Estimation of GPS ionospheric delay using L1 code and carrier phase observables

摘要

Free electrons in the earth's ionosphere cause a frequency-dependent group delay in the bands used for the spread-spectrum GPS ranging signals. This delay constitutes a potential source of error in timing measurements. The ionospheric delay can be removed by dual-frequency ranging using the L1 and L2 signals. Two-frequency time receivers are currently expensive, and are not very reliable when tracking low elevation satellites when Anti-Spoofing is enabled, unless decryption can be used. Single-frequency, L1, receivers can correct for the delay using a detailed model of the ionosphere scaled by data contained in the 'navigation message' broadcast by the satellites. However, because of unpredictable variations of the ionosphere, this so-called single-frequency correction is only expected to absorb 50