S. S. Matyugov

Attenuation and scintillation of radio waves in the Earth's atmosphere from radio occultation experiments on satellite‐to‐satellite links

A theoretical analysis of refractive loss of radio waves by the Earths atmosphere in radio occultation measurements along the satellite-to-satellite line for various altitude profiles of the refractive index is given. Experimental results for refractive loss on the orbital spacecraft - geostationary satellite link are presented. Theoretical calculations are compared with experimental data, and a conclusion is drawn that the signal amplitude during radio occultation is strongly dependent on the layered structure of the refractive index profile. Amplitude scintillations of centimeter (λ1 = 2 cm ) and decimeter (λ2 = 32 cm ) radio waves used in radio occultation experiments are described. Dependences of the rms value of the amplitude scintillations versus the minimum altitude of the ray line for the two above wavelength bands are presented. The frequency spectra of the log-amplitude scintillations are analyzed together with the dependence of the rms amplitude on the wavelength. Experimental data are compared to the theory of scintillations in a turbulent atmosphere, and the altitude model of the structure constant of refractivity fluctuations is determined.

Investigation of the Venus atmosphere and surface by the method of radiosounding using Venera-9 and 10 satellites

Abstract Using the Venera-9 and 10 satellites radio occultation measurements of the atmosphere and bistatic radar measurements of the surface of the planet Venus were realized from October 1975 to March 1976. The altitude dependence of the molecular number density, pressure and temperature on the night and day sides were derived. An analysis is made of the stratified structure and turbulence in the atmosphere of Venus. The results of pressure measurements on the surface by the method of bistatic radar are presented. The diagrams and the tables of the parameters of the atmosphere are given.

Radio Occultation Measurements of the Radio Wave Absorption and the Sulfuric Acid Vapor Content in the Atmosphere of Venus

The results of the determination of centimeter (λ = 5 cm) radio waves absorption in the radio occultation experiments, carried out using the Venera-15and Venera-16spacecraft, are presented. The altitude distribution of the absorber substance is analyzed. The absorbing layer is shown to exist at altitudes of 64 to 58 km in the near-polar regions of the planet. At middle latitudes such an absorbing layer was not found. In the altitude range from 56 to 46 km the radio wave absorption by the sulfuric acid (H2SO4) vapor is observed. The content of the sulfuric acid vapor is shown to increase with decreasing altitude: in the mid-latitude region at altitudes of 56.7 and 53 km it equals 5 and 20 ppm, respectively, and at polar latitudes the same content of H2SO4vapor is observed at altitudes of 51.2 and 47 km, respectively. A comparison of these results with the data of radio wave absorption in the λ = 13 cm band, obtained in the Pioneer Venus Orbiterradio occultation experiments, leads to the conclusion that the obtained values of the sulfuric acid vapor content well agree in the regions of overlap of the data.

Sporadic structures and small-scale irregularity in the nighttime polar ionosphere in the period of high solar activity according to the data of radio occultation measurements on satellite-to-satellite paths

Results of the analysis of 327 sessions of radio occultation on satellite-to-satellite paths are presented. The data are taken in the nighttime polar ionosphere in the regions with latitudes of 67°–88°, and in the period of high solar activity from October 26, 2003 to November 9, 2003. Typical ionospheric changes in the amplitude and phase of decimeter radio waves on paths GPS satellites-CHAMP satellite are presented. It is demonstrated that these data make it possible to determine characteristics of the sporadic Es structures in the lower ionosphere at heights of 75–120 km. Histograms of distribution of the lower and upper boundaries, thickness, and intensity of the Es structures are presented. Dispersion and spectra of amplitude fluctuations of decimeter radio waves caused by small-scale irregularity of the ionospheric plasma are analyzed. The relation of the polar Es structures and intensity of small-scale plasma irregularity to various manifestations of solar activity is discussed. The efficiency of monitoring the ionospheric disturbances caused by shock waves of the solar wind by the radio occultation method on satellite-to-satellite paths is demonstrated.

