Standard Ionspheric and Tropospheric Models for GPS on Aerospace Applications: Geometrical Extension

Paper number

IAC-06-D1.P.2.01

Author

Mr. Gustavo Baldo Carvalho, Center of Applied Space Technology and Microgravity - ZARM - University of Bremen, Germany

Coauthor

MSc. Per Gustavsson, Luleå Technical University, Sweden

Coauthor

Dr. Stephan Theil, Center of Applied Space Technology and Microgravity, Germany

Coauthor

Dr. Helio Koiti Kuga, Instituto Nacional de Pesquisas Espaciais (INPE), Brazil

Year

2006

Abstract

In order to determine a GPS receiver position, satellite pseudoranges to the receiver antenna must be determined. 
However, the signal paths are affected by troposphere and ionosphere delays, among other effects. 
While the ionosphere is a dispersive medium with respect to GPS signals, the Troposphere is a non dispersive 
medium and frequency independent for GPS signals.
As a result the GPS carrier frequencies L1 and L2 can be used to eliminate the ionospheric delay, 
but this approach is not feasible to the tropospheric correction.
Furthermore, even for ionospheric corrections, when single frequency receivers are used, the advantage of using  
both carriers is not possible.\\
For this purpose the Klobuchar ionospheric correction model can be applied by a single carrier GPS receiver 
together with the Hopfield tropospheric correction model, allowing a better calculation of the receiver position.
However, the deviations are highly dependent on the relative position between receiver antenna and transmitting 
satellite. Since the troposphere extends up to 40 km and ionosphere from 50 km up to 1000 km above Earth, 
as the altitude increases the antenna can be outside of their boundaries. In such situations, if the satellite sight 
acquires negative elevations the signal can cross their boundaries and cause the effects to be still present, which 
is not treated by the mentioned models. Furthermore, even if the antenna is still inside the troposphere, poor satellite 
availability can lead to situations where the use of satellites with negative elevations is inevitable, however being 
the model applicability impossible. This leads that these models in their standard form are not suitable for systems 
operating under aerospace flights conditions.\\
Through this motivation, this work proposes a geometrical extension modeling in order to allow the mentioned models 
to be also suitable for aerospace systems. 
Such an extension presents an approach for keeping the validity of these very same and unmodified models through the definition 
of auxiliary effect calculation points where the models are still valid, thus being also suitable for use in systems operating under 
aerospace flights conditions.

Abstract document

IAC-06-D1.P.2.01.pdf

Manuscript document

IAC-06-D1.P.2.01.pdf (🔒 authorized access only).

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