Mathematical Minutia: Geomatics Incremental Impact

The Geosciences Division provides the normalized, geopotential coefficients for both the new NGA/NASA EGM96 n=m=360 and the WGS 84 n=m=180 Earth Gravitational Model. It also provides two geoid products, the 15-minute, worldwide geoid height file for EGM96 and the 30-minute worldwide geoid height file for the original WGS 84 model.
By James Friederich, Geomatics Office

Through the end of the Second World War, military operations were historically theater based. But with the advent of global mission profiles, the requirement for precise positioning, navigation and timing became essential. The advent of unmanned weapons, precision- point positioning and Global Navigation Satellite Systems established the importance of accurate geospatial intelligence, which became a dependency for shaping U.S. military doctrine.

The National Geospatial-Intelligence Agency’s role in the defense and intelligence communities is predicated on providing the critical accuracy and precision that defines the geospatial location of events and features on the surface of the Earth. NGA also provides this same accuracy and precision to airborne and orbital platforms to enable and maximize their own intelligence gathering and navigation missions.

Over the course of 50-plus years, NGA geodesists, orbit analysts and geodetic surveyors in the Geomatics Office within the Source directorate have been global leaders in defining, refining and updating models of the Earth that provide the fundamental basis of accurate geospatial intelligence. It was once said that one of NGA’s predecessors, the Defense Mapping Agency, was the best keep secret in the Department of Defense. And today, perhaps the geomatics tradecraft is best keep secret within NGA. The foundational math and science of geomatics unpins all positioning, navigation and timing operations throughout the National System for Geospatial Intelligence.

Geomatics is a relatively new term within NGA, but it is built upon traditional geodesy and cartography components, including work from the Greek mathematician Eratosthenes, studies on gravity by Carl Gauss, and modern mathematical applications of geodetic surveying and satellite orbital mechanics.

The disjointed theater and regional based maps of the 1940s were unsuited for the evolving post-World War II global missions. The DOD needed global maps and charts to support international positioning and navigation, and the existing regional geodetic systems could not provide an accurate worldwide basis.

Necessity is the mother of invention, and in 1960, the Army Map Service, an NGA legacy agency, began to develop the required worldwide system to unify geodetic and cartographic data and provide compatibility between the coordinates of widely separated areas of interest. The combined efforts of the Army, Navy and Air Force lead to the DOD’s World Geodetic System 1960, or WGS 60.

The WGS is the standard for DOD use in mapping, charting, positioning and navigation. It comprises a standard coordinate system for the Earth, a standard ellipsoidal reference surface (the datum or reference ellipsoid) for the size and shape of the Earth, and a gravitational equipotential surface (the geoid) that defines the nominal mean sea level.

Other factors driving the WGS development were the start of the space age for satellite tracking and earth monitoring and the advent of the Cold War. Preparedness necessitated a standardized, NATO-wide geodetic reference system in accordance with NATO standardization agreements. Not only does the WGS provide one geodetic framework for multinational operations, but it ties together ground-, airborne- and space-based operations into a single geodetic framework.

Since 1960, there has been an increasing amount of earth observations, data gathering, refinements, and technology and technique improvements. Data from satellites and new surface gravity revealed better information about the size and shape of the Earth. Updates to the WGS were published in 1966 and 1972. In 1987, the latest global geodetic reference frame, World Geodetic System 1984, was published and it is the current global geodetic system for DOD.

In the last 25 years, NGA geodesists have updated WGS 84 several times to meet two important criteria — an increase in precise users’ accuracy requirements and maintaining alignment to the Earth, which is always changing.

“These updates include improvements to the Earth Gravitational Model, the World Magnetic Model and the reference coordinates for the WGS 84, which defines the center of the Earth,” said JN Markiel, Ph.D., a senior orbit scientist in the Geomatics Office. “Each of these changes introduces incremental improvements, sometimes only a few centimeters, but they are necessary to meet the increasingly stringent requirements for precise positioning and navigation and to maintain alignment with our dynamic planet.”

Refinements derived from NGA’s geodesists may seem like mathematical minutia or scientifically arcane to a layman, but this work is critical to understanding the world and integrating that scientific knowledge into intelligence gathering, positioning and navigation.

James Friederich is a senior geosciences scientist in the Geomatics Office and is well positioned in the agency to deal with the gravity of ensuring the accuracy in geospatial intelligence.

 Pathfinder Magazine