This sounds like it's probably the sonar system of a submarine.
In 1915, Paul Langévin invented the first sonar type device for detecting submarines called an "echo location to detect submarines" using the piezoelectric properties of the quartz.
radar
location and ranging submarines
ASDIC
e-nose
A periscope.
A standard viewing device used on a submarine is a periscope.
Ballast tank
None. The megapixels are in the detecting device. e.g. a camera, a CCD device.
It's called a "Motion Detector"!
A Passive InfraRed Sensor (PIR)
The Piranah Water 3000