Gavrik A.L., Kopnina T.F., Bondarenko M.I., Smislov A.A. Multi-frequency phase-coherent systems: new instrument for occultation in the project Venus-D. In: The Sixth Moscow Solar System Symposium (6MS3), October 5-9, 2015, Space Research Institute, Moscow, Russia , 243-ab.
Полный текст не доступен из этого репозитория.Аннотация
Introduction: Since 1975, Venus-orbiting spacecraft (S/C) have carried out more than 600 two frequency radio occultation measurements of the atmosphere and ionosphere density. Radio science experiments could be accomplished using no more than two coherent downlink signals. The quantities observed during occultation are the phases and powers of radio signals received at a ground station. Such simple systems allow performing the standard radio sounding experiments solely using the well-known and adequately developed techniques. The aim of the report is to present planned non-standard and effective radio science investigations of Venus atmosphere, ionosphere and the solar wind plasma in the project Venera-D. Multi-frequency phase-coherent system for occultation: The Cassini Telecommunication System was a pioneer to use two coherent uplinks (X- and Ka-band) and four coherent downlinks (S-, X-, and Ka-band two downlinks). The main scientific objective of such complex Cassini Radio Science System (RSS) was performance of unique gravitational and relativistic investigations and certain radio sounding experiments. Applying a similar multifrequency phase coherent system on board the S/C Venus-D opens up new opportunities for planetary envelope occultation and space plasma sounding. The theory of multi-frequency phase-coherent RSS for the deep space exploration considers RSS as a unified system consisting of several coherent uplinks and downlinks. Two coherent uplink signals emitted by the ground transmitter acquire the appropriate phase shifts due to changes in the distance, neutral and ionized components of the space medium propagating between Earth and the S/C. The S/C transponder receives the two signals forming coherently four downlink signals which are received at the ground-station in their passage of the return path S/C-Earth. We make these four signals a measurand Ψ(t) as a linear combination of the signal phases Ψ(t)=К1Φ1(t)+К2Φ2(t)+К3Φ3(t)+К4Φ4(t) using appropriate coefficients К1, К2, К3 and К4. For plasma investigation the function Ψ(t) must not depend on neutral component and a distance between Earth and the S/C. It means that the certain conditions for coefficients must be satisfied. We can get three cases which may be realized simultaneously: 1) the time dependence of uplink total electron content variations; 2) the time dependence of downlink total electron content variations; 3) variations of a mean value of a longitudinal component of a magnetic field for ordinary and extraordinary radio waves. The principal requirement of this method is clear now: RSS must provide simultaneous coherent radiation of both two uplinks and four coherent downlink signals in two-way mode. Accordingly ground station must provide coherent simultaneous receiving of four downlink signals and digital processing of the signals allows to realize the phase measurements. One of the most important sources of the radio occultation experiment errors is total electron content variations in the radio wave path including the Earth ionosphere. We can use multi-frequency phase-coherent RSS for solving the radio occultation inverse problem excluding the unfavorable Earth ionosphere effect. We also offer the new technique of the data analysis that allows us to separate influence of noise, ionosphere and atmosphere on the radio occultation results. Variations of the defocusing attenuation in the occultation experiments are proportional to the velocity of residual frequency changes. Good agreement between frequency data and observed power attenuation has been registered in many occultation events. Coincidence between signal energy and frequency deviations is indicative of the influence of the stratified layers in the atmosphere and ionosphere under investigation. The absence of this correspondence is an indication of the influence of any factors that are not taken into account. This technique considerably increases the sensitivity of the radio probing method to refractive index variations, makes possible to detect wave-like structure in the atmosphere and ionosphere and cleanly separates noise, ionospheric and atmospheric influences during an occultation experiment. The developed methods provide the ability to obtain high quality information about the Venusian ionosphere and atmosphere. A multi-frequency phasecoherent system in the project Venus-D is capable of carrying out new, nonstandard and effective radio science exploration in the field of the space plasma studies: measurements of the total electron content on both the uplink and downlink made simultaneously and/or separately; Venus atmosphere and ionosphere sounding by a new two-way method; location of solar wind plasma clouds and measurement of the plasma cloud magnetic field. Acknowledgements: The work is partially supported by the RAS Presidium Program № 9.
| Тип объекта: | Доклад на конференции или семинаре (Доклад) |
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| Авторы на русском. ОБЯЗАТЕЛЬНО ДЛЯ АНГЛОЯЗЫЧНЫХ ПУБЛИКАЦИЙ!: | Гаврик А.Л., Копнина Т.Ф., Бондаренко М.И., Смыслов А.А. |
| Подразделения (можно выбрать несколько, удерживая Ctrl): | 114 лаб. исследований космической плазмы радиофизическими методами 119 лаб. распространения радиоволн и дистанционного зондирования атмосферы |
| URI: | http://cplire.ru:8080/id/eprint/1916 |
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