INTERFEROMETRIC PATH MODELS FOR GNSS GROUND-BASED PHASE ALTIMETRY

Within the MOSAiC expedition, GNSS was used to monitor variations in atmospheric water vapor. Based on 15 months of continuously tracked data, coordinates and hourly zenith total delays (ZTDs) were determined using kinematic precise point positioning. The derived ZTD values agree within few millimeters with ERA5 and terrestrial GNSS and VLBI stations. The derived integrated water vapor corresponds to the frequently launched radiosondes (0.08 ± 0.04 kg m⁻², rms of the differences of 1.47 kg m⁻²).

In this study, we expected to learn what are the potential effects of GNSS atmospheric delays from this unique experiment. The results show that the instrument effects on GNSS zenith delays were mitigated by using the same instrument. The radome causes unexpected bias of GNSS zenith delays in this study. Additionally, multipath effects at low-elevation observations degraded the tropospheric east gradients.

This study focuses on the comparison of different solar radiation pressure (SRP) strategies combined with a-priori information and empirical SRP parameterization. Analysis of precise orbits as well as estimated empirical SRP parameters based on various SRP strategies shows visible differences and indicates the deficiencies of a-priori model or empirical parameterization. The orbit difference patterns presented in this study may give the view on how to improve the current SRP models.

The HY-2A calibration microwave radiometer (CMR) water vapor product is validated using ground-based GNSS observations along the coastline and shipborne GNSS observations over the Indian Ocean. The validation result shows that HY-2A CMR PWV agrees well with ground-based GNSS PWV, with 2.67 mm in rms within 100 km and an RMS of 1.57 mm with shipborne GNSS for the distance threshold of 100 km. Ground-based GNSS and shipborne GNSS agree with HY-2A CMR well.

The paper focuses on the analyses of the global occurrence of equatorial plasma bubble events using S4 data that were calculated from GPS radio occultation measurements of the FormoSat-3/COSMIC mission. The advantage in using radio occultation data is that we get information not only on the occurrence and intensity of the equatorial bubble events, but also on the altitude distribution. We analyzed a 10.5-year time series of COSMIC data and demonstrated a strong dependence on the solar cycle.

Nowadays, new GNSS, like European Galileo or Chinese Beidou are available. Some members of the International GNSS Service (IGS) provide multi-GNSS precise satellite orbits, but no final orbit combination exists yet. We developed a new algorithm to combine satellite orbits for all GNSS constellations. Two different strategies were applied. To validate our results we compared our GPS orbits with the official IGS orbits. Our results show that the best strategy applied reached an agreement ~15 mm.

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The recent dramatic development of multi-GNSS constellations brings great opportunities and potential for more enhanced precise positioning, navigation, timing, and other applications. In this contribution, we develop a numerical weather model (NWM) constrained PPP processing system to improve the multi-GNSS precise positioning. Compared to the standard PPP solution, significant improvements of both convergence time and positioning accuracy are achieved with the NWM-constrained PPP solution.