Patent ID: 8335129

Claim:
A computerized process to use a correlation SONAR system in shallow water comprising: transmitting from a pulse generator an initial burst of pulses towards a bottom of a body of water; receiving echoes of the initial burst of pulses on a hydrophone array; after the receiving the echoes of the initial burst of pulses, transmitting a second burst of pulses towards the bottom of the body of water; receiving echoes of the second burst of pulses on the hydrophone array; using a processor to correlate a pulse from the initial burst of pulses and a pulse from the second burst of pulses to calculate a velocity estimate; prior to the transmission of the initial burst of pulses towards a bottom of a body of water: calculating a desired correlation time between an early pulse and a later pulse; and calculating a maximum transmit burst duration; and after determining that the desired correlation time is greater than the maximum transit burst duration, thereby indicating that the second burst of pulses is needed, and after the transmission of the initial burst of pulses and the transmission of the second burst of pulses: selecting a pulse from the initial burst of pulses and a pulse from the second burst of pulses such that the pulse from the initial burst of pulses and the pulse from the second burst of pulses are separated by an amount of time that is close to the desired correlation time; wherein shallow water comprises a depth of water wherein an achievable correlation time is less than the desired correlation time when two pulses are from either the initial burst or the second burst; wherein the desired correlation time is calculated as follows: τ d = ( 3 * H ) ( 2 * max ⁡ ( abs ⁡ ( V FA ) , abs ⁡ ( V ATW ) ) ) wherein H is a distance separating adjacent hydrophones in the hydrophone array; V FA is an estimate of fore-aft velocity; and V ATW is an estimate of athwartship velocity; and wherein the achievable correlation time is close to the maximum transit burst duration.