GPS & Meteorology: exploring the confines of GPS applications
Meteorology has been for hundreds of years a key case of study for science and therefore, numerous measurement instruments have been utilised for weather forecasting purposes. Nowadays, with the so called remote sensing, which relays on the exploitation of different kind of signals for sensing physical characteristics of an area, GPS has become a key element for meteorology study.
Yes, the same GPS we all use to navigate towards our destination. This system provides us with signals that are useful for much more than positioning. Today we wil see the tight relationship that exists between navigation satellites and meteorology.
But how is it possible that a signal which is intended to povide the user with a location on Earth can also be used for such a different purpose as weather forecasting? The answer remains in an element which is a common root of both GPS and meteorology. On its way from the satellite, the GPS signal travels through space and enters into the Earth by traversing its atmosphere. Within it, there are two layers that strongly affect GPS: troposphere and ionosphere. In fact, when our smartphone, GPS receiver or any other device carrying a GPS chip outputs our position, it must first correct for the errors produced by the atmospheric bending and delay. These errors are the common root between GPS and meteorology.
Now that we are aware of these kind of GPS errors, we can mention that since the signal is slowed (delayed) and refracted (bended) by the atmosphere, GPS meteorology can be carried out by characterizing these phenomena. GPS based meteorology can be devided into two areas: space-based and ground-based. The former lays on the measurement of the signal’s bending angle produced by the atmospheric refraction, while the latter is based on the measurement of the signal delay.
Space-based GPS meteorology
The main idea behind space-based GPS meteorology relays on measuring the signal’s bending angle by the atmosphere. The method employed for this is GNSS Radio Occultation (GNSS-RO). Actually the system COSMIC has more than six satellites in orbit to apply the RO conccept and accurately measure water vapour, pressure and temperature with global coverage, as well as electron density in the ionosphere, more related to space weather. This method can produce atmospheric profiles from about 40 km to the surface, to almost the LEO satellites height, which is about 800 km.
Ground-based GPS meteorology
Differently from the previous appoach, these techniques are based in measuring the signal delay caused by the atmosphere with fixed receivers on the ground. Space-based was focused in radio occultation, but ground-based is focused in two different methods: Slanth-Path Signal Delay, which measures the signal delay on its way from the satellite towards a point on Earth, and Integrated Precipitable Water Vapor, which gives the total precipitable water vapor directly above the site.
These meteorological applications of GPS rely on the remote sensing category, being just another example of GNSS applications taking advantage of the signal structure. As we can see, GPS is more than just positioning.
Thank you for reading!
|Businger, Steven, University of Hawaii. Applications of GPS in Meteorology. Retrieved from: https://www.gps.gov/cgsic/states/2009/honolulu/businger.pdf|
|UCAR. NEWLY RELEASED SATELLITE DATA POISED TO SIGNIFICANTLY IMPROVE WEATHER FORECASTS. Retrieved from: https://news.ucar.edu/132710/newly-released-satellite-data-poised-significantly-improve-weather-forecasts|
|UCAR. Global Navigation Satellite System Radio Occultation (GNSS-RO). Retrieved from: https://www.cosmic.ucar.edu/what-we-do/gnss-radio-occultation/|