Gavrik A.L.

1. A new concept radio occultation experiment to study the structure of the atmosphere and determine the plasma layers in the ionosphere. Kotelnikov Institute of Radio Engineering and Electronics of RAS Gavrik A.L. alg248@ire216.msk.su • октября 2011 • ВЕНЕРА - Д • ИКИ РАН

2. Dual frequency radio wave sounding on the ray path Orbiter → Earth The scientific goals in the project VENERA-D h, km 600 500 400 300 200 100 1. Variation in the Solar wind plasma. (analysis of amplitudes and phases of two coherent radio signals) 2. Monitoring the electron density on the Venus ionosphere. (analysis of amplitudes and phases of two signals during occultation) 3. Thermal and density profiles for the Venus atmosphere. (analysis of amplitudes and phases of two signals during occultation) 4. Investigate of Venus surface. (analysis of bistatic echoes from Venus surface) Venera 11-16 Venera-15 Pavelyev et.al. Night-time N(h) Day-time N(h) pass into night-time N(h) λ 250 240 230 Venera -15,-16 Savich et. al. Magellan Jenkins et.al Vishlov et.al. 7071 72 73 74φ -3 0 3 -3 0 3 T,K Changes in parameters of Solar wind plasma The electron densities in the Venusian day andnight time ionosphere Variations in the temperature profiles of atmosphere Anomalous reflectivity from bistatic radar echoes 102 104 102 104 102 104102 Ne, cm-3

3. Dual frequency VENERA-15,-16 occultation (4 & 1 GHz or 8 & 32 см) Схема двухчастотного радиопросвечивания The theory of occultation experiments is based on integral equations that relate the electron density N(h) to the measured characteristics of radio signals. Measured refraction attenuations induced by daytime Ionosphere and atmosphere ХСМХDМ 8 см32 см Measured residual frequency in the ionosphere and atmosphere fDМ 32 см The electron density ofdaytime Venusian ionosphere N(h), см-3 The time of occultation 2…20 minutes ionosphere atmosphere Radio rays to the Earth

4. Altitude distributions N(h) of the electron densities in the Venus day-time ionosphere Распределения электронной концентрации N(h) в дневной ионосфере Венеры 700 600 500 400 300 200 100 19.09.84г. 560 14.10.83г. 580 20.09.84г. 550 Time-to-time variability 14.10.83г. 820 12.10.83г. 810 28.03.84г. 820 Coincidence of N(h) for some days 09.09.84г. 820 12.10.83г. 810 30.10.83г. 820 Time-to-time variability 12.10.83г. 560 20.03.84г. 520 23.09.84г. 610 Coincidence of N(h) for some days Altitude, км 102 103 104105102103 104 105102 103 104105102103 104 105 Electron density, см-3

5. The traditional method to determine N(h) leads to wrong conclusions about the bottom ionosphere. We can see discrepancies between the model and calculated N(h). The error can be greater than the actual value of N(h) at altitudes of h < 120 km. That is why we can see the bottom boundary of the ionosphere at altitude of h = 117 km on the experimental profile N(h). But the real influence of ionospheric plasma is observed up to 85 km in the occultation data. 300 280 260 240 220 200 180 160 140 120 100 80 200 180 160 140 120 100 80 Model N(h) Calculation N(h) Calculation N(h) Altitude, km N(h) VENERA-15 25.10.1983 г. bottom part of the ionosphere 102 103104105 102 103104105 0 0.5 1.01.5 2.0 Electron density, сm-3 Refraction attenuation

6. In the field of heights 80 < h < 120 km it is impossible to define atmosphere temperature precisely. It is impossible to define any parameters of Venus atmosphere for h < 35 km from occultation data because of super refraction of the radio rays. VENUS-EXPRESS M. Pätzold et al. Altitude, km Temperature, K

7. The well-known relationships The ray asymptote distance Н – the altitude of straight-line ray The refractive bending angle Δf – residual frequency in the ionosphere ΔF –residual frequency in the atmosphere The refraction attenuation L – the distance between the spacecraft and point  V┴ – the velocity of the satellite’s ingress The electron density f – the radiated frequency(1 GHz) The following result is obtainedfromp(t), (t), X(t): Variations of the defocusing attenuation X(t) in the occultation experiments are proportional to the velocity of residual frequency changes.

8. New method provides a possibility to distinguish the layers in the atmosphere and ionosphere during occultation. It is necessary to determine same parameters from the experimental data: XDM(t) - the refraction attenuations of L-band (32 cm) signal. XCM(t) - the refraction attenuations of C-band ( 8 cm) signal. δf(t) =16/15(fDM(t) - fCM(t)/4) - the reduced frequency difference (plasma influence). Δf(t) = function [δf(t)] - frequency variation of L-band (32 cm) signal. XΔf (t) = 1 + value*d/dt[Δf(t)] - predicted refraction attenuation of the L-band signal. Coincidence between variations of refraction attenuation of the radio signal XDM(t) and variations XΔf (t) will be indicative of the influence of the regular structures of the ionosphere under investigation. The absence of this correspondence is an indication of the influence of the noise or other factors that are not taken into account. This method considerably increased the sensitivity of the radio probing method to refractive index variations and makes possible to detect small variations of electron density and atmosphere density.

