Special measures: wells, seabed
Measuring the Earth's gravity field

Gravity meters can be adapted for specific uses. For example, some gravimeters have been modified for use suspended from a cable, placed on the seabed from a surface vessel or landed on the Earth's surface from a helicopter. Others have been adapted to be handled by a submersible such as the Nautile. This requires the instrument to be installed in a watertight housing capable of withstanding water pressure and/or shock, and to be self-levelling.

These are known as seabed gravimeters. These are always relative spring-loaded instruments. However, the Scripps Institution of Oceanography in San Diego, California, has developed a prototype absolute instrument that can be installed on the seabed.

Similarly, spring-loaded relative gravimeters have been adapted for installation in borehole logging probes. These are well gravimeters. They enable gravity to be measured at different depths in...