- Full paper
- Open Access
Initial performance of the radio occultation experiment in the Venus orbiter mission Akatsuki
- Takeshi Imamura1Email authorView ORCID ID profile,
- Hiroki Ando2,
- Silvia Tellmann3,
- Martin Pätzold3,
- Bernd Häusler4,
- Atsushi Yamazaki5,
- Takao M. Sato5,
- Katsuyuki Noguchi6,
- Yoshifumi Futaana7,
- Janusz Oschlisniok3,
- Sanjay Limaye8,
- R. K. Choudhary9,
- Yasuhiro Murata5,
- Hiroshi Takeuchi5,
- Chikako Hirose5,
- Tsutomu Ichikawa5,
- Tomoaki Toda5,
- Atsushi Tomiki5,
- Takumi Abe5,
- Zen-ichi Yamamoto5,
- Hirotomo Noda10,
- Takahiro Iwata5,
- Shin-ya Murakami5,
- Takehiko Satoh5,
- Tetsuya Fukuhara11,
- Kazunori Ogohara12,
- Ko-ichiro Sugiyama13,
- Hiroki Kashimura14,
- Shoko Ohtsuki15,
- Seiko Takagi16,
- Yukio Yamamoto5,
- Naru Hirata17,
- George L. Hashimoto18,
- Manabu Yamada19,
- Makoto Suzuki5,
- Nobuaki Ishii5,
- Tomoko Hayashiyama20,
- Yeon Joo Lee5 and
- Masato Nakamura5
© The Author(s) 2017
- Received: 4 July 2017
- Accepted: 20 September 2017
- Published: 3 October 2017
- Radio occultation
The main goal of the Venus orbiter mission Akatsuki is to understand the mechanisms driving the atmospheric circulation and maintaining the cloud layer (Nakamura et al. 2011). For this purpose, five cameras onboard, having bandpass filters, take images of Venus at different wavelengths to observe the horizontal distributions of clouds and minor constituents at different heights. Radio occultation measurement in Akatsuki, termed RS (Radio Science), aims at exploration of the vertical structure of the atmosphere (Imamura et al. 2011), being complementary to the imaging observations by onboard cameras.
The orbiter was launched in May 2010 and arrived at Venus in December 2010. The first attempt on Venus orbit insertion has failed, and the second attempt conducted in December 2015, after 5-years of interplanetary cruise, was successful (Nakamura et al. 2016). Regular observations of the Venusian atmosphere with radio occultation technique have started in March 2016. In addition to the observation of Venus, radio occultation observations of the solar corona were conducted during the solar conjunction periods in 2011 and 2016 using the same equipment (Imamura et al. 2014b).
Radio occultation has played a crucial role in determining the structures of the planetary atmospheres (e.g., Eshleman 1973; Tyler 1987; Pätzold et al. 2007; Imamura et al. 2012). In a radio occultation experiment conducted with a spacecraft equipped with a stable frequency source, the spacecraft transmits radio waves toward the Earth, while it goes behind the planet and reemerges as seen from the Earth. During such occultation events, the planetary atmosphere causes bending and attenuation of the radio waves. Assuming a local spherical symmetry, the analysis of the frequency and the signal intensity time series obtained at the tracking station yields vertical profiles of the refractive index and the absorption coefficient. Temperature profiles are obtained from the refractive index profiles assuming hydrostatic balance. The advantages of this technique over other remote sensing techniques are its high vertical resolution (typically < 1 km) and high temperature resolution (typically < 1 K) (Hinson and Jenkins 1995; Tellmann et al. 2009). Radio occultation can cover altitudes from the sub-cloud region (< 50 km) to the upper atmosphere (~ 90 km). The quality of the measurement declines below 40 km due to defocusing loss and absorption, and no information is obtained below ~ 32 km since the curvature of the ray path exceeds that of the planetary surface (Fjeldbo et al. 1971; Häusler et al. 2006).
