The Neutral Atmosphere of Venus as Studied with the Mariner V Radio Occultation Experiments

The radio occultation technique, consisting of the observation of changes in the phase, frequency, and amplitude of a radio signal from a spacecraft as it passes through the atmosphere of a planet before and after occultation, was first applied to measure the atmosphere of Mars with the Mariner IV spacecraft in 1965. The interpretation of these changes in terms of refraction of the radio beam by the neutral atmosphere and ionosphere of the planet provided the first direct and quantitative measurement of its vertical structure and established the surface atmospheric pressure of Mars as lying between 5 and 9 mb. The presence of a daytime ionosphere with a peak electron density of about 105 el cm−3 was also measured. The Mariner VI and VII spacecraft flew by Mars in 1969 and provided an additional four measurements of the atmosphere and surface radius of the planet. They confirmed the surface pressure values measured by Mariner IV and provided data for a crude estimate of the shape of the planet.By far the greatest volume of radio occultation information on the atmosphere and surface of Mars was returned by the Mariner IX orbiter which was placed in orbit about Mars in November of 1971. During three occultation episodes in November-December 1971, May-June 1972, and September-October 1972, the Mariner IX mission provided 260 successful radio occultation measurements.The early measurements, made at the time of the Martian dust storm of 1971, showed greatly reduced temperature gradients in the daytime troposphere, indicating the heating effect of the dust. The temperature gradients that were measured later in the mission, when the atmosphere was apparently free of dust, were still much lower than expected under conditions of radiative-convective balance, indicating that dynamics may play a large part in determining the temperature structure of the Martian troposphere. Temperatures taken at night near the winter poles were consistent with the condensation of carbon dioxide.The surface atmospheric pressure was observed to vary widely with topography ranging from about 1 mb at the summit of the Middle Spot volcano (Pavonis Mons) to over 10 mb in the North circumpolar region. In the South equatorial region the highest surface pressure of about 9 mb was measured at the bottom of the Hellas basin.The radius of the planet was measured with accuracies ranging from about 0.25 to about 2.1 km over latitudes ranging from 86° to −80°. These measurements have shown that Mars has pronounced equatorial and north-south asymmetries, which make it difficult to represent its shape by a simple triaxial figure.The daytime ionosphere measurements indicated that the main ionization peak was similar in behavior to a terrestrial F1 layer and is probably produced by photoionization of carbon dioxide by solar extreme ultraviolet. Comparison of the heights of the maximum between the early data taken in November-December, 1971, and the Extended Mission of May-June 1972, showed that the lower atmospheric temperatures decreased by about 25%, which is consistent with clearing of the atmosphere.The experience gained from Mars radio occultation experiments suggests that the quality of data can be significantly improved by such features of the spacecraft radio system as a stable oscillator, dual frequency downlink capability, and a steerable high-gain antenna.

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The FengYun-3C radio occultation sounder GNOS: a review of the mission and its early results and science applications

Atmospheric Measurement Techniques ◽

10.5194/amt-11-5797-2018 ◽

2018 ◽

Vol 11 (10) ◽

pp. 5797-5811 ◽

Cited By ~ 11

Author(s):

Yueqiang Sun ◽

Weihua Bai ◽

Congliang Liu ◽

Yan Liu ◽

Qifei Du ◽

...

Keyword(s):

Quality Evaluation ◽

Radio Occultation ◽

Global Climate ◽

Weather Prediction ◽

Satellite System ◽

Navigation Satellite ◽

Neutral Atmosphere ◽

Scientific Applications ◽

Early Results ◽

Global Navigation Satellite

Abstract. The Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) is one of the new-generation payloads on board the Chinese FengYun 3 (FY-3) series of operational meteorological satellites for sounding the Earth's neutral atmosphere and ionosphere. FY-3C GNOS, on board the FY-3 series C satellite launched in September 2013, was designed to acquire setting and rising radio occultation (RO) data by using GNSS signals from both the Chinese BeiDou Navigation Satellite System (BDS) and the US Global Positioning System (GPS). So far, the GNOS measurements and atmospheric and ionospheric data products have been validated and evaluated and then been used for atmosphere- and ionosphere-related scientific applications. This paper reviews the FY-3C GNOS instrument, RO data processing, data quality evaluation, and preliminary research applications according to the state-of-the-art status of the FY-3C GNOS mission and related publications. The reviewed data validation and application results demonstrate that the FY-3C GNOS mission can provide accurate and precise atmospheric and ionospheric GNSS (i.e., GPS and BDS) RO profiles for numerical weather prediction (NWP), global climate monitoring (GCM), and space weather research (SWR). The performance of the FY-3C GNOS product quality evaluation and scientific applications establishes confidence that the GNOS data from the series of FY-3 satellites will provide important contributions to NWP, GCM, and SWR scientific communities.

