Electron density profiles in the ionospheric D-region estimated from MF radio wave absorption

Adv. Space Res. Vol. 25, No. I, pp. 33-42, 2000 0 1909 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0279. I 177100 $20.00 + 0.00

Pergamon www.~lsevier.nl/locateiRsr

PII: SO273- I 177(‘)9)008‘J4-7

ELECTRON

DENSITY

PROFILES

REGION ESTIMATED

I. Nagano’

IN THE

IONOSPHERIC

D-

FROM MF RADIO WAVE ABSORPTION

and T. Okada’

‘Depurtment

oj’Electricu1

urd Computer

‘Depurtment

of Electrotlics

Engineering,

Kunuxwu

Universit?;

Toyumu Prqfecturul

utld Ir!formatic.s,

Kur~uzuwu 920-8667

University,

Kosugi,

Japan,

Toyama

939-0398

Jupun

ABSTRACT

Electron

density

measurements

period

from

Japan).

Low electron

based radio signals kind of methods, D-region

electron which

densities

were estimated

the

rockets

were carried launched

density

by comparing

from the absorption

measurement.

D-region

is presented.

method

at mid-latitude

methods

In particular

electron

intensity

and MF absorption

the observed

density

Finally

derived

in Japan are compared

methods

are introduced

ionospheric

measured

rocket

from electron

by onboard

receivers.

were developed

attention

experiment

the altitude density

variation

the

by a full wave

to the capability

of low

in detail,

of MF radio

so far measured

with those of the IRI-95 model. 0199~ COSPAR. Published

in

Two

to estimate

is discussed

profiles

the

Center

mode of ground-

with that calculated

paying

during

Space

of the characteristic

wave intensity

the S-310-18

profile

the lower

out more than 6 times

at KSC (Kagoshima

(17.4 kHz and 873 kHz) in the lower ionosphere

In this paper, both absorption density

ionosphere

sounding

i.e., VLF mode absorption

electron

treatment.

in the lower

1975 to 1992 by using

by Elsevier

in

wave

by those Science

Ltd.

1. INTRODUCTION

In-situ

measurement

frequency

of the impedance

standard

method

experiments covers

separate

density

between

to measure

in Japan was first made by a method

the electron

density

shift frequency

above

density

in the ionosphere well-known

modes

for almost

as the gyro-plasma

On the other hand, the electron

of the MF or VLF radio wave propagating

et ul, 1964 and Kimura the characteristic

IO” els/cc.

et ul., 1967).

to measure

(Oya et ul., 1966). This technique

two electrodes

at KSC (Oya et ul., 1969) and it became

the electron

the doppler (Maeda

of the electron

In this VLF doppler

of the VLF wave

33

density

was adopted

all sounding

such as L and R (left-

as a rocket

probe (GPP) which was calculated

from the ground-based experiment,

a resonant

Kimura

and right-

from

transmitter

was successful handed

circular

I. Nagano and T. Okada

34

polarized

waves)

disappears

at a specific

and left-handed them

wave

polarized

by comparing

density

the observed

the electron

within

the electron

density

electron

density

absorption frequency

on the MF radio

density

profiles

years in Japan

by comparing full

to the atmospheric simple

compared

absorption

in the lower are compared

(Nagano

with the corresponding

pressure.

ranges

to obtain

obtained

electron

rocket.

that

Reference

The

the collision

to measure

the MF radio

In this paper we will

density.

Finally

the electron

by these VLF and MF radio wave methods

with those of the International

of

with the MF radio wave

instrument

the D-region

from 5 els/cc

by S-310-18

the assumption

The onboard

by the

was estimated

the small scale variation

wave intensity under

1978).

field calculated

with that of VLF R and L mode waves.

method

ionosphere

method

L mode the right-

which enabled

of 70 km in the daytime

the observed

the

et ~1.. 1976 and

by this VLF mode absorption

wave

that

to separate

electrically,

a MF radio wave was used in the daytime

by the generalized

relatively

antenna

ionosphere

the altitude

estimated

indicated

15%. On the other hand, in order to detect

was obtained

is proportional

wave becomes

around

and

an apparatus

the receiving

in the lower

density

in the D-region

calculated

spectrum,

et al. developed

R mode intensity

density

an error of +

profile

observed

Nagano

waves by rotating

ef ul., 1981). The electron

to lO’els/cc

in the

density.

the low electron

method,

(Nagano

focus

independently low electron

circularly

to estimate

Furthermore, full

modes

Ionosphere

during

model revised

20

in 1995

(IRI-95).

