1 , further comprising:
determining a current inclination and a current temperature of the seismic data acquisition unit;
determining a stored seismic data acquisition unit inclination corresponding to the current operation temperature stored in the data structure; and
adjusting the frequency of the local oscillator based on the difference between the current inclination and the stored seismic data acquisition unit inclination.
7. The method of claim 1 , further comprising:
determining a current power supply operating voltage and a current operating temperature of the local oscillator;
determining a stored power supply operating voltage corresponding to the current operating temperature stored in the data structure; and
adjusting the frequency of the local oscillator based on a difference between the current power supply operating voltage and the stored power supply operating voltage.
8. The method of claim 1 , further comprising:
monitoring the at least one environmental parameter; and
responsive to identifying a change in the at least one environmental parameter, updating the data structure with the change and a corresponding time stamp of the local timing signal.
9. The method of claim 1 , further comprising:
responsive to determining a timing error, updating the data structure with the timing error, a corresponding measured environmental parameter, and a corresponding time stamp of the local timing signal.
10. The method of claim 1 , wherein the local timing signal is aperiodic voltage having a nominal frequency.
11. A system for providing a stable timing signal for a seismic data acquisition unit, comprising:
a local oscillator configured to generate a local timing signal;
a wireless receiver configured to receive an external time reference, and discipline the local oscillator based on the external time reference;
at least one environmental sensor configured to measure at least one environmental parameter for the seismic data acquisition unit, the environmental parameters including an inclination of the seismic data acquisition unit;
a memory element; and
a processor communicatively coupled to the memory element, the processor configured to:
determine a frequency error of the local oscillator by differencing time stamps of the external time reference over a frequency measurement time interval, wherein the frequency measurement time interval corresponds to a frequency accuracy for a variable time stamp uncertainty;
store, in the memory element of the seismic data acquisition unit, a data structure comprising (i) the frequency error, (ii) the time stamps from the external time reference, and (iii) measured environmental parameters encountered over the frequency measurement time interval; and
during a time interval in which the wireless receiver is disabled, adjust a frequency of the local oscillator to correct for at least one timing error using data stored in the data structure.
12. The system of claim 11 , wherein the processor is further configured to:
determine an average of a plurality of measurements of the at least one environmental parameter; and
store the average in the data structure.
13. The system of claim 11 , wherein:
the processor is further configured to enable the wireless receiver to receive the external time reference during the frequency measurement time interval, and disable the wireless receiver at the end of the frequency measurement time interval; and
the wireless receiver is further configured to enter a low power state responsive to being disabled.
14. The system of claim 11 , wherein the processor is further configured to:
receive historical environmental characteristic data corresponding to the at least timing error; and
store the historical environmental characteristic data in the data structure.
15. The system of claim 11 , wherein:
the at least one environmental sensor is further configured to measure a temperature of the seismic data acquisition unit; and
the processor is further configured to store, in the data structure, measured temperatures encountered over the frequency measurement time interval.
16. The system of claim 11 , wherein the processor is further configured to:
determine a current inclination and a current temperature of the seismic data acquisition unit;
determine a stored seismic data acquisition unit inclination corresponding to the current operation temperature stored in the data structure; and
adjust the frequency of the local oscillator based on the difference between the current inclination and the stored seismic data acquisition unit inclination.
17. The system of claim 11 , wherein the processor is further configured to:
determine a current power supply operating voltage and a current operating temperature of the local oscillator;
determine a stored power supply operating voltage corresponding to the current operating temperature stored in the data structure; and
adjust the frequency of the local oscillator based on a difference between the current power supply operating voltage and the stored power supply operating voltage.
18. The system of claim 11 , wherein the processor is further configured to:
monitor, via the at least one environmental sensor, the at least one environmental parameter; and
responsive to identifying a change in the at least one environmental parameter, update the data structure with the change and a corresponding time stamp of the local timing signal.
19. The system of claim 11 , wherein the processor is further configured to:
update, responsive to determining a timing error, the data structure with the timing error, a corresponding measured environmental parameter, and a corresponding time stamp of the local timing signal.
20. The system of claim 11 , wherein the local timing signal is aperiodic voltage having a nominal frequency.