Residuals of Tropospheric Delays from GNSS Data and Ray-Tracing as a Potential Indicator of Rain and Clouds

Abstract

The Global Navigation Satellite System (GNSS) is commonly recognized by its all-weather capability. However, observations depend on atmospheric conditions which requires the induced tropospheric delay to be estimated as an unknown parameter. In the following study, we investigate the impact of intense weather events on GNSS estimates. GNSS slant total delays (STD) in Precise Point Positioning technique (PPP) strategy were calculated for stations in southwest Poland in a 56 days period covering several heavy precipitation cases. The corresponding delays retrieved from Weather Research and Forecasting (WRF) model by a ray-tracing technique considered only gaseous parts of the atmosphere. The discrepancies are correlated with rain rates and cloud type products from remote sensing platforms. Positive correlation is found as well as GNSS estimates tend to be systematically larger than modeled delays. Mean differences mapped to the zenith direction are showed to vary between 10 mm and 30 mm. The magnitude of discrepancies follows the intensity of phenomena, especially for severe weather events. Results suggest that effects induced by commonly neglected liquid and solid water terms in the troposphere modeling should be considered in precise GNSS applications for the atmosphere monitoring. The state-of-art functional model applied in GNSS processing strategies shows certain deficits. Estimated tropospheric delays with gradients and post-fit residuals could be replaced by a loosely constrained solution without loss of quality.

The Convective Rainfall Rate from Cloud Physical Properties Algorithm for Meteosat Second-Generation Satellites: Microphysical Basis and Intercomparisons using an Object-Based Method

“…The evolution of the CRPh includes the investigation of frequencies that can be used 24/7 to derive the microphysical information of the cloud. The integration of more direct microwave information from orbital radiometers [38,39], radars [40][41][42][43][44] or by using attenuation techniques [45][46][47][48] is another possible avenue for the improvement of the product, although the coarse spatial and temporal resolutions may preclude the operational use for nowcasting. The latency of the microwave products is another concern.…”

The Convective Rainfall Rate from Cloud Physical Properties Algorithm for Meteosat Second Generation Satellites: Microphysical Basis and Intercomparisons using an Object-Based Method

“…Evolution of the CRPh includes the investigation of frequencies that can be used 24/7 to derive microphysical information of the cloud. The integration of more direct microwave information from orbital radiometers [39][40], radars [41][42][43][44][45] or using attenuation techniques [46][47][48][49] is another possible avenue for improvement of the product albeit the coarse spatial and temporal resolutions may preclude the operational use for nowcasting. The latency of the microwave products is another…”

Modeling the Slant Wet Delays From One GPS Receiver as a Series Expansion With Respect to Time and Space: Theory and an Example of Application for the Tahiti Island

“…GPS carrier phase postfit residuals contains all unmodeled tropospheric effects not covered by the estimated tropospheric parameters and other unmodeled effects such as multipath, errors in antenna-phase center variations, or satellite clocks [7], [36]- [38], [43]. Some studies add them to the SWD estimates, but this is controversial as residuals are supposed to be residuals that is showing up no correlation with the SWD values, or even better, being white noise [40], [41]. In our case, the postfit phase residuals are the zero-differenced residuals based on the PPP approach in our GPS data processing.…”

“…It can be noticed that the postfit residuals and the application of north and east horizontal gradients in GPS data processing based on Bernese Software Version 5.2 are only minor amplitude components in the derivation of SWDs [41].…”