New I- · 2011. 5. 15. · I-I L~) AFGL-TR-88-0034 ENVIRONMENTAL RESEARCH PAPERS, NO. 296. VLF/LF...

I-

I L~) AFGL-TR-88-0034ENVIRONMENTAL RESEARCH PAPERS, NO. 296.

VLF/LF Reflection Properties of the LowLatitude Ionosphere D~

WAYNE 1. KLEMETTI MR2418PAULA. KOSSEYJOHN E. RASMUSSENMARIA SUELI da SILVEIRA MACEDO MOURA

4 Februaryl1988

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IONOPHEIC PYSIS DVISIN PR OJECT231

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HANSCOM ~ ~ AF, A013

This technical report has been reviewed and is approved for publication.

FOR THE COt*WIDER

-.---. c ~ /{ii~c~.. J L<i -Z 2,71

JOHN E. RASMUSSEN, Chief ROBL(R A. SKRIVANEK, Director

Ionospheric Interactions Branch Ionospheric Physics Division

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VLF/LF Reflection Properties of the Low Latitude Ionosphere

12 PERSONAL AUTHOR(S)

Klemetti, W.I., Kosse, P.A., Rasmussen, J.E. and Maria Sueli da Silveira Macedo Moura*13a. TYPE OF REPORT 13b.CTIME COVERED 14 DATE OF REPORT (Year, Month, Oay) 15 PAGE COUNT

Scientific Interim FROM TO 1988 February 416 SUPPLEMENTARY NOTATION

*IAE: Instituto de Ativadades Espaciais, CTA, 12.200 SaoJose dos Campos, SP, Brazil

17. COSATI CODES 18 SUBJECT TERMS (Continue on reverse if necesary and identify by block number)

FIELD GROUP SUB-GROUP VLF Propagation04 1 .F Propagation

\17 02 Ionospheric Reflectivity D4Region.19A TRACT (Continue on reverse if necessary and identify by block number)

Low latitude observations of VILF/IF pulse reflections from the lower ionosphereobtained at nine locations to the east and west of a transmitter in southeastern Brazil aredescribed. The dataAcouired durnig__a-two-month experimental campaign conducted by theAir Forces of the United States and Brazil,) provide a variety of information on the reflection properties of the ionosphere below about 90 km altitude. Aspects of the data arepresented in quasi three-dimensional formats useful for identifying ionospheric structureand variability, and detailed analyses of portions of the data are provided, which charac-terize the effective heights of the reflection and the reflection coefficients of theionosphere at noon and midnight, over a frequency range from 15 to 65 kHz. Electrondensity models ofthe ionosphere, derived from the VLF/L.F reflection data are also dis-cussed. ,

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Preface

The authors are indebted to the many people who made this cooperative effort between the AirForces of the United States and Brazil possible. The research program was a highly successful jointendeavor, with responsibilities and efforts equally shared by the United States and Brazil. The U.S.team expresses their deep appreciation for the warm hospitality and the outstanding cooperationshown by all the Brazilian organizations and individuals involved. Their skill and generosity notonly guaranteed the success of the program, but also made the effort a distinct pleasure for the U.S.personnel. Although it is virtually impossible to mention all the individuals who contributed, wewish to especially acknowledge the following: Dr. Jose Luiz Rodolpho Muzzio and Captain BasilioBaranoff, both of Centro Tecnico Aerospacial (CTA), San Jose Dos Campos, Brazil, who were the focalpoints in the Brazilian Air Force for organizing and carrying out the program; and Prof. Phenix M.Ramirez Pardo, of Fundacao Educacional da Regiao de Blumenau (FURB), who planned the day-to-dayexperimental efforts and who provided valuable technical Insight and guidance to all aspects ol theprogram. In addition, the authors wish to warmly acknowledge Dr. Edward A. Lewis who, as a U.S. AirForce scientist, conceived the novel pulse ionosounding technique used for obtaining the VLF/LFreflection data described in this report.

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iii ,q i [

Contents

1. INTRODUCTION 1

2. VLF/LF IONOSOUNDING TECHNIQUE 1

3. DATA DISPLAY AND REDUCTION FORMATS 4

3.1 Three-dimensional Data Displays 83.2 Reflection Heights and Coefficients as a Function of Time 83.3 Reflection Heights and Coefficients as a Function of Frequency 8

4. DATA FROM EACH OF THE RECEIVING LOCATIONS 12

5. SELECTED FEATURES OF THE REFLECTION DATA 73

5.1 Day/Night Reflection Heights 735.2 Day/Night Variations in the Reflection Coefficients 735.3 Azimuthal Variations in the Reflection Coefficients 735.4 Variations in the Reflection Coefficients with Range 765.5 Comparison of Normal and Converted Reflection Coefficients 765.6 Evidence of Weak Reflections from Below the Normal D-Region 805.7 Unusual Moving High Altitude Nighttime Reflections 83

6. ELECTRON DENSITY MODELS OF THE LOWER IONOSPHERE 84

7. SUMMARY 87

REFERENCES 88

v

Illustrations

1. Brazilian Air Force High Resolution VLF/LF lonosounding Transmitter Site inPaula Freitas, Brazil. 2

2. Transmitting and Receiving Field Sites for the May-June 1980 Measurements. 3

3. Basic VLF/LF Ionosounding Technique. 5

4. Orthogonal Loop Antennas used During Experiment (Small Loop used to InduceCalibration Signals). Site Pictured was at Blumenau, Brazil. 6

5. Example of Observed Waveforms. 7

6. Fourier Spectrum for Groundwave Pulse Shown in Figure 5. 7

7. Example of 3-Dimensional Display of Groundwave and Normal Skywave PulsesReceived at Canasvieiras Stacked Front to Back with Advancing Time. 9

8. Example of Group Heights of Reflection and Normal Reflection Coefficients Derivedfrom Data Presented in Figure 7. Group Heights Calculated from Data at 30.5 kHzand Normal Reflection Coefficients Calculated at 15, 30, 45 and 60 kHz. 10

9. Example of Group Heights of Reflection and Normal Reflection Coefficients vsFrequency at Local Midnight (a) and Local Noon (b) Derived from Data of16 May (Day of Year 137) 1980. 11

10. Solar Zenith Angle Variations for the Transmitter at Paula Freitas During theMeasurements Between 8 May and 27 June, 1980. 13

11. Path Parameters for Paula Freitas to Dr. Pedrinho 15

11.1. Three-Dimensional Display of Data Received at Dr. Pedrinho.

a. Normal Skywave. 16b. Converted Skywave. 17

vi

Illustrations

11.2. Group Heights of Reflection and Reflection Coefficients vs Frequency Derived fromData Received at Dr. Pedrinho.

a. Local Midnight (0315 ). 18b. Local Noon (1515 IT), 18

11.3. Group Heights of Reflection and Reflection Coefficients vs Frequency Derived fromData Received at Dr. Pedrinho.

a. Local Midnight (0315 UT). 19b. Local Noon (1515 UT. 20

11.4. Averaged Values of Group Heights of Reflection and Reflection Coefficients vs.Frequency Derived from Data Received at Dr. Pedrinho.

a. Group Heights of Reflection. 21b. Reflection Coefficients. 21

12. Path Parameters for Paula Freitas to Timbo. 23

12.1. Three-Dimensional Display of Data Received at Timbo.

a. Normal Skywave. 24

b. Converted Skywave. 25

12.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15, 30, 45and 60 kHz from Data Received at Timbo.

a. Normal Skywave. 26b. Converted Skywave. 26

12.3 Group Heights of Reflection and Reflection Coefficients vs Frequency Derivedfrom Data Received at Timbo.

a. Local Midnight (0315 U11. 27

b. Local Noon (1515 LIT). 28

12.4 Averaged Values of Group Heights of Reflection and Reflection Coefficients vsFrequency Derived from Data Received at Timbo.

a. Group Heights of Reflection. 29

b. Reflection Coefficients. 29

13. Path Parameters for Paula Freitas to Blumenau. 31

13.1. Three-Dimensional Display of Data Received at Blumenau.



13.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15, 30, 45and 60 kHz from Data Received at Blumenau.



vii

Illustrations

13.3. Group Heights of Reflection and Reflection Coefficients vs Frequency Derivedfrom Data Received at Blumenau.

a. Local Midnight (0315 UT). 36

b. Local Noon (1515 UT). 37

13.4 Averaged Values of Group Heights of Reflection and Reflection Coefficients vsFrequency Derived from Data Received at Blumenau.



