Three methods to retrieve slant total electron content measurements from ground‐based GPS receivers and performance assessment

Abstract

The high sampling rate along with the global coverage of ground‐based receivers makes Global Positioning System (GPS) data particularly ideal for sensing the Earth's ionosphere. Retrieval of slant total electron content measurements (TECMs) constitutes a key first step toward extracting various ionospheric parameters from GPS data. Within the ionospheric community, the interpretation of TECM is widely recognized as the slant total electron content along the satellite receiver line of sight, biased by satellite and receiver differential code biases (DCBs). The Carrier‐to‐Code Leveling (CCL) has long been used as a geometry‐free method for retrieving TECM, mainly because of its simplicity and effectiveness. In fact, however, the CCL has proven inaccurate as it may give rise to TECM very susceptible to so‐called leveling errors. With the goal of attaining more accurate TECM retrieval, we report in this contribution two other methods than the CCL, namely, the Precise Point Positioning (PPP) and the Array‐aided PPP (A‐PPP). The PPP further exploits the International GPS Service (IGS) orbit and clock products and turns out to be a geometry‐based method. The A‐PPP is designed to retrieve TECM from an array of colocated receivers, taking advantage of the broadcast orbit and clock products. Moreover, A‐PPP also takes into account the fact that the ionospheric effects measured from one satellite to all colocated receivers ought to be the same, thus leading to the estimability of interreceiver DCB. We perform a comparative study of the formal precision and the empirical accuracy of the TECM that are retrieved, respectively, by three methods from the same set of GPS data. Results of such a study can be used to assess the actual performance of the three methods. In addition, we check the temporal stability in A‐PPP‐derived interreceiver DCB estimates over time periods ranging from 1 to 3 days.

A 4D tomographic ionospheric model to support PPP-RTK

“…The GNSS network is located in NSW (Australia); therefore, in order to account for the boundary conditions of the tomographic grid, endpoint-interpolating B-splines are used. For further details as to how to compute B-splines and their properties please see Zeilhofer (2008).…”

“…Altogether considered, those are the main reasons to use B-splines as basis functions for the 4D ionospheric model. Moreover, although not considered in the present work, B-splines provide tools for data compression (Mautz et al 2005;Zeilhofer 2008), a property that might help to increase the resolution of ionospheric corrections broadcast in a fashion that is compliant with the Radio Technical Commission for Maritime Services (RTCM) State Space Representation (SSR) standards.…”

A Long Baseline Three Carrier Ambiguity Resolution with a New Ionospheric Constraint

“…Each portion contains two hours of data and has been, respectively, processed by the new and old methods. We use the TFFS and positioning experiments to evaluate the AR performance [26][27][28][29][30]. In the positioning experiments, we take station HOFN as base station; its precise coordinate comes from weekly solutions.…”

Estimating and Analyzing Long-Term Multi-GNSS Inter-System Bias Based on Uncombined PPP

“…With the implementation and improvement of multi-GNSS constellations, precise point positioning (PPP) is rapidly developing from traditional GPS-only dual frequency systems to multi-system-multi-frequency systems. PPP is widely used in many areas, e.g., seismic rescue and ocean exploration [1][2][3][4][5]. As of 4 June 2019, there are 115 globally distributed satellites form the four different systems that can provide user location services.…”