Session A4c: Future Augmentation Systems, Correction Services and Integrity 2

Providing Trimble CenterPoint RTX GNSS Atmosphere Corrections - In Heterogeneous Networks and During Scintillation
Moritz Rexer, Andreas Goss, Ulrich Weinbach, Xiao Liu and Markus Brandl, Trimble
Location: Holiday 6 (Second Floor)
Date/Time: Thursday, Sep. 11, 5:08 p.m.

The ionosphere describes the charged part of the Earth’s upper atmosphere between 50km and 1000km above the Earth’s surface. It is characterized by the presence of free electrons and ions of temporarily and spatially varying density, mainly driven by solar activity. In near-polar regions and in the vicinity of the geo-magnetic equator, ionospheric scintillations make any modeling of electron density very challenging due to increased variability and high amplitudes of the total electron content (TEC). Also, the lower part of the atmosphere, known as troposphere, interferes with the GNSS ranging signals and causes a delay on the signal. Especially, the precise knowledge of the ionospheric delays are a key factor for the fast recovery of the unknown integer number of cycles of the carrier phase measurements which is essential for cm-level positioning accuracy.
Trimble, as leading provider of GNSS correction services, has been broadcasting precise models of ionospheric and tropospheric delay to its customers already for more than a decade, serving GNSS applications in agriculture, construction, surveying and the automotive sector. Trimble’s CenterPoint RTX Fast service, which is based on a dense network of GNSS receivers in Europe and North America, allows the computation of satellite-individual ionospheric slant TEC models, and models of the tropospheric delay in zenith. In these regions, the atmosphere models allow convergence to an accuracy level of 2.5cm and 5cm within 1 minute, horizontally and vertically, respectively.
With the latest generation of RTX, new gridded atmosphere and scintillation activity models will become available that can also serve smaller regions, large cities, urban areas or exposed islands with the RTX Fast service.
The new modelling approach requires only a very small number of GNSS network stations in order to generate high-resolution and precise atmosphere models. These so-called RTX grid models describe a station based model. Thereby, the RTX Server software transforms the stations’ ionosphere and troposphere observations into three parts to be disseminated to a GNSS rover for positioning, namely a polynomial and a residual part, as well as a corresponding measure of quality.
The scintillation grid models unveil Trimble's IonoGuard Technology for RTX customers. Currently it is provided for costumers in South America, keeping up their productivity also in scintillated times.
Currently, the grid model approach is under test in different networks globally relying on 20 or less network stations per area. Even tests with networks of only 6 network stations show that aforementioned demanding RTX Fast specifications are met or superseded. This means that in the near future new customers world-wide may benefit from Trimble’s top-class PPP-service in areas which are currently not served by Trimble RTX Fast corrections. In already existing RTX Fast service areas the new atmospheric models allow a seamless transition when entering or leaving an area which is served by RTX grid models.