Pressure and Blanchard Altitudes Computed from Atmospheric Data Gathered from May through July 2000 at White Sands, New Mexico

Te-Chang Li and Donald N. Thunborg

Abstract:	An altitude reference is usually required to damp the error growth in the inherently unstable vertical channel of an Inertial Navigation System (INS). This altitude reference is commonly obtained by computing the pressure altitude based on a standard atmospheric model for the standard day via the aircraft Central Air Data Computer (CADC). However, due to significant errors in pressure altitude, the altitude and vertical velocity errors exhibited by the pressure altitude stabilized vertical channel can be unacceptably large and this can adversely impact high accuracy applications such as landing on an aircraft carrier and weapon delivery. A more precise altitude reference for use in the INS vertical channel can be obtained using the Blanchard algorithm, which computes altitude from atmospheric pressure, temperature, aircraft ground velocity, and wind velocity data. In order to compare the pressure and Blanchard altitude errors, atmospheric data gathered from May through July 2000 at White Sands Missile Range, New Mexico was utilized from radiosonde measurements taken at altitudes from approximately 4,100 ft to 60,000 ft (18.3 km). The radiosonde is an instrument carried aloft by a balloon; it sends atmospheric pressure, temperature, and humidity to the ground by means of a small radio transmitter. This paper describes the algorithms and results of the pressure and Blanchard altitude computations from the weather data collected at White Sands Missile Range from May through July 2000. Comparison of pressure and Blanchard altitude errors shows that Blanchard altitude is a much more precise altitude reference than pressure altitude for the atmospheric data gathered in the May through July 2000 time frame at White Sands Missile Range.
Published in:	Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001) June 11 - 13, 2001 Albuquerque, NM
Pages:	325 - 333
Cite this article:	Li, Te-Chang, Thunborg, Donald N., "Pressure and Blanchard Altitudes Computed from Atmospheric Data Gathered from May through July 2000 at White Sands, New Mexico," Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, June 2001, pp. 325-333.
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