1. The measurement of the depths of oceans, seas, or other large bodies of water: Since Thomas was interested in oceanography, he learned more about bathymetry and found out that it was the underwater equivalent to "hypsometry" or "topography".
2. The data derived from such measurements: The material obtained from bathymetry, and compiled in a topographic map, provides good information for navigation.
3. The science of measuring ocean depths in order to determine the sea floor topography: Judy decided to study bathymetry, since she was very interested in oceanography and vessels.