20 - Passive Figure of Merit

Question 1

What is Figure of Merit (FOM)?

Answer 1

Max allowable transmission loss for 50% Probability of Detection

FOM < TL : < than 50% P_D
FOM > TL : > than 50% P_D

Higher FOM = Greater Detection Range

Question 2

Source Level in relation to PASSIVE SONAR operations

Answer 2

The sound generated by the target

Passive FOI = target noise frequency

Question 3

What is Directivity Index (DI)?

Answer 3

SONAR’s ability to block out sounds coming from directions other than the direction of interest

Larger DI = Improved detection/FOM

Question 4

What is Detection Threshold (DT)?

Answer 4

Signal minus the noise required inboard of the hydrophone array for an operator using installed equipment to detect a target 50% of the time.

Smaller/more negative DT = Improved Detection/FOM

Question 5

How can you improve FOM?

Answer 5

• Increase Source Level
• Decrease Noise LEvel
• Increase Directivity Index (DI)
• Decrease Detection threshold (DT)