2. EXPERIMENTS

The S-3 10-l 8 sounding

rocket

was launched

degrees

Space

Center

at Kagoshima

(Institute

of Space

and reached

sec. after firing. based

station

Kumamoto

and Astronautical

210 km horizontally We observed (137.OIE,

broadcasting

at 1 I:00 JST on January

(13 1.04E. Science).

34.36N) station

near

(130.SOE,

in Geographic

The rocket

in the direction a VLF signal

3l.lSN,

measured

NDT (17.4kHz,

200KW)

Nagoya

estimate ray paths

the D-region

and a MF radio

density

signals

during

the daytime.

from the ground-based

coordinate

Figure

angle of 78

system)

by ISAS

of 202 km at 223 sec.

anti-clockwise transmitted

wave

30.SON) in both ascending

paths of radio waves from ground-based

electron

of the received

at an elevation

went up to an apogee

30 degrees

from South,

at 430

from Yosami’ground-

(873kHz,

SOOKW) from

and descending

flights,

NHK

in order to

JJ Y 8MHz

NAZAKI

Fig.1 Propagation

26,1988

stations

to the S-310-18

1 shows the trajectory

transmitters.

In this rocket

rocket.

of the rocket and

experiment,

a wide-

35

D-Region from Radio Wave Absorption

band loop antenna

Figure

2 shows

antenna

system

at 17.4kHz

and the MF radio wave at

antenna

to respond

widely

preamplifier

is coupled up to

However,

the instant

of the launch

material.

The intensity

of the wave intensity effect remains

attenuation

profile

almost

constant

is due to collisional

effective

amplifiers length

through

of the

is just

exceeding

twice

a series

loop

system

transformer including

the

located

intensity

decreases

abruptly

amplitude

at the reflection

are also

point

flight

altitude

frequency

because

of the

level is clearly

in the area

is shown

evanescent

medium.

frequency

that

at higher

the wave

of a few km below

and shape

the reflection

with an is 4 Hz,

to 2 Hz by

polarization

reflected

The

intensified

effect appearing

of the modulation level.

is

at 88km and the

altitudes.

3. This seems to be a focusing The pitch

The

rocket.

SO km, and decreases

of modulation

The

up to 87 km. This

is seen to be modulated

on board the S-310-18

mode

in Fig.3.

to the rocket.

gradually

of 70 km. The wave is perfectly

seen in Figure

of a dielectric

up to 20 km. This is due to a

70 km. The modulation

of 2 Hz below

by the depth

at an abitude

The envelope

below

of the wave receiver

in an inhomogeneous

distorted

the ascent

the MF radio

was made

on the ray path from the transmitter

30 dB at altitudes

spinning

to elliptical

during

could detect

of the rocket

with increasing

in the D region.

It is confirmed

from linear

the nose fairing

fairing

observed

of 58 km at 45 sec. after launch.

up to 65 km and then it tends to decrease

about

the rocket

of the rocket.

at the reflection

at an altitude

the nose

gradually

damping

changing

intensity

low-noise

was deployed

of the wave increases

Fig.2 A block diagram

which

The

because

from the mountains

variation

despinning

two

with an area of 78 cm2 held inside

envelope

intensity

1MHz.

The loop antenna

the loop antenna

from

diffraction

with

loop

with 20 dB gain are 24 cm at 17.4kHz and 22 cm at 873kHz.

wave ohservatlon

intensity

1990).

with an area of 0.106 m’ was used to detect the NDT signal loop

of the wave instruments

and Nagano,

A triangular-shaped

The

diagram

(Okada

the rocket.

network

the block

the JJY 8MHz signal

onboard

873 kHz.

wave

was tested by receiving

This

of the

is due to the

36

1. Nagano and T. Okdda

collisional

damping

of the downgoing

wave.

80

0

Fig.3 An altitude

profile

at 873 kHz measured

3. ESTIMATION

of magnetic

during

OF D-REGION

ionosphere

depends density

on both

ELECTRON

integrated

over

frequency

in the lower

Wyller,

..

We adopt

lower ionosphere.

with energy

expressed

by the equation

cross

section

analyze using

which

of neutral pressure

both electron

electron

density

K, thus

estimated

procedure decrease

slightly

The intensity

value observed

calculated

of the MF radio

above

and K, is called

by the gyro-plasma the calculated

absorption

shown

we use it as a constant

wave can be calculated

by using

in Figure

model

as an

value of K, to by

of 85 km by the same range from 85 km

full wave method

using

the

the same rocket.

fits the observed 4. Though

one.