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Aspects of design antennas for radio occultation method of ionosphere diagnostics

ITM Web of Conferences ◽

10.1051/itmconf/20193005012 ◽

2019 ◽

Vol 30 ◽

pp. 05012

Author(s):

Alexander Generalov ◽

Elchin Gadzhiev ◽

Pavel Shmachilin ◽

Yuri Polushkovskiy ◽

Vladimir Skripachev ◽

...

Keyword(s):

Solar Radiation ◽

Radio Occultation ◽

Practical Importance ◽

Atmospheric Electricity ◽

Upper Atmosphere ◽

Radio Propagation ◽

Neutral Atmosphere ◽

The Earth

The ionosphere is the ionized part of Earth's upper atmosphere, from about 60 km to 1,000 km altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. The region below the ionosphere is called neutral atmosphere, or neutrosphere. In this paper aspects of design antennas for radio occultation method of ionosphere diagnostics are presented.

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GNSS radio occultation profiles in the neutral atmosphere from inversion of excess phase data

Terrestrial Atmospheric and Oceanic Sciences ◽

10.3319/tao.2018.10.12.01 ◽

2019 ◽

Vol 30 (2) ◽

pp. df

Author(s):

Paweł Hordyniec ◽

Cheng-Yung Huang ◽

Chian-Yi Liu ◽

Witold Rohm ◽

Shu-Ya Chen

Keyword(s):

Radio Occultation ◽

Neutral Atmosphere ◽

Excess Phase ◽

Phase Data

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Empirical model of the ionosphere based on COSMIC/FORMOSAT-3 for neutral atmosphere radio occultation processing

10.5194/amt-2017-217 ◽

2017 ◽

Cited By ~ 1

Author(s):

Miquel Garcia-Fernandez ◽

Manuel Hernandez-Pajares ◽

Antonio Rius ◽

Riccardo Notarpietro ◽

Axel von Engeln ◽

...

Keyword(s):

Electron Density ◽

Empirical Model ◽

Radio Occultation ◽

Scintillation Index ◽

Neutral Atmosphere ◽

Vertical Profiles ◽

New Feature ◽

Occultation Data ◽

Relevant Level ◽

Made In

Abstract. The Radio Occultation instrument at the upcoming EUMETSAT Polar System – Second Generation (EPS-SG) mission will be devoted primarily to monitor the neutral atmosphere through this payload, consisting of a GNSS receiver and occultation antennae pointing slightly below the Earth's limb. The resulting data will be processed by EUMETSAT (primarily for L1B data) and by the ROMSAF's Radio Occultation Processing Package (ROPP) software to obtain the vertical profiles of temperature, pressure and other relevant level 2 parameters of the neutral atmosphere. Newer versions of this software might include a feature by which empirical models of the ionosphere (i.e. vertical profiles of electron density) can be included in the processing in order to increase the accuracy of the inverted bending angle profiles. In order to test this new feature, this work includes the efforts that have been made in order to provide an empirical model of the ionosphere purely based on vertical profiles of electron density inverted from data of previous radio occultation (RO) missions (i.e. COSMIC/FORMOSAT-3). The methodology used in this work is based on using the separability hypothesis, to overcome the spherical symmetry assumption of the Abel inversion as well as a new mechanization of the inversion process, based on a joint processing of all the occultation data via a linear mean square filter, rather than adopting the classical peel onion approach. Additionally, with the development of this empirical model, efforts have been made to construct a proxy index for scintillation monitoring based on the inverted profiles (Occultation Scintillation Proxy Index or OSPI), which shows reasonable correlation with the amplitude scintillation index S4.

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Mutual radio occultation experiment between ExoMars Trace Gas Orbiter and Mars Express: algorithms testing

10.5194/epsc2021-605 ◽

2021 ◽

Author(s):

Bruno Nava ◽

Yenca Migoya-Orue ◽

Anton Kashcheyev ◽

Beatriz Sánchez-Cano ◽

Olivier Witasse ◽

...

