A numerical technique for two‐way radio occultations by oblate axisymmetric atmospheres with zonal winds

Schinder, P. J.; Flasar, F. M.; Marouf, E. A.; French, R. G.; Anabtawi, A.; Barbinis, E.; Kliore, A. J.

doi:10.1002/2015rs005690

Cited by 28 publications

(58 citation statements)

References 22 publications

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“…Note that the contributions of the classical Doppler shift and neutral gas are eliminated in this weighted difference. This result also holds in the relativistic case where all non-plasma-related shifts are proportional to frequency (Bocanegra-Bahamón et al, 2018;Pätzold et al, 2004;Schinder et al, 2015). Consequently, the rate of change of the plasma column density along the ray path can be determined straight-forwardly from time series of the received frequency at two different frequency bands.…”

Section: From Time Series Of Frequency To Slant Profiles Of Integratementioning

confidence: 87%

“…Its scientific payload included the Radio Science Subsystem (RSS; Kliore et al, 2004). The investigations conducted by the RSS instrument included radio occultation observations of the atmosphere and ionosphere of Saturn (Del Genio et al, 2009;Moore et al, 2006;Nagy et al, 2009Nagy et al, , 2006Schinder et al, 2011aSchinder et al, , 2015, the atmosphere and ionosphere of Titan (Cravens et al, 2010;Flasar et al, 2010;Kliore et al, , 2011Schinder et al, 2011bSchinder et al, , 2012Strobel et al, 2010;Tokano, 2014), and the plumes of Enceladus (Schinder et al, 2015, and a series of conference abstracts by Kliore and colleagues). In radio occultation observations, a radio signal is transmitted between the spacecraft and a ground station such that the radio signal passes through the atmosphere and ionosphere of a target object.…”

Section: Introductionmentioning

confidence: 99%

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Cassini Radio Occultation Observations of Titan's Ionosphere: The Complete Set of Electron Density Profiles

Dalba

Withers

2019

JGR Space Physics

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Titan's ionosphere is an important component of the moon's environment. Ionospheric densities above ≈900 km have been studied with in situ measurements, but few density profiles for lower altitudes has been reported. Here we report the generation of the complete set of twenty ionospheric electron density profiles from the Cassini Radio Science Subsystem instrument, including seven profiles not previously reported (inbound and outbound profiles for flybys T101, T102, and T117 and outbound profile for flyby T119). Uncertainties on average electron density profiles are generally 100–250 cm−3. On the whole, the main features of the new profiles are generally consistent with previous studies. Specifically, a single layer of plasma with peak density of 1,000–3,000 cm−3, peak altitude of 1,000–1,300 km, and full‐width at half maximum of a few hundred kilometers. Two new profiles are “disturbed” similar to three identified by previous studies. Based on inspection of the underlying individual profiles, which generally come from two ground stations on opposite sides of Earth, disturbed terrestrial ionospheric conditions are not responsible for the disturbed nature of these Titan ionospheric profiles. A significant plasma layer is present at 500–700 km in several profiles. This low‐altitude plasma layer can occur in profiles that are not disturbed.

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Section: From Time Series Of Frequency To Slant Profiles Of Integratementioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Cassini Radio Occultation Observations of Titan's Ionosphere: The Complete Set of Electron Density Profiles

Dalba

Withers

2019

JGR Space Physics

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“…in the context of elementary theory of dispersion [19]), it becomes obvious that the surface of constant n also coincide with the surfaces of constant Φ. Such a dependence between n and Φ has also been used recently in [17] to analyze the radioscience data of Cassini in the context of occultations by Saturn's atmosphere.…”

Section: Refractive Profile Dependencymentioning

confidence: 99%

“…Thus, all formulas which are presented in this section are determined under this assumption and should only be applied when the index of refraction is exactly given by Eq. (17). Although they should not be used in general, they provide a simplified and compact version of the formulas derived in appendix A.…”

