Methods for Improving WAAS Availability in Alaska

Daniel G. O'Laughlin, Emily Q. Calle, Roland O. Lejeune, M. Bakry El-Arini, James P. Fernow and James K. Reagan

Abstract:	The Wide-Area Augmentation System (WAAS) Initial Operational Capability (IOC) will provide significant en route through non-precision approach availability in Alaska. However, it will provide only limited Lateral and Vertical Navigation (LNAV/VNAV) and Lateral Precision Approach with Vertical guidance (LPV) precision approach availability. According to current predictions for precision approach, only a small portion of the southeast corner of Alaska will have availability greater than 0.95, while most of the state will have less than 0.90 availability. The low precision approach availability in Alaska is due primarily to the limited sampling of the ionosphere that is possible with the three Alaskan Wide-Area Reference Stations (WRSs) and because the ionosphere is more active in Alaska than the rest of the United States. The purpose of this paper is to analyze various methods by which the LNAV/VNAV and LPV availability in Alaska can be improved. The following methods are analyzed: 1) adding WRSs in Alaska, and 2) making improvements to the WAAS Grid Ionospheric Vertical Error (GIVE) monitor. Adding WRSs will increase the number and density of Ionospheric Pierce Points (IPPs) and thereby lower the GIVE, which is an error bound on the ionospheric correction provided for an Ionospheric Grid Point (IGP). Smaller values for this error bound will translate to greater availability for the user. Similarly, there are ways in which the WAAS GIVE monitor could be improved to provide smaller values for this error bound. This paper investigates one technique where a higher order ionospheric model than that currently used in the GIVE monitor is used to fit the ionospheric delay at an IGP. This technique has the potential to reduce the residuals of the surface fit resulting in smaller GIVEs. With these simple improvements, this paper shows that LNAV/VNAV and LPV availability for most of Alaska can be increased to well over 0.95.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	773 - 781
Cite this article:	O'Laughlin, Daniel G., Calle, Emily Q., Lejeune, Roland O., El-Arini, M. Bakry, Fernow, James P., Reagan, James K., "Methods for Improving WAAS Availability in Alaska," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 773-781.
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