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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. [email protected] октября 2011 ВЕНЕРА - Д ИКИ РАН.

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Gavrik a l

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.

[email protected]

  • октября 2011

  • ВЕНЕРА - Д

  • ИКИ РАН


Gavrik a l

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


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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


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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


Gavrik a l

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


Gavrik a l

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


Gavrik a l

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.


Gavrik a l

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.


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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


Gavrik a l

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


Gavrik a l

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.


Gavrik a l

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


Gavrik a l

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


Gavrik a l

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


Gavrik a l

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


Gavrik a l

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.


Gavrik a l

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


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