Line array doppler processing

摘要

A method is taught to extract more information about the motion of an acoustic wave emitter moving relative to a line array of hydrophones that are part of a sonar system by determining the variation in Doppler shift across the entire line array of hydrophones together with the a range measurement of the emitter to calculate the emitter's velocity.

主权项

1. A method of determining the velocity of an underwater object moving parallel to an underwater line array of a plurality of N equally spaced acoustic sensors that are part of an active sonar system comprising:
making contact with the underwater object with a narrow band continuous wave pulse from the active sonar system at a frequency f0; determining the range R of the object from the line array with a shorter pulse from the active sonar system centered at a frequency f0, wherein the time duration of the pulse is shorter than the time duration of the first narrow band continuous wave pulse; receiving a frequency fN at every acoustic sensor of the line array of N acoustic sensors; calculating the frequency shift (TN−f0) for each of the N individual acoustic sensors of the line array of N acoustic sensors; plotting a line of frequency shift versus acoustic sensor for the measured Doppler shifts of a plurality of interior acoustic sensors to allow for confirmation of any difference in frequency using a linear least squares fit of the frequency shifts and to determine whether there is a measurable variation in the Doppler shift of the entire line array; calculating the variation in Doppler shift of the entire line array of N acoustic sensors, based on the frequency shift of the first acoustic sensor and the Nth acoustic sensor of the line array of N acoustic sensors, expressed asΔ⁢⁢fN-Δ⁢⁢f1f0;and
determining the velocity of the underwater object according to the equationΔ⁢⁢f2-Δ⁢⁢f1f0≅v⁢⁢Δ⁢⁢θc,wherein c is the speed of sound in water and wherein Δθ is equal to the length of the line array of N acoustic sensors divided by the range R of the underwater object.