UNB Neutral Atmosphere Models: Development and Performance

R. Leandro, M. Santos, and R. Langley

Abstract:	Several hybrid neutral atmosphere delay models have been developed by UNB researchers over the past decade or so. The most widely applicable current version is UNB3, which uses the Saastamoinen zenith delays, Niell mapping functions, and a look-up table with annual mean and amplitude for temperature, pressure, and water vapour pressure varying with respect to latitude and height. These parameters are computed for a particular latitude and day of year using a cosine function for the annual variation and a linear interpolation for latitude. The UNB3 model has been extensively used in several regions of the world, being capable of predicting total zenith delays with average uncertainties of 5 cm under normal atmospheric conditions. A modified version of UNB3 has been used in GPS receivers utilizing the Wide Area Augmentation System and other space-based augmentation systems. Other versions of the UNB neutral atmosphere model have been developed aiming at getting better predictions for the non-hydrostatic delay component. One of the new versions is UNB3m, whose performance has been investigated using radiosonde data and compared to that of UNB3. Based on ray-tracing analyses of 703,711 profiles from 223 stations in North America and surrounding territory from 1990 to 1996, the prediction errors of UNB3m have a mean value -0.5 cm and standard deviation of 4.9 cm. Although the standard deviation of the prediction error of UNB3m is similar to that of UNB3, the absolute mean error has been reduced by almost 75%.
Published in:	Proceedings of the 2006 National Technical Meeting of The Institute of Navigation January 18 - 20, 2006 Hyatt Regency Hotel Monterey, CA
Pages:	564 - 573
Cite this article:	Leandro, R., Santos, M., Langley, R., "UNB Neutral Atmosphere Models: Development and Performance," Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, January 2006, pp. 564-573.
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