Simultaneous Troposphere Estimation with Precise Point Positioning

• Applicant: Professor Dr. Thomas Hobiger
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography ; Atmospheric Science
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465090690

Troposphere delay remains a major error source for precise GNSS (Global Navigation Satellite System) positioning. The hydrostatic component of troposphere delay is well described by empirical models, but the wet component depends on the content of water vapor, which varies rapidly over time and space. Therefore, the wet delay has to be estimated together with the coordinates of the receiving antenna. In this way, a very dense network of GNSS ground stations turns into a powerful all-weather tool for remote sensing of water vapor in the troposphere, which is also called GNSS meteorology. Other than state-of-the-art approaches for dealing with wet troposphere delay, we will demonstrate that it is feasible that the 4-D wet troposphere refractivity field can be retrieved from simultaneous processing of undifferenced and uncombined multi-GNSS multi-frequency observations by using a network of ground and moving GNSS stations. We name this revolutionary method the Simultaneous Troposphere Estimation with Precise Point Positioning (STEPPP). Contrary to classical GNSS tomography, STEPPP operates on raw observation data instead of products. Values of wet refractivity in grid nodes are estimated from all stations simultaneously, i.e., they appear as common parameters in Precise Point Positioning (PPP). Wet refractivity obtained from STEPPP can be further converted to water vapor density. Thus, a complete 4 D water vapor distribution model is obtained. The research project includes the development of functional and stochastic models for the STEPPP approach, taking into account a variety of data sources as well as spatio-temporal correlations of the refractivity field. We will study the structure of the grid depending on the receivers' locations and algebraic/numerical limitations. We will develop a dedicated software-suite which implements STEPPP on a multi-threaded architecture. We will use simulated GNSS observations and sensor data to validate both the STEPPP model and the software. Then we will perform real-data experiments, using a dense network of receivers distributed in a challenging environment, e.g., an urban area. Refractivity fields obtained with STEPPP will be validated against classical GNSS tomography, GNSS radio occultation and water vapor radiometer. Additionally, we will explore the potential of low-cost receivers to provide reliable troposphere estimates and investigate applications of STEPPP for positioning, navigation, timing (PNT) and meteorology.

• DFG Programme: Research Grants
• International Connection: Poland
• Cooperation Partner: Professor Dr. Tomasz Hadas