14. Path Parameters for Paula Freitas to Gaspar. 39

14.1. Three-Dimensional Display of Normal Skywave Data Received at Gaspar. 40

14.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15, 30, 45and 60 kHz Derived from Normal Skywave Data Received at Gaspar. 44

14.3. Group Heights of Reflection and Reflection Coefficients vs Frequency Derivedfrom Data Received at Gaspar.

a. Local Midnight (0315 UTl. 45

b. Local Noon (1515 U11. 45

14.4. Averaged Values of Group Heights of Reflection and Reflection Coefficients vsFrequency Derived from Data Received at Gaspar.



15. Path Parameters for Paula Freitas to Camboriu. 47

15.1. Three-Dimensional Display of Normal Skywave Data Received at Camboriu. 48

15.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15, 30, 45and 60 kHz Derived from Normal Skywave Data Received at Camboriu. 52

15.3. Group Heights of Reflection and Reflection Coefficients vs Frequency Derived fromData Received at Camboriu.

a. Local Midnight (0315 U11. 53

b. Local Noon (1515 U11). 53

15.4. Averaged Values of Group Heights of Reflection and Reflection Coefficients vsFrequency Derived from Data Received at Camboriu.



16. Path Parameters for Paula Freitas to Canasvieiras. 55

16.1. Three-Dimensional Display of Normal Skywave Data Received at Canasvieiras. 56

16.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15, 30, 45and 60 kHz Derived from Normal Skywave Data Received at Canasvieiras. 56

viii

Illustrations

16.3. Group Heights of Reflection and Reflection Coefficients vs Frequency Derived fromData Received at Canasvieiras.



16.4. Averaged Values of Group Heights of Reflection and Reflection Coefficients vsFrequency Derived from Data Received at Canasvieiras.



17. Path Parameters for Paula Freitas to Figueira. 59

17.1. Three-Dimensional Display of Normal Skywave Data Received at Figueira. 60

17.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15, 30, 45and 60 kHz Derived from Normal Skywave Data Received at Figueira. 61

17.3. Group Heights of Reflection and Reflection Coefficients vs Frequency Derived fromData Received at Figueira.



17.4. Averaged Values of Group Heights of Reflection and Reflection Coefficients vsFrequency Derived from Data Received at Figueira.



18. Path Parameters for Paula Freitas to Pinhalzinho. 65

18.1. Three-Dimensional Display of Normal Skywave Data Received at Pinhalzinho. 66

18.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15, 30, 45and 60 kHz Derived from Normal Skywave Data Received at Pinhalzinho. 66

18.3. Group Heights of Reflection and Reflection Coefficients vs Frequency Derived fromData Received at Pinhalzinho.



18.4. Averaged Values of Group Heights of Reflection and Reflection Coefficients vsFrequency Derived from Data Received at Pinhalzinho.



19. Path Parameters for Paula Freitas to Irai. 69

19.1. Three-Dimensional Display of Normal Skywave Data Received at Irai. 70

ix

Illustrations

19.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15, 30, 45and 60 kHz Derived from Normal Skywave Data Received at Iral. 70

19.3. Group Heights of Reflection and Reflection Coefficients vs Frequency Derived fromData Received at Irai.



19.4. Averaged Values of Group Heights of Reflection and Reflection Coefficients vsFrequency Derived from Data Received at Irai.



20. Summary of Noon and Midnight Group Heights of Reflection Derived from DataObtained at all the Receiving Locations. 74

21. Normal Reflection Coefficients for Midnight and Noon Derived from Data atSelected Locations to the East and West of the Transmitter.

a. Approximately 200 km Propagation Paths (Paula Freitas to Blumenau/Figueira). 75

b. Approximately 215 km Propagation Paths (Paula Freitas to Gaspar/Pinhalzinho). 75

c. Approximately 250 km Propagation Paths (Paula Freitas to Camboriu/Irai). 75

22. Variation in Normal Reflection Coefficients with Range and Angle of Incidence forLocations East of the Transmitter. 77

23. Normal Reflection Coefficients for 20 kHz Derived from Midnight and Noon DataObtained at Receiving Locations to the East and West of the Transmitter. 78

24. Normal and Converted Reflection Coefficients Derived from Midnight and Noon Datafrom Three Locations East of the Transmitter. 79

25. Data Obtained at Camboriu Showing Weak Reflections (Circled Areas) from Altitudes

Below the Normal D-Region. 81

26. Data Recorded on 17 May (Day 138) 1980 at Timbo, Camboriu and Canasvieiras.

a. Normal Skywave Data Showing Weak Reflections Below the Normal D-Region (C). 82

b. Normal Reflection Coefficients Derived from the "C" Portions of the Received Skywaves. 82

27. Data Obtained at Camboriu Showing Moving Reflections (Circled Areas) During theNighttime Coming from Relatively High Altitudes Above the D-Region. 85

28. Electron Density Profiles of Low Latitude Ionosphere Derived from the VLF/LF ReflectionData Gathered During this Series of Measurements. 86

x

Table

Locations and Propagation Path Parameters of the Transmitting and ReceivingLocations for the Experiment. 12

xi

VFL/LF Reflection Properties ofthe Low Latitude Ionosphere

1. INTRODUCTION

This report summarizes data describing the longwave reflection properties of the low-latitudeionosphere in Brazil. obtained during an experimental program conducted jointly by the Air Forces ofthe United States and Brazil. The data were obtained during May and June of 1980 in southern Brazilusing a unique VLF/LF pulse-ionosounding system operated by the Brazilian Air Force. The

transmitter of the ionosounder was located near Paula Freitas (see Figures I and 2). and three portablereceiving systems were used to obtain measurements at nine locations to the east and west of it. at

distances ranging from 156 km to 280 km, as indicated in Figure 2.

2. VLF/LF IONOSOUNDING TECHNIQUE

Details of the VLF/LF pulse-ionosounding technique are given in a number of reports describingIts use in other experiments conducted at low-, mid-, and high-latitudes (Rasmussen et a]1. Lewis et

(Received for publication on 25 January 1988)

1. Rasmussen. J.E., Lewis, EA., Kossey, P.A., Reginaldo Dos Santos, Edsel De Freitas Coutinho,Kahler, R-C.. and Klemetti, W.I. (1975) Low Frequency Wave-Reflection Properties of theEquatorial Ionosphere, AFCRL-TR-75-0615, AD A02511 1.

1

IL44

Fiur 1.BaiinArFreFihRslto L/Flnsudn

Trasmite Site AtPul retsBa'

2 5 5

-; " MAGNETIC~NORTH~

Brazil

IF-.

Paula 1-reitas

Dr. PedrinhoePinhaizinho Blumenau

OFigueira 6sa41

Camborium

lrai-,C~*& ' lA?* 0 50 too 150 200 .. 47

kilometers Cnsiij

w TRANSMITTER 'SITE

*RECEIVER SITES6

Figure 2. Transmitting and Receiving Field Sites for the May-June 1980 Measurements.

al 2 , and Kossey et a13 , respectively). Figure 3 illustrates the technique. The transmissions consist of a

series of cxtremely short pulses (55 lsec for the experiment in Brazil), precisely controlled by a cesium

beam time standard, and radiated from a vertical antenna (130 m in Brazil). The transmitted pulses

are so short that, for distances out to several hundred kilometers, the groundwaves arrive and are

recorded before the arrival of the ionospherically reflected skywaves. Thus, data are received free of

ambiguities arising from groundwave and skywave interference. The transmitted pulses are

vertically polarized, but because of the effects of the geomagnetic field the reflected skywaves arei liptically polarized. Separate loop antennas are used to sense the so-called "normal" (I[ -) and

"converted" (I-) components of the downcoming skywaves. One antenna, with its axis oriented in the

plane of propagation. senses the groundwaves and the normal components of the skywaves, while the

other antenna, orthogonal to it, is nulled on the groundwaves and senses the converted components of

the skywaves. Examples of the loop antennas used in Brazil are shown in Figure 4.

