A new concept radio occultation experiment to study the structure of the atmosphere and determine the

plasma layers in the ionosphere.

Gavrik A.L.

Kotelnikov Institute of Radio Engineering and Electronics of RAS

alg248@ire216.msk.su

25 октября 2011

ВЕНЕРА - ДИКИ РАН

Dual frequency radio wave sounding on the ray path

Orbiter → Earth

The scientific goals in the project VENERA-D

-3 0 3 -3 0 3 T,K 70 71 72 73 74 φ

λ250

240

230

1. Variation in the Solar wind plasma.(analysis of amplitudes and phases

of two coherent radio signals)

2. Monitoring the electron density onthe Venus ionosphere.

(analysis of amplitudes and phases of two signals during occultation)

3. Thermal and density profiles forthe Venus atmosphere.

(analysis of amplitudes and phases of two signals during occultation)

4. Investigate of Venus surface.(analysis of bistatic echoes from

Venus surface)

The electron densities in the Venusian

day and night time ionosphere

Changes in parameters

of Solar wind plasma

Variations in the

temperature profiles of

atmosphere

Anomalous reflectivity

from bistatic radar echoes

Venera 11-16

Vishlov et.al.

Venera -15,-16 Savich et. al.

MagellanJenkins et.al

Venera-15 Pavelyev et.al.

h, km

600

500

400

300

200

100

102 104 102 104 102 104 102 Ne, cm-3

Day-time N(h)

pass into night-time

N(h)

Night-time N(h)

Dual frequency VENERA-15,-16 occultation (4 & 1 GHz or 8 & 32 см) Схема двухчастотного радиопросвечивания

The electron densityof daytime Venusian

ionosphere

N(h), см-3

Measured refraction attenuationsinduced by daytime

Ionosphere and

atmosphere

ХСМ ХDМ

8 см 32 см

Measured residual

frequency in the ionosphere

and atmosphere

fDМ

32 смThe time of occultation

2 … 20 minutes

atmosphere

Radio rays to the Earth

ionosphere

The theory of occultation experiments is based on integral equations

that relate the electron density N(h) to the measured characteristics

of radio signals.

700

600

500

400

300

200

100 102 103 104 105 102 103 104 105 102 103 104 105 102 103 104 105

Alt

itu

de,

к

м

Electron density, см-3

Altitude distributions N(h) of the electron densities in the Venus day-time ionosphere

Распределения электронной концентрации N(h) в дневной ионосфере Венеры

12.10.83г. 560

20.03.84г. 520

23.09.84г. 610

Coincidenceof N(h) forsome days

09.09.84г. 820

12.10.83г. 810

30.10.83г. 820

Time-to-timevariability

14.10.83г. 820

12.10.83г. 810

28.03.84г. 820

Coincidence of N(h) for

some days

19.09.84г. 560

14.10.83г. 580

20.09.84г. 550

Time-to-time variability

102 103 104 105 0 0.5 1.0 1.5 2.0

300

280

260

240

220

200

180

160

140

120

100

80

200

180

160

140

120

100

80

102 103 104 105

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.

The traditional method to determine N(h) leads to wrong conclusions

Model N(h)

Calculation N(h)

Calculation N(h)

N(h)VENERA-1525.10.1983 г.

bottom part of the

ionosphere

Alt

itu

de,

k

m

Electron density, сm-3 Refraction attenuation

Alti

tude

, km

Temperature, K

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 kmfrom occultation data

because of super refraction of the radio rays.

VENUS-EXPRESSM. Pätzold et al.

)t(F)t(fdt

d

Vf

Lc1)t(X

2

The following result is obtained from p(t), (t), X(t) :

1

)t(dpd

L1 )t(X

)t(F)t(fVfc

)t(

),t(L)t(H )t(p

∫⊥

i

222

H

pr

dr fp

eV

c f m 2)p(N

The well-known relationshipsThe 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)

Variations of the defocusing attenuation X(t) in the occultation experiments are proportional to the velocity of residual frequency changes.