New Applications and Advances of the GPS Radio Occultation Technology as Recovered by Analysis of the FORMOSAT-3/COSMIC and CHAMP Data-Base

Comparative analysis of phase and amplitude variations of GPS radio-holograms allows one to separate the influence of the layered and irregular structures. A possibility exists to measure important parameters of internal waves: the intrinsic phase speed, the horizontal wind perturbations, and, under some assumptions, the intrinsic frequency as function of height in the atmosphere. A new technique was applied to measurements provided during CHAllenging Minisatellite Payload (CHAMP) and the Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) radio occultation (RO) missions. As an example of this approach, we establish the atmospheric origin of amplitude and phase variations in the RO signal at altitudes 10–26 km. We observed for the first time in the RO practice examples of internal wave breaking at altitudes between 38 km and 45 km. We obtained geographical distributions and seasonal dependence of atmospheric wave activity with global coverage within the years 2001–2003.

Radio Wave Propagation Phenomena from GPS Occultation Data Analysis.

The RO remote sensing can be performed with any two cooperating satellites located on opposite sides with respect to the Earth’s limb and moving to radio shadow. Several RO missions are working now aboard the Low Earth Orbit satellites. These missions provide global monitoring of the atmosphere and ionosphere of the Earth at different altitudes with high spatial resolution and accuracy. Their data are very important for meteorology, weather prediction. The RO data can be used to detect the climate changes, connections between the ionospheric, atmospheric processes, and solar activity, and to estimate conditions for radio navigation and radio location.

Amplitude Variations in CHAMP Radio Occultation Signal as an Indicator of the Ionospheric Activity

We showed that the amplitude of GPS occultation signal is important indicator of the ionospheric activity. Amplitude is more sensitive to small-scale ionospheric disturbances than the phase of the radio occultation (RO) signals. Local mechanism of strong ionospheric influence on the amplitude and phase of RO GPS signals is described. Critical points (tangent points) in the ionosphere, where the gradient of the electron density is perpendicular to the RO ray trajectory, strongly influence on the amplitude and phase of RO signals, and introduce multi-RO ionospheric effect in the experimental RO data. Positions of the critical points depend on the structure of the ionospheric disturbances. Analytical model for description of multi-RO ionospheric effect is introduced. Model accounts for the horizontal gradients in the ionosphere and gives analytical expressions for the phase path excess and refraction attenuation of the radio wave propagating through the disturbed ionosphere. Analytical model and analysis of the CHAMP RO data indicated that the centers of strong ionospheric influence on RO signals can exist, for example, in the sporadic E-layers inclined by 3–6 degrees relative to the local horizontal direction. In this case one can observe simultaneously with atmospheric RO the appending ROs in the ionospheric layers. Multi- RO effect can be a cause of the ionospheric interference in the communication and RO signals. Multi- RO effect can be used to study the structure of the ionospheric disturbances using the amplitude variations in RO signals. Multi- RO effect allows introducing a classification of the ionospheric influence on RO signals using the amplitude data. This indicates a possibility for separating the regular and random parts in the ionospheric contribution in the RO signals.

Observation of Reflected Signals in MIR/GEO and GPS/MET Radio Occultation Missions

Recovering reflected signals in MIR/GEO (wavelength 2 and 32 cm), GPS/MET and CHAMP (wavelength 19 and 24 cm) radio occultation experiments opened new perspectives for bistatic monitoring of the Earth at small elevation angles. Experimental observation of the propagation effects at low elevation angles has also principal importance for fundamental theory of radio waves propagation along the Earth’ surface. The aim of this contribution consists of a short review of parameters of reflected signals, observed in MIR/GEO and GPS/MET experiments at wavelength 2, 32, 19 and 24 cm and in consideration of effect of boundary layer on parameters of reflected signal at low elevation angles.