The scientific background of the measurement has been described in Imamura et al. (2011); here, we briefly describe the background with recent updates. Previous radio occultation experiments of the Venusian atmosphere revealed the meridional structure of the atmospheric temperature, including the horizontally near-uniform temperature below the cloud layer, the cold collar and the mid-latitude jet at cloud heights, and the warm high latitudes above clouds (Kliore and Patel 1980; Newman et al. 1984; Piccialli et al. 2012). The dynamical stability of the atmosphere was studied using radio occultation temperatures (Piccialli et al. 2012). The static stability is near neutral in the middle and lower cloud regions (50–58 km), suggesting occurrence of vertical convection (Pollack et al. 1980; Tellmann et al. 2009). At altitudes above ~ 58 km, propagation of gravity waves is suggested from wavelike features in the temperature profiles (Hinson and Jenkins 1995; Tellmann et al. 2012; Ando et al. 2015a). In spite of these findings, the relationship among the variations of the temperature field, the wind field and the cloud distribution has not been studied. Local time dependence of the thermal structure in the cloud is also unclear, although numerical models predict significant diurnal variations (Imamura et al. 2014a).
Mixing ratios of H2SO4 vapor, which is concentrated in the sub-cloud region, have been retrieved from the attenuation of radio occultation signals (Jenkins et al. 1994; Kolodner and Steffes 1998; Oschlisniok et al. 2012). The observed H2SO4 vapor distribution suggests control of the H2SO4 distribution by condensation and evaporation in clouds, thermal decomposition in the lower atmosphere, and global-scale circulation (Krasnopolsky and Pollack 1994; Imamura and Hashimoto 1998, 2001). Using Venus Express radio occultation data, Oschlisniok et al. (2012) revealed complicated meridional distribution and local time dependence of the mixing ratio, which are not reproduced in numerical models. The relationship among the variations of the thermal structure, the H2SO4 vapor distribution, and the cloud distribution is a key to understanding the cloud system; regional cloud models predict significant variability of the clouds (McGouldrick et al. 2008a, b), and Venus Express VIRTIS showed mesoscale variability of the cloud optical thickness (McGouldrick et al. 2012).
The occurrence of small-scale atmospheric density fluctuations, having scales smaller than the Fresnel diameter given later, has been inferred from the scintillation of radio occultation signals. The scintillation, which is enhanced around 60 km altitude and at high latitudes, might be caused by turbulence (Woo et al. 1980) or gravity waves (Leroy and Ingersoll 1996). Ando et al. (2015a) argued, based on a spectral analysis of radio occultation temperatures, that saturation of gravity waves through convective instability occurs above clouds, although there is no direct evidence for wave breaking. A detailed comparison of the distribution of scintillation with wavy temperature structures might provide clues to wave breaking and resultant turbulence.
Ionospheric electron densities have primarily been measured by radio occultation technique (Kliore and Luhmann 1991). The peak electron density is an order of magnitude higher on the dayside than nightside, and multiple layers are observed on the dayside (Pätzold et al. 2007). The structure of the ionosphere is affected by the input of energy and momentum from the solar wind to the upper atmosphere, and also by the dynamical coupling with the lower neutral atmosphere. The latter is particularly unexplored and should be studied with simultaneous observations of the variability of the lower atmosphere and the upper atmosphere.
This paper presents the initial performance, the observation plan, and the expected science themes of Akatsuki RS. Scientific results will be reported elsewhere. The observation plan was largely changed from the original given in Imamura et al. (2011) because of the change of the orbit around Venus. The originally planned orbit is a 30 h-period elliptical orbit with the apoapsis altitude of ~ 13 Venus radii, while the current orbit is a 10.5-day-period elliptical orbit with the apoapsis altitude of 59 Venus radii.
One-way downlink at X-band (8410.932 MHz) is used in the experiment. The experiment relies on the frequency stability of both the onboard radio wave source and the recording system at the ground station. Akatsuki RS employs an ultra-stable oscillator (USO) as the onboard frequency source; the performance of the USO is given in “Performance of the ultra-stable oscillator”. The USO is almost identical to those onboard ESA’s Rosetta and Venus Express spacecraft (Häusler et al. 2007). The absence of the second frequency (such as S-band) prevents dual-frequency occultation method, which is sensitive only to plasma along the radio propagation path (e.g., Imamura et al. 2010; Pätzold et al. 2007). This might have some influence on the detection of ionospheric fine structures at low ionospheric altitudes but will not alter the coarse ionospheric electron density profiles.
