A Preliminary Application of Variometric Approach for ZTD Variation Estimation in a Real-Time Scenario

The increasing occurrence of extreme rainfall events, intensified by ongoing climate change, underscores the need for tools capable of rapidly monitoring tropospheric water vapor variations. Because the tropospheric delay in GNSS signals is directly linked to the amount of water vapor in the lower atmosphere, real-time tracking of this delay offers valuable insights into the evolution of severe weather systems. This study investigates the potential of the variometric approach as a standalone technique for near-real-time estimation of tropospheric delay variations. The algorithm was tested using Galileo multi-frequency observations simulated with a Spirent signal simulator. The obtained results confirm the correct implementation of the main components of the variometric algorithm and demonstrate its capability to capture rapid changes in the tropospheric path delay. The simulated Zenith Tropospheric Delay (ZTD) was compared with a standard Precise Point Positioning (PPP) solution to assess the consistency and reliability of the estimated behavior. The comparison with PPP solutions further indicates that the reconstructed variometric ZTD differs from the PPP no-SET trend by a mean of about 1.8 mm, with an RMS of about 2.3 mm, suggesting that the residual upward drift may be partly associated with geophysical effects, most notably solid Earth tides. Overall, these findings highlight the potential of the variometric approach for real-time atmospheric monitoring and for supporting early warning systems for extreme meteorological events.