Impact and Implementation of Higher‐Order Ionospheric Effects on Precise GNSS Applications

Abstract

High precision Global Navigation Satellite Systems (GNSS) positioning and time transfer require correcting signal delays, in particular higher‐order ionospheric (I2+) terms. We present a consolidated model to correct second‐ and third‐order terms, geometric bending and differential STEC bending effects in GNSS data. The model has been implemented in an online service correcting observations from submitted RINEX files for I2+ effects. We performed GNSS data processing with and without including I2+ corrections, in order to investigate the impact of I2+ corrections on GNSS products. We selected three time periods representing different ionospheric conditions. We used GPS and GLONASS observations from a global network and two regional networks in Poland and Brazil. We estimated satellite orbits, satellite clock corrections, Earth rotation parameters, troposphere delays, horizontal gradients, and receiver positions using global GNSS solution, Real‐Time Kinematic (RTK), and Precise Point Positioning (PPP) techniques. The satellite‐related products captured most of the impact of I2+ corrections, with the magnitude up to 2 cm for clock corrections, 1 cm for the along‐ and cross‐track orbit components, and below 5 mm for the radial component. The impact of I2+ on troposphere products turned out to be insignificant in general. I2+ corrections had limited influence on the performance of ambiguity resolution and the reliability of RTK positioning. Finally, we found that I2+ corrections caused a systematic shift in the coordinate domain that was time‐ and region‐dependent and reached up to −11 mm for the north component of the Brazilian stations during the most active ionospheric conditions.

A Unified Model for Multi-Frequency PPP Ambiguity Resolution and Test Results with Galileo and BeiDou Triple-Frequency Observations

“…where the subscript f = (1, 2, 3, · · ·) refers to a specific carrier frequency, superscript s refers to a specific satellite; ρ s r indicates the geometric distance between the satellite and receiver; dt r and dt s are the clock errors of receiver and satellite; dT is the slant tropospheric delay; dI s r,1 is the slant ionospheric delay on the first carrier frequency and a f = λ 2 f /λ 2 1 is the carrier frequency-dependent factor; D r, f and D s f are the receiver and satellite specific code hardware delays; λ f and N s r, f are the wavelength in meter and integer ambiguity in cycle; B r, f and B s f are the receiver-dependent and satellite-dependent uncalibrated phase delays; ε P f and ε Φ f are the pseudo-range and carrier phase measurement noise, respectively. Note that the higher-order ionospheric effects are neglected, as they have limited influence on the performance of ambiguity resolution [42].…”

Global Ionosphere Mapping and Differential Code Bias Estimation during Low and High Solar Activity Periods with GIMAS Software

“…The ionospheric delay could be expressed up to the third order, and the first order term (with a dependence on f −2 ) accounted for more than 99.9% of the total ionospheric delay. The higher-order ionospheric delay may exceed 10 mm (0.1 TECU [TEC Unit], 1 TECU = 1 × 10 16 electrons/m 2 ) [27], but the magnitude was very small in the global ionosphere mapping. The ionospheric delay could be expressed with a good approximation, without the higher-order ionospheric delay, as follows:…”

The Prediction of Geocentric Corrections during Communication Link Outages in PPP

“…PPP can be an effective option for precise real-time positioning, but it requires more information than GNSS observations alone. Reliable satellite orbit and clock corrections [1][2][3][4][5], ionosphere [6] and troposphere model parameters [7], and antenna phase center offsets and variations must be provided in order to obtain precise results [8]. In PPP, orbit and clock errors are of major importance.…”