Figure 5 gives typical examples of groundwave and skywave pulses received in Brazil. The

separation in time between the normal skywave pulse and the groundwave pulse, which is a feature of

the ionosounding technique, is illustrated clearly in the figure. Figure 6 shows the Fourier spectrum

of a transmitted pulse to illustrate the wide range of VLF/LF frequencies which were available to probe

the ionosphere. In practice, the pulses were transmitted at a precisely controlled repetition rate of 399pulses/sec. so that the spectrum of the received pulses consisted of discrete frequency components. 399

Hz apart.

As described by Lewis et a12 (op. cit.), after Fourier analyses of the received pulses, the group

delays between the skywaves and groundwaves can be used to determine effective heights of the

ionosphere; and, the relative amplitudes of the skywave and groundwave frequency components can

be used to determine magnitudes of the normal ( IR 11) and converted (RI R) reflection coefficients of theIonosphere 4 . The experiments in Brazil yielded ionospheric reflection heights and effective plane-

wave reflection coefficients over a range of about 15-65 kHz. Such data provide a means for developing

phenomenological models of the lower ionosphere, useful for VLF/LF propagation prediction

purposes.

3. DATA DISPLAY AND REDUCTION FORMATS

Three formats have been chosen for representing the data obtained during the experiments, and

for describing the VLF/LF reflection properties of the lower ionosphere that were derived from it. A

2. Lewis, E.A., Rasmussen, J.E., and Kossey, PA. (1973) Measurements of ionospheric reflectivityfrom 6 to 35 kHz, J. Geophys. Res. 78: 3903-3912.

3. Kossey, PA, Turtle, J.P., Pagliarulo, R.P., Klemetti, W.I., and Rasmussen, J.E. (1983) VLFreflection properties of the normal and disturbed polar ionosphere in northern Greenland,Radio Sc. 18: 907-916.

4. Bracewell, R.N., Budden. K.G., Ratcliffe, JA, Straker, T.W., and Weekes, K. (1951) Theionospheric propagation of low- and very-low-frequency radio waves over distances less than1000 km, Proc. InsL Electr. Eng. 98(111), 221-236.

4

CONVERTEDSKY WAVE PULSE

TRANSMITTERPUS

G ROUN DWAV E-PULSE

Figure 3. Basic VLF/LF lonosounding Technique.

5

Figure 4. Orthogonal Loop Antennas Used During Experiment (Small Loop

Used to Induce Calibration Signals). Site Pictured was at Blumenau, Brazil.

6

GROUN DWAVE

NORMAL SKYWAVE (1I-)

CONVERTED SKYWAVE UI-)

0 100 200 300 400 500TIMlE (MICROSECONDS)

Figure 5. Example of Observed Waveforms.

2. 2 0.0 40. 6b.0 80.0 0 0.0FREQUENCYH HZ I

Figure 6. Fouirier Spectrum for Groundwave Pulse Shown in Figure 5.

7

brief description and a few samples of the data formats are given below; following that, data obtainedat each of the nine receiving locations are presented.

3.1. Three-Dimensional Data Displays

Figure 7 shows a three-dimensional presentation of a sample of data to illustrate the manner inwhich data from each receiving location were acquired and initially displayed. The presentationconsists of waveforms stacked one-behind-the-other, with time progressing linearly from bottom-to-top, for (in this example) a three-day period. Although the raw data were recorded every 2.8 minutes,for display purposes each waveform in the figure represents a 15 minute-average of approximately325,000 pulses. The horizontal scale is linear in time, measured from the start of the groundwaves.The groundwaves remain fixed in time, while the skywaves move back and forth in accordance withthe solar zenith angle (and hence, in accordance with the varying effective height of the lowerionosphere). The waveforms represent the averaged wave amplitudes as a function of time, as sensedby the receiving-loop antennas. The data in Figure 7 correspond to the normal component of theionospherically reflected waves. Similar displays are given later showing converted components ofthe reflected waves received at a number of locations during the experimental campaign.

3.2 Reflection Heights And Coefficients As A Function Of Time

Data, such as that illustrated in Figure 7, provide the bases for deriving effective heights ofreflection and plane-wave reflection coefficients of the.ionosphere, as outlined in Section 2 of thisreport. Figure 8 gives examples of reflection coefficients, plotted as a function of time for 15, 30, 45,and 60 kHz, as derived from the sample of data given in Figure 7. In doing this, the received skywavedata were averaged over 2-hr intervals. Such data presentations are given to show longer- term trendsin the data (days or weeks), rather than short-term characteristics (minutes or hours). Also shown inFigure 8 is a plot of the effective height of the lower ionosphere at 30.5 kHz, as derived from the samedata.

3.3 Reflection Heights And Coefficients As A Function Of Frequency

By fixing a time (for example, local noon), the pulse reflection data can be used to derive effectiveheights of reflection and plane-wave reflection coefficients as a function of frequency. For example,Figure 9 illustrates the results of such an analysis, derived from the first day's data at local midnightand local noon, as shown in Figure 7. The data provide reflection properties of the lower ionosphereover a wide frequency range, from about 15-65 kHz. The resolution of the system is such that a changein the effective height of the ionosphere by as little as 0.5 km can be discerned. In addition, reflectioncoefficients as small as about 0.02 in amplitude can be determined. Data such as that shown in Figure9 were derived from 15-min averages of the raw data.

8

139 0000-

136 0000-

2 400

TIME -/L SECOND$

Figure 7. Example of 3-Dimensional Display of Groundwaveand Normal Skywave Pulses Received at Canasvieiras StackedFront to Back with Advancing Time.

9

0 eg 00

0 - see - goo - ge

U.0

a

10K~

C~w6SIES.S 55 7 S'. S C..55113. 0.7 07 ~kU E

o C

C ~ CT oS 48

C

FRE051NC, 7.553 FREOUENCY 6-13

aLOCAL MIDNIGHT

37.33*5RA DAY 137 1515, 1940 CANAIM*A DA, 137 15151 198

lie a

.0

as F

E 0

S 40 FT

Iv '.I 5 V 75 55 55 15 6 35 55 55 ,6 65 65 ' 5 7 5 C 5 5 5 55 7.FNEOUEN1CY

7 ...s' FREO.JENCY f-.21

b. LOCAL NOON

Figure 9. Example of Group Heights of Reflection and Normal Reflection Coefficientsvs Frequency at Local Midnight (a) and Local Noon (b) Derived from Data of 16 May(Day of Year 137) 1980.

11

4. DATA FROM EACH OF THE RECEIVING LOCATIONS

In this section the data obtained during the experiment in Brazil are displayed. The data weretaken during the late fall and early winter, when the day-to-day variations in the solar zenith angles,as a function of time of day, were not large and the periods of sunlight and darkness were about equal,as shown in Figure 10. In the presentations that follow, the displays parallel those described inSection 3; specifically: three-dimensional displays of the data are first shown; these are followed byvlots of effective heights of reflection (at 30.5 kHz) and plane-wave reflection coefficients (at 15, 30, 45,and 60 kHz), as a function of time; finally, reflection heights and reflection coefficients are given, as afunction of frequency, for local midnight and local noon for the days data were obtained at eachreceiving site. Table 1 gives the geomagnetic coordinates, the great-circle propagation distances, and

the magnetic azimuths from the transmitter to each receiving location. The specific periods for whichdata were acquired at each of the receiving locations are shown on charts immediately preceding thedata displays for that location. Those charts also indicate if only the normal components of thereflected skywaves were received, or whether the converted components were received as well.

Table 1. Locations and Propogation Path Parametersof the Transmitting and Receiving Locations for the Experiment.