The 3 dB half beam width of the high-gain antenna is ~ 1°; since the ray bending exceeds the beam width, the spacecraft performs attitude maneuvers to compensate for the changing direction of the signal path. The direction of the antenna beam is changed along a polygonal (zigzag) curve in such a way that the difference between the controlled beam direction and the ideal beam direction based on the Venus International Reference Atmosphere (VIRA) (Seiff et al. 1985) is less than 0.05°. The difference sometimes exceeds this limit because of an inaccurate trajectory prediction at the time of command generation, leading to non-negligible decline of the signal intensity. The effect of such antenna mispointing on the measured signal intensity is corrected before analysis using the measured antenna pattern (Toda et al. 2010) and the trajectory data reconstructed after the experiment. The accuracy of this intensity correction is estimated to be better than 1 dB in most of the cases.
The accuracy of the altitudes in the derived atmospheric profiles relies on the accuracy of trajectory determination. According to the analysis of flight dynamics, the position of Akatsuki relative to Venus typically has an error of 100–500 m during radio occultation experiments. This error causes uncertainties of the altitude offset of similar magnitude in the atmospheric profiles.
The primary ground station used for the experiment is the 64-m antenna of Usuda Deep Space Center (UDSC) of JAXA, which is located at 138°21′54″ East longitude, 36°07′44″ North latitude. In addition to UDSC, for increasing the number of observation opportunities, we started to use the 32-m antenna of Indian Deep Space Network (IDSN) of Indian Space Research Organization (ISRO), which is located at 77°22′08″ East longitude, 12°54′11″ North latitude, from March 2017.
The received signals are down-converted to < ~ 1 MHz by an open-loop heterodyne system stabilized by a hydrogen maser (Allan deviation < 3 × 10−13 for 1 s, < 3 × 10−15 for 1000 s) and 8-bits digitized. The sampling rate is 0.5–4 MHz so that the received signal can be confined in the recording bandwidth, while the frequency changes with time due to Doppler shift. The detail of the observation system is given in Imamura et al. (2011).
The uniqueness of the Akatsuki RS is that the observation points cluster in the low and middle latitude because of the near-equatorial orbit. Since the onboard cameras are designed to observe wide areas in the low latitude, the locations probed by RS can be observed by the cameras a short time (h) before or after each occultation experiment. Mostly dawn and dusk regions have been probed by April 2017.
In the processing of recorded data, we first subtract the Doppler shift calculated from the orbital information and a model atmosphere from the original signal by heterodyning, thereby suppressing the frequency variation and enabling narrow-band filtering. Then, approximate carrier frequencies are determined for successive time blocks by fitting a theoretical signal spectrum (sinc function) to the discrete Fourier transforms (Lipa and Tyler 1979). The resultant frequency variation is subtracted from the signal by heterodyning in order to apply another narrow-band filtering. The signal frequency and intensity time series to be used for the analysis of the atmospheric structure are obtained by successively fitting a sinc function to the narrow-band filtered data.
The sum of the frequency variation in the final product like Fig. 4 and the frequency variation that has been subtracted via heterodyning in the course of the processing gives the total Doppler shift. Subtraction of the “straightline Doppler shift”, which is the frequency variation to be observed if Venus does not exit, from the total Doppler shift gives the contribution of the Venusian atmosphere termed “atmospheric Doppler shift”. Although the atmospheric Doppler shift should be zero in the portion of the data above the height of the ionosphere, we usually observe a smoothly varying frequency component that is attributed to the error in the trajectory data. To remove this frequency offset, we fit a linear function to this portion of the frequency time series and subtract it from the whole time series; this procedure is termed “baseline fit”. The atmospheric Doppler shift corrected by baseline fit is combined with the trajectory data to calculate the bending angle and the impact parameter.