Section: Limiting Casementioning

confidence: 99%

“…This solution based on a Taylor series expansion is suited for a numerical evaluation, but does not provide a clear understanding of the effect of non-spherical symmetry on the photon path and the time-delay. More recently, in order to account for additional effects such the light dragging effect by the winds, [17] proposed a purely numerical ray-tracing technique to solve the inverse problem. This method is of course more general than analytical models but necessitates a much higher computational cost.…”

Section: Introductionmentioning

confidence: 99%

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Analytical ray-tracing in planetary atmospheres

Bourgoin

Zannoni

Tortora

2019

A&A

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Context. Ground-based astro-geodetic observations and atmospheric occultations, are two examples of observational techniques requiring a scrutiny analysis of atmospheric refraction. In both cases, the measured changes in observables (range, Doppler shift, or signal attenuation) are geometrically related to changes in the photon path and the light time of the received electromagnetic signal. In the context of geometrical optics, the change in the physical properties of the signal are related to the refractive profile of the crossed medium. Therefore, having a clear knowledge of how the refractivity governs the photon path and the light time evolution is of prime importance to clearly understand observational features. Analytical studies usually focused on spherically symmetric atmospheres and only few aimed at exploring the effect of the non-spherical symmetry on the observables.Aims. In this paper, we analytically perform the integration of the photon path and the light time of rays traveling across a planetary atmosphere. We do not restrict our attention to spherically symmetric atmospheres and introduce a comprehensive mathematical framework which allows to handle any kind of analytical studies in the context of geometrical optics.Methods. Assuming that the index of refraction of the medium is a linear function of the Newtonian potential, we derive an exact solution to the equations of geometrical optics. The solution's arbitrary constants of integration are parametrized by the refractive response of the medium to the gravitational potential, and by the first integrals of the problem. Varying the constants, we are able to reformulate the equation of geometrical optics into a new set of osculating equations describing the constants' evolution for any arbitrary changes in the index of refraction profile.Results. The osculating equations are identical to the equation of geometrical optics, however, they offer a comprehensive framework to handle analytical studies which aim at exploring non-radial dependencies in the refractive profile. To highlight the capabilities of this new formalism, we carry out five realistic applications for which we derive analytical solutions. The accuracy of the method of integration is assessed by comparing our results to a numerical integration of the equations of geometrical optics in the presence of a quadrupolar moment J 2 . This shows that the analytical solution leads to the determination of the light time and the refractive bending with relative errors at the level of one part in 10 8 and one part in 10 5 , for typical values of the refractivity and the J 2 parameter at levels of 10 −4 and 10 −2 , respectively. * adrien.bourgoin@unibo.it arXiv:1901.08461v1 [physics.class-ph]

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Radio occultations of the Io plasma torus by Juno are feasible

Phipps

Withers

2017

JGR Space Physics

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The flow of material from Io's volcanoes into the Io plasma torus, out into the magnetosphere, and along field lines into Jupiter's upper atmosphere is not adequately understood. The lack of observations of spatial and temporal variations in the Io plasma torus impedes attempts to understand the system as a whole. Here we propose that radio occultations of the Io plasma torus by the Juno spacecraft can measure plasma densities in the Io plasma torus. We find that the line‐of‐sight column density of plasma in each of the three regions of the Io plasma torus (cold torus, ribbon, and warm torus) can be measured with uncertainties of 10%. We also find that scale heights describing the spatial variation in plasma density in each of these three regions can be measured with similar uncertainties. Such observations will be sufficiently accurate to support system‐scale studies of the flow of plasma through the magnetosphere of Jupiter.

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A numerical technique for two‐way radio occultations by oblate axisymmetric atmospheres with zonal winds

Cited by 28 publications

References 22 publications

Cassini Radio Occultation Observations of Titan's Ionosphere: The Complete Set of Electron Density Profiles

Cassini Radio Occultation Observations of Titan's Ionosphere: The Complete Set of Electron Density Profiles

Analytical ray-tracing in planetary atmospheres

Radio occultations of the Io plasma torus by Juno are feasible

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