Ionospheric pierce point
Encyclopedia
Most Global Positioning System
s (GPS) are subjected to errors induced by the ionosphere
. Because ionospheric delay affects the speed of microwave signals differently depending on their frequency—a characteristic known as dispersion
—delays measured on two or more frequency bands can be used to measure dispersion, and this measurement can then be used to estimate the delay at each frequency. (see Atmospheric Effects in "Sources of Errors in GPS")
The principal source of the dispersion comes from the total electron content
(TEC) in the ionosphere, along the line of sight from the satellite
to the receiver. Because it is difficult to measure the TEC along the line of sight, instead a prediction can be made using a simplified model of the ionosphere.
This model assumes that the ionosphere is a thin, uniform-density shell about the earth, located near the mean altitude of maxium TEC (approx. 350 km). Using geometry, a slant intersection with this shell model can be determined and a vertical TEC measurement inferred.
The point where the line-of-sight between the satellite and the ground receiver intersects this shell is called the Ionospheric Pierce Point (IPP).
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
s (GPS) are subjected to errors induced by the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
. Because ionospheric delay affects the speed of microwave signals differently depending on their frequency—a characteristic known as dispersion
Dispersion (optics)
In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency, or alternatively when the group velocity depends on the frequency.Media having such a property are termed dispersive media...
—delays measured on two or more frequency bands can be used to measure dispersion, and this measurement can then be used to estimate the delay at each frequency. (see Atmospheric Effects in "Sources of Errors in GPS")
The principal source of the dispersion comes from the total electron content
Total electron content
Total electron content is an important descriptive quantity for the ionosphere of the Earth. TEC is the total number of electrons present along a path between two points, with units of electrons per square meter, where 1016 electrons/m² = 1 TEC unit .TEC is significant in determining the...
(TEC) in the ionosphere, along the line of sight from the satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
to the receiver. Because it is difficult to measure the TEC along the line of sight, instead a prediction can be made using a simplified model of the ionosphere.
This model assumes that the ionosphere is a thin, uniform-density shell about the earth, located near the mean altitude of maxium TEC (approx. 350 km). Using geometry, a slant intersection with this shell model can be determined and a vertical TEC measurement inferred.
The point where the line-of-sight between the satellite and the ground receiver intersects this shell is called the Ionospheric Pierce Point (IPP).