Lieutenant Commander Ben Evans of the Office of Coast Survey at the National Oceanic and Atmospheric Association (NOAA) presented on his work in underwater charting and navigation at the College’s Natural Science and Mathematics Colloquium (NS&M) lecture last Wednesday, in a presentation titled Hydrography: Science, Art, and Sea Stories of Seafloor Mapping.
A friend of two College professors, Evans was introduced by Physics Assistant Professor Josh Grossman and Mathematics Assistant Professor Alex Meadows, all of whom went to Williams College for their undergraduate degrees. “Two of us actually finished the Physics degree there,” said Grossman, referring to himself and Evans.
Evans began the presentation in Schaefer Hall by giving the audience of students, faculty, and community members an idea of what hydrography entails.
“‘Hydrography’ is not a word,” said Evans. “But, hydrographic relates to the characteristic features (as flow or depth) of bodies of water,” referring to the Webster’s Dictionary definition.
Hydrography is a specific discipline in the study of oceans and other bodies of water, known as oceanography.
The goal of hydrographers has not changed for thousands of years: to make nautical charts for maritime commerce. “The majority of goods we import come from water,” said Evans.
In 2008, annual cargo tonnage reached 8,720 million tons, over twice as much as its value in 1980 (3,704 million tons).
Ships that used to draw 30 feet of water due to their large size and cargo now can draw as many as 51 feet, and shipping miles have increased by 123 percent.
With the contraction of the Arctic ice caps, allowing for more trade routes and a potentially ice-free Arctic by as early as 2013, these routes and cargo sizes are expected to increase even further, placing more importance on safe, accurate navigation.
From 1973 to 1982, the United Nations Third Conference on the Law of the Sea (UNCLOS III) resulted in the Law of the Sea Treaty, which dictated that signatories of the treaty could claim seabed resources of the Extended Continental Shelf (ECS) around the country, beyond its Exclusive Economic Zone (EEZ).
While the United States did not sign the latest 1994 greement of the treaty (Article XI), which concerned the establishment of the International Seabed Authority (ISA) to monitor a country’s underwater activities beyond its EEZ, its EEZ’s monetary worth approaches $1 trillion, and is 25 percent larger than the U.S. land mass.
In 2010, President Obama approved the National Ocean Policy on Coastal and Marine Spatial Planning to zone (chart) the EEZ.
But President Thomas Jefferson, in 1807, had begun the process of coastal surveying by establishing the Survey of the Coast, the first U.S. scientific agency.
The Survey of the Coast merged with several other nautical agencies to form the NOAA in 1970.
The NOAA has about 1,000 charts that detail the depths of the U.S. coast, including charts from Jefferson’s era that focused on depth measurements.
These were done using lead lines that were spun in the air on a ship and thrust into a body of water, with a measurement of the line when the lead weight hit the bottom of the sea floor.
Combined with horizontal positioning techniques where two relative points on the coast were referenced to determine nautical position, accurate depth charts were generated that are still maintained by the NOAA.
The process of lead lining was abandoned in the 1930s with the development of SONAR (or, the Vertical Beam Echosounder).
With this technology, a sound would be emitted below a ship, which would quickly travel through water to the sea floor.
The sound waves would echo to the surface and be detected by a receiver, which would use the echo time delay and known speed of sound in water to calculate depth.
The development of computers in the 1990s that could handle vast depth calculations and data aided in the development of more thorough nautical charts.
“The physics aren’t strenuous,” said Evans, “but suddenly in the 90s, we had computers that could handle this vast array of data.”
While the science may not be difficult, the navigation and depth determination can bring its own challenges to hydrographers.
With changes in tide and vessel conditions (if heaving, pitching, rolling, or yawing), it can be difficult to maintain frames of reference, as well as modify measurements (due to sound speed changes in the water) or survive the water itself. “The sea doesn’t care about you,” said Evans.
The process has been further advanced with the development of Autonomous Underwater Vehicles (AUVs), which can do SONAR sweeps for about a day underwater for mass depth calculations, and FLIP (or Floating Instrument Platform), which is a platform ship resting on two buoyant supports that decrease the buoyant force on the ship to prevent depth data skewing.
Evans concluded the lecture with a discussion of the AUVs’ recent practical application: they were used to survey for underwater debris of Space Shuttle Columbia, which disintegrated upon re-entry on Feb. 1, 2003, over much of Texas and Louisiana.
While the in-flight data recorder was not found, a video of the seven astronauts that ends four minutes before the shuttle began to disintegrate was recovered
The next NS&M lecture will be on Feb. 16 at 4:40p.m., presented by Brigham Young University’s Dr. Michael Dorff and titled Shortest Paths, Soap Films, and the Shape of the Universe.