Patent ID: 7710822

Claim:
A while-drilling vertical-seismic-profiling (VSP) apparatus comprising: (a) a source of substantially repeatable seismic signals positioned proximately of the Earth's surface; (b) a seismic signal controller having a first clock for initiating signals from said source at selected moments, said selected moments occurring exclusively within time windows selected from among a regularly recurring series of time windows (c) a drill string element having a data processor, a second clock and an operatively associated seismic signal receiver secured thereto; and, (d) a data processor control program for; i. analyzing successive seismic signals received within said selected time windows by said signal receiver for amplitude-time correspondence and for verifying a signal received by said receiver as being initiated by said source; ii. measuring a first time differential between a predetermined moment relative to an opening of the selected window and receipt of a verified signal; and, iii. measuring a second time differential between successive first time differentials to determine a clock synchronization drift value.