Keyword(s):

Experimental Data ◽

Electron Density ◽

Doppler Shift ◽

Radio Occultation ◽

Trace Gas ◽

Neutral Atmosphere ◽

Ionospheric Electron Density ◽

Density Profiles ◽

Mars Express ◽

Electron Density Profiles

Radio Occultation (RO) is a very powerful technique to probe a planetary atmosphere, in providing vertical density profiles of the neutral atmosphere and ionosphere. The standard method uses a radio link between a spacecraft and an Earth ground station. Nevertheless, the possibility to obtain information about the Martian atmosphere with mutual RO events, using data from NASA Mars Odyssey and Mars Reconnaissance Orbiters (MRO), has been demonstrated by Ao et al. (2015). Taking advantage of two European spacecraft in orbit around Mars, the European Space Agency is currently preparing experiments of mutual RO between Mars Express (MEX) and the ExoMars Trace Gas Orbiter (TGO). In preparation of MEX and TGO data inversion and analysis, a simulation-based strategy has been adopted and an algorithm able to retrieve vertical electron density profiles from Doppler shift measurements has been implemented and validated. Subsequently, in order to test the mentioned algorithm with experimental data, the same three RO events considered in the paper by Ao et al. (2015) have been processed. In particular, for each RO event, having the information about the satellites&#8217; orbit, the (excess) Doppler shift values corresponding to the Mars Odyssey-MRO ray-paths have been converted to bending angles as a function of impact parameter. Then, assuming a spherical symmetry (Fjeldbo et al., 1971) for the ionosphere electron density, the bending angles have been transformed (through Abel integral) to a vertical refractivity profile, which, in turn, has been converted to an ionospheric electron density profile. In this work, the results obtained by the application of the mentioned inversion algorithm to experimental data will be presented, with particular focus on the retrieval of the ionospheric electron density profiles. References Ao, C. O., C. D. Edwards Jr., D. S. Kahan, X. Pi, S. W. Asmar, and A. J. Mannucci (2015), A first demonstration of Mars crosslink occultation measurements, Radio Sci., 50, 997&#8211;1007, doi:10.1002/2015RS005750. Fjeldbo, G., A. J. Kliore, and V. R. Eshleman (1971), The neutral atmosphere of Venus as studied with the Mariner V radio occultation experiments, Astron. J., 76, 123&#8211;140.

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Activity of Small-Scale Internal Waves in the Northern Polar Atmosphere of Venus by Radio Occultation Measurements of Signal Intensity (Λ = 32 cm) from Venera-15 and -16 Satellites

Solar System Research ◽

10.1134/s0038094621010044 ◽

2021 ◽

Vol 55 (1) ◽

pp. 1-10

Author(s):

V. N. Gubenko ◽

I. A. Kirillovich ◽

D. V. Gubenko ◽

V. E. Andreev ◽

T. V. Gubenko

Keyword(s):

Internal Waves ◽

Signal Intensity ◽

Radio Occultation ◽

Small Scale ◽

Atmosphere Of Venus

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Ionospheric correction of GPS radio occultation data in the troposphere

Atmospheric Measurement Techniques ◽

10.5194/amt-9-335-2016 ◽

2016 ◽

Vol 9 (2) ◽

pp. 335-346 ◽

Cited By ~ 13

Author(s):

Z. Zeng ◽

S. Sokolovskiy ◽

W. Schreiner ◽

D. Hunt ◽

J. Lin ◽

...

Keyword(s):

Radio Occultation ◽

Neutral Atmosphere ◽

Ionospheric Correction ◽

Bending Angle ◽

Gps Radio Occultation ◽

Strong Inversion ◽

Occultation Data ◽

Horizontal Inhomogeneity ◽

L1 And L2 ◽

Bending Angles

Abstract. For inversions of the GPS radio occultation (RO) data in the neutral atmosphere, this study investigates an optimal transition height for replacing the standard ionospheric correction using the linear combination of the L1 and L2 bending angles with the correction of the L1 bending angle by the L1–L2 bending angle extrapolated from above. The optimal transition height depends on the RO mission (i.e., the receiver and firmware) and is different between rising and setting occultations and between L2P and L2C GPS signals. This height is within the range of approximately 10–20 km. One fixed transition height, which can be used for the processing of currently available GPS RO data, can be set to 20 km. Analysis of the L1CA and the L2C bending angles shows that in some occultations the errors of standard ionospheric correction substantially increase around the strong inversion layers (such as the top of the boundary layer). This error increase is modeled and explained by the horizontal inhomogeneity of the ionosphere.

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Evaluation of atmospheric profiles derived from single- and zero-difference excess phase processing of BeiDou radio occultation data from the FY-3C GNOS mission

Atmospheric Measurement Techniques ◽

10.5194/amt-11-819-2018 ◽

2018 ◽

Vol 11 (2) ◽

pp. 819-833 ◽

Cited By ~ 7

Author(s):

Weihua Bai ◽

Congliang Liu ◽

Xiangguang Meng ◽

Yueqiang Sun ◽

Gottfried Kirchengast ◽

...