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 attenuationof the radio signal XDM(t) and variations XΔf (t)

will be indicative of the influence of the regular structuresof 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.

New method provides a possibility to distinguish the layers in the atmosphere and ionosphere during occultation.

A variations of refraction attenuation of DM signal

coincide with calculated data Х∆f(t)

in the day-time ionosphere of Venus.

Altitude of spacecraft-Earth straight-line h, км

The

ref

ract

ion

atte

nuat

ion,

ХVenera-15,-16Gavrik A. et al.

A variations of refraction attenuation of DM signal

coincide with calculated data Х∆f(t)

in the night-time ionosphere of Venus.

bottomionosphere

One layer night-time ionosphere

Two layers night-time ionosphere

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.

25 50 75 100 125

Refraction attenuation of a DМ-signal in the atmosphere

Refraction attenuation of a CМ-signal in the atmosphere

layered structure in the atmosphere

Correlation between the powers of DM- and CM-signals due to the wavestructure

Refraction attenuation in the ionospherecalculated from the frequency of a DМ-signal

Хдм and Хf are different in the atmosphere

Х

1

0

Layers in the bottom ionosphere:correlation between ХDМ and Хf

Altitude of the spacecraft-to-Earth straight line h, km

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.

This method can be extended to occultation experimentSatellite → Satellite

21

21

2

LL

LLL

)t(fdt

d

Vf

Lc1)t(X

R e

s I

d u

a l

f

r e

q u

e n

c y,

H

z

Altitude of radio ray straight line h, km

http://isdc.gfz-potsdam.de

L1= 19 cm, L2= 24 cm, Δt = 0.02 s

GPS → CHAMP

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.

Realization of informative experiments requires the development of a good on-board receiver.

Small frequency fluctuations in the occultation experiments VENERA-15,-16 → Earthachieved by the high output transmitter power (100 W) and large diameter (>2m) on-board antenna.

In these occultation experiments GPS → CHAMP

we can see the frequency fluctuations, which exceed the influence of the ionosphere.

http://isdc.gfz-potsdam.de

plasma influence

ВЕНЕРА-16 → Земля

λ = 32 см, Δt = 0.058 s

λ = 19 см, Δt = 0.02 s

GPS → CHAMP

invalid measurements (little signal/noise)

Res

idua

l f

requ

ency

,

Hz

Altitude of radio ray straight line h, km

Mean-square deviation Δf(t) from 0.003 to 0.03 Hz

The frequency Δf(t)in the Venus daytime

ionosphere

40 60 80 100 120 140 160 180 2000

1

2

3

4

0

1

2

3

4

0

1

2

3

4

40 60 80 100 120 140 160 180 200

0

1

2

3

4

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.

Altitude of radio ray straight line h, km

The

ref

ract

ion

atte

nuat

ion,

Х

Δt = 0.06 s

Δt = 0.11 s

Δt = 0.23 s

Δt = 0.47 s

The method gives correct results for high-precision measurements during dual frequency radio sounding.Invalid

data(little S/N)

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.

radar experiment

bistatic radar experiment

Interplanetary plasma on the two separated tracks Earth → OA and Earth → SS

ОА SS

Two-frequency radio sounding of the ionosphere

Two-frequency radio sounding of the atmosphere

sign

als

to

th

e E

Ts…

0 35 100 1000 km

Radio signal

Echo-signal

Venera D

Venera

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.

C o n c l u s i o n sWe 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:

1.High-precision phase measurements. 2.High-precision power measurements with the necessary dynamic range. 3. All the measurements should be carried out within a short time interval.4.Radiation from the Earth two coherent radio signals (that will explore the unknown properties of the atmosphere and ionosphere of Venus).

Спасибо за внимание Thank you for attention Работа выполнена при частичной поддержке программы Президиума РАН №VI.15