Validation of Radio Occultation Retrieval Methods for Canadian Conditions

L. de Groot, S. Skone, and K. O'Keefe

Abstract:	GPS radio occultation is a method for determining vertical profiles of temperature and pressure in the troposphere by observing GPS signals received at a low earth orbiting (LEO) satellite from a GPS satellite visible behind the Earth’s atmosphere. Non-atmospheric error sources are removed, and residual phase delay is used to compute the bending of the ray, and from bending the index of refraction is derived. From the index of refraction, temperature and pressure can further be derived given a known boundary value. Boundary conditions are often taken from the ECMWF numerical weather prediction model. Within Canada, the standard numerical weather prediction model in use is the GEM model. In this paper, the suitability of the GEM model as a source of boundary conditions alternative to ECMWF is investigated. The sensitivity of retrieved temperature profiles to errors in the boundary condition is investigated for a data set of occultation events occurring within Canada. Biases are introduced into the boundary condition, and the resulting errors in the retrieved temperature profile are examined as a function of altitude. The impact of boundary condition errors is also assessed as a function of season. The accuracy of temperature profiles derived using boundary condition values from the GEM model are assessed. Multiple methods of deriving boundary conditions from GEM are compared. Results indicate that the GEM model is adequate for radio occultation retrieval methods in Canada.
Published in:	Proceedings of the 63rd Annual Meeting of The Institute of Navigation (2007) April 23 - 25, 2007 Royal Sonesta Hotel Cambridge, MA
Pages:	173 - 180
Cite this article:	de Groot, L., Skone, S., O'Keefe, K., "Validation of Radio Occultation Retrieval Methods for Canadian Conditions," Proceedings of the 63rd Annual Meeting of The Institute of Navigation (2007), Cambridge, MA, April 2007, pp. 173-180.
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