Passive Sonar
Passive sonar listens without transmitting. It is often employed in military settings, although it is also used in science applications, e.g., detecting fish for presence/absence studies in various aquatic environments - see also passive acoustics and passive radar. In the very broadest usage, this term can encompass virtually any analytical technique involving remotely generated sound, though it is usually restricted to techniques applied in an aquatic environment.
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Famous quotes containing the word passive:
“The best emotions to write out of are anger and fear or dread.... The least energizing emotion to write out of is admiration. It is very difficult to write out of because the basic feeling that goes with admiration is a passive contemplative mood.”
—Susan Sontag (b. 1933)