8.2.2 Introduction to Ambiguity Resolution

APRIORI VALUES OF THE AMBIGUITY PARAMETERS

The apr iori values of the ambiguities are generally provided by a double-difference solution in the form of real-valued quantities plus the variance-covariance information. The likeliest values of the ambiguities therefore are the nearest, "round-off" integer values. In some cases the estimate may be very near an integer, but in other cases the real-valued estimate is not obviously near an integer. The reliability of these estimates is a function of the baseline length, satellite-receiver geometry and length of observation session, and they are affected by multipath, residual biases and cycle slips.

There are several approaches which can be used, some of which are particularly useful for modern GPS surveying techniques. These include:

• Estimate ambiguities with the aid of pseudo-range data:

(8.2-1)

• Use other geometric information, such as the known length of the baseline:

(8.2-2)

• Make use of dual-frequency relationships that permit the L1 (or L2) ambiguities to be estimated from the wide-lane or ionosphere-free "lumped" ambiguity terms (section 8.4.2).

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© Chris Rizos, SNAP-UNSW, 1999