Monitoring of the Neutral Atmosphere
Global navigation satellite system (GNSS )-based atmosphere sounding techniques have become a widely recognized and operationally used remote sensing tool. A major milestone of this development was the beginning of the continuous use of GNSS data for impr
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Gunnar Elgered, Jens Wickert
Global navigation satellite system (GNSS)-based atmosphere sounding techniques have become a widely recognized and operationally used remote sensing tool. A major milestone of this development was the beginning of the continuous use of GNSS data for improving regional and global forecasts in 2006. The principle behind these techniques is the utilization of atmospheric propagation effects on the GNSS signals on their way from the navigation satellites to receivers on the ground or aboard satellites. The atmosphere delays the time of arrival and introduces a curvature of the signal path. These effects can be accurately estimated and be used for the monitoring of the atmospheric variability. There are two different observation geometries. Therefore, we focus in the first part of this chapter on ground-based networks which are used to estimate the amount of water vapor above each receiver site. The second part deals with the use of radio occultation measurements from GNSS receivers aboard low Earth orbit satellites for global atmosphere sounding. We introduce and describe both techniques which provide observations suitable for the short-term weather forecasting and the long-term time series for climate research and monitoring.
This chapter deals with two distinctly different geometries: observations using ground-based global navigation satellite system (GNSS) networks and occultation observations from low Earth orbit (LEO) satellites. These are illustrated by the sketches in Fig. 38.1. In both geometries, the refractivity along the propagating path is determined by the atmospheric properties mainly in terms of pressure, temperature, and humidity. The main application of the ground-based geometry is to infer the water vapor content above each receiver site on the ground. In principle, all the water vapor can be found within the troposphere, ranging from the ground up to 8−15 km. With a reasonable view of the
38.1
Ground-Based Monitoring of the Neutral Atmosphere ................ 38.1.1 Accuracy of Propagation Delays ........... 38.1.2 From Delays to Water Vapor Content .... 38.1.3 Applications to Weather Forecasting.... 38.1.4 Applications to Climate Research......... 38.2 38.2.1 38.2.2 38.2.3 38.2.4 38.2.5 38.2.6 38.2.7 38.2.8 38.2.9 38.3
GNSS Radio Occultation Measurements .................................. Introduction and History .................... Basic Principles and Data Analysis .............................. Occultation Missions .......................... Occultation Number and Global Distribution...................... Measurement Accuracy ....................... Prospects of New Navigation Satellite Systems................................ Weather Prediction ............................ Climate Monitoring ............................ Synergy of GNSS Radio Occultation with Reflectometry ............................
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