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Combination of GNSS Measurements

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Title Combination of GNSS Measurements
Author(s) J. Sanz Subirana, J.M. Juan Zornoza and M. Hernández-Pajares, Technical University of Catalonia, Spain.
Level Intermediate
Year of Publication 2011

Starting from the basic observables (described in GNSS Basic Observables) the following combinations can be defined (where and , , indicate measurements in the frequencies and ):

  • Ionosphere-free combination: It removes the first order (up to 99.9%) ionospheric effect, which depends on the inverse square of the frequency (, see article Ionospheric Delay).

Satellite clocks are defined relative to combination (see article Combining pairs of signals and clock definition).

  • Geometry-free combination: it cancels the geometric part of the measurement, leaving all the frequency-dependent effects (i.e., ionospheric refraction, instrumental delays, wind-up) besides multipath and measurement noise. It can be used to estimate the ionospheric electron content, to detect cycle-slips in the carrier phase, or also to estimate antenna rotations as well. Note the change of terms order in and .

  • Wide-laning combinations: These combinations are used to create a signal with a significantly wide wavelength. This longer wavelength is useful for cycle-slips detection and ambiguity fixing. Other feature of this combination is the change of the sign in the ionospheric term, which is exploited by the Melbourne-Wübbena combination to remove the ionospheric refraction.

  • Narrow-laning combinations: These combinations create signals with a narrow wavelength. The signal in this combination has a lower noise than each separated component. It is used to reduce the code noise in the Melbourne-Wübbena combination to estimate the wide-lane ambiguity.

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