Echolocation was a form of scanning. When one performed echolocation, pulses were sent out into space. When the pulses hit something, they were reflected back to the original source. By timing the pulses, the object's location could be determined. However, this could also lead to the ship performing the echolocation being located as well.
The Bajoran Resistance used echolocation to locate Cardassian ships in the Badlands.
In 2372, a form of echolocation was used by the USS Defiant to locate two Jem'Hadar ships in the atmosphere of a gas giant. (DS9: "Starship Down")