Patent ID: 6957580

Claim:
A survey tool for use in a wellbore, the survey tool comprising: a downhole portion having an axis, the downhole portion adapted to move within the wellbore with the axis generally parallel to the wellbore; a first acceleration sensor mounted at a first position within the downhole portion, the first acceleration sensor adapted to generate a first signal indicative of an acceleration of the first acceleration sensor along the axis; a second acceleration sensor mounted at a second position within the downhole portion, the second position being spaced from the first position by a non-zero distance along the axis, the second acceleration sensor adapted to generate a second signal indicative of an acceleration of the second acceleration sensor along the axis; and a controller adapted to receive the first signal and the second signal and to calculate a depth, a velocity, or both a depth and a velocity of the downhole portion in response to the first signal and the second signal.