Abstract: Apparatus has at least one processor and at least one memory having computer-readable code stored thereon which when executed controls the at least one processor: to store a model with parameters for extending ephemeris data for a first satellite; to receive first ephemeris data from the first satellite, the first ephemeris data relating to clock error data and/or orbit data for the first satellite at a first time; to receive second ephemeris data from the first satellite, the second ephemeris data relating to clock error data and/or orbit data for the first satellite at a second time; to use the model to predict clock error data and/or orbit data for the first satellite at the second time; to calculate a measure of deviation between the predicted clock error data and/or orbit data for the first satellite at the second time and the clock error data and/or orbit data for the first satellite at the second time as described in the second ephemeris data; to use the measure of deviation to determine whether there

Abstract: Apparatus comprises: one or more memories configured to store data sets for each of plural positioning satellites, the data set for a satellite comprising ephemeris extension data and data relating to a lifetime or expiry of the ephemeris extension data, wherein the data relating to a lifetime or expiry of the ephemeris extension data is different for at least two satellites; and one or more processors.

Abstract: The invention relates to a time and location dependent atmosphere model and especially determining the altitude of a mobile terminal based on this model and the measured barometric pressure at the location of the terminal. The atmosphere model provides a long term, wide area barometric pressure model estimate.