Water vapour GNSS monitoring

Low-cost GNSS receivers and antennas are used to deploy spatially dense networks of units capable of monitoring the integrated content of atmospheric water vapor with high spatial and temporal resolutions.
Technology demonstrated in relevant environment.
Representative model or prototype system, which is well beyond that of TRL 5, is tested in a relevant environment. Represents a major step up in a technology’s demonstrated readiness. Examples include testing a prototype in a high-fidelity laboratory environment or in a simulated operational environment.
We should actually consider two different TRLs: - the hardware (i.e. the monitoring units which will be deployed on the field) is at TRL 9, since the same GNSS units have been used by large clients of GReD for critical infrastructure (i.e. bridges, dams, high-voltage towers) and land (i.e. landslides) displacement monitoring for more than 1 year. - the overall water vapour monitoring system, which includes innovative (server-side) components such as the local ionospheric delay modelling and the continuous estimation of tropospheric delays, from which the integrated amount of precipitable water vapour can be inferred. This is more likely at TRL 6, since the technology has been demonstrated in relevant environment, namely by dedicated dense networks deployed for testing; however, it was not demonstrated in an actual operational environment, where water vapor data would have to be analysed for probabilistic nowcasting in order to issue timely early warnings.

How does it work?

One of the possible applications of GNSS receivers networks is to monitor atmospheric water vapour, e.g. in the framework of an early warning system for nowcasting or forecasting local heavy rain. Nevertheless, when we apply this system to monitor wide areas, we may need to install several hundreds of GNSS receivers in order to obtain a significant monitoring capability. In order to keep down the system cost, we use low-cost single-frequency GPS receivers (basically the same chipsets that are used within smartphones and car navigation systems). However, it is necessary to compensate for the ionosphere-induced delay, which cannot be estimated with a single-frequency signal. Therefore, we have successfully tested local ionosphere models that interpolate the ionospheric delay in order to compensate the single-frequency measurements. Local ionospheric models to be used with a dense network of low-cost receivers can be estimated by using existing dual-frequency GNSS receivers located in the vicinity of the network, as for example those belonging to existing national/regional networks. In collaboration with Proteco, a consortium of ICT enterprises based in Genoa, we have designed and developed IP67-certified weather-proof monitoring units, since this kind of units exploiting low-cost GNSS receivers was not available on the market. Although developed with the main target of precise GNSS monitoring of critical infrastructure and/or terrain deformation/movement, the same units can be used also for atmospheric water vapour monitoring, when local ionospheric models are used as explained above.