Patent ID: 8605543
Filing Date: 2013-12-10
Classification: G01C,G01V

Abstract:
1. A method for providing a stable timing signal for a seismic data acquisition unit, said method comprising: a. enabling wireless access by the seismic data acquisition unit to an external time reference; b. disabling wireless access by the seismic data acquisition unit to the external time reference; c. generating a local timing signal for the seismic data acquisition unit; d. providing a device capable of adjusting said local timing signal; e. providing a first set of environmental characteristic data, including a time of measurement of the local timing signal for the device, wherein said first set of environmental characteristic data relates environmental characteristic data to timing errors; f. measuring environmental parameters; g. using said first set of environmental characteristic data and measured environmental parameters to produce an adjustment for said local timing signal; h. while wireless access to the external time reference is disabled, over a time interval, utilizing the device to adjust the local timing signal multiple times over the time interval to correct for the timing errors, thereby producing the stable timing signal; i. providing a local sample clock to generate the local timing signal; j. determining local oscillator frequency error by differencing external time reference time stamps of the local sample clock over a frequency measurement time interval, the frequency measurement time interval chosen to provide a given frequency accuracy for a variable time stamp uncertainty; k. storing in a frequency compensation table on board said seismic data acquisition unit a parameter structure comprising (i) measured frequency error, (ii) a time reference determined from the external time reference, and (iii) a measured oscillator operating environmental condition, encountered over the frequency measurement time interval; l. wherein the device capable of adjusting the local timing signal includes a local oscillator disciplined by the external time reference when wireless access is enabled; and m. wherein storing further comprises measuring an average inclination of the seismic data acquisition unit over the frequency measurement time interval and including the measured average inclination in the frequency compensation table.