The temperature profiles clearly show differences in the stratification characteristics among the altitude regions. Almost constant lapse rate of ~ 10 K/km, which is close to the adiabatic lapse rate (Seiff et al. 1985), is observed in the middle and lower cloud region (50–58 km); this region is considered as a convective layer driven by the heating of the cloud base by the thermal infrared flux from below (Pollack et al. 1980). The region below the cloud (< 50 km) is weakly stable. The region above 58 km is also stable and is dominated by short-vertical scale (< 5 km) fluctuations, being consistent with Venus Express radio occultation experiments (Tellmann et al. 2012). The range of the temperature variation near the top is ~ 50 K, which is smaller than the day-to-day variability of ~ 80 K in the same height region observed by the solar occultation experiment SOIR onboard Venus Express (Mahieux et al. 2012; Limaye et al. 2017). More measurements are needed to better understand the variability.
Comparing the morning and the afternoon profiles, local time-dependent features are seen at various vertical scales. The amplitudes of the fine structures with vertical scales of < 5 km below 70 km altitude seem to be larger on the morning side, and the phase of the background wavy structure with a vertical scale of > 10 km above 70 km seems to be shifted in altitude between these local time regions. The detail of the local time dependence will be reported elsewhere.
Radio occultation observation of the Venusian atmosphere in the Akatsuki mission has started in March 2016. Ten occultation experiments, including 10 ingress and 9 egress measurements, have been conducted by February 2017. From the open-loop recorded data, the altitude distributions of the temperature, the H2SO4 vapor mixing ratio, and the electron density are being successfully retrieved.
The dataset will be used for a variety of scientific researches. The temperature and H2SO4 vapor profiles are analyzed in combination with cloud images obtained successively from Akatsuki and also with cloud-tracked vectors obtained from those images. Complementary uses of those data enables studies on the interaction between cloud physics and thermal structure, the three-dimensional structures of atmospheric circulation and waves, and the vertical coupling between the cloud-level atmosphere and the mesosphere. The combination of the electron density profiles with the whole Akatsuki dataset will provide clues to the role of the variation of the neutral atmosphere in the variability of the ionosphere. Comparison of Akatsuki RS results with the previous radio occultation results from Pioneer Venus (Kliore and Patel 1980) and Venus Express (Pätzold et al. 2007; Tellmann et al. 2009) would reveal long-term variation of the Venusian atmosphere. The radio occultation temperatures are used in the radiative transfer calculation for the analyses of data taken by ground-based telescopes. The results from those studies will be presented in separate papers.
Apart from Venus researches, radio occultation observations of the solar corona were conducted during the solar conjunction periods in June–July 2011 and May–June 2016. The outward flow velocity can be retrieved from the signal intensity fluctuation, and the plasma density fluctuation can be retrieved from the frequency fluctuation. The 2011 observation has revealed the radial profile of the flow velocity (Imamura et al. 2014b), the radial distribution of compressible waves (Miyamoto et al. 2014), and the internal structure of a coronal mass ejection (Ando et al. 2015a, b).
TI is the principal investigator of the experiment. HA, ST and JO contributed to data analysis. MP, BH, YM, HT, TT, AT, ZY, IN, TH and MN contributed to the development of the observation system. KN, YF, SL, TA, HN and TI contributed to science planning. AY, TS, TS, CH, TF, KO, KS, HK, SO, ST, MY, MS and LY contributed to command planning and spacecraft operation. TI represents the orbital dynamics team. SM, YY, NH and GLH contributed to data archiving. RKC represents the ISRO RS Team. All authors read and approved the final manuscript.
We would like to acknowledge all members of the Akatsuki project team and the staff of UDSC for supporting the preparation of the experiment. The high performance of the USO was achieved by the tremendous efforts made by Theo Schwall, Wolfgang Schäfer and other engineers of TimeTech GmbH. We thank Richard Simpson at Stanford University and Kevin McGouldrick at University of Colorado, Boulder for supporting data archiving. We also thank Koh-ichiro Oyama for continuous encouragement.
The authors declare that they have no competing interests.
Availability of data and materials
The radio occultation data used in this study will become open to the public at DARTS (Data ARchives and Transmission System) of JAXA and the PDS (Planetary Data System) of NASA.
