Realtime PPP Position Error Monitoring

Global Navigation Satellite System (GNSS) technology pervades a multitude of devices we use in our daily lives, from single frequency navigation devices on consumer grade smart-phones to multi-frequency receivers used as part of critical national infrastructure. Precise Point Positioning (PPP) is methodology for validating and correcting positional data that is growing in use across industries that rely on GNSS. However, PPP is not without its limitations or accuracy concerns. Like most space based systems it is still vulnerable to Space Weather and ionospheric conditions.  

That is where the ASTRA PPP Tool comes in. Through the NOAA funded PPP SBIR project, ASTRA has demonstrated a framework for nowcasting positioning errors for single and dual-frequency GPS receivers using data from ground based GPS receivers across the United States. These maps quantify the positioning errors in real-time, while also providing a proxy measure of GNSS signal degradation as seen by ground based receivers.

Position Errors


Precise Point Positioning (PPP) can be affected by many factors, including tropospheric and ionospheric delays. By accounting for these errors, it can be assumed that any errors in the previously known locations will be caused by space weather effects. This can then be used by critical positioning services to understand the accuracy of GPS based positioning in a given area. ASTRA's PPP Tool uses data collected by the ground stations to calculate real-time position errors.


The Rate Of TEC Index (ROTI) is defined as the standard deviation of the rate of TEC and provides a measure of space weather activity. ASTRA has shown that the derived ROTI map is quite similar to the phase scintillation index maps. However the ROTI maps generated by ASTRA PPP Tool provide a more robust data product. The maps show the ROTI values calculated from data collected at receivers across the nation, for each visible GPS satellite


Most Recent ROTI Map

Mitigate the impacts of space weather.

ASTRA can provide expertise in understanding space weather impacts on positioning errors and signal dropouts due to ionospheric scintillation.


ASTRA also maintains an archive of GNSS data to generate positioning error and ROTI maps for past space weather events. Fill out the contact form to acquire recent data sets and to learn more.