DISTANCE MAGNETICSITE COORDINATESKM AZUTKM. AZIMUTH

TRANSMITTER

PAULA FREITAS 26°15'S 500 57'W

RECEIVER

DR. PEDRINHO 26043'S 49029'W 156 1230TIMBO 26049S 49016'W 180 1240

BLUMENAU 26050'S 4905'W 197 1220GASPAR 26055'S 48°55'W 215 123 °

CAMBORIU 27°00'S 48037'W 246 1230CANASVIEIRAS 27°26'S 48°28'W 280 1320FIGUEIRA 2653'S 52°50'W 200 260 °

PINHALZINHO 26051'S 5259'W 213 2620IRAI 2711' S 53015'W 250 256 °

12

0 8MAY....27 JUNE

345-LjW

o

90-

z /

N 4

1I35-

0 Ib 2TIME (GMT)

Figure 10. Solar Zenith Angle Variations for the Transmitter at PaulaFreitas During the Measurements Between 8 May and 27 June, 1980.

13

DATA

PROPAGATION PATH: PAULA FREITAS TO DR. PEDRINHO (PF-PED)

DISTANCE; 156 KM

AZIMUTH: 1230

DATA: NORMAL AND CONVERTED POLARIZATIONS

MEASUREMENT PERIOD: 17 MAY - 21 MAY 1980

BAGAE. .. . :.Brazil

PinalznhotoDr. Pedin ie

n~ireitrs Gasa,-

Irai ! " i" Consvidiras¢

Figure 11. Path Parameters for Paula Freltas to Dr. Pedrinho.

15

1200-

21 MAY 198042 0000- -

20 MAY 1980

141 2000000-0-0

1206

1200

21 MAY 1980

20MY10

20 MAY 190

400000

3 0000-

(b)

160 260 360 400o 500TIME - j SECOtEOS

Figure 11. 1. Three -Dimensional Display of Data Received at Dr. Pedrinho.

b. Converted Skywave.

17

: .. .... .: ... ... ......

I~~ is--t S5K a, --. - " KHz

45KHz

(a) NORMAL SKYWAVE

(b) CONVERTED SKYWAVE

Figure 11.2. Group Heights of Reflection for 30.5 kJ-Iz and ReflectionCoefficients at 15, 30, 45 and 60 kHz from Data Received at Dr. Pedrinho.

a. Normal Skywave.b. Converted Skywave.

18

PAS.LLIL G~8 041WS5 - WQEISIP6 11'IAL.IL ILICTION COPP5C19011 - WO826?l10Ipo i"m DAY Is Sf low S O @A1 142 Else OR mM N- DAYU. 11111 110, ON@ lm6u Do, 14 31ISI Is"

I .I -- io 0I

p Fo L

U £C

04 s

so CI

0S 49

I.~ ~ ~ ~ ~~~~~ III, . ..... __ _ _ _ _ _ __ _ _ _ _ _ __ _ _ _ _ _

FRE0Ij£NCY (K021 F*EOUENC, 1-11

NORMAL SKYWAVE

(a)

I l ISO~ I S~ CrS

o 4 4 , **

UI7. C ......

F F

K I54 C

08 w

,40UENCY 11.4.1 F4£0FNC, .O

CONVERTED SKY WAVE

Figure 11.3. Group Heights of Reflection and Reflection Coefficients

vs Frequency Derived from Data Received at Dr. Pedrinho.

a. Local Midnight (0315 UT)

19

CO 1"110104 I&A in tIsol 10 TPI CA, 0 '40 m 1111 OR REAINSI 04' I ' US f90 TRIO OR, '40 9 6 t lo

1; 70 £ .0 ..

P ~ C

C p

0

IS I

FREOUIENCI 19..) FRE0.AC' A,.

NORMAL SKYWAVE

(b)REtAOICULAR CROUP ICAC - U DC90AUOSCC hCP L.'6FSFC OFIIN OISAA6PK0OR -(01N-0 0., 5 904C 1-. a6. , 's ''0 1. '0on P , OI.0 £'C S.65 'S ~ 0' S*~C 5

050

30

C C

28 E

CONVERTED SKYWAVE

Figure 11.3. Group Heights of Reflection and Reflection Coefficientsvs Frequency Derived from Data Received at Dr. Pedrinho.

b. Local Noon (1515UfLT

20

I I ,,, ' 'I, I

too[-_ _ _ __ _ _ _

* 0- MIDNIGHT . -

Bo-

i SON- -___NOON _....

7C -

(a) soE

Z 40

0

0 20-

0 10 20 30 40 50 60 70FREQUENCY - kHz

1.0

MIDNIGHT

S-2

Ii.

(b) 8o., NOON,-

Z I

o

a

10 20 30 40 50 60 70FREQUENCY - kHz

Figure 11.4. Averaged Values of Group Heights of Reflection and Reflection

Coefficients vs Frequency Derived from Data Received at Dr. Pedrinho.

a. Group Heights of Reflection.

b. Reflection Coefficients.

21

DATA

PROPAGATION PATH: PAULA FREITAS TO TIMBO (PF-TIM)

DISTANCE; 180 KM

AZIMUTH: 1240



Brazil NORT

P Nnlolzinho Dr. m 7L

eRECEIVER SITES

Figure 12. Path Parameters for Paula Freltas to Tlmbo.

23

(a) 0000 000

137 20030000 50

12024

J38 0000

1200-

137 00000

15 MAY 1980

3500 -

160 200 300 400 0IME - 1A SECONDS

Figure 12. 1. Three-Dimensional Display of Data Received at Tlrnbo.


25

-45KHi

A~ ~ it A~ d " A "7 B7


Figure 12.2. Group Heights of Reflection for 30.5 kHz and ReflectionCoefficients at 15, 30, 45 and 60 kHz from Data Received at Timbo.

a. Normal Sicywave.b. Converted Skywave.

26

*0MLLEL Elc 4 mn[ - WOI$S5u0 *AtCL *(rC']31 COIF~lCIENI - 4..3IS ED',OO D01 I3 l'3. I666 s Iau 0*, 'U0 S'S. '66 'iJso o. 15 3ii 1 6 30'1 '3 IS.l li0o

p0 6

01 1 $ S. 9 $*$V Q* 16 $R .0

o,- t11?, .=f=='" s.............. *-It;.

0

p C

56 0S 4D f0F

is I'8 ... Nis.W.h W-, W6 wig____W__W__h_____a,___w,____

FEQUNCY rKNI) S ' FREQUENCY I---' sNORMAL SKYWAVE

(a)PxPI5e0 ;CU~L& 60.# WEINT$ . VkOISIURAE3 (PF*f0ICW A*,,PC. CTI0N COEFFiClC T - UNOISfI0I[O1143 0 .. 33 313. I68 l.U O0V 36 3l5l 006 ''"63 2A. 3 3t.. 'Is6 SISK a0" 0. InS. 366ls,is

S................

.U 7S ..

E ........

so 06

.4 C

S 40

S 46 F

s ,I ,11

rngQ.ANCv [KKR] FREQUENCY SKll

CONVERTED SKYWAVE


vs Frequency Derived from Data Received at Timbo.

a. Local Midnight (0315 UT).

27

Ira o " 'Its to,. Too CA, 147 1,01 low 'Neo is. usI'o Co"ss I sI , U011 i UIIs IMSI kMt 0ln' 6 i 5 f *I It

In

o

0c

Ce CCI

1,00 ' a C 75 5*, * . , , Go5Y*1 0.1 .3 los 25o 35 915 45 a111115 S l

ledC4'~*ajFEIA~ .j

NORMALSKYWAV

(b

9E

o - tit os aya@

b. Loa on 11 M

I28

too-

E 90- "-MIDNIGHT = J-

s o0o79 NOON

( so

• 40

0 30

0 o 20 -L-_0 o 20 30' 40 5'0 60 7

FREQUENCY - kH z

1.0 1 -, T- -T - - -- , - -

MIDNIGHT

2

,,~ 0NOON

w

0 -

ILh, \\

*l 0 10 20 30 40 50 60 O1FREQUENCY -kH

Figure 12.4. Av'eraged Values of Group Heights orf l,,ection and Reflection

Coefficients vs Frequency Derived from Data Received at Timbo.