Consent for publication
Ethics approval and consent to participate
This work was supported by JSPS KAKENHI Grant Nos. JP22244060, JP24540482, JP16H04060, JP00706335 and JP16H02231.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Ando H, Imamura T, Tsuda T, Tellmann S, Pätzold M, Häusler B (2015a) Vertical wavenumber spectra of gravity waves in the Venus atmosphere obtained from Venus Express radio occultation data: evidence for saturation. J Atmos Sci 72:2318–2329. doi:10.1175/JAS-D-14-0315.1 View ArticleGoogle Scholar
- Ando H, Shiota D, Imamura T, Tokumaru M, Asai A, Isobe H, Päzold M, Häusler B, Nakamura M (2015b) Internal structure of a coronal mass ejection revealed by Akatsuki radio occultation observations. J Geophys Res 120:5318–5328. doi:10.1002/2015JA021076 View ArticleGoogle Scholar
- Eshleman VR (1973) The radio occultation method for the study of planetary atmospheres. Planet Space Sci 21:1521–1531View ArticleGoogle Scholar
- Essen L, Froome KD (1951) The refractive indices and dielectric constants of air and its principal constituents at 24,000 Mc/s. Proc Phys Soc London Sect B 64:862–875. doi:10.1088/0370-1301/64/10/303 View ArticleGoogle Scholar
- Fjeldbo G, Eshleman VR (1968) The atmosphere of Mars analyzed by integral inversion of the Mariner IV occultation data. Planet Space Sci 16:1035–1059View ArticleGoogle Scholar
- Fjeldbo G, Kliore AJ, Eshleman VR (1971) The neutral atmosphere of venus as studied with the Mariner V radio occultation experiments. Astron J 76:123–140View ArticleGoogle Scholar
- Häusler B, Pätzold M, Tyler GL, Simpson RA, Bird MK, Dehant V, Barriot J-P, Eidel W, Mattei R, Remus S, Selle J, Tellmann S, Imamura T (2006) Radio science investigations by VeRa onboard the Venus Express spacecraft. Planet Space Sci 54:1315–1335View ArticleGoogle Scholar
- Häusler B, Pätzold M, Tyler G L, Simpson R A, Hinson D, Bird M K, Treumann R A, Dehant V, Eidel W, Remus S, Selle J (2007) Atmospheric, ionospheric, surface, and radio wave propagation studies with the Venus Express radio science experiment VeRa. ESA Scientific Publication, ESA-SP-1295, pp 1–30Google Scholar
- Hinson DP, Jenkins JM (1995) Magellan radio occultation measurements of atmospheric waves on Venus. Icarus 114:310–327View ArticleGoogle Scholar
- Imamura T, Hashimoto GL (1998) Venus cloud formation in the meridional circulation. J Geophys Res 103:31349–31366View ArticleGoogle Scholar
- Imamura T, Hashimoto GL (2001) Microphysics of Venusian clouds in rising tropical air. J Atmos Sci 58:3597–3612View ArticleGoogle Scholar
- Imamura T, Iwata T, Yamamoto Z, Mochizuki N, Kono Y, Matsumoto K, Liu Q, Noda H, Hanada H, Oyama K-I, Nabatov A, Futaana Y, Saito A, Ando H (2010) Studying the lunar ionosphere with SELENE radio science experiment. Space Sci Rev 154:305–316View ArticleGoogle Scholar
- Imamura T, Toda T, Tomiki A, Hirahara D, Hayashiyama T, Mochizuki N, Yamamoto Z, Abe T, Iwata T, Noda H, Futaana Y, Ando H, Häusler B, Pätzold M, Nabatov A (2011) RS: Radio Science investigation of the Venus atmosphere and ionosphere with Venus orbiter, Akatsuki. Earth Planets Space 63:493–501. doi:10.5047/eps.2011.03.009 View ArticleGoogle Scholar
- Imamura T, Nabatov A, Mochizuki N, Iwata T, Hanada H, Matsumoto K, Noda H, Kono Y, Liu Q, Futaana Y, Ando H, Yamamoto Z, Oyama K-I, Saito A (2012) Radio occultation measurement of the electron density near the lunar surface using a subsatellite on the SELENE mission. J Geophys Res 117:A06303. doi:10.1029/2011JA017293 View ArticleGoogle Scholar
