Satellite-Derived Bathymetry (SDB) is the calculation of shallow water depth from active or passive satellite sensors. The technology requires a sensor (hardware) and relevant algorithms (software) to derive bathymetric measurements from the data recorded by the sensor. [1]
SDB methods can provide bathymetric data with varying spatial resolution, depending on the analysis method and its underlying physics. The most common methods for coastal and very high resolution (1 to 30 meters) bathymetric data are based on multispectral satellite sensors and the analytical inversion of the radiative transfer equation - often referred to as physical SDB methods [2] or empirical approaches [3] . Other approaches rely on photogrammetry [4] or visual image interpretation.
Moderate resolution bathymetric data (50 several 100 meters of spatial resolution) use multispectral or synthetic aperture radar satellite data and generate bathymetric information by the inversion of the wave dispersion equation [5]
The International Hydrographic Organisation IHO operates a project team on Satellite-derived bathymetry supporting the Hydrographic Surveys Working Group. It has published the B-13 IHO publication an Guidlines for Satellite-derived bathymetry which provides more detailed information on each method. [1]
In contrast to other bathymetric survey methods, such as ship-based echo sounding or airborne lidar bathymetry surveys, advanced Satellite-derived bathymetry methods can be used to map the seabed morphology without physically being on-site. The frequent revisit times of satellites and historical data archives also allow a continuous environmental monitoring of the shallow water zone. Therefore, Satellite-derived bathymetry finds uptake in applications which require to map and monitor shallow waters, which might be not accessible or cover significant geographical areas and support charting in those areas [6] . SDB data are part of the European harmonized bathymetry grid EMODnet bathymetry [7] , and as such integrated into the General Bathymetric Chart of the Ocean.
Software tools for the creation of Satellite-derived bathymetry range from desktop-based cookbook solutions [8] up to web-based software solutions [9]
The International Hydrographic Organization (IHO) is an intergovernmental organisation representing hydrography. As of November 2023, the IHO comprised 99 Member States.
Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their change over time, for the primary purpose of safety of navigation and in support of all other marine activities, including economic development, security and defense, scientific research, and environmental protection.
Echo sounding or depth sounding is the use of sonar for ranging, normally to determine the depth of water (bathymetry). It involves transmitting acoustic waves into water and recording the time interval between emission and return of a pulse; the resulting time of flight, along with knowledge of the speed of sound in water, allows determining the distance between sonar and target. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes.
Hydrographic survey is the science of measurement and description of features which affect maritime navigation, marine construction, dredging, offshore wind farms, offshore oil exploration and drilling and related activities. Surveys may also be conducted to determine the route of subsea cables such as telecommunications cables, cables associated with wind farms, and HVDC power cables. Strong emphasis is placed on soundings, shorelines, tides, currents, seabed and submerged obstructions that relate to the previously mentioned activities. The term hydrography is used synonymously to describe maritime cartography, which in the final stages of the hydrographic process uses the raw data collected through hydrographic survey into information usable by the end user.
Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Earth and other planets. Remote sensing is used in numerous fields, including geophysics, geography, land surveying and most Earth science disciplines. It also has military, intelligence, commercial, economic, planning, and humanitarian applications, among others.
A bathymetric chart is a type of isarithmic map that depicts the submerged topography and physiographic features of ocean and sea bottoms. Their primary purpose is to provide detailed depth contours of ocean topography as well as provide the size, shape and distribution of underwater features. Topographic maps display elevation above ground and are complementary to bathymetric charts. Charts use a series of lines and points at equal intervals to showcase depth or elevation. A closed shape with increasingly smaller shapes inside of it can indicate an ocean trench or a seamount, or underwater mountain, depending on whether the depths increase or decrease going inward.
The Canadian Hydrographic Service (CHS) is part of the federal department of Fisheries and Oceans Canada and is Canada's authoritative hydrographic office. The CHS represents Canada in the International Hydrographic Organization (IHO).
Bathymetry is the study of underwater depth of ocean floors, lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water depth measurements are from Ancient Egypt over 3000 years ago. Bathymetric charts, are typically produced to support safety of surface or sub-surface navigation, and usually show seafloor relief or terrain as contour lines and selected depths (soundings), and typically also provide surface navigational information. Bathymetric maps may also use a Digital Terrain Model and artificial illumination techniques to illustrate the depths being portrayed. The global bathymetry is sometimes combined with topography data to yield a global relief model. Paleobathymetry is the study of past underwater depths.
Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, including light from frequencies beyond the visible light range, i.e. infrared and ultra-violet. It can allow extraction of additional information the human eye fails to capture with its visible receptors for red, green and blue. It was originally developed for military target identification and reconnaissance. Early space-based imaging platforms incorporated multispectral imaging technology to map details of the Earth related to coastal boundaries, vegetation, and landforms. Multispectral imaging has also found use in document and painting analysis.
MEdium Resolution Imaging Spectrometer (MERIS) was one of the main instruments on board the European Space Agency (ESA)'s Envisat platform. The sensor was in orbit from 2002 to 2012. ESA formally announced the end of Envisat's mission on 9 May 2012.
A multibeam echosounder (MBES) is a type of sonar that is used to map the seabed. It emits acoustic waves in a fan shape beneath its transceiver. The time it takes for the sound waves to reflect off the seabed and return to the receiver is used to calculate the water depth. Unlike other sonars and echo sounders, MBES uses beamforming to extract directional information from the returning soundwaves, producing a swathe of depth soundings from a single ping.
The Molloy Deep is a bathymetric feature in the Fram Strait, within the Greenland Sea east of Greenland and about 160 km west of Svalbard. It is the location of the deepest point in the Arctic Ocean. The Molloy Deep, Molloy Hole, Molloy Fracture Zone, and Molloy Ridge were named after Arthur E. Molloy, a U.S. Navy research scientist who worked in the North Atlantic, North Pacific and Arctic Oceans in the 1950s-1970s.
Acoustic seabed classification is the partitioning of a seabed acoustic image into discrete physical entities or classes. This is a particularly active area of development in the field of seabed mapping, marine geophysics, underwater acoustics and benthic habitat mapping. Seabed classification is one route to characterizing the seabed and its habitats. Seabed characterization makes the link between the classified regions and the seabed physical, geological, chemical or biological properties. Acoustic seabed classification is possible using a wide range of acoustic imaging systems including multibeam echosounders, sidescan sonar, single-beam echosounders, interferometric systems and sub-bottom profilers. Seabed classification based on acoustic properties can be divided into two main categories; surficial seabed classification and sub-surface seabed classification. Sub-surface imaging technologies use lower frequency sound to provide higher penetration, whereas surficial imaging technologies provide higher resolution imagery by utilizing higher frequencies.
The General Bathymetric Chart of the Oceans (GEBCO) is a publicly available bathymetric chart of the world's oceans. The project was conceived with the aim of preparing a global series of charts showing the general shape of the seafloor. Over the years it has become a reference map of the bathymetry of the world's oceans for scientists and others.
Teledyne CARIS, A business unit of Teledyne Digital Imaging, Inc. is a Canadian software company that develops and supports geomatics software for marine and land applications. The company is headquartered in Fredericton, New Brunswick, Canada. CARIS also has offices in the Netherlands, the United States and Australia, and has re-sellers offering sales and support of software products to more than 75 countries.
Sandy Island is a non-existent island that was charted for over a century as being located near the French territory of New Caledonia between the Chesterfield Islands and Nereus Reef in the eastern Coral Sea. The island was included on many maps and nautical charts from as early as the late 19th century. It was removed from French hydrographic charts in 1974. The island gained wide media and public attention in November 2012 when the R/V Southern Surveyor, an Australian research ship, passed through the area and "undiscovered" it. The island was quickly removed from many maps and data sets, including those of the National Geographic Society and Google Maps.
Bathymetric Attributed Grid (BAG) is a file format designed to store and exchange bathymetric data.
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.
The International Bathymetric Chart of the Southern Ocean (IBCSO) is a regional mapping initiative of the General Bathymetric Chart of the Oceans (GEBCO). IBSCO receives support from the Nippon Foundation – GEBCO Seabed 2030 Project.
Thermal remote sensing is a branch of remote sensing in the thermal infrared region of the electromagnetic spectrum. Thermal radiation from ground objects is measured using a thermal band in satellite sensors.