GPS Meteorology

GPS Meteorology by Wayan Suparta

The book can be found here. In terms of concept, GPS meteorology has been introduced by Bevis et al. (1992). Brief of concept explanation is now appear at wikipedia. The book describing how that GPS meteorology can be applied for atmospheric studies in Antarctica. Antarctica is the coldest, driest, windiest, and most isolated continent on Earth. It is situated in the region of the Southern Hemisphere, where Earth magnetic field is very strong than the equator region. The concept is using the GPS receiver and meteorological sensors to measure the water vapor content in the atmosphere. For ground-based, the system is placed at fixed location on the Earth, and for the space-based it is placed at low-Earth orbit (LEO) satellite. The purpose is to measure precipitable water vapor (PWV) globally with high temporal and spatial variation and capable used as an indicator of global climate change as well as to support space weather prediction [1]. The data obtained would be valuable for meteorological applications such as improving numerical weather prediction (NWP), nowcasting and forecasting, and viable use to study the thunderstorms, flooding, natural climate variability (global warming, climate change and El Niño–Southern Oscillation), precipitation budget, teleconnections, terrestrial coupling, etc. For ground-based how the system work? When the radio signals traveling through the Earth’s atmosphere to a receiver on the ground, it is retarded and affected significantly by the presence of free electrons in the ionosphere and the refraction. The refraction of the GPS signal is induced by refractivity of gases, hydrometeors, and other particulates in the neutral atmosphere (the troposphere and stratosphere). During the propagation, the difference between transmits time and receiver time is so-called pseudorange. Accurate pseudorange determination from GPS data is required to account all of these propagation effects and time offsets. For detail, you can find here the concept. Figure 1 shows how to setup the measurement system for PWV based on the ground-based GPS meteorology.

Why we use the GPS? As mentioned above, the data provided is with high resolution and capable used not only for the study of lower atmosphere phenomena, but it can use to study the dynamic of upper atmosphere through total electron content (TEC) as one of indicators. The system is relatively stable for long duration (3~5 years) without any calibration. As long as no disruption on electricity and PC, the system is fine in recording the data. For studying the lower atmosphere dynamics, we also successfully develop one-system that can compute the GPS meteorology parameters which include PWV, ZTD, ZWD and ZHD, so-called the Tropospheric Water Vapor program (TroWav). The source code for TEC calculation was also developed using MATLAB.