Bathymetry is the measurement and mapping of water depth in bodies of water. Sonar requires an elastic medium like water, air and soil. Sonar waves travel 1500 meters per second in water with little absorption. Great depths and data are possible in water bodies with sonar.
Information about objects on the water body floor is determined by two factors: the length of time the signal takes to return and the strength of the signal. For example, a hard surface like bedrock will reflect most of the sonar wave and will produce a strong signal. Fine sediments absorb most of the signal gravel reflects. Following is an example of this principle:
(Bathymetric map) courtesy of the U.S. Geological Survey Atlantic trench
A contoured map can be produced with bathymetric data. This is very useful in location of old shorelines by combining this data and Geographic Information Systems software. The following map of the Florida shelf is an example of the result of combining the data and the software:Florida Bathymetry NOAA Bathymetric map of Florida shelf