Patent ID: 7362655

Claim:
An underwater acoustic ranging system for determining a range to a target object, comprising: an acoustic receiver for detecting acoustic energy and determining an angle of arrival of said acoustic energy in at least one plane; an acoustic transmitter for transmitting acoustic energy pulses, said active transmitter being spaced apart from said acoustic receiver; a receiver clock joined to said acoustic receiver; and a transmitter clock joined to said transmitter, said acoustic receiver clock and said transmitter clock being synchronized, said transmitter being operable for transmitting said acoustic energy pulses with a timing based on said transmitter clock, said timing being determinable with said receiver clock, said receiver calculating the range based on said timing and the angle of arrival wherein said range to said target object is determined based on the following equation: R T = ( Δ ⁢ ⁢ t 2 + Δ ⁢ ⁢ t 1 ⁢ cos ⁢ ⁢ α - ( Δ ⁢ ⁢ t 1 ⁢ sin ⁢ ⁢ α ) 2 Δ ⁢ ⁢ t 2 - Δ ⁢ ⁢ t 1 ⁢ cos ⁢ ⁢ α ) ⁢ c 2 where: R T =range to target object; Δt 1 =time from transmission to receipt in a direct transmitter/receiver path; Δt 2 =time from transmission to receipt in a reflected path; α=difference in angle of arrival of paths; and c=sound speed in medium.