1. Mehreen RIZVI 3310408 GMAT9205 - Geopositioning
GPS METEOROLOGY
Mehreen RIZVI
GMAT Geopositioning

2. WHAT IS GPS METEOROLOGY
use of effect of atmosphere on propagation of GPS radio signals to derive info on state of (lower, neutral) atmosphere
Instruments (compatible with GPS reference stations) are now available for ground-based measurements of barometric pressure, temperature, and humidity
GPS has been developed as a tool of measuring the movement of the earth's crust by earthquakes however, almost 10 years ago it has been discovered that GPS signals can be used to measure precipitable Water vapour (PWV). This is known as GPS meteorology.
Several GPS compatible meterological instruments are now available. I have shown an example of Digiquartz MET4 instrument.

3. WHAT IS GPS METEOROLOGY
Technology now deployed world-wide to supplement GPS data
This figure shows the sensor mounted on a GPS reference station.
Next thing I’m gonna discuss are how this is achieved.
Typical GPS Reference Station

4. GPS water vapour monitoring
propagation delay caused by atmosphere on the microwaves due to H2O > or atmosphere gases, like N2, O2, Ar or CO2
Total atmospheric delay is determined using GPS
Calculated contribution by well-mixed "dry" gasses (ZHD) is then subtracted
A measure (ZWD) for absolute water vapour content of atmosphere is obtained referred to as "total precipitable water vapour“ (PWV).
The propagation delay on the microwave is 20 times stronger due to polar nature of water molecule.
GPS signals from a satellite to a surface station are delayed by existence of the atmosphere. Total zenith delay is estimated during GPS signal processing. This can be separated into Zenith Hydrostatic delay (ZHD) and zenith Wet delay (ZWD). ZHD is proportional to the surface pressure which can be easily found. ZWD is found by subtracting the ZHD from the total delay, which can then be converted into GPS-PWV by using meteorolgical observation data at the stations.
Zenith Wet Delay (ZWD) can vary from a few millimeters in desert conditions to more than 350 mm in very humid conditions.

5. GPS water vapour monitoring
Propagation path delay is proportional to
This makes it possible to solve separately for zenith delay in GPS computations
Ground-based GPS receivers (at fixed locations) can be used to gather data that can be used to determine integrated Precipitable Water Vapor (PWV).
GPS-determined PWV observations can significantly improve weather forecasting accuracy.
Absolute measurements of humidity rather than relative humidity (RH) which depends on not so well measured temperature.
Total atmospheric delay depends on zenith or elevation angle of satellite, in addition to solving for station coordinates and receiver clock delays.
It is not possible to predict wet delay with any useful degree of accuracy from surface measurements of pressure, temperature, and humidity

6. Application of GPS PWV Monitoring
This slide shows how PWV values can be used to predict extreme rainfall events. The slide shows the daily rainfall data for Nerima, Japan. On the RHS the rainfall intensity in mm is plotted, while on the LHS is the PWV. It can be seen from the figure that the peak rainfall event is preceded with a steep increase in PWV value.

7. CONCLUSIONS
GPS Meteorology – a milestone improvement in environmental sensing technology
Improved surface, coastal, and air travel safety due to more accurate prediction of storm systems
Agriculture and farming (improved crop yields)
GPS meteorology has given a whole new dimension to conventional meteorology. More precise weather forecasts and prediction of extreme weather events helps to provide better and more productive crop yields, safe and reliable air and sea travel, building industry, outdoor sports and disaster management etc.

8. THANK YOU
References
Digiquartz - GPS Meteorology [Online]. - Parroscientific Inc., 2007.  , 15. -
Remote Sensing of Atmospheric Water Vapor using GPS [Article] / auth. M Bevis [et al.] // Journal of Geophysical Research. - October 20, 1992. - Pages 15,787-15,801 : Vols. 97, No. D14.