The This

K, is reported

in the lower ionosphere the generalized

transfer

K, is estimated

in the altitude

probe (GPP) onboard

can be

the collision

the momentum

the altitude

in the

and mono-energetic

of K,,. The empirical

at 17.4kHz

(Sen and

temperature,

and the CIRA

by the generalized

to the first step in the flow chart altitude,

experiments,

of the NDT signal

85 km when

pressure

the wave intensity

to be 6.3, by using

the

that the collision

molecules

pressure

to estimate

1966). In this paper, we use an empirical

of the theoretical

simultaneously

with decreasing

to calculate

in the lower

of the absorption

and Te is the electron

in laboratory

absorption

because

It is well-known

the neutral

constant

and VLF wave intensity

is 4.4 above

between

It is difficult wave

to the atmospheric

frequency

theoretically

and Piggott,

the wave absorption

corresponds

v,,

frequency

observed

wave in plice

observed

proportional

for the collision

can be calculated

to 95 km with the corresponding

frequency.

of the radio

K,, x 10” P. Here P is atmospheric

particles

density

We compare

of the wave propagating

in the ionosphere.

k is Boltzman’s

model (Thrane

the MF radio

rocket.

this theory

v,,=

and collision absorption

is theoretically

kTe, where

factor,

atmospheric

from

In this case, collision

electrons

The absorption

propagation

ionosphere

of the MF radio wave

DENSITY

density

only

the path of wave

1960).

proportional

electron

at any altitude

field intensity

the rocket ascent (OdBp=lpV/m).

v ornti

electron

1

.80 60 intensity(dBp)

40 Field

20

to

in this paper.

full wave calculation

37

D-Region from Radio Wave Absorption

Observed data

I

Electron density above 85 km

Estimation of collision frequency = 4.4 P = CIRA

x IO’P model

“,

VLF intensity above 85 km

4 Initial electron density profile

Final electron

N

density profile

Fig.4 A flow chart for the procedure

taking

account

collision

frequency

calculated profile

using

.

letting

dependent

of the observed

the observed

MF wave, and modify

the collision

frequency

component

discussed

with various

in the previous

are calculated

every

the reflection

altitude

electron

good agreement Thus, profile

density

we can get the final

that a distinct

profile

electron

by the broken

profile

peak in the initial

depression

indicated

in the electron

is modified

iteratively

density

profile

abruptly

by the broken density

line obtained around

variation

of the

is determined calculated

at any altitude

by value.

is calculated

shown in Figure

rates of the up-going

density

by taking

profile

until the observed

appears

density

profile.

profile

models

is

5 and

horizontal

of 6Skm up to 90km as shown in Figure

electron

near the reflection

that appears

density

rate at any altitude

is explained

slope in the D-region

density

profile

electron

the altitude

density

The attenuation

indicated

density

fit the corresponding

electron

range

from the effective

an initial

a maximum

shown

wave intensity

in Figure 4. profile

from 65 km to near the reflection by the solid line as shown in the next chapter. at 71km. The density altitude

73 km corresponds

onboard

in Figure

It is interesting is almost

and then connects

by the GPP method

value

from 65 km up to near

7. On the basis of the procedure

one in the altitude

line in this figure

800 els/cc up to 8Skm and increases density

an initial

by the dots in Figure

with the calculated

indicated

absorption

3. Then we can obtain

as shown

electron

1 km from the altitude

6. On the other hand, we can get the observed in one spin from Figure

it until

kinds of ionospheric

section.

profile.

the electron

one, and then get a final electron

rate of the MF wave at any altitude

full wave calculation

Then

we first estimate

The initial

absorption

density

which is different

formula.

rate per 1 km of the MF wave for a specified

by the generalized

an electron

frequency,

4. Namely,

. .

The attenuation

the initial

collision

in Figure

fits best to the observed

.

to estimate

in the Appleton-Hartree outlined

the absorption

absorption

magnetic

energy

appearing

by the procedure

calculated

L

of the electron

I

is in

height. 7. The to note

constant

the same rocket.

to the similar

at

to the electron The

dip in the wave

1. Nagano and T. Okada

Co1 1 ision -

frequency

&Iz)

1

I

-

N

Elecrtron

density

Fig3

Altitude

density

and collision

evaluate

the

Electron

(l/cc)

profiles

of

electron

frequency

attenuation

of

Fig.6

used to

of

up-going

Relationship

wave

density

waves.

the

between

magnetic

at several MF

Kumamoto

densi ty(I/cc)

attenuation

field

and

altitudes

radio

electron

over KSC for

wave

from

NHK

station.

95 / 901

ld

density 90km

profiles

(u,,) (N):

and The

the

variation

the

chain

attenuation

collision electron

in

curve

measured

the

over

with the

rates

estimated

frequency

The density line

hbgnetic

Fig.8

The error bars represent

when the collision by f30%.

of

estimated dashed

is the profile

GPP technique.

