Michel Tossaint

Enhanced Precise Point Positioning for GNSS Users

This paper summarizes the main results obtained during the development of an Enhanced Precise Point Positioning (EPPP) Global Navigation Satellite Systems multifrequency user algorithm. The main innovations include the application of precise ionospheric corrections to facilitate the resolution of undifferenced carrier phase ambiguities, ambiguity validation, and integrity monitoring. The performance of the EPPP algorithm in terms of accuracy, convergence time, and integrity is demonstrated with actual GPS and simulated Galileo data. This can be achieved with very limited bandwidth requirements for EPPP users (less than 300 b/s for dual-frequency GPS data).

Wide Area RTK: A satellite navigation system based on precise real‐time ionospheric modelling

[1] The Wide Area Real Time Kinematic (WARTK) is an augmentation system concept for multi-frequency users based on precise real-time ionospheric modeling. It is able to provide a high accuracy and integrity GNSS positioning service over continental areas using the infrastructure of a network of permanent ground monitor stations, such as the European Geostationary Navigation Overlay Service (EGNOS) network of Ranging and Integrity Monitoring Stations (RIMS) in Europe. In this way, it allows an additional benefit to be obtained from these reference stations, that is, the network has the potential to support two independent systems: a satellite-based augmentation system, such as EGNOS, and a high-precision positioning service, based on WARTK. Indeed, thanks to the accuracy of the ionospheric corrections provided, WARTK users have available in real-time an extra constraint per satellite between the carrier phase ambiguities, which helps solve them quickly. Once such ambiguities have been solved, the GNSS user obtains navigation accurate to within 20 cm at the 95th percentile (about 10 cm RMS). Moreover, this precise positioning is achieved in a few minutes (with two frequency signals) or in a single epoch, after initial convergence of the tropospheric delay (with three frequency signals), even up to hundreds of kilometers away from the nearest reference station. While previous WARTK research has been devoted to implementing the concept and assessing its feasibility, considering in particular the accuracy achievable, the work reported in this paper focused on consolidating the results by analyzing a large and representative data set, and on deeper analysis of the integrity issue. It was carried out in the context of the Multi-constellation Regional System (MRS) project, within the European Space Agency GNSS Evolution Programme, with the aim of designing a high accuracy service for GPS and/or Galileo. Three months of actual data, from more than 25 permanent GPS stations in Europe, have been processed (some of them as a roving user), for high-, mid- and low-solar cycle conditions (in 2002, 2004 and 2006 respectively). In addition, several ionospheric storms occurred during the selected periods, with Dst values reaching up to � 150 nT. Results based on these data show that user domain integrity was maintained for baselines of up to 400 km. At the 95th percentile, the daily horizontal and vertical position errors were 20 and 30 cm, respectively, and the corresponding protection levels were about 1 and 2 m. The convergence time was around 5 minutes with actual GPS constellation data. The benefits of using a multi-constellation system were also studied, with simulated GPS and three-frequency Galileo data, showing that it is possible to reduce the convergence time to a few seconds.

Integrated navigation and communication system based on OFDM

In this paper, an Orthogonal Frequency-Division Multiple Access (OFDMA) signal based on the IEEE 802.16 WiMAX standard with integrated navigation and communication capabilities is presented. The work has been carried out by DEIMOS Space under ESA contract for the Feasibility Study for a Reduced Planetary Navigation and Communication System (PLANCOM), which aims the definition of a local infrastructure for future Mars and Moon exploration mission using an integrated, flexibly and low-cost approach. An integrated communications and navigation signal covering all requirements for human, robotic, surface assets, and orbit vehicles in a planetary environment (in the context of this paper, “planetary” refers to Mars and Moon) has been devised, following the guidelines of the Aurora Programme.

StereoSAR: a multi-static SAR mission concept to enhance Sentinel-1 capabilities for measuring ocean dynamics

We present a new mission concept, referred to as StereoSAR, with as primary aim to measure ocean surface currents at sub-mesoscales. To improve our understanding of the role surface currents play in a large variety of geophysical processes the mission will gather global measurements with high spatial and temporal resolution. A multi-static configuration based on a receive-only C-band dual polarimetric Synthetic Aperture Radar system working in synergy with Sentinel-1 is proposed. The Doppler Centroid Anomaly technique is used in order to measure Total Surface Current Velocity vectors by combining the mono-static observation and the squinted bi-static one. Simultaneous retrieval of Ocean Surface Wind Vectors and Ocean Swell Spectra is also performed. This paper presents an overview of the proposed mission concept and scenario. Some issues specific to multi-static Synthetic Aperture Radar are described and solutions offered. Finally, a preliminary performance assessment of the mission concept is included.

Satellite navigation data mining (SENDAI)

SENDAI is a project funded by ESA under the European GNSS Evolution programme to develop algorithms and models for estimation of navigation satellites orbit and clock errors, and their failure rates.