Internet-based Station Investigation Service
Background & Objectives
From time to time everybody working in the field of satellite navigation has need of determining a station position or characterising the quality of data coming from a monitoring station. Normally data is collected and processed with some commercial or self-developed software in the office. More accurate solutions can be obtained when precise GNSS satellite orbit and clock data are used from the Internet, like IGS data.
However, some amount of time is needed to search and obtain the right data and do the proper processing and analysis. Hence, the idea of ISIS is to ease this process by offering a web-based service to provide the best processing products in an automated way.
The products here are not auxiliary intermediate products helping the user in the processing, but are actually the final processing results. The final service is considered relevant for potential customers like engineers and researchers in satellite navigation and geodesy domains, as well as for authorities who are in need of setting up navigation sensor or monitoring stations for whatever purpose. The products will help to identify issues related to the sensor station receiver and clock quality, and also to the environmental conditions of the site.
ISIS is a processing service that allows automated processing of GNSS observation data via a web-interface. The service provides products characterising the measurement station in terms of accurate position, measurement data quality, as well as the station clock. The service automatically searches and uses the International GNSS Service (IGS) for precise satellite clock and orbit data to produce high-accuracy products.
A set of service products has been defined within a storyboard that was used as a basis for development. The storyboard contains several characteristic products for a station-like position, quality of pseudorange and carrier-phase data, range accuracy after synchronisation, signal-to-noise figures, as well as clock characteristics in terms of Allan-variance curves. Different views on these data are available, like statistics per frequency or elevation or values versus elevation and azimuth, etc. The ISIS demonstrator consists of two components: the web-component and the processing component. While for the web-component a use of standard web-hosting tools like Tomcat have been made, the processing component has been built on an internally developed software core that is called GSPF â€“ GNSS simulation and processing framework (which is a registered trademark and a product of IFEN).
This C++ software is platform independent and provides an ideal basis for data processing, algorithm development and performance analyses, and has been customised to the ISIS project needs. The GSPF allows the design of any operational data processing capability in a very modular way, thus allowing an easy replacement of algorithmic models and extensions to additional functionalities. Compared to other services that provide measurement corrections for high-accuracy data processing, the ISIS approach is quite innovative in that it provides complete solutions instead of corrections. The processing is not done at the user side, but at the central ISIS server, which is hosted and maintained by the service provider IFEN.
The objective of the service is to allow for web-based online data processing of GNSS raw data without the need for user interaction. The results from this processing allow a characterisation of a GNSS observation station. For this processing, sources of additional auxiliary data are used, for example precise satellite orbit and clock data, which are available on the Internet. The basic idea, therefore, is to make use of such available data in an automated way and take the burden of searching for and obtaining such data away from the user.
Work performed & results
The result of the ISIS project has been defined as being a service demonstrator without charging, but dependent upon the acceptance of this service, a later commercialisation is anticipated. For this purpose different service levels are defined providing products at different detail levels. The project succeeded in setting up a demonstrator service that allows for automatic GNSS data processing. The data processing carried out so far is according to the objectives of data from a single static station. The outputs are all the service products as defined within the storyboard. However, as ISIS is an operational service, the product availability is currently limited to GPS only. An extension to Galileo is foreseen at a later stage. As a result of the project, all the relevant development documentation has been generated. The final report and the user manual of the service are available to the public. Other deliverable design documentation is confidential to the consortium. At the moment the ISIS demonstrator may be used for free. The decision for a final commercialisation will be taken at a later stage when more user feedback and suggestions have been gathered and evaluated. Several further improvements have been identified like usage of EGNOS SISNet or extending the service with differential or kinematic capabilities.