Applications of global navigation satellite systems in upper and lower atmosphere research over the Philippines
Global navigation satellite systems (GNSS) were originally used for the navigation of vehicles and other related activities. Given the time of flight of the radio waves obtained by the receiver from the satellites, the receiver calculates its geographic position. However, these radio waves encounter several sources of errors, such as receiver and satellite biases, orbital errors, relativistic effects, and atmospheric effects. Only after removing these errors can one determine its position accurately and precisely. In recent years, GNSS has been used to study lower and upper atmospheres. Here, the errors brought about by lower and upper atmospheric effects are used to estimate specific atmospheric parameters, such as precipitable water vapor for the lower atmosphere and total electron content in the upper atmosphere. Precipitable water vapor is a quantitative measure of the moisture content in the atmosphere. It is a measure of how much moisture can be converted into precipitation, which has a great effect on hydro-meteorological processes.
On the other hand, the total electron content measures the ionization in the ionosphere (the ionized part of the upper atmosphere). The ionization in the region brought about by solar radiation affects radio-wave propagation. At lower frequencies, the ionosphere acts like a mirror where signals from the ground can traverse farther distances through reflection off this layer. At higher frequencies, radio waves pass through. Any transient changes in the state of the ionosphere could affect technological applications that use radio wave propagation, such as navigation and communication. In this work, observations of these parameters are done over the Philippine context—this research is done to understand better how these parameters vary in time and space.