Tropospheric delay information of GNSS microwave is estimated in GNSS processing as introduced in "Atmospheric Sensing with GPS (GNSS) ".
The studied using GNSS tropospheric delay (PWV, ZTD, slant-pass delay) for meteorology is called ground-based GNSS meteorology (GPS meteorology).
On the other hand, study of GPS radio occultation of atmosphere in GPS antenna/receiver attached in low earth orbit (LEO) satellites for meteorology is called space-based GNSS meteorology.
"GNSS (GPS) meteorology" covers both ground-based and space-based GNSS meteorology.
Real-time Estimates of GNSS PWV
The map above shows real-time GPS PWV of GEONET (GPS Earth Observation NETwork) of GSI, Japan. processed with RTNet software.
The processing is done in a few seconds just after getting real-time streaming data for all about 1,200 GEONET stations, and conversion from ZTD to PWV is done with latency of 1 to 2 minutes.
Such latency is almost similar with general meteorological sensors which also be needed to transfer observation data.
The real-time PWV data is mainly used as input for NWP (called as data assimilation).
Also, researches to use real-time PWV (or ZTD) for nowcasting of moisture/precipitation have been performed.
The primary contribution of GNSS tropospheric delay is weather forecast.