Precise Timing Applications at the Defense Mapping Agency

Stephen Malys

Abstract: The mission of the Defense Mapping Agency (DMA) focuses on satisfying the Mapping, Charting and Geodesy (MC&G) requirements of the U.S. Department of Defense (DoD). DMA satisfies these requirements by supplying a broad spectrum of products and services to its DoD customers. In many cases, DMA's products and services are also available to civilian and international organizations. Within this myriad of products and services, two DMA processes employ atomic frequency standards. Both of these operational processes fall in the discipline of geodesy. DMA's geodetic exploitation of the Navstar Global Positioning System (GPS) is one area which requires precise timing. Since 1989, DMA has generated precise ephemerides and clock state estimates for the GPS satellites. This process depends on the performance of atomic oscillators in place at five DMA and five Air Force GPS monitor stations. This geodetic application also requires routine knowledge of the difference between Coordinated Universal Time (UTC) and the Earth's rotation rate (UTI). Another DMA process which relies on precise timing falls under the discipline of gravimetric geodesy. In addition to the routine collection of conventional (relative) gravity observations, DMA also collects measurements of absolute gravity at discrete points on the Earth's land surface. These absolute gravity observations are collected with a specialized instrument (an absolute gravity meter) which measures the speed of a falling object. This instrument employs an integrated rubidium frequency standard which is used in the measurement process. These DMA applications of precise timing are reviewed and discussed.
Published in: Proceedings of the 26th Annual Precise Time and Time Interval Systems and Applications Meeting
December 6 - 8, 1994
Hyatt Regency Reston Town Center
Reston, Virginia
Pages: 17 - 24
Cite this article: Malys, Stephen, "Precise Timing Applications at the Defense Mapping Agency," Proceedings of the 26th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 1994, pp. 17-24.
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