Understanding Submarine Viewing Instruments

Submarines operate underwater, often at significant depths. However, they frequently need to observe the surface and surroundings without fully surfacing. This requires a specialized instrument that can extend above the water level to provide a view.

Identifying the Correct Instrument

Let's examine the given options to determine which instrument is used for this specific purpose in submarines.

• Hypsometer: A hypsometer is an instrument used to measure altitude by determining the boiling point of water, which varies with atmospheric pressure. This is not used for viewing objects above sea level from a submarine.
• Ondometer: An ondometer is an instrument used to measure the wavelength or frequency of electromagnetic waves. This has no relevance to visual observation from a submarine.
• Periscope: A periscope is an optical instrument that uses a system of prisms, mirrors, or lenses to allow viewing of an object otherwise obstructed by a barrier, such as a submarine hull or trench wall. A periscope in a submarine extends vertically, allowing the submerged vessel to see objects on the surface. This aligns perfectly with the question's requirement.
• Pyrheliometer: A pyrheliometer is an instrument used to measure direct solar radiation. It is used in meteorology and solar energy studies, not for submarine observation.

Based on the function of each instrument, the periscope is the correct tool used in submarines to view objects above sea level while remaining submerged or near the surface.

How a Submarine Periscope Works

A submarine periscope typically consists of a long tube with mirrors or prisms at each end. Light from the object above the water enters the top lens/mirror, travels down the tube, is reflected by another mirror/prism, and reaches the observer's eye. This allows the observer inside the submarine to see what is happening on the surface.

Therefore, the instrument specifically designed for this purpose is the periscope.