Local-Scale Precipitable Water Vapor Retrieval from High-Elevation Slant Tropospheric Delays Using a Dense Network of GNSS Receivers

Local-scale monitoring of the temporal and spatial variability of precipitable water vapor (PWV) is crucial to improve the nowcasting and forecasting of localized meteorological hazards. While GPS is now routinely employed to retrieve PWV from estimated tropospheric delays (GPS meteorology), even the densest GPS networks available have a spatial resolution of the order of tens of kilometers, which is too coarse for detecting local fluctuations of water vapor. A densification of existing networks, at least in urban areas, is necessary to provide reliable and continuous water vapor monitoring with sufficiently high horizontal resolution. Densifying existing networks down to few kilometers of inter-station distances, however, introduces at least two issues: first, a horizontal smoothing effect occurs, induced by the significant overlapping of the inverse cones above low elevation angles typically used for GPS observation processing; second, an issue of economic nature might arise if geodetic receivers are used for large-scale densifications (e.g. for early warning systems serving large cities). We tackle the first issue by using only high-elevation slant delays for PWV retrieval, and in particular by exploiting the Japanese Quasi-Zenith Satellite System (QZSS), and the second issue by investigating the use of low-cost single-frequency receivers with local ionosphere delay models. In this work we describe the results obtained in PWV retrieval from high-elevation GPS and QZSS slant delays, estimated using a dense network of receivers installed near Kyoto, Japan.