The measurement and charting of the spatial variation of the ocean depths.
Bathymetry refers to the measurement of water depth at various places in a body of water. For the oceans, visible range remote sensing can be used to determine the bathymetry of shallow areas and coastal regions to some extent, provided the water is essentially clear of absorbing substances. For the deep ocean, ships must be used to determine the exact depth of the water, but sea surface height (altimetry) data can be used to map the ocean's bathymetry by measuring the stable "shape"
of the ocean surface that is created by slight variations in gravity due to the shape of the ocean floor.
Coral reef mapping
Fisheries and habitat monitoring
Visible (400-700 nm), Microwave (100-1000 microns)
Other sources for data