GNSS-BICS - GNSS Bias Calibration System

P. D'Angelo, J. Pulido, A. Fernandez, J. Bandeiras, P. Vieira, P. Silva, M. Bento, F. Amarillo

Abstract:	The usage of GNSS receivers onboard LEO satellites is becoming quite common, or even standard, for position and time determination, given the excellent performances that can be achieved (e.g. JASON-2/GPSP, future Sentinels), or used with scientific objectives like radio occultation, (e.g. METOP/GRAS). Compared to measurements gathered by ground stations, GNSS multi-frequency observables from LEOs are mostly unaffected by the ionosphere, therefore representing a very especial source of information about the GNSS satellites Signal-In-Space Biases Amongst different Frequencies (SISBAF). Nowadays, both SISBAF and ionospheric Total Electron Content (TEC) values are estimated at the different GNSS Control Centers by processing GNSS multi-frequency observables gathered by ground sensor stations, following the approach described in [1]. For example, in Galileo this is performed by the Galileo Independent Orbits and Clocks Estimation Facility IOCE, developed by DEIMOS Engenharia, which uses the algorithms proposed in [2] and [3]. Since the used measurements are affected by the ionosphere, the estimation of both types of parameters is performed in a joint process that provides an accuracy of 10-15 centimeters (1-s) for SISBAF. With the availability of GNSS measurements from LEO, the estimation of SISBAF and TEC can be de-coupled. On a first step, SISBAF can be estimated with an accuracy of a few centimeters (1-s) using the LEO measurements. On a second step, TEC values are estimated using the ground measurements, taking advantage of the improved SISBAF estimation performed in the first step. From the user side, the linkage between the improved SISBAF and the apparent clocks would allow reducing the User Equivalent Range Error (UERE) for many types of GNSS receivers, either single-frequency (SF) or multi-frequency (MF); the improvement in the TEC estimation would also allow decreasing the ionospheric contribution to the SF-UERE. The purpose of this paper is to present the GNSS Bias Calibration System as it has been preliminary defined in GNSS-BICS project, being carried out by DEIMOS Space (Spain) and DEIMOS Engenharia (Portugal) in the frame of the ESA’s General Studies Programme (GSP). This study consists on the definition of a system capable of estimating in pseudo-real-time the SISBAF, benefiting from LEO observations and using this information for an improved TEC estimation. This system represents a complementary and independent ground infrastructure that does not require the modification of any of the space systems currently in use. The projects includes the development of a prototype (GNSS-BICS-P) with the proposed algorithms and processing steps, and capable of processing real data, with the objective of assessing the improvements that the additional GNSS observations coming from LEO S/C have in the accuracy of the SISBAF and TEC estimations and its impact in the UERE at user level.
Published in:	Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012) September 17 - 21, 2012 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2702 - 2708
Cite this article:	D'Angelo, P., Pulido, J., Fernandez, A., Bandeiras, J., Vieira, P., Silva, P., Bento, M., Amarillo, F., "GNSS-BICS - GNSS Bias Calibration System," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 2702-2708.
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