Oceanography is literally the science of mapping the floor, geometry, and configuration of large bodies of water. The history of deep-sea exploration began with practical applications of oceanography, such as the laying of undersea cables, and was extended by natural and scientific curiosity. Aspects of the condition of the oceans studied by oceanographers include relief of the sea floor, volumes of ocean basins and numerous subareas, character of the ocean surface including atmospheric effects, transportation and properties of sediments found in marine environments (as well as their origins, such as land, volcanic, organic, and inorganic sources), the chemistry of sea water (including the gas content), physical properties of sea water like density and pressure, characteristics of ice and icebergs, and biological oceanography (including plankton, bacteria, and plant nutrients as well as more familiar plants and animals).
Based on the surface map of the world, the oceans cover 71% of the globe. In the past century, oceanography has dramatically changed our understanding of the importance of the sea to land dwellers. Not only have people become more environmentally aware, but we are more knowledgeable of the vastness of Earth's seas.
Oceanography led to the development of a number of instruments that are used to chart the bottom of the sea; some of these are also used in undersea exploration for other purposes. Sounding devices were the first key oceanographic tool. The first sounding weight, the Baillie sounding machine, was used on the Challenger expedition and consisted of a large weight dropped to the sea floor. When the weight hit the bottom, the line was pulled taut and the depth measurement was read from the line. The Baillie sounding machine also had a tube below the weight that drove into the sea-floor sediments. Samples could be retrieved in this fashion. Early explorations also collected samples from the seabed using dredges (that were pulled along the sea floor) and an assortment of scoops. These tools collected soil, rock, some plant life, and other biological specimens.
Weight-sounding techniques were replaced after World War II by echo-sounding that uses sounds or acoustic impulses from ships on the ocean surface to measure reflections of the sound waves off the bottom. The time lapse of the sound wave's return to the ship indicates the depth, although early uses of echo-sounding were often in error if the device was not properly calibrated for the density of saltwater.
Science EncyclopediaScience & Philosophy: Two-envelope paradox to VenusUnderwater Exploration - History, Oceanography, Instrumentation, Diving Tools And Techniques, Deep-sea Submersible Vessels, Key Findings In Underwater Exploration - Deep-sea pioneers