Sound in the water
Sonar uses sound to investigate the underwater environment. NOAA explains that sound travels through water farther than light or radar waves can, making it useful for mapping and detecting objects. Its applications include scientific exploration, navigation, and locating hazards or wrecks. Military uses are part of a larger family of technologies built around the same physical medium.
Active and passive approaches
Active sonar sends a sound signal and analyzes returning echoes. Their timing and other characteristics provide information about what the sound encountered. Passive sonar instead listens for sound already present. These are different approaches to gathering information, not simply two names for the same display. A sensor may be installed on a vessel, towed, or carried by another platform, depending on its purpose.
A measurement is not the whole ocean
A sonar image or recording reflects equipment, conditions, processing, and interpretation. Readers should ask what was measured and what the source can actually conclude from it. A general description of active or passive sensing does not reveal how a particular military system performs. It is also useful to separate exploration imagery from claims about identifying a specific object. Good reporting explains the question being investigated before presenting the dramatic image. That gives the public a clearer understanding of why underwater observation can be difficult and why skilled interpretation matters. Sonar makes otherwise inaccessible environments more understandable, but every result still needs context and evidence.