Investigating the use of WAAS as a navigational tool for coast guard and civilian maritime use

Document Type

Conference Proceeding

Date of Original Version



Since 2003, the Federal Aviation Administration (FAA) has employed WAAS for precision approaches to airports and navigational use for aircraft over the continental United States, adjacent ocean regions, and parts of Alaska. This was due in part to GPS/DGPS not meeting the FAA's strict guidelines for accuracy, integrity, and availability. Currently, the FAA rates WAAS for 250ft and above the surface of the earth; this 250-foot barrier ensures 100% coverage over the United States from two existing INMARSAT satellites. Because of this height restriction, the Coast Guard has not accepted WAAS as an individual stand-alone source of navigation for military and civilian use. In 2005, the FAA plans on launching additional geostationary satellites to increase system redundancy and provide overlapping coverage [1]. By placing one to three more satellites due south of the United States, it might be possible to provide the coverage needed for the maritime community to use WAAS as a primary form of navigation at ground level. The current system of two satellites does not provide double or even single coverage in parts of the United States at ground level due to line of sight issues. By adding more satellites, the 250-foot barrier might be able to be brought down and double coverage for the United States might be possible in all navigable areas. This paper reports on a project to develop software tools to predict coverage of WAAS satellites (both existing and future) at user selectable locations in the continental United States. To account for topographical features, the Digital Terrain Elevation Data (DTED) Level 1 database with a spacing of 3 arc seconds (or 100 meter resolution) is incorporated into the tool. The results of the predictions are compared to actual field measurements made during 2004 as part of a DGPS/WAAS Accuracy and Availability Study conducted by John J. McMullen Associates in support of the U.S. Coast Guard Academy.

Publication Title, e.g., Journal

Proceedings of the Institute of Navigation, National Technical Meeting

This document is currently not available here.