29

DATA

PROPAGATION PATH: PAULA FREITAS TO BLUMENAU (PF-I3LU)

DISTANCE; 197 KM

AZIMUTH: 1220


MEASUREMENT PERIOD: 21 MAY - 4 JUNE 1980

D~r. Pedn'l1Ih% Blumea

* * hgueira TGnibIIre \

(amboriu(2raeia

s TRANSMITTER SITE

* RECEIVER SITESx/

Figure 13. Path Parameters for Paula Freitas to Blumenau.

31

290A 00900

450 0000 -

26 MAY 910so41000 0000

27 MAY 91980 ~ -..

48 0000

(a) 22Y MA89

147E 00S008

1202

55 000--

154 0000-

(a) cont

1O0 200 300 400O 50

TIME -pL SECONDS

Figure 13. 1. Three-D imensional Display of Data Received at Blumenati.

a. Normal Skywave. (Cont.)

33

29 MAY 1980150 0000

28 MAY 198049 0000

1200

26 MAY 1980148 0000

1200

25 MAY 1980,46 0 000 0, . ~

200o

24 MAY 1980465 00000

23 MAY '980

200

0oo 200 300 400 500TIME JILSECONDS

Figure 13,.1. Three -Dimensional Display of Data Received at Blumenau.


34

. .-...... ....... .--..... .. ..... . . .. . ..... .,. ... .. ...... .'...... ..,=......

4 it a 's a is 0 a it d i''' K * .- '" ' 6 d

(a) NORMAL SKYWAVE

. .. .... .. ..... .

a Is 0 -It '6 t- - - "t 6

4 - -,-..I15KHz

-t' -* ' 30KHz

• _.;_.6d . ;45K ,


Figure 13.2. Group Heights of Reflection for 30.5 kHz and ReflectionCoefficients at 15, 30, 45 and 60 kI-lz from Data Received at Blumenau.

a. Normal Skywave.b. Converted Skywave.

35

.. . .. = m m mmmmm m mm mmm m mm mm mm m

PAAALIEL GROWP .4rtCTS - 4C1ST 04CO PARALLEL Ssd1cJio[ s C :01,310 *. WIS"44.60k= 4. D.9 -- 1 15 I M l156U 05 15 3358 3A k510, 10" 0A, . 5 99$

556U 0'a., I S3. m

It m a *li~,N i• q * 6

. . . . . . . . . . . . . . . . . . . . . . ..

C .. . . . . . . .

(f C99 L

U Is . . . . . . . . . , . . . ..3 [. . .J . . . . .. ..56 C

20 C

Sm~~~~~s w t5 t t bgf hh.FREOUENCY ..... ,REOUENCV 39,13

NORMAL SKYWAVE

(a)565'-OCU- 50Z3,, -(3E35 G33'S 1l.s3IS,.9EO AtROE601Cs-.8 9Ec d

155 (35EIII!E-1 - sS.13

1KC)

9,.P!65 , all 1.5 315 '90883 0 '49 5, 3988 9, E u A,8 .1 35 3966 _U9 5.8 1.9 35. low9

go *%

P 78 c ., .3

O "C

0!4 4E

28

rII U I.'C -21 IRE__ _ _ _ I--,'

CONVERTED SKYWAVE


vs Frequency Derived from Data Received at Blumenau.


36

O*AMLL 0050414"'S - 6QISALOWD POALLL MUIFCYJ0" CORFFICII'. - W1152D01DtihL40m DA, 514 1tt 9K0 I-U 0.1 164 155ION D ItuCIu DA, -44 ISIS, ON sWU 047 'S. I*9* SM

I :

IN*

70 ...... CIS _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ P . . . .

(b)W

9,..'(N4 04. 0. 0'a 3 54' 46 5, 1900 9'(.1. 0' 55 5 6 0 04'DA 146 1515, 040

'of

C

RU

0S 46

C.

CNETDSKYAV

Figure 13.3. Group Heights of Reflection and Reflection Coefficientsvs Frequency Derived from Data Received at Blumenau.

b. Local Noon (1515ULM.

37

100-

E 90-IMIDNIGT~=

0-

2 70-

La

• 40a-

0 3050 60 7

Ix

FREQUENCY -k~z

2.0

ILI

30-FREQUENCY -kHz

0

-I - -----------2

ILL

FRQUNC 0.1 NOON

Figure 13.4. Averaged Values of Group Heights of Reflection and ReflectionCoefficients vs Frequency Derived from Data Received at Blumnenau.

38

DATA

DISTANCE; 215 KM

AZIMUTH: 1230

DATA: NORMAL POLARIZATION ONLY


1 JUN - 27 JUN 1980

NORTH

' , keitas

PinhaizinhoDr. Pe? Blumnau

V guetraGapr0; Cam&.."-~

I r (anaseiras

8 TRANSMITTER SITE 4L.

* RECEIVER SITES

Figure 14. Path Parameters for Paula Freitas to Gaspar.

39

3 JUN 980Z

200

2J154 0000 - ------

I JUN 1980 -

100 20000000-0

1240

I? ~JUN 198016900000-

1200-

161 JUN 9800

cont JUN JUN198

161640000-

1020000 40 0

12041

12 JUN 1980184 0000--

16 6 0000 -

2200

0 JUN 9800160 0000

100200~

;6t 00000

1200 5 00

160 00000000 50

%242

27 JUN 1980179 0000-

26 JU N 1980 =Ile 0000 1 . -

1200

25 JUN 1980

17ir400001200

2 JUN 19807 000

1200

2 JUN 980I1 7 000

1200

2 JUN 980 *-

73 0000

cont1. 1200

100 200 300 400 500TIME -/A S0COND

Figure 14. 1. Three -Dimensional Display of Normal Skywave Data Received at Gaspar. (Cont.).

43

..... ..... .. ...

4-4--+-95KHz

--- 30KNZ.t ft it "' ft 845KHz

t .1 ,t N- .... f - , 1 ft -'.-60KHz

NORMAL SKYWAVE

Figure 14.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficientsat 15, 30, 45 and 60 kHz Derived from Normal Skywave Data Received at Gaspar.

44

'A*ALCL C*t. 4I"'S ~ ISIQ~lO '4AtL0g *( (~tCC O COO" IC C r .-nL u t.A03

- 0L[ IN$ - JO~U K C Sa O ' ,o i O i 15 6 P

Sc ."'1'

'EL G C.(.:. ..... -- ...... .. .

C ,, , . U.- - ., . ..

l.. .... .

I

78 C

20

I.. . . . .. . . . . . . . . . .a 00' ...... '3 3

S 5 5 C 5 3 5 9 * 0 5 6 6 S 'S

NORMAL SKYWAVE

'r4 [ 'C' S(I - uOStU.@Ello 11 £ 11 Cr~ 1o011;11:.111 IS"uO*

Figur 13'14.3 Grou Heiht of9 Refco an'elcto9offcet

,I "

. Loaid h 035U)

b.bLcalNoo (11 U)

C 45

S . • ,

NORMAL SKYWAVE


vs Frequency Derived from Data Received at Gaspar.

a. Local Midnight (0315 U17).

b. Local Noon (1515 UT).

45

E 90-MIDNIGHT

S80Bo,-

70 NOON II-

(a so0cc 50-

X 40-

o 3002o

0 10 20 30 40 50 60 70FREQUENCY - kHz

1.0 '

MIDNIGHT _NOON -

zw

(b) ,."°°= o0.,20

w

-jILw

0a to 20 30 40 50 60 70FREQUENCY - kHz


Coefficients vs Frequency Derived from Data Received at Gaspar.



46

DATA

PROPAGATION PATH: PAULA FREITAS TO CAMBORIU (PF-CAM)

DISTANCE; 246 KM

AZIMUTH: 1230


MEASUREMENT PERIOD: 12 MAY - 3 JUN 1980

MAGNETICN

PinhazinoD,. Palf Blumeilau

J~Camborin

IraiCanasvieira

1 TRANSMITTER SITE

OR REEIVER SITES

Figure 15. Path Parameters for Paula Freitas to Camboriu.

47

121%

18 MAY 1980 r39 0000-

200

130 0000

200 --

16 MAY 1980 -

37 0000-

1200--

15 MAY 1990

360000- -

1200

14 MAY 19801 35 0000

1200

f3 M4AY 1980_2'~--~'

154 0000

I 200 400 500TIMiE - jL SECON08

Figure 15. 1. Three -Dimensional Display of Normal Skywave Data Received at Camboriu.

