NEW METODS FOR THE DETECTION OF PLASMA LAYERS

IN THE IONOSPHERE DURING RADIO OCCULTATION

A. L. Gavrik, Y. A. Gavrik, T. F. KopninaKotelnikov Institute of Radio Engineering and Electronics of RAS, Fryazino, Russia, alg248@ire216.msk.su

ИКИ РАН10…14. 10.2011 г.

The second Moscow Solar System Symposium (2M-S3)

Moons of planets Moscow 2011

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.

Mariner-5 2

Mariner-10 2

Pioneer-Venus 441

Венера-15,16 155

Magellan 20

Venus-Express >120

Венера-9,-10 34

Число солнечных пятен(Wolf number)

Год

Количество сеансов радиопросвечиванияКоличество сеансов радиопросвечивания ~800 (number of occultations)

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

В области высот 80 < h < 120 kmметодом радиопросвечивания не

определяется точно температура атмосферы.

In the field of heights 80 < h < 120 km

it is impossible to define atmosphere temperature

precisely.

VENUS-EXPRESSM. Pätzold et al.

)t(F)t(fdt

d

Vf

Lc1)t(X

2

The following new 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 in electron density.

New method provides a possibility to distinguish the effect of plasma and to detect the ionized layers during occultation.

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

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,

Х

Two layers night-time ionosphere

Venera-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

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

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 very high frequency fluctuations.

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

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.

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…

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 planetary ionospheres and atmospheres 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.

Спасибо за внимание Thank you for attention

Работа выполнена при частичной поддержке программы Президиума РАН №VI.15