NESDIS News Archive

Mapping Oceans Depths from Heights above the Earth

August 3, 2012

Satellite image of the Puerto Rico Trench, the deepest known spot in the Atlantic Ocean [Click image to enlarge]

Do you ever wonder how deep the oceans really are in their vastness in separating continents, enveloping mountains, volcanoes and sunken treasure, while consuming nearly two thirds of the earth's surface? Ocean mapping started around 1770, when Benjamin Franklin mapped the Atlantic's Ocean Gulf stream. Today, NOAA's Satellite and Information Services' products play an important role in the mapping of the ocean and in determining its depth as well as its effects on climate. This vast, deep liquid metropolis of coral reef communities, schools of fish, layers of vegetation, and a sometimes sanctuary for scuba divers remains 95 percent unexplored by humans.

Recent research shows that the Puerto Rico Trench is the deepest known spot in the Atlantic Ocean with water depths exceeding 8,400 meters. Southwest of the U.S. Territorial island of Guam, below the western Pacific Ocean is the deepest part of the ocean and is called the Challenger Deep. It measures at a depth of nearly 7 miles or 11,033 meters. According to NOAA, the term "bathymetry" originally referred to the ocean's depth relative to sea level. It is the study of the "beds" or "floors" of water bodies, including the ocean, rivers, streams and lakes. Let's look at the benefits that NOAA's satellites and information bring to the study of bathymetry and ultimately to our Nation.

Early studies of lakes and oceans were primarily concerned with geographical discoveries, trade, and marine life. Today, using satellite-derived gravity data, bathymetry and ocean research is concerned with all aspects of the world's ocean, including its physical and chemical properties, origin and life forms, and how the ocean affects climate change. Data from radar altimeter aboard a satellite provides detailed measurements of sea surface height over the oceans and supports a variety of our Nation's concerns. NOAA's advanced satellite technology supports remote sensing of oceanic processes and predicts environmental changes. Satellite-based radar cannot see the bottom of the ocean, but it can observe gravity anomalies. These anomalies can be correlated with ocean floor topography. The surface of the ocean bulges outward and inward creating tiny bumps and dips. According to NOAA researchers and scientists, these bumps and dips mimic the topography of the ocean floor and can be mapped using a very accurate radar altimeter mounted on a satellite. The depth of the ocean is measured by using satellite altimetry data. These measurements, captured in a data set, provide estimates of what lies beneath the surface of the ocean, and may predict bathymetry.

We measure the ocean because it has a great influence on our climate and can offer valuable ecological information. The terrain below the ocean surface influences circulation and mixing patterns that induce hazards facing coastal communities (i.e., tsunamis). Research proves that an accurate knowledge of seafloor depths is important for hazardous waste disposal, marine planning for protected areas and conservation zones and can provide important navigational information.

National Geophysical Data Center (NGDC) Builds Elevation Models

NOAA's National Geophysical Data Center is the nation's primary resource for data on the ocean floor, which is used for charting, environmental and fisheries management, and helps determine international boundaries. NGDC, based in Boulder, Colo., collaborates with various international organizations in the development of formats and standards to expedite bathymetric data exchange on regions with depths greater than 100 meters. NGDC builds digital elevation models of US coastal zones that are used to model potential tsunamis as well as the effect of sea level changes on coastal areas. These are hugely important issues for coastal communities in their future planning and economies. NGDC's suite of bathymetry products and services lessen the impacts that threaten the vitality of our ocean and planet and is a gift to the future. This enhances society's ability to plan and respond to climatic hazards and changes.

Center for Satellite Applications and Research (STAR) Satellite Gravity Data Helps Develop Bathymetry Models

NOAA's STAR uses NOAA and other satellites' observations to produce products that monitor and predict changes in the Earth's atmosphere, land and oceans. STAR researchers are continually trying to improve the accuracy of seafloor observations from space. They use satellite radar altimeter measurements of the ocean surface sea level to infer the presence of mountains below the ocean. The depths derived from satellite gravity data are combined with ship measurements to produce the very best estimated depth maps of the worlds' seafloor available. This bathymetric model has been widely used in the scientific community for more than a decade and was recently incorporated into the popular web application Google Earth.

Applications used in biology, geology, education and oceanography require a model of worldwide ocean depths. With their Bathymetric Model Error Analysis, they analyze errors in the global altimetric bathymetric model that combines satellite altimetry with ship depth soundings. Detecting and correcting these problems leads to better altimetric bathymetry models and better global statistics.

The foundation for much of ocean science is accurate bathymetry. As scientists seek to learn more about the oceans effect on climate change and the environment, satellite bathymetric data will become more important. These data help alert scientists to potential beach erosions, landslides, sea-level rise and coastal subsidence. In the same degree, bathymetry plays a key factor in scientists' and researchers' efforts to determine where fish and other marine life live, eat, and breed.

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