16

density(l/cc)

Altitude

frequency

104

103

ld Electron

Fig.7

I

/”

\

profile

is estimated

profile shown from

for the incident

of the wave changing

with altitude.

estimated

in the

angle

profile

intensity(dB)

altitude

profile

field intensity

generalized Figure

is changed

An

magnetic

field

full

wave

density 7. The

actually

of

calculated method

profile

dotted measured

line

wave by a

with the shown

in

shows

the

by the rocket.

D-Region from Radio Wave Absorption

Note that this small

intensity.

rocket

attitude

the observed in Figure effect

scale

and the instantaneous wave intensity

8. As is seen,

of the antenna,

above 75 km. It implies

of the wave intensity

variation

of the gain of the wave receiver.

and the intensity

calculated

resultant

the standing

that damping

wave

pattern

of the up-going

can not be proved

(up and down of L and R modes corresponding

by the Appleton-Hartree

No reflection

slightly

a difference

standing

wave of the calculated

This

is because

comparison

between

the spin

between

intensity

modulated

reflection

height.

from

intensity

effect

appears

consisting

of the up- and down-

In fact Figure

to Booker

above

and the calculated

by the rocket

spin agrees

going

perfectly

waves

wave. This

the characteristic from the There

in the range

of 75 km as shown

including

is shown

the spinning

frequency.

profiles

in the calculation.

intensity

almost

intensity

between

independently

in the MF radio

the altitude

account

9 shows

roots) separated

the observed

into

the observed

profile

which does not include

is recognized

and

was not taken

density

line),

formula.

the D-region

the calculated

The comparison

wave is less than that of the down-going

modes

waves.

is never

from the final electron

wave (solid

effect

resultant

generated by the effect of

variation

the calculated shows

39

is

where

in the Figure

Figure

10 shows

8. the

the effect of spin. The calculated

with the observations,

especially

near the

95 90 i

85

40 hifignelic

Fig.9 Altitude profiles of characteristics mode (L and R for right- and lefthanded polarized modes, and up and down for up- and down-going modes). 4. EVALUATION

In estimating

OF THE ESTIMATION

the electron

density

-30 field

40

-io

inlensitykll3)

Fig.10 An altitude profile of wave magnetic field intensity with spinning motion of the rocket taken into account.

ERRORS

based on the procedure

as shown in Figure 4, the following

factors

may

cause errors: (1) The parameters (2) Ambiguity

except

the incident

of the collision

frequency

angle shown in Table

I used in the full wave calculation

(CIRA mode is used as a pressure

profile)

(3) Plane wave approximation As for the item (l), these values and transmitter, caused

so that they will not cause any serious

by the item

atmospheric

are fixed by the geographical

pressure

(2) and (3) must be evaluated. on the collision

frequency

conditions

error to the electron We evaluated

over the entire

between density.

the effect altitude.

locations

of the rocket

Errors which may be

of f 30% changes

The corresponding

in the

variation

40

1. Nagano and T. Okada

ranges

of the estimated

no big variation

electron

density

are indicated

in local time and day, the pressure

by the error bars in Figure model

adopted

The incident Table 1. Parameters used in a generalized full wave calculation ___--_____----____-_~~~~_--~~~~_~--~~~~ Gyro-frequency

the average

Incident

angle

176.6”

angle

reflection

69.6”

Frequency

line in Figure

7. The error of the electron

evaluated

to be within

the range from -20% to +30%.

THAT

sunspot

number

All electron

ELECTRON

methods,

11. The electron

profiles

density

profile electron

12 shows

density

PROFILES

experiments

by the experiments

density

shown

flight

for the descent

between

when D-region

the observed

electron

density

angle.

at

In this

is indicated

by

is finally

AT KSC

WITH

table

out at KSC by using

shows

the date,

were carried

is added

shifted

densities

experiments

together

in Figure

in this figure.

downwards

with those of the IRI-95

were carried

out

Jan. 28 1992

16:OO

11 :oo

11 :oo

2l:OO

94

68

54

54

134

84

80

237

136

94

231

16

23

224

46

44

187

40 kHz

40 kHz 17.4 kHz

17.4 kHz

17.4 kHz 8 MHz

17.4 kHz 873 kHz

17.4 kHz 873 kHz

0

0

0

0

VLF

VLF

VLF

VLF

,MF

MF

19:45

19:lS

10s

Solar F10.7 cm flux Sunspot number

1 K-9M-72

The

by about

Jan. 26 1988

K-9M-67

the

angle,

out over 1.5 solar cycle.

