Coordinates Computation from Almanac Data

Fundamentals
Title	Coordinates Computation from Almanac Data
Author(s)	J. Sanz Subirana, J.M. Juan Zornoza and M. Hernández-Pajares, Technical University of Catalonia, Spain.
Level	Basic
Year of Publication	2011

The almanac data allow to compute a raw estimation of the satellites coordinates (1-2 km [math]\displaystyle{ 1- \sigma }[/math] error), which is needed for signal acquisition by the receiver.

The almanac data consist of a reduced set of parameters (with respect to broadcast ephemeris), as it is shown in table 1 for GPS satellites. Similar data is broadcast for Galileo.

Table 1: GPS broadcast almanac parameters.

Thence, the same equations as in article GPS and Galileo Satellite Coordinates Computation can be used to compute the coordinates from almanac, just taking:

[math]\displaystyle{ \Delta n = \dot{i} = C_{uc}=C_{us}=C_{rc}=C_{rs}=C_{ic}=C_{is}=0 \qquad \mbox{(1)} }[/math]

and

[math]\displaystyle{ i_{0}=54^o+\delta i \qquad \mbox{(GPS satellites).} \qquad \mbox{(2)} }[/math]