GPS Satellite Surveying, 4th Edition

Chapter 8Troposphere and Ionosphere

The impact of the atmosphere on GNSS observations is the focus of this chapter. In Section 8.1 we begin with a general overview of the troposphere and ionosphere as it relates to GPS satellite surveying and introduce the general form of the index of refraction. Section 8.2 addresses tropospheric refraction starting with the expression of refractivity as a function of partial pressure of dry air, partial water vapor pressure, and temperature. The equation for the zenith hydrostatic delay (ZHD) by Saastamoinen (1972), the expression for the zenith wet delay (ZWD) by Mendes and Langley (1999), and Niell (1996) to relate slant delays and zenith delays are given without derivation. We then establish the relationship between the zenith wet delay and precipitable water vapor (PWV).

Section 8.3 deals with tropospheric absorption and water vapor radiometers (WVR) that measure the tropospheric wet delay. We present and discuss the radiative transfer equation and the concept of brightness temperature. To demonstrate further the principles of the water vapor radiometer, we discuss the relevant absorption line profiles for water vapor, oxygen, and liquid water. This is followed by a brief discussion on retrieval techniques for computing wet delay and on radiometer calibration using tipping curves.

Section 8.4 concentrates on ionospheric refraction. We begin with the Appleton-Hartree formula for refraction index and derive expressions for the first-order, ...