Fluctuations of radio occultation signals in sounding the Earth's atmosphere

Valery Kan,Viktoria F Sofieva,Michael E Gorbunov

doi:10.5194/amt-11-663-2018

Abstract

Abstract. We discuss the relationships that link the observed fluctuation spectra of the amplitude and phase of signals used for the radio occultation sounding of the Earth's atmosphere, with the spectra of atmospheric inhomogeneities. Our analysis employs the approximation of the phase screen and of weak fluctuations. We make our estimates for the following characteristic inhomogeneity types: (1) the isotropic Kolmogorov turbulence and (2) the anisotropic saturated internal gravity waves. We obtain the expressions for the variances of the amplitude and phase fluctuations of radio occultation signals as well as their estimates for the typical parameters of inhomogeneity models. From the GPS/MET observations, we evaluate the spectra of the amplitude and phase fluctuations in the altitude interval from 4 to 25 km in the middle and polar latitudes. As indicated by theoretical and experimental estimates, the main contribution into the radio signal fluctuations comes from the internal gravity waves. The influence of the Kolmogorov turbulence is negligible. We derive simple relationships that link the parameters of internal gravity waves and the statistical characteristics of the radio signal fluctuations. These results may serve as the basis for the global monitoring of the wave activity in the stratosphere and upper troposphere.

Highlights

For the first time the regular radio occultation (RO) monitoring of the Earth’s atmosphere was implemented with the aid of the low Earth orbiter (LEO) Microlab-1, which was equipped with a receiver of highly stable GPS signals at wavelengths of λ1 = 19.03 cm and λ2 = 24.42 cm at a sampling rate of 50 Hz (Ware et al, 1996)
The averaging of RO signal fluctuations along the whole ray inside the atmosphere damps the influence of intermittence, which is typical for turbulence under stable stratification conditions
We presented simple relationships and theoretical estimates of the amplitude and phase variances of RO signal for typical parameters of 3-D spectra based on two models: (1) the Kolmogorov turbulence and (2) saturated internal gravity waves (IGWs)

Summary

Introduction

For the first time the regular radio occultation (RO) monitoring of the Earth’s atmosphere was implemented with the aid of the low Earth orbiter (LEO) Microlab-1, which was equipped with a receiver of highly stable GPS signals at wavelengths of λ1 = 19.03 cm and λ2 = 24.42 cm at a sampling rate of 50 Hz (Ware et al, 1996). Occultation-based methods of sounding atmospheric inhomogeneities have a long and successful history. They were used for sounding the atmospheres of other planets of the solar system, using occultations of stars and artificial satellites (Yakovlev et al, 1974; Woo et al, 1980; Hubbard et al, 1988).

Objectives

Discussion

Conclusion