6.3.6 GPS Observation Modelling



Bias parameters which are constant with time may be eliminated by forming the between-epoch difference. The operator is used to represent this difference, and is applied to double-difference observables to obtain the triple-difference observables (see Figure below). If the nominal reception times, in receiver clock time, are ta and tb, then applying eqn (6.3-7):


Note that all the clock bias terms, including the integer ambiguities, have been eliminated from this model. If the assumption that the integer ambiguity is constant in time is wrong then an extra term will be required to account for any cycle slip. In fact, not only have the (unknown) clock biases been eliminated, but in addition, the effect of other biases arising from atmospheric delay, satellite ephemeris error and receiver coordinate error, have been substantially reduced by the process of double- and triple-differencing.

The triple-difference observable.

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© Chris Rizos, SNAP-UNSW, 1999