9. Venera-15,-16 Gavrik A. et al. bottom ionosphere A variations of refraction attenuation of DM signalcoincide with calculated dataХ∆f(t) in the day-time ionosphere of Venus. The refraction attenuation, Х One layer night-time ionosphere A variations of refraction attenuation of DM signalcoincide with calculated dataХ∆f(t) in the night-time ionosphere of Venus. Two layers night-time ionosphere Altitude of spacecraft-Earth straight-lineh, км

10. This technique will allow one to investigate wave processes in the top atmosphere and the bottom ionosphere.We observed wave processes in the top atmosphere and bottom ionosphere of Venus. Refraction attenuation of a DМ-signal in the atmosphere Х 1 0 Refraction attenuation of a CМ-signal in the atmosphere Refraction attenuation in the ionosphere calculated from the frequency ofa DМ-signal Correlation between the powers of DM- and CM-signals due to the wave structure layered structurein the atmosphere Layers in the bottom ionosphere: correlation between ХDМandХf ХдмandХf are different in the atmosphere 25 50 75 100 125 Altitude of the spacecraft-to-Earth straight lineh, km

11. This method can be extended to occultation experiment Satellite → Satellite L1 – the distance between the first spacecraft and point of ray closest to the surface of planet. L2 – the distance between the second spacecraft and point of ray closest to the surface of planet. The method is correct for high-precision measurements of signal power and phase during dual frequency radio sounding.

12. http://isdc.gfz-potsdam.de In these occultation experiments GPS → CHAMP we can see very high frequency fluctuations and the lack of coherence of the signals of two ranges L1 & L2. Hence, the onboard USO must be very stable on short time intervals. GPS → CHAMP R e s I d u a l f r e q u e n c y,Hz L1= 19 cm, L2= 24cm,Δt = 0.02 s Altitude of radio ray straight lineh, km

13. Realization of informative experiments requires the development of a good on-board receiver. http://isdc.gfz-potsdam.de In these occultation experiments GPS → CHAMP we can see the frequency fluctuations, which exceed the influence of the ionosphere. GPS → CHAMP λ = 19 см, Δt = 0.02 s Residual frequency,Hz invalid measurements (little signal/noise) Small frequency fluctuations in the occultation experiments VENERA-15,-16 → Earth achieved by the high output transmitter power (100 W) and large diameter (>2m) on-board antenna. plasma influence λ = 32см, Δt = 0.058 s ВЕНЕРА-16 → Земля The frequency Δf(t) in the Venus daytime ionosphere Mean-squaredeviationΔf(t)from0.003to0.03Hz Altitude of radio ray straight lineh, km

14. Δt = 0.06 s The method gives correct results for high-precision measurements during dual frequency radio sounding. Δt = 0.11 s Invalid data (little S/N) The refraction attenuation, Х If we choose a very long measurement interval Δt, then the effects of focusing of a signal and layered structures will not manifest themselves. Therefore, it is necessary to provide a high S/N ratio during the experiments. Δt = 0.23 s Δt = 0.47 s Altitude of radio ray straight lineh, km

15. High S / N ratio can be achieved if emit powerful coherent radio signals from Earth. In this case, at the same time we can perform six radio physical experiments, in addition to the work of other onboard devices. High S / N ratio give the possibility of obtaining new information concerning the structure of the planetary ionospheres and atmospheres. ОА SS Interplanetary plasma on the two separated tracks Earth → OA and Earth → SS Two-frequency radio sounding of the ionosphere signals to the ETs… Two-frequency radio sounding of the atmosphere bistatic radar experiment radar experiment

16. Echo-signal Venera D i o n o s p h e r e a t m o s p h e r e Radio signal near the surface atmosphere Venera 0 35 100 1000 km It is important that the high potential allows regular bistatic location. We can determine the parameters of the Venus atmosphere near its surface from the characteristics of the echo signals. Consequently, it is possible to monitor the bottom of the Venusian atmosphere, details of which are very limited.

17. C o n c l u s i o n s • We have shown that the new methods proposed • make it possible to carry out high-quality analysis • of the Venus ionosphere and atmosphere • during dual-frequency occultation experiments. • There are a few conditions for this investigation: • High-precision phase measurements. • High-precision power measurements • with the necessary dynamic range. • 3. All the measurements should be carried out • within a short time interval. • Radiation from the Earth two coherent radio signals (that will explore the unknown properties of the atmosphere and ionosphere of Venus). Спасибо за вниманиеThank you for attention Работа выполнена при частичной поддержке программы Президиума РАН №VI.15