in Table 2 are plotted

is clearly

zenith

Feb. 11 1982

Oct. 18 1979

Method

wave intensity

1 S-310-21

Aug. 11 1976

Polarization

is not

1 S-310-18

1 S-210-11

Aug. 26 1975

Wave Frequency

This variation

MEASURED

electron

density

Date

angle

the at the

from the

by the MF absorption

of the S-3 lo-18 flight

K-9M-53

Zenith

to calculate

incident

so far carried

This

The experiments

ROCKET

Time (JST)

We take

The intensity

angle.

electron

we estimated

of S-310-18.

for the descending

the comparison

Table 2. Conditions

density

the case

of experiments.

obtained

of the D- region

km. Figure

from

angle

with the corresponding

DENSITY

electron

including

and the method

density

angle decreases

BY IRI-95

a list of the D-region

absorption

bottom

THE

CALCULATED

Table 2 shows radio

OF

of the

fS dB for +3” deviation

the estimated

a broken

S.COMPARISON

varies

to the

the intensity

so that we have to calculate

any altitude case,

to be valid.

of the rocket.

of the incident

value of the incident

negligible,

__________-_______--~~~~_---~~~~~----~~

altitude

in the ionosphere.

level

averaged

873kHz

value

intensity

affects

The incident

72” to 68” with increasing

wave Azimuthal

significantly

wave in the ionosphere.

43”

7. Since in fact there is is considered

angle of the wave from the transmitter

lower ionosphere

1.2MHz

Dip angle

from ClRA

2 at

D-Region from Radio Wave Absorption

41

the launch site for the corresponding

solar activities. We can roughly state that the IRI-95 model for low

solar activity

with the measurement

is in good agreement

of the D-region electron density in Japan.

However for the high solar activity the IRI model electron density in day time is significantly than the observation

smaller

and in night time slightly larger.

80

Electron

Density

[els/cc]

Fig. 11 Altitude profiles of electron density estimated from wave measurements in several rocket experiments: The dashed lines show the profiles measured with the GPP method.

Fig. 12 Comparison of the estimated electron density profiles with the international

reference ionosphere (IRI-95) model.

6. SUMMARY We have introduced

the measurements

of the D-region electron density by the radio wave absorption

42

1. Nagano and T. Okada

methods from

which

the

were developed

viewpoint

navigation

signals

of the estimated

from

10 els/cc

rockets

method

density

up to more than

for MF radio

during

becomes

in the lower

waves

the IRI-95

the ground-

for communication

important

lO’els/cc.

version

was discussed

transmitters

in detail

for OMEGA

of the D-region

were made. As a result,

electron

by the MF absorption

that the receiver

The comparison

observed

VLF

estimated

It is also a merit

profile

based

measurements

in the daytime

with the observed

method

with the ships on the sea have been dismantled,

for in-situ

ionosphere

model and the density

the MF absorption

Since

are very simple.

20 years and the IRI-95

was in fairly good agreement

Especially

error.

and the NDT signal

the MF absorption The electron

in Japan.

between

and the antenna

the D-region

a large difference

density. method

is

on board

profiles

obtained

has been found between

in day time for high solar activity,

however

the model

one for low solar activity.

ACKNOWLEDGMENTS

These

experiments

thank

emeritus

University

were carried

Professor

out with the full cooperation

I. Kimura

and Professor

K. Oyama

of Kyoto

University,

of the rocket

emeritus

of ISAS for their continual

group

Professor

of ISAS.

M. Mambo

We wish to of Kanazawa

advice and encouragement.

REFERENCES

Kimura,

I., R. Nishina,

doppler Maeda,

and K. Maeda,

Nagano,

Nagano,

I. Kimura,

of the doppler I, M. Mambo,

multi-layerd

and G. Hutatsuishi, Radio Sci.,

medium,

I., M. Mambo,

Nagano,

I., M. Mambo,

D region

Okada,

IEICE

Oya, H., and T. Obayashi, experiment Oya,

Rocket

North-Holland,

calculation

density

observation

the VLF

of the ionosphere

by

1964

of electromagnetic

68-74,

waves

Measurement

E-59,6-7,

in isotropic

Estimation

from a ground

derived

from

1976

ionosphere

Plurlet Spuce Sci., 26, 219-227,

electron

density

by

1978

of electron

density

based transmitter,

profile

in the

Electronics

and

198 1

of VLF and MF radio wave measurement

237-244,

by using a single

1990

of ionospheric

electron

probe, Rep.Ionos.Space probe.

in Small

The collision

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