Patent ID: 8094064

Claim:
A processing function to monitor a horizontal delay gradient in satellite signals, the processing function comprising: a satellite differencing module configured to receive carrier phase measurements for at least two satellites from at least two reference receivers, the at least two satellites including a monitored satellite and at least one other satellite, wherein the at least two reference receivers have a known geometric relationship to each other, and wherein the satellite differencing module determines differences in the carrier phase measurements between signals from the monitored satellite and at least one of the at least one other satellite; a double differencing module configured to: form double-differences between one or more pairs of the at least two reference receivers based on the differences in the carrier phase measurements, compensate the double-differences between the pairs for the known difference-in-position of the reference receivers in the pairs, perform a modulo operation to limit the compensated double-differences to a range of minus one-half wavelength to plus one-half wavelength, for the monitored satellite, average the double differences over the other satellites among the at least two satellites; and a gradient estimator module configured to estimate a magnitude of the horizontal delay gradient based on the averaged compensated double-differences for the monitored satellite.