Sonar system with area moving target indicator

A sonar system, comprising:

• means for generating a frequency modulated sonar signal in a predetermined sonar frequency band for transmission through a body of water;
• projector means for receiving the sonar signal and continuously transmitting acoustic energy through the body of water representative of the sonar signal;
• hydrophone means for receiving portions of the acoustic energy reflected by a plurality of underwater objects in a predetermined beam pattern and generating output signals representative thereof;
• telemetry means for receiving the output signals from a plurality of successive scans of the hydrophone means and generating frequency variance and bearing signals for each scan;
• FFT means for parsing the frequency variance and bearing signals for each scan into a grid of range by bearing resolution elements;
• and
• AMTI means for calculating a T statistic value for each resolution element over a predetermined number of contiguous range and bearing resolution elements according to the formula:
• T=(X-m)/sigma
• where:
• X is the value of the incoming signal,
• m is the time updated means, and sigma is the standard deviation defined as the square root of the time updated variance,
• and for determining if the T statistic exceeds a predetermined threshold value,
• whereby a moving one of the underwater objects will be detected.