Ch 30. GNSS for Neutral Atmosphere and Severe Weather Monitoring

Hugues Brenot, Royal Belgian Institute for Space Aeronomy, Belgium

Chapter Overview: The severe weather is defined by a range of meteorological events, such as pouring rain, flashfloods, thunderstorms, heavy snow or freezing rain. The water vapor content of the neutral atmosphere is a key parameter for all these events, as it influences cloud formation, water redistribution and temperature control. Thus, accurate monitoring of atmospheric water vapor distribution is essential in predicting the severity and life cycle of heavy rain or other extreme events. Since the early 90’s, GNSS became a key technique in operational meteorological observations, as in any weather condition, it provides measurements of wet delays and integrated water vapor contents (IWV), with high precision and stability in time. After presenting a historical background about the correction of radio signals through the neutral atmosphere, an overview of the process used to retrieve tropospheric parameters from geodetic software is presented. Then following on from this, the conversion technique of these parameters into wet delays and water vapor contents is described. The use of GNSS meteorology for monitoring severe weather is then illustrated‚ highlighting the interest in very short-range forecasts, which is called nowcasting. Finally, future applications and synergy with other techniques is mentioned using derivative products.

On this page you can:

Obtain hi-res copies of selected figures from the chapter, for use with attribution.
See a cartoon describing the three tropospheric parameters retrieved in GNSS meteorology.
Take a look at an illustration about the interest of using GNSS products (zenith total delays of the neutral atmosphere, horizontal delay gradients, and on-way post-fit residuals) in order to study a flashflood event

Figure 30.3: Illustration of the contribution of the Zenith Total Delay of the neutral atmosphere (ZTD), delay gradients‚ and one-way post-fit residuals to Slant Total Delays (STD) for the direction of a given satellite (10° elevation and 90° azimuth). The azimuth (α) is the angle relative to the north in the clockwise direction (α = 180^∘ + α’). The contribution of these three tropospheric parameters is respectively, L_sym^10° (symmetric isotropic contribution), L_az^(10°,90°) (asymmetric anisotropic contribution), L_az^(10°,90°) = residuals (10°,90°). The residuals contain any signal not modeled and absorbed by the adjustment of the first two tropospheric parameters (i.e. ZTD and gradients). In some cases, residuals can represent an additional contribution to the tropospheric delay or the multipath effect (see Chapters 22 and 34).

Source: Chapter 30 “GNSS for Neutral Atmosphere and Severe Weather Monitoring” H. Brenot, From: “Position, Navigation, and Timing Technologies in the 21st Century”, Morton, van Diggelen, Spilker, and Parkinson. IEEE-Wiley 2021.

Figure 30.5: Contributions to slant delays (along the axes in black), for the direction of satellite PRN09 (trajectory in brown line; elevation in gray and azimuth described by cardinal points in black), mapped at 90° for CHRN (Château-Renard) station on 8 September 2002 during a flashflood in southeastern France (convective cell located northwestern of CHRN at 16:00 UTC). The red line shows the isotropic contribution (L_sym), the black line the additional anisotropic contribution (L_sym + L_az), and the blue line the STD with residuals (L_sym + L_az + L_res). Note that for all these contributions, a delay of 2.4 m has been subtracted to show the variations of the slant delays more clearly.