48

24 MAY 19130145 0000-

1200 --

23 MAY 1980 ~144 0000- -

-4-

200-- - -

43 000 0---

12 00--- ..

20 MAY 9800

cont. V -1

100 200 S00 400 50TIME -jL SECONDS

Figure 15. 1. Three-Dimensional Display of Normal Skywave Data Received at Camboriu. (Cont.).

49

29 MAY 1980150 0000 Y, -

28 MAY 1980-49 0000-

27 MAY 1980 >48 0000 ~

26 MAY 1980 -

2 MAY 1980

C t. 145 0 000

100 200 300 400 50TIME /.L SECOND$

Figure 15. 1. Three -Dimensional Display of Normal Skywave Data Received at Camboriu. (Cont.).

50

1200 -

3 JUN 1980 ~--- -- z -

155 0000--

1200

JUN 198054 0000

1200 I .--

7~

I JUN 1980153 000 j~ ~ -~-.-

1200 -

31 MAY 1980 ~->

15 2000 - Ni.

30 MAY (980 - A'-'

1 0

1200

29 MAY 1980 -I

150 0000 I 5

10 200 300 460 50TIME -/i SECONOS

Figure 15. 1. Three -Dimensional Display of Normal Skywave Data Received at Carnboriu. (Cont.).

51

"° . .. . .. , . . . . "... . ... ... .. . .. .. o . . . .. . .

T- 8; ' *r ------- w-T'

"4-

6-. i q 64 7

' ! " l " : , 7. t i -, :- '

c 0 t

W' .1 19

% ....... .. ..... .....

-i. "" I.. ......

NORMAL SKYWAVE

Figure 15.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficientsat 15, 30, 45 and 60 kHz Derived from Normal Skywave Data Received at Camboriu.

52

6 6 1 6 1 m m6mmm 6 m m m 6 6 6m mm6mmm 6 ) m 6 6 6 6 6 6 . 6 6 6 6 . 6 6 6 6 1 0

PA* I(LII 41. 1 u IIIAUOQ P2 LL tL RIEF(C'IO6 COF'FIrCIE4T - UDIST6 WO

'U1 I* :E - fl~ r Sq I.: r.1 0, o IUC ,15 1.1"C ll . It I,$ I" . U OA 1" 1* 1.lo

8*e d4 I ee*° $o*

vl~~ ~ TLI l e **. . .. .. ..... .... . ... ........

c ..................... =. ..... ~~ ................• %

(I

N

28

rgfOrj(NCI -11. FREOUENCv IK..NORMAL SKYWAVE

Pn5ALL[IE 0JOU 41C"S -JUDISTIA O( A* .PAP (E ¢*6 co£5rcrlcs( - ojU, I % ippD

0U~I A, .9 Is'%. G"6 I~u 0.1 5 192 Isis .9"0 :C9 S5 IEN:43* 5 .5 e

IIIL

u

o C. .

, . " F

•. F. 1-11

NORMAL SKYWAVE


vs Frequency Derived from Data Received at Camboriu.



53

100

E 90 _________________Migo iTII-MOID~GHT

'80

S'70 NOON

(a) 60

50Ilg

2 400-o

20

0 10 20 30 4 50 60 70FREQUENCY -kH z

MONIGHT

NOON

2tJ

ILIwli_

(b) 0 N

w-J

0 0 20 30 40 50 60 70FREQUENCY -kHz


Coefficients vs Frequency Derived from Data Received at Camboriu.

a. Group Heights of Reflection.b. Reflection Coefficients.

54

DATA

PROPAGATION PATH: PAULA FREITAS TO CANASVIEIRAS (PF-CAN)

DISTANCE; 280 KM

AZIMUTH: 1320



1N

Qm Cmbo0* a

I aiCanosviea

*TRANSMITTER SITE b

0RECEIVER SITES

Figure 16. Path Parameters for Paula Freitas to Canasvieiras.

55

-77

1200 -

Is MAY 1980 -p ?'139 000

200 ~ , l

17 MAY 1980138 000 -. i

16 M6AY 1980137 0000

160 260 300 460 50TIME -/J SECONDS

Figure 16. 1. Three -Dimensional Display of Normal Skywave Data Received at Canasvielras.

++--4+-5KHz

I '~i *---~30KHz

~~ - 45KHz

In o" In o----60Kw 3

NORMAL SKYWAVE

Figure 16.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at 15. 30, 45and 60 kHz Derived from Normal Skywave Data Received at Canasvieiras.

53.SC.1IICNAu OAT 33'C* S130 0. 35 940 U C3AS IAS UT. 33T 3'5 los H11.,V 01 I3N .52 'a"

. . . . . . . . . . . . . . ..... ...........go

.C. .. ...........

U 70

S 40

26

NORMAL SKYWAVE

640ALLE4 50336 WEIGH'$ - 3N03C3303 P*63AL.EC. E l.(CION, COEFFICIENT - LM.33333036

CXNASVIEIAS OAT 157 I3SM 0 0 41 3 a., 3 3 5.IN CS4SIEIAS OAT 133 C5r30 loss 3303t a., 'so C . Ism

C

ao EU C

S40

so3

20

toUESC '3.30501s 65 FREOUENCT V.33:3

NORMAL SKY WAVE


vs Frequency Derived from Data Received at Canasvieiras.

a. Local Midnight (0315 ULM.

b. Local Noon (IS15UTM.

57

9 MIDNIGHT -

7 NOON

(a) 6 ,i 40F

330

020

0 10 20 30 40 50 60 70FREQUENCY - k H z

MIDNIGHTNOON II-

2

U.Ll

U.

(b) 8 o.,0Z

.o il I [ I _

0 10 20 30 40 50 io 70FREQUENCY - kHz


Coefficients vs Frequency Derived from Data Received at Canasvieiras.


58

DATA

PROPAGATION PATH: PAULA FREITAS TO FIGUETRA (PF-FIG)

DISTANCE; 200 KM

AZIMUTH: 2600


MEASUREMENT PERIOD: 20 MAY -26 MAY 1980

NMAGNETIC

Brazil '

Dr. Ped---o -1uws

W/iuera G 'aua rtIrs-j-eIM

Iraiiera

[ I TRANSMITTER SITEtRECEIVER SIES

Figure 17. Path Parameters for Paula Freitas to Figueira.

59

200- -

26 MAY 1980 '-

47 0000--

1200

25MAY 1980146 0000 -

1200

24 MAY 1980 f~~145 0000 ~

1200- - -

23 MAY 1980 ~ -144 000 --.

1200 ;

22 MAY 1980143 0000 -

1200

100 200 300 400 50TIME -~SECONOS

Figure 17. 1. Three-Dimensional Display of Normal Skywave Data Received at Figuelra.

60

.... . ... . °.....

ff\ ~ 5KHz-e-e-e-e- ~30KHz

: 45KHz

A AAd Ad ------ 60KHZ

NORMAL SKYWAVE

Figure 17.2. Group Heights of Reflection for 30.5 kHz and Reflection Coelicients at15, 30, 45 and 60 kHz Derived from Normal Skywave Data Received at Figucira.

61

*&ISLLf G00 ,:C.TS - NCIS'"ED PAPALLEL RIF'ECTION C 0FWICIE2N - 2nOIS 02ItUf#. 0'v '2 35Se MIO T'' O'" 2S: i'S, 588 i2IP. 0'' ''2 3,5. MWi 5*.8 08' '4 SS. llW

, '4 ;Up;

In "*' .... ,$.*

98 * . 2#iilit t ? ? ; silli .......... e......

N 33

Li

fI

70 N

SQEZENC, 5' . 2 5 6E02NC' IN2 5 5 2 85 '

NORMAL SKYWAVE

1*01.IS 0 4 1 751SI s 09 1 1 108 8 115. lose C . D.. 0 S 151% O ?6' 0' '46 D 515 go

fl 8 4' 8 8 4

50 N

CC

S20 -.5 4a 0 . 5 t e t z o 0

22 EC -E3E - -.. . .. .. . . . . .. 52 55'6" 6- " ' 2 2-- --5 - " "

NORMAL SKYWAVE


vs Frequency Derived from Data Received at Figueira.



