Performance Analysis of Near Realtime Tropospheric Delay Estimation using Low-cost GNSS Receivers

Permanent GNSS stations are routinely used for the estimation of tropospheric delays and gradients and provide valuable atmospheric parameters for numerical weather modelling. The spatial resolution of existing geodetic GNSS networks is usually too low to retrieve the high spatial variability of atmospheric water vapour. Densifying the existing geodetic GNSS networks with low-cost receivers may provide a good solution to improve the resolution. Recently, a GNSS based atmospheric remote sensing system has been established in the Pannonian basin using both geodetic grade and lower cost permanent GNSS stations (Septentrio PolarX5 receivers). Tropospheric delays and gradients are estimated on an hourly basis and the products are disseminated in the frame of the EUMETNET E-GVAP programme. Furthermore a countrywide GNSS network was also established for agricultural applications using low-cost ublox F9P dual frequency multi-GNSS receiver. The available GNSS observations provide a good opportunity to compare the accuracy of the ZTD estimates obtained at stations equiped with geodetic grade and low-cost GNSS receivers. A key question in the application of the low-cost receivers and antennas is the lack of the proper antenna phase center models for all the available GNSS systems. To avoid this problem, both low-cost antennas used for this study were calibrated using a relative calibration technique using an absolute calibrated geodetic antenna as reference. The results show that the Septentrio PolarX5 receivers shows similar performance to the geodetic grade receivers in terms of the monthly RMS of the ZTD residuals compared to numerical weather models proving that low-cost GNSS instruments can be beneficial for the densification of existing GNSS networks used for meteorological purposes.