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.

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 =C_{uc}=C_{us}=C_{rc}=C_{rs}=C_{ic}=C_{is}=0 }[/math]

and

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

Table 1: GPS broadcast almanac parameters.