62

100-

E190 II-MIDNIGHT

'80z -I

- 7 NOON

(a) ,so0w 50

2 409.0: 30

020-

0 1 20 0 4'0 5'0 60 70FREQUENCY -kH z

I.0e

MIDNIGHT

Z

2

ILL

U

wc"10

IL

w

10 20 30 40 50 60 701

FREQUENCY - kHz


Coefficients vs Frequency Derived from Data Received at Figueira.


63

DATA

PROPAGATION PATH: PAULA FREITAS TO PINHALZINHO (PF-PIN)

DISTANCE; 213 KM

AZIMUTH: 2620


MEASUREMENT PERIOD: 29 MAY - 1 JUN 1980

j rPaul Freitas

I Puimlln Dr. Pedriahoe

2 TRANSMITTER SITE k,

[1RIECEIVER SITES

Figure 18. Path Parameters for Paula Freitas to Pinhalzinho.

65

200-

4 'e

I JUN 198053 000_

1200-- ~-

31 MAY 1980152 000 -

30 MAY 1980

Y- 0

100 200 30 4&0 50TIME - LSECOND$

Figure 18. 1. Three-Dimensional Display of Normal Skywave Data Received at Pinhaizinho.

4 44++5KHz

45KHz1 b I i ----- 60KHZ

NORMAL SKYWAVE

Figure 18.2. Group Heights of Reflection for 30.5 kHz and Reflection Coefficients at15, 30, 45 and 60 kl-z Derived from Normal Skywave Data Received at Pinhaizinho.

66

*4S4L t E, GIOUP 14G-S - uNO!I? miSVO 0:L. a 4 C'I 0'. -31 : D ISIOK [*:*.ALZI O DA' 151 '1i1 V4% C4' I I'S. 'SM .j..,ZL.O O1 '', CA' 1'6 3iSk O00 SI CSA. ''O.

06S**. . .........:* "*...

~(a) ""40

0 -

a0 0 ,5 tg

NORMAL SKYWAVE

*40*LLE, GPOUI .(O'S 11 4S BO 1 0 s 0(100. .ISIASE 0.i .z;.o oAT Sl 'SlS. 'iSO ' U 0Y '52 IS'. aggg - e, 0 0A. 5, , SZ ?050 I ,P 0"Z '52 'ss. '

'0

go

u L

'00

20NN

,@ 25 11 3 0~ 0 5 7 7 0 2 4,2 5 1 3 1 4 1 5 6 7

NORMAL SKYWAVE

Figure 18.3. Group Heights of Reflection and Reflection Coefficientsvs Frequency Derived from Data Received at Pinhaizinho.

a. Local Midnight (0315 UT).b. Local Noon (1515 Ur).

67

100

E 90 i-MIDNIGHT'80

o-

(a 6 NOON

(a) 6 0o0w 50

340-I.

_1 30 _

020-

0 10 20 30 40 50 60 70FREQUENCY -k H z

1.0'

II-

U.'A.

(b) 3 .0.1 NOON4 i

2 -

i

00 0 20 30 4050'070

FREQUENCY - k~z


Coefficients vs Frequency Derived from Data Received at Pinhalzinho.



68

DATAPROPAGATION PATH: PAULA FREITAS TO IRAI (PF-IRA)

DISTANCE; 250 KM

AZIMUTH: 2560



Figure19. Pth Paametes forPaula Freitas t rl

Dr69dino

1200 -1.

29 MAY 1980 - -

150 000 0 I---N ZZ-

1200 -

28 MAY 1980149 0000 -

1200 -- ,4- -

27 MAY 1980 -,-

48 0000 ~

100 200 300 400 50TIME -,USEC0P408

Figure 19. 1. Three -D imensional Display of Normal Skywave Data Received at Irai.

d ~ d d i~ d~ -4+-*++*15KHz

~'--~30KHz-45KHz

------ 60KHz

NORMAL SKYWAVE

Figure 19.2. Group Heights of Reflection for 30.5 kl-z and Reflection Coefficients

at 15, 30, 45 and 60 kd-z Derived from Normal Skywave Data Received at Irai.

70

PARALLEL. &&B2U 011COGS - UNDZS'GDMD PARALLE 0EFtC' JON CUBIPPCIW - J.NO11'GBDL1-. NA' GA5 19" 'OW SNAO' U 5S OW 19 Al 011 A.S 315. G009 VA., 0.1 1 W 5. 19"

luI U.1 C .a J 6'

00

o Fo C

(a) !

S E

P c8

30 C

20 N

FBE[OLNCY IK~ FGE OUENCv NAVZI

NORMAL SKY WAVE

*AG0ALL6 LoONp .41C."s NNOU OSG(DI[ *GGGAL.l. AEa EC JON CO(.FrJC C' - UOISTUBGECJIlOGJ 14N I SllSG '066 PItl SGN G4A 5l~ NA 0

soe

0

(b) -~: N

* VA

so c,I

FREOUENCY N-HZI FREOUENC 6'HT)

NORMAL SKYWAVE


vs Frequency Derived from Data Recieved at Iral.

a. Local Midnight (0315 UT).b. Local Noon (1 515 UT).

71

100-

E 90-__________

J9~~ ~ Mii NIG

a MIDNIGHT II-

I-

070 NOON

(a) = so-d: 50-

2 40

0 30-

20 20 20 30 40 50 60 70

FREQUENCY -kHz

1.0 -1- 1 T -r - - -- 1 T - T

MIDNH- --.

2

U.

( b) oU 0.

C-)

0 10 20 30 40 50 60 70FREQUENCY - kHz

Figure 19.4. Averaged Values of Group Heights of Reflection and ReflectionCoefficients vs Frequency Derived from Data Recieved at Irai.

a. Group Heights of Rpflection.


72

.. ... .. ..

5. SELECTED FEATURES OF THE REFLECTION DATA

In this section data are shown to illustrate variations in the VLF/LF reflection properties of the

ionosphere with such factors as time-of-day. direction of propagation, range and skywave

polarization. In addition, a brief description is given of weak daytime pulses, seen from time-to-time.which were reflected from altitudes somewhat lower than those normally observed.

Due to the limited amount of data obtained at many of the receiving locations, the variations

described below should be considered to be indicative of trends, rather than more-fully established

characterizations. These trends, however, are consistent generally with those observed in earlier

experimental programs, conducted at both mid- and low-geomagnetic latitudes 2, 1

5.1 Day/Night Reflection Heights

A summary of noon and midnight reflection heights, derived from the data obtained at all thereceiving locations, is given in Figure 20. As shown, the effective heights of reflection varied little

over the frequency range from 15 kHz to 60 kHz. At noon the average height of reflection was 69 kni atmidnight, it was 86 km. Throughout the 15-60 kHz range, the spreads in the heights were relatively

small, usually well less than 2.5 km and 1.5 km for the noon and midnight data, respectively.

5.2 Day/Night Variations In The Reflection Coefficients

Normal (11R1) reflection coefficients, derived from noon and midnight data obtained at a number

of receiving locations to the east and west of the transmitter, are given in Figure 2 1. In all cases thereflection coefficients at midnight were substantially larger than those at noon, ranging from a factorof about 2 for the lowest frequencies observed (15 kHz) to an order of magnitude or more at muchhigher frequencies (40-60 kHz). At midnight and at noon the magnitudes of the reflection coefficients

generally decreased as the frequency increased. At midnight, however, the variations were relativelysmall, usually being only about a factor or two over the 15-60 kHz band. In contrast, at noon themagnitudes of the reflection coefficients varied by an order of magnitude or more over the same

frequency range. These results suggest that at midnight the reflections effectively came from asharply bounded layer, while at noon there was weak ionization, below the altitudes at which the

waves were reflected, that absorbed appreciable energy from the up- and down-going waves. The fact

that the effective heights of reflection varied so little over the 15-60 kHz band (see Section 5. 1) also

supports such a characterization of the difference between the midnight and noon reflect ionprocesses.

