For more than 20 years the International GNSS Service (IGS) has provided access to a large number of GNSS reference stations and high quality GNSS products to anyone, free of charge. To continue to support their mission of providing quality GNSS data to the public and providing convenient access to the International Reference Frame (ITRF) the IGS operates a real-time GPS/GNSS network supported by governmental, university and private sector organizations.
Real-Time GNSS Tracking Network
The real-time network provides GPS and GNSS observations from approximately 140 continuously operating reference stations. The stations provide real-time observations in RTCM 3.x format via NTRIP. The network can be accessed via free registration using tools such as BKG's free NTRIP software.
In addition to observations, the IGS along with individual analysis centres, provide precise orbit and clock products that allow users with dual frequency receivers to obtain 10 cm accuracy in real-time via their real-time product streams.
When the IGS announced their intentions to provide a real-time network as well as products for precise positioning there was some controversy as to why a non-profit organization would compete with for-profit private organizations who already offered GNSS products as well as real-time observations similar to what the IGS was proposing. Because of this, the IGS released a statement Why is the IGS involved in Real-time? outlining their position. Their main reasons for targeting the real-time domain included:
- Support public-benefit organizations for applications such as natural hazard monitoring
- Support scientific research and studies which cannot access the for-profit services due to high costs (although the cost continues to drop with more and more providers)
- Provide direct and high accuracy access to the International Terrestrial Reference Frame (ITRF)
Below is an example of the performance of the real-time orbit and clock products being used for PPP for a station in Germany (FFMJ).
The draw back of the PPP approach is that there is still a significant convergence period required before the 10cm is acheived. For example in the figure below, it takes ~50 minute for the solution to converge to 10 cm.
Additionally, obstruction to satellites, or connection loss could require the user to wait and allow for their solution to re-converge. But there are some tricks that can be used to reduce these occurrences including starting from a known point and bridging outages.
Currently, applications such as automated agriculture, deformation monitoring, ocean mapping and GIS can all benefit from PPP particularly for users requring sub-meter or decimeter level accuracy. By providing these corrections in real-time it simplifies the work flow and removes the need for post-processing of data.
Several great websites exist that provide real-time monitoring of the product streams so that users can see how the products perform without needing thier own hardware/software. These include:
Generally, these websites choose a subset of stations from the IGS network and show continuously monitoring using PPP.
Moving towards GNSS
The real-time IGS service also provides GNSS products on a demonstration basis and expects to transition to offering multi-constellation support (add in GALILEO, BEIDOU) as more satellites/stations become available and analysis centres support these constellations in real-time.