Patent ID: 7274990

Claim:
A method of seismic surveying of an earth formation, the method comprising: (a) generating a first seismic signal at a first time at a first location on or proximate to a surface location and propagating a first seismic wave through said earth formation; (b) receiving a first signal comprising a direct arrival of said first propagating seismic wave on a bottomhole assembly (BHA) at a first depth at a time within ten seconds of said first time; (c) determining from said received first signal a reference wavelet; (d) generating a second seismic signal at a second time greater than said first time at a location at or near the first location and propagating a second seismic wave through said earth formation; (e) using said reference wavelet to determine an arrival time of said second seismic wave at said BHA, and (f) recording the arrival time of the second seismic wave on a suitable medium.