The first order ionospheric term (I1) is the main contributor to the ionospheric delay of GNSS observations, compared with the less than 0.1% corresponding to the higher order ionospheric terms. However, higher order ionospheric effects (I2+) are one of the main limiting factors in very precise GNSS processing, for applications where millimeter accuracy is demanded.
Figure 1. I2+ corrections for L1 and L2 signals, station KUTN, 24-30 October 2014.
The consortium of Leica Geosystems Poland, WUELS (GNSS&Meteo team), the University of Warmia and Mazury in Olsztyn and the Technical University of Catalonia deals with higher order ionospheric mitigation under the HORION (Higher Order Ionospheric modelling campaigns for precise GNSS applications – HORION.) project, supported by the European Space Agency. This HORION project is focused on the routinely implementation over Poland of the mitigation of higher order ionospheric terms for the improvement of precise GNSS processing (like precise positioning), taking as baseline the main conclusions and suggestions provided in the ESA funded project IONO-DeCo (Hernández‐Pajares et al., 2014).
As an outcome of the project, the HORION-PL web service was developed. Its main purpose is to clear submitted user observational RINEX files from higher order (I2+) ionospheric effects, but leaving the first order effect so the user can form iono-free linear combination that will be free from I2+ effects. The service is designed to be operational over the Polish territory, however global tests are also carried out. Beta-version of the service is available here: http://www.smartnetleica.pl/o-nas/horion/#horion-pl
Hernández‐Pajares, M., Aragón‐Ángel, À., Defraigne, P., Bergeot, N., Prieto‐Cerdeira, R., & García‐Rigo, A. (2014). Distribution and mitigation of higher‐order ionospheric effects on precise GNSS processing. Journal of Geophysical Research: Solid Earth, 119(4), 3823-3837.