Keyword(s):

Standard Deviation ◽

Radio Occultation ◽

Global Climate ◽

Weather Prediction ◽

Neutral Atmosphere ◽

Change Analysis ◽

Bending Angle ◽

New Instrument ◽

Single Difference ◽

Excess Phase

Abstract. The Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) is one of the new-generation payloads onboard the Chinese FengYun 3 (FY-3) series of operational meteorological satellites for sounding the Earth's neutral atmosphere and ionosphere. The GNOS was designed for acquiring setting and rising radio occultation (RO) data by using GNSS signals from both the Chinese BeiDou System (BDS) and the US Global Positioning System (GPS). An ultra-stable oscillator with 1 s stability (Allan deviation) at the level of 10−12 was installed on the FY-3C GNOS, and thus both zero-difference and single-difference excess phase processing methods should be feasible for FY-3C GNOS observations. In this study we focus on evaluating zero-difference processing of BDS RO data vs. single-difference processing, in order to investigate the zero-difference feasibility for this new instrument, which after its launch in September 2013 started to use BDS signals from five geostationary orbit (GEO) satellites, five inclined geosynchronous orbit (IGSO) satellites and four medium Earth orbit (MEO) satellites. We used a 3-month set of GNOS BDS RO data (October to December 2013) for the evaluation and compared atmospheric bending angle and refractivity profiles, derived from single- and zero-difference excess phase data, against co-located profiles from European Centre for Medium-Range Weather Forecasts (ECMWF) analyses. We also compared against co-located refractivity profiles from radiosondes. The statistical evaluation against these reference data shows that the results from single- and zero-difference processing are reasonably consistent in both bias and standard deviation, clearly demonstrating the feasibility of zero differencing for GNOS BDS RO observations. The average bias (and standard deviation) of the bending angle and refractivity profiles were found to be about 0.05 to 0.2 % (and 0.7 to 1.6 %) over the upper troposphere and lower stratosphere. Zero differencing was found to perform slightly better, as may be expected from its lower vulnerability to noise. The validation results indicate that GNOS can provide, on top of GPS RO profiles, accurate and precise BDS RO profiles both from single- and zero-difference processing. The GNOS observations by the series of FY-3 satellites are thus expected to provide important contributions to numerical weather prediction and global climate change analysis.

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Systematic residual ionospheric errors in radio occultation data and a potential way to minimize them

Atmospheric Measurement Techniques ◽

10.5194/amt-6-2169-2013 ◽

2013 ◽

Vol 6 (8) ◽

pp. 2169-2179 ◽

Cited By ~ 27

Author(s):

J. Danzer ◽

B. Scherllin-Pirscher ◽

U. Foelsche

Keyword(s):

Solar Activity ◽

Solar Cycle ◽

Radio Occultation ◽

Simulated Data ◽

Correction Method ◽

High Solar Activity ◽

Neutral Atmosphere ◽

Atmospheric Parameters ◽

Ionospheric Correction ◽

Bending Angle

Abstract. Radio occultation (RO) sensing is used to probe the earth's atmosphere in order to obtain information about its physical properties. With a main interest in the parameters of the neutral atmosphere, there is the need to perform a correction of the ionospheric contribution to the bending angle. Since this correction is an approximation to first order, there exists an ionospheric residual, which can be expected to be larger when the ionization is high (day versus night, high versus low solar activity). The ionospheric residual systematically affects the accuracy of the atmospheric parameters at low altitudes, at high altitudes (above 25–30 km) it even is an important error source. In climate applications this could lead to a time dependent bias which induces wrong trends in atmospheric parameters at high altitudes. The first goal of our work was to study and characterize this systematic residual error. In a second step we developed a simple correction method, based purely on observational data, to reduce this residual for large ensembles of RO profiles. In order to tackle this problem, we analyzed the bending angle bias of CHAMP and COSMIC RO data from 2001–2011. We could observe that the nighttime bending angle bias stays constant over the whole period of 11 yr, while the daytime bias increases from low to high solar activity. As a result, the difference between nighttime and daytime bias increases from about −0.05 μrad to −0.4 μrad. This behavior paves the way to correct the solar cycle dependent bias of daytime RO profiles. In order to test the newly developed correction method we performed a simulation study, which allowed to separate the influence of the ionosphere and the neutral atmosphere. Also in the simulated data we observed a similar increase in the bias in times from low to high solar activity. In this simulation we performed the climatological ionospheric correction of the bending angle data, by using the bending angle bias characteristics of a solar cycle as a correction factor. After the climatological ionospheric correction the bias of the simulated data improved significantly, not only in the bending angle but also in the retrieved temperature profiles.

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