Which acoustic technique is chiefly employed to measure ocean characteristics over considerable distances?

Acoustic tomography is the technique primarily employed to measure ocean characteristics over considerable distances. It utilizes the transmission of sound waves through the ocean to capture data about temperature, salinity, and other properties within the water column. By analyzing the time it takes for sound to travel between various points, researchers can infer the physical conditions of the ocean over vast areas.

This method is particularly valuable because it can cover large distances—often hundreds to thousands of kilometers—making it much more effective for studying oceanographic features than techniques that sample more localized areas.

In contrast, acoustic inversion focuses on interpreting underwater sound data to derive environmental parameters but is more specific in scope and often used for shorter ranges. Passive acoustic monitoring primarily listens for sounds without actively transmitting signals, mainly for biological study, and does not measure ocean characteristics directly. Biosonar methods typically involve biological entities, like marine mammals, using sound for navigation and hunting, but they are not specifically designed for large-scale oceanographic measurement. Thus, acoustic tomography stands out as the most suitable method for extensive ocean characteristic assessments.