- Imamura T, Higuchi T, Maejima Y, Takagi M, Sugimoto N, Ikeda K, Ando H (2014a) Inverse insolation dependence of Venus’ cloud-level convection. Icarus 228:181–188View ArticleGoogle Scholar
- Imamura T, Tokumaru M, Isobe H, Shiota D, Ando H, Miyamoto M, Toda T, Häusler B, Pätzold M, Nabatov A, Asai A, Yaji K, Yamada M, Nakamura M (2014b) Outflow structure of the quiet Sun corona probed by spacecraft radio scintillations in strong scattering. Astrophys J 788:117(10pp). doi:10.1088/0004-637X/788/2/117 View ArticleGoogle Scholar
- James EP, Toon OB, Schubert G (1997) A numerical microphysical model of the condensational Venus cloud. Icarus 129:147–171View ArticleGoogle Scholar
- Jenkins JM, Steffes PG, Hinson DP, Twicken JD, Tyler GL (1994) Radio occultation studies of the Venus atmosphere with the Magellan spacecraft. 2. Results from the October 1991 experiments. Icarus 110:79–93View ArticleGoogle Scholar
- Kliore AJ, Luhmann JG (1991) Solar cycle effects on the structure of the electron density profiles in the dayside ionosphere of Venus. J Geophys Res 96:21281–21289View ArticleGoogle Scholar
- Kliore AJ, Patel IR (1980) Vertical structure of the atmosphere of Venus from Pioneer Venus orbiter radio occultations. J Geophys Res 85:7957–7962View ArticleGoogle Scholar
- Kolodner MA, Steffes PG (1998) The microwave absorption and abundance of sulfuric acid vapor in the Venus atmosphere based on new laboratory measurements. Icarus 132:151–169View ArticleGoogle Scholar
- Krasnopolsky VA, Pollack JB (1994) H2O–H2SO4 system in Venus’ clouds and OCS, CO, and H2SO4 profiles in Venus’ troposphere. Icarus 109:58–78View ArticleGoogle Scholar
- Leroy SS, Ingersoll AP (1996) Radio scintillations in Venus’s atmosphere: application of a theory of gravity wave generation. J Atmos Sci 53:1018–1028View ArticleGoogle Scholar
- Limaye SS et al (2017) The thermal structure of the Venus atmosphere: intercomparison of Venus Express and ground based observations of vertical temperature and density profiles. Icarus 294:124–155. doi:10.1016/j.icarus.2017.04.020 View ArticleGoogle Scholar
- Lipa B, Tyler L (1979) Statistical and computational uncertainties in atmospheric profiles from radio occultation: Mariner 10 at Venus. Icarus 39:192–208View ArticleGoogle Scholar
- Mahieux A, Vandaele AC, Robert S, Wilquet V, Drummond R, Montmessin F, Bertaux JL (2012) Densities and temperatures in the Venus mesosphere and lower thermosphere retrieved from SOIR on board Venus Express: carbon dioxide measurements at the Venus terminator. J Geophys Res 117:E07001. doi:10.1029/2012JE004058 View ArticleGoogle Scholar
- McGouldrick K, Toon OB (2008a) Modeling the effects of shear on the evolution of the holes in the condensational clouds of Venus. Icarus 196:35–48View ArticleGoogle Scholar
- McGouldrick K, Toon OB (2008b) Observable effects of convection and gravity waves on the Venus condensational cloud. Planet Space Sci 46:1112–1131View ArticleGoogle Scholar
- McGouldrick K, Momary TW, Baines KH, Grinspoon DH (2012) Quantification of middle and lower cloud variability and mesoscale dynamics from Venus Express/VIRTIS observations at 1.74 μm. Icarus 217:615–628. doi:10.1016/j.icarus.2011.07.009 View ArticleGoogle Scholar
- Miyamoto M, Imamura T, Tokumaru M, Ando H, Isobe H, Asai A, Shiota D, Toda T, Häusler B, Pätzold M, Nabatov A, Nakamura M (2014) Radial distribution of compressive waves in the solar corona revealed by Akatsuki radio occultation observations. Astrophys J 797(1):51. doi: 10.1088/0004-637X/797/1/51 View ArticleGoogle Scholar
