Underwater exploration

Underwater exploration is the exploration of any underwater environment, either by direct observation by the explorer, or by remote observation and measurement under the direction of the investigators.
Systematic, targeted exploration is the most effective method to increase understanding of the ocean and other underwater regions, so they can be effectively managed, conserved, regulated, and their resources discovered, accessed, and used.
Less than 10% of the ocean has been mapped in any detail, less has been visually observed, and the total diversity of life and distribution of populations is similarly obscure.
Types of exploration include investigation of the form and extent of the body of water or part thereof, investigation of the geological characteristics of the seabed and freshwater equivalents, and investigation of the geological structure, strata, and sediments underlying the body of water, investigation of the physical and ecological characteristics of the body of water and its containing geographical features, discovery and investigation of shipwrecks and archeological sites, and direct and remote visual observation of what is there.
The oceans can be divided into deep ocean and coastal waters. Inland waters are mostly fresh, and consist of rivers, lakes and ground water, some of which is in accessible caves.
Underwater exploration is largely a recent development, as it relies heavily on fairly advanced technology over almost all of the relevant territory.

Scope

Exploration is the process of exploring, which has been defined as :

To examine or investigate something systematically.
To travel somewhere in search of discovery.
To experience first hand.
To wander without any particular aim or purpose.

According to the definition. this does not necessarily require the explorer to be present at the point of investigation, so exploration of the underwater environment by remotely operated equipment, remote measurement, and autonomous devices programmed to explore the underwater environment is included. Surveys of the underwater environment, particularly geographical surveys, are also considered to be underwater exploration in a broad sense, as they are a form of systematic investigation for information not yet known in the desired detail.
Systematic investigation is the realm of science, both professional and amateur, particularly when findings are published in some way for the benefit of the wider community. Some results of systematic exploration are kept hidden from the general public for commercial and political reasons.
To travel in search of discovery is a luxury that most people and organisations cannot afford. This form of exploration is largely the domain of the wealthy and the dedicated. When financial backing occurs, the investigations tend to become systematic and targeted.
To seek experience first hand and to wander without any particular aim or purpose is recreation, and the discoveries from this aspect of exploration are likely to be personal, limited, and repetitive, as various people explore the same environment at different times. Discovery by this route tends to be published only when something obviously unusual is found, and is likely to be published as news.

Objectives

The scope of underwater exploration includes the distribution and variety of marine and aquatic life, measurement of the geographical distribution of the chemical and physical properties, including movement of the water, and the geophysical, geological and topographical features of the Earth's crust where it is covered by water.
Systematic, targeted exploration is the most effective method to increase understanding of the ocean and other underwater regions, so they can be effectively managed, conserved, regulated, and their resources discovered, accessed, and used. The ocean covers approximately 70% of Earth's surface and has a critical role in supporting life on the planet but knowledge and understanding of the ocean remains limited due to difficulty and cost of access.
The distinction between exploration, survey, and other research is somewhat blurred, and one way of looking at it is to consider the baseline surveys and research as exploration, as previously unknown information is gathered. Updating and refining the data is less exploratory in nature, but may still be exploration for the people involved, in the sense that the experience is new to them.

Status

Oceans

According to NOAA, as of January 2023: "More than eighty percent of our ocean is unmapped, unobserved, and unexplored." Less than 10% of the ocean, including about 35% of the ocean and coastal waters of the United States, have been mapped in any detail using sonar technology. According to GEBCO 2019 data, less than 18% of the deep ocean bed has been mapped using direct measurement and about 50% of coastal waters were not yet surveyed.
Most of the data used to create seabed maps are approximate depths derived from satellite gravity measurements and sea surface heights which are affected by the shape and mass distribution of the seabed. This method of approximation only provides low resolution information on large topographical features, and can miss significant features.

Inland waters

Subterranean waters

The extent of flooded caves is largely known as a result of underwater exploration and survey of those caves by divers. ROV and AUV technology is starting to be used in larger and deeper caves. Data collected is often shared and may be stored on databases to help optimise the effectiveness of such surveys, and make the information generally available.
Underwater cave mapping is complicated by a lack of access to the surface for GPS positions, darkness, with short line-of-sight, and limited visibility, which complicate optical measurement. The usual methods for survey and mapping of underwater caves are dead reckoning and direct measurements of distance, compass direction and depth, by scuba divers. Hand-held sonar may be used for distance measurement where available.

Types of underwater exploration

Investigation of the form and extent of the body of water or part thereof.
*Remote acoustic and satellite sensing, radar altimeters
*Sonar, high resolution with multibeam
*Direct measurement by divers of cave and reef structure using depth gauge, compass, clinometer and surveyor's tape, hand held sonar, and other instruments where applicable.
Investigation of the geological characteristics of the seabed and freshwater equivalents, and through-ground investigation of the geological structure, strata, and sediments.
Investigation of the physical and ecological characteristics of the body of water and its containing geographical features.
*Identification and recording of numbers and distribution of biological specimens
*Collection of biological samples by divers, grabs, nets, dredges, manned and unmanned submersibles
*Infra-red and microwave radiometers for sea surface temperature measurement
*Bottom sampling: Grabs, dredges, gravity core sampler, piston corer, hydraulic piston corer core drill
*Measurement and recording of the physical and chemical characteristics if the water
Discovery and investigation of shipwrecks and archeological sites
*Magnetometer, multibeam sonar
Direct and remote visual observation
*Divers and crewed observation submersibles, remotely operated underwater vehicles and autonomous underwater vehicles, video and still photography.
Regions of the underwater environment

The oceans can be divided into deep ocean and coastal waters. Inland waters are mostly fresh, and consist of rivers, lakes and ground water, some of which is in accessible caves.

Deep-sea

Deep-sea exploration is the investigation of physical, chemical, and biological conditions on the sea bed, and water column beyond the continental shelf for scientific, commercial or other purposes. Deep-sea exploration is considered a relatively recent human activity compared to the other areas of geophysical research, as the depths of the sea have been investigated only during comparatively recent years. The ocean depths still remain a largely unexplored part of the Earth, and form a relatively undiscovered domain.
In general, modern scientific deep-sea exploration can be said to have begun when French scientist Pierre-Simon de Laplace investigated the average depth of the Atlantic Ocean by observing tidal motions registered on Brazilian and African coasts. He calculated the depth to be, a value later proven quite accurate by echo-sounding measurement techniques. Later on, due to increasing demand for the installment of submarine cables, accurate measurements of the sea floor depth were required and the first investigations of the sea bottom were undertaken. The first deep-sea life forms were discovered in 1864 when Norwegian Michael Sars obtained a sample of a stalked crinoid at a depth of.

Coastal waters

Coastal waters and waters of the continental shelf have been explored more systematically than deeper waters, since they are to a large extent within the exclusive economic zone of adjoining countries, and are relatively accessible.

Relatively shallow, seldom more than 200 m, so generally accessible to ambient pressure diving, though special procedures may be necessary for most offshore diving.
*A small part of inshore coastal waters is shallower than 50 m, making it reasonably easily accessible to divers.
Most is accessible to surface vessels, ROUVs and AUVs. Very shallow areas of heavy reef may be relatively inaccessible to vehicles of any kind, particularly in high energy zones, but may be occasionally be accessible to Lidar.
Very large in extent.
Economically and strategically important for navigation.
Relatively extensively and intensively surveyed. Extent and approximate depths are mostly known. Detailed topography is being systematically surveyed in some places. According to GEBCO data, about 50% of coastal waters were not yet surveyed as of 2019.