GNSS Atmospheric and Ionospheric Sounding – Methods and Results - Global Navigation Satellite Systems: Signal,Theory and Applications - page 359

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GNSS Atmospheric and Ionospheric Sounding
- Methods and Results

Shuanggen Jin
Shanghai Astronomical Observatory, Chinese Academy of Sciences
China

1. Introduction

The GPS atmospheric and ionospheric delays have been considered as an error source for a
long time. In 1992 when the GPS became fully operational, Ware (1992) suggested limb
sounding the Earth atmosphere using GPS atmospheric delay signals. In April 1995, the
small research satellite of Microlab-1 was successfully put into a Low Earth Orbit (LEO) to
validate the GPS radio occultation method (Feng and Herman, 1999). Since then, the
GPS/Meteorology Mission (GPS/MET) has been widely used to produce accurate, all
weather pressure, temperature, density profiles in the troposphere and the ionospheric total
electron content (TEC) as well as electron density profiles (Rocken, 1997; Hajj and Romans,
1998; Syndergaard, 2000), to improve weather analysis and forecasting, monitor climate
change, and monitor ionospheric events. While traditional observing instruments, e.g. water
vapour radiometer (WVR), incoherent scatter radars (ISR), ionosonde, topside sounders
onboard satellites, in situ rocket and satellite observations, are expensive and also partly
restricted to either the bottomside ionosphere or the lower part of the topside ionosphere
(usually lower than 800 km), such as ground based radar ionospheric measurements. While
GPS satellites in high altitude orbits (~20,200 km) are capable of providing details on the
structure of the entire atmosphere, even the plasma-sphere. Moreover, GPS is a low-cost, all-
weather, near real time, and high-temporal resolution (1~30s) technique. Therefore, GPS is a
powerful tool to sound the atmosphere and ionosphere as well as their application in
meteorology, climate and space weather.

2. Tropospheric sounding

The tropospheric delay of GPS signal through the neutral atmosphere was one of major
error sources in navigation and positioning, which contributes a bias in height of several
centimetres (Tregoning et al. 1998). Nowadays, GPS has been used to determine the zenith
tropospheric delay (ZTD) (Jin and Park, 2005) through mapping functions (Niell, 1996).
The ZTD is the integrated refractivity along a vertical path through the neutral
atmosphere:

∞

−
== ∫

6

ZTD c τ 10 N s ds ( ) (1)

0