Ground-based system and method to monitor for excessive delay gradients

A method of monitoring for a delay gradient to a monitored satellite, the method comprising:

• receiving carrier phase measurements from at least two reference receivers, wherein the at least two reference receivers substantially simultaneously receive radio frequency signals from the monitored satellite and at least one other satellite;
• determining differences in the carrier phase measurements between the signals from the monitored satellite and at least one other satellite for the at least two reference receivers;
• forming double-differences between pairs of the at least two reference receivers;
• compensating the double-differences for the known difference-in-position of the reference receivers in the pairs;
• performing a modulo operation on the compensated double-differences to limit the compensated double-differences to a range of minus one-half wavelength to plus one-half wavelength;
• averaging the compensated double differences over the at least one other satellites;
• and
• estimating a magnitude of a horizontal delay gradient based on the averaged compensated double-differences.

A ground based system to monitor for a horizontal delay gradient to a monitored satellite, the system comprising:

• at least two reference receivers positioned in a known geometric relationship to each other, the at least two reference receivers configured to substantially simultaneously receive radio frequency signals from the monitored satellite and at least one other satellite;
• and
• a processing function communicatively coupled to the at least two reference receivers, the processing function configured to:
• receive carrier phase measurements for the monitored satellite and at least one other satellite from the at least two reference receivers,
• determine differences in the carrier phase measurements between the signals transmitted from the monitored satellite and at least one other satellite and substantially simultaneously received at the at least two reference receivers,
• form double-differences between pairs of the at least two reference receivers based on the differences in the carrier phase measurements,
• compensate the double-differences 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,
• average the compensated double-differences over the other satellites for the monitored satellite at the pairs, and
• estimate a magnitude of the horizontal delay gradient based on the averaged compensated double-differences.