Dolphins - Echolocation

Dolphins' senses are very developed. Most dolphins have acute eyesight both in and out of the water, and they can hear frequencies ten times or more above the upper limit of adult human hearing. Hearing is also used for echolocation, which all dolphins have. Dolphin teeth are believed to function as antennae to receive incoming sound and to pinpoint the exact location of on object. Beyond locating an object, echolocation also provides the animal with an idea on the object's shape and size, though how exactly this works is not yet understood. The dolphin's sense of touch is also well-developed, with tree nerve endings densely packed in the skin, especially around the snout pectoral fins and genital area. However, dolphins lack an olfactory nerve and lobes and thus are believed to have no sense of smell. They do have a sense of taste and show preferences for certain kinds of fish. Dolphins are capable of making a broad range of sounds using nasal air sacs located just below the blowhole. Individual dolphins communicate using a variety of clicks, whistle-like sounds, and other vocalizations. The clicks are directional and ore for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals. Which of the following are close to the meaning of echolocation in this passage?