5.3 Azimuthal Variations In The Reflection Coefficients

Comparison of the east-west (magnetic) data in Figure 21 reveals that the reflection coefficientsat noon were appreciably larger for propagation to the east. This directional effect, which is due to theinfluence of the geomagnetic field, is in accordance with earlier experimental observations 2 and

73

| I I I I I I I I I I

100-

E 90 __soG-,a¢ MIDNIGHT _ -- -T]I1 n .... - iP

a~80-

7O NOON .

x 6 0 -

a50-

~40-

~30-

020

I I I p p p p I I a a ! a

0 10 20 30 40 50 60 TOFREQUENCY - kH z

Figure 20. Summary of Noon and Midnight Group Heights of Reflection

Derived from Data Obtained at all the Receiving Locations.

74

9.0-

MIDNIGHT

-- ~ - - -- - ------

Z

2IIL

~a ~~i NN N N N NOON

0

IU.L I

- 7kmEAST-BLUMENAU

- -- 200km WEST- FIGUEIRA 10 20 30 40 50 60 TO

FREQUENCY - kHz

1.0 - 1 . I . I

MIDNIGHT

_2N

U.

0LI

(b) oo., N.. N ooN

2j 7

cc - 215kin EAST -GASPAR

-- --- 13kin WEST - PINHALZINHO

of0 I0 20 30 40 50 60 TOFREQUENCY -kHz

1.0

U.

w NOON

0

,.j\

wJ I- 246km EAST -CAMBORIU \

------ 250kffiWEST- 1RAI

01 0 90 20 30 40 50 60 70

FREQUENCY - kHz

Figure 2 1. Normal Reflection Coefficients for Midnight and Noon Derived from

Data at Selected Locations to the East and to the West of the Transmitter.

a. Approximately 200 km Propagation Paths (Paula Freitas to Blumenau/Figueira).b. Approximately 215 kmi Propagation Paths (Paula Freitas to Gaspar/ Ptnhalzinho).c, Approximately 250 km Propagation Paths (Paula Freitas to Camboriu/Irai).

75

theoretical expectations 5 . The midnight data exhibit little east-west difference, even though thereflections came from much higher altitudes where such geomagnetic effects would normally bc

expected to be stronger. because of the reduced collisional forces associated with the lower neutraldensities a, those heights. The absence of appreciable geomagnetic effects in the midnight data

suggests again, as described in Sections 5.1 and 5.2, that the nighttime reflection process can becharacterized as having been more sharply bounded than the daytime process.

5.4 Variations In The Reflection Coefficients With Range

Figures 22 and 23 sunimarize the variations in the magnitudes of the normal reflection

coefficients with range (or. in effect, incidence angle) that were derived from the pulse reflection data.In Figure 22 data are ;iverni at four frequencies over the 15-60 kHz band for six receiving locations,ranging from about 156 to about 280 km to the east of the transmitter. This corresponds. effectively,to a measure of the reflectivity of the ionosphere over a range of incidence angles from about 48-64degrees in the clay. or, about 42 48 degrees al night. The data show that the magnitudes of thereflection coefficients generally increase with increasing range, or more grazing incidence angle, withthe trend being especially pronounced in the daytime.

Figure 23 shows 20 kHz reflectiont coefficients derived from data obtained at locations to the eastand west of the transmitter. To the east, the reflection coeffVi(ent Increases monotonically as thelength of the propagation path Increases. To the west, however, there Is an apparent dip in thecoefficient at a range of about 215 km (corresponding to an incidence angle of 57 degrees), which maybe indicative el a quasi-Brewster's angle effect in the ionosphere. These data agree almost exactly withsimilar data obtaincd near the geomagnetic cquaftcr in Brazil in an earlier experimental program 1

(Rasmussten ct al).

5.5 Comparison Of Normal And Converted Reflection Coefficients

Only a sniall amount of dala pertaining to the polarization rotation effects produced in theionosphere by the eo'f{mwetic field were acquired during the experimental campaign. The results of

those obscrvations are suumarized in Figure 24, which gives normal k11Rj1) and converted (11RLreflection coefficients derived ironm noon and midn~ight data obtained at three locations to the east of

the transmitter. As sh; .'n, the nonnal reflection coefficients were larger than the converted

coefficients, with the difference being especially great during the daytime for frequencies below about30 kt{z. In g'neral. the polaritat in convcrsion at night was substantially greater than in thedaytine. ;s expecied from considici i'. ,:1l The reldive effccts of electron-neutral collisions in the

reflectol FrO css. 'hoeteti,-il conisd .. it lin; alslo inr!icrle, generally, that while the normalrefleel ii(. c' iflit iciti,, ,11( ,jld iia ase a tle, dist ts froml ie transmitter become greater and

gie; r c'as 1,, 1r' Se i l :. I1t ill: .1.h . 1ver'i or- ir's should decrease. Unfortunately, the

5. Cronbic, D. D. (19 51 f )ilcrenct.., ht.iwccn E i V,d 'XV E pinpagation ol VLF signals over long(listait.s. ,.. Att mr s. Terr. P l.s 12- ()

76

RANGE - km150 200 250 3001.0 w.kz -- MIDNIGHT

-~~-I5HzNOON

"-44--- 45k -4---

z

0C-) 01

z 5U U

C,, zW C)

485 52.5 55.0 57.0 60.7 63.7 DAY42.2 46.3 48.9 51.3 55.4 58.4 NIGHT

APPROXIMATE ANGLE OF INC IDENCE -deg

Figure 22. variation in Normal Reflection Coefficients with Rangeand Angle of incidence for Locations East of the Transmitter.

77

RANGE-km150 200 250 300

EAST

oWES

L)

w NO0

z .

0

w U)

_j -0 0

52.5 55. 5.60. 63.DA

4. 46348.9 .55.4 6. 53.7 NIGH

APPROXIMATE ANGLE OF INCIDENCE-deg

Figure 23. Norma] Reflection Coefficients for 20 kllz Derived from Midnight and Noon

Data Obtained at Receiving Locations to the East and West of the Transmitter.

78

1.0 _

z R MIDNIGHT -- ..............

. .. . . .

i.w N0 156km - DR PEDRINHO

NOON -. 180km- TIMBOZ0 -,R...... - *.... ....... 197km - BLUMENAU

oi

,, \ ... \ .\~....

,, .. . "..

I0 I I I I I I I t I

0 10 20 30 40 50 60 70FREQUENCY - kHz

Figure 24. Normal and Converted Reflection Coefficients Derived fromMidnight and Noon Data from Three Locations East of the Transmitter.

79

polarization rotation data that was acquired during the experimental campaign was too sparse to testthis theoretical expectation adequately.

5.6 Evidence Of Weak Reflections From Below The Normal D-Region

The data acquired during sunrise periods were inspected for evidence of reflections coming fromaltitudes below the normal D-region, such as those observed earlier in similar mid-latitudeexperiments 6, 7 which were attributed to a 'C-layer' of ionization produced by the combined action ofcosmic rays and solar illumination. A total of 57 sunrise recordings were made during the 22 dayscomprising the experimental campaign. Only rarely were recordings made during any given sunrise atmore than two locations. Of the 57 sunrise recordings, approximately 40 percent showed evidence ofreflections below the normal D-region. In most cases, however, the reflections were very weak andpartially mixed with the D-region reflections; that is, only the leading edge of the received pulses couldbe resolved from the later arriving. D-region, reflections. In addition, there were sunrises for whichthe low altitude reflections were observed at one receiving location, but not another.

Figure 25 shows data acquired over a four-day period at Camboriu, 246 km to the east of thetransmitter. Examples of weak reflections, believed to have come from a C-layer, are outlined bycircles in the Figure. Such reflections are most easily seen in the data of May 17, where the leadingedges of the daytime skywaves were nearly stationary, and distinct from later arriving (D-region)reflections that moved in accordance with the solar zenith angle. However, on other days shown inthe Figure, such distinct reflections could only be seen for very short periods around sunrise andsunset.

Very clear evidence of the reflections occurred during sunrise on May 17, in observations madesimultaneously at Timbo, Camboriu and Canasvieiras, at distances of 180