- Nakamura M, Imamura T, Ishii N, Abe T, Satoh T, Suzuki M, Ueno M, Yamazaki A, Iwagami N, Watanabe S, Taguchi M, Fukuhara T, Takahashi Y, Yamada M, Hoshino N, Ohtsuki S, Uemizu K, Hashimoto GL, Takagi M, Matsuda Y, Ogohara K, Sato N, Kasaba Y, Kouyama T, Hirata N, Nakamura R, Yamamoto Y, Okada N, Horinouchi T, Yamamoto M, Hayashi Y (2011) Overview of Venus orbiter, Akatsuki. Earth Planets Space 63:443–457. doi:10.5047/eps.2011.02.009 View ArticleGoogle Scholar
- Nakamura M et al (2016) AKATSUKI returns to Venus. Earth Planets Space 68:75. doi:10.1186/s40623-016-0457-6 View ArticleGoogle Scholar
- Newman M, Schubert G, Kliore AJ, Patel IR (1984) Zonal winds in the middle atmosphere of Venus from Pioneer Venus radio occultation data. J Atmos Sci 41:1901–1913View ArticleGoogle Scholar
- Oschlisniok J, Häusler B, Pätzold M, Tyler GL, Bird MK, Tellmann S, Remus S, Andert T (2012) Microwave absorptivity by sulfuric acid in the Venus atmosphere: first results from the Venus Express Radio Science experiment VeRa. Icarus 221:940–948View ArticleGoogle Scholar
- Pätzold M, Häusler B, Bird MK, Tellmann S, Mattei R, Asmar SW, Dehant V, Eidel W, Imamura T, Simpson RA, Tyler GL (2007) The structure of Venus’ middle atmosphere and ionosphere. Nature 450:657–660View ArticleGoogle Scholar
- Piccialli A, Tellmann S, Titov DV, Limaye SS, Khatuntsev IV, Pätzold M, Häusler B (2012) Dynamical properties of the Venus mesosphere from the radio-occultation experiment VeRa onboard Venus Express. Icarus 217:669–681View ArticleGoogle Scholar
- Pollack JB, Toon OB, Boese R (1980) Greenhouse models of Venus’ high surface temperature, as constrained by Pioneer Venus measurements. J Geophys Res 85:8223–8231View ArticleGoogle Scholar
- Seiff A, Kirk DB, Young RE, Blanchard RC, Findlay JT, Kelly GM, Sommer SC (1980) Measurements of thermal structure and thermal contrasts in the atmosphere of Venus and related dynamical observations: Results From the four Pioneer Venus Probes. J Geophys Res 85:7903–7933View ArticleGoogle Scholar
- Seiff A, Schofield JT, Kliore AJ, Taylor FW, Limaye SS et al (1985) Models of the structure of the middle atmosphere of Venus from the surface to 100 kilometers altitude. Adv Space Res 5(11):1–305View ArticleGoogle Scholar
- Tellmann S, Pätzold M, Häusler B, Bird MK, Tyler GL (2009) Structure of the Venus neutral atmosphere as observed by the Radio Science experiment VeRa on Venus Express. J Geophys Res 114:E00B36. doi:10.1029/2008JE003204 View ArticleGoogle Scholar
- Tellmann S, Häusler B, Hinson DP, Tyler GL, Andert TP, Bird MK, Imamura T, Pätzold M, Remus S (2012) Small-scale temperature fluctuations seen by the VeRa radio science experiment on Venus Express. Icarus 221:471–480View ArticleGoogle Scholar
- Toda T, Hayashiyama T, Kamata Y, Ishii N, Nakamura M (2010) Flight model development of PLANET-C telecommunication subsystem. In: The 27th international symposium on space technology and science, transactions of japan society for aeronautical and space sciences, space technology Japan 8, No. ists27:Tj_17-Tj_22Google Scholar
- Tyler GL (1987) Radio propagation experiments in the outer solar system with Voyager. Proc IEEE 75:1404–1431View ArticleGoogle Scholar
- Woo R, Armstrong JW, Ishimaru A (1980) Radio occultation measurements of turbulence in the Venus atmosphere by Pioneer Venus. J Geophys Res 85:8031–8038View ArticleGoogle Scholar