Gea and Gemini are monitoring systems based on GNSS receivers.
They are designed to monitor large structures (bridges, dams, high rise buildings) as well as landslides and subsidences.
Our GNSS monitoring systems are based on a combination of M-rovers that are placed in the zone to be monitored, R-rovers that are placed outside the monitored zone and used as reference points, and a PC running the software. The PC can also be a remote server.
Rovers are based on dedicated hardware; a GNSS receiver plus power supply and communication. The PC running our software gathers data from the deployed rovers.
GEA rover differs from GEMINI in terms of performance and thus of cost.
GEA is suited for low phenomena such as landslides or subsidence and can reach a precision of 1mm over 7 days of continuous function.
GEMINI is suited for higher rate monitoring (up to 50Hz) and therefore is best suited to structural monitoring, its precision can go below one millimeter over 7 days.
GEA and GEMINI improves the precision of GNSS system, but how do they work?
The principle is to correct the GNNS error sources, that are:
Ionospheric Delay, the Ionospheric layer contains ions particles which delay the satellites signals and affect the position accuracy. The Ionospheric delay varies with solar activity, time of year, season, time of the day and location. Ionospheric models are used to reduce ionospheric delay errors.
Tropospheric Delay Variations in tropospheric delay are caused by the changes to the humidity levels, temperature and atmospheric pressure in the troposphere. Tropospheric models are used to estimate the amount of error caused by tropospheric delay.
Multipath occurs when a GNSS signal is reflected off an object, such as the wall of a building, to the GNSS antenna. Because the reflected signal travels farther to reach the antenna, the reflected signal arrives at the receiver slightly delayed. This delayed signal can cause the receiver to incorrect calculate the position.
Orbit Errors GNSS satellites travel in very precise, well known orbits. However, the orbits do vary a small amount. Also, like the satellite clocks, a small variation in the orbit results in a significant error in the calculated position.
Receiver Noise Receiver noise refers to the position error caused by the GNSS receiver hardware and software.