Monitoring the Water Vapor Content at High Spatio-Temporal Resolution Using a Network of Low-Cost Multi-GNSS Receivers

The global navigation satellite system (GNSS) has the capacity for remote sensing of water vapor content in the atmosphere. Post-processing of GNSS data can provide integrated water vapor (IWV) with accuracies comparable to measurements of traditional sensors, i.e., water vapor radiometers. While GNSS meteorology benefits from thousands of permanent GNSS stations operating worldwide the spatial resolution of GNSS-derived IWV is limited to tens of kilometers. Further densification of GNSS networks is achievable with low-cost GNSS receivers. We investigated the feasibility of low-cost multi-GNSS receivers for monitoring IWV. The post-processing and the real-time (RT) solution are validated against: 1) the results from a geodetic-grade GNSS receiver; 2) colocated water vapor radiometer; and 3) numerical weather model (NWM). Despite the high variability of the IWV during the validation period, the standard deviation of IWV differences with respect to the water vapor radiometer was 1.0 and 1.5 kg/
$\text{m}^{2}$
in post-processing and RT, respectively. The city-scale variability of water vapor content in the atmosphere was monitored by a network of 16 low-cost GNSS receivers deployed in the city of Wroclaw, Poland. During rapidly changing weather conditions, the disagreement between the low-cost GNSS-derived IWV field and the NWM reached up to 5.4 kg/
$\text{m}^{2}$
and interstation IWV differences exceeded 5 kg/
$\text{m}^{2}$
. It has been demonstrated that low-cost GNSS receivers are reliable tools for precise determination of IWV, also in RT. This study is the first to measure the water vapor content with a spatial resolution of single kilometers and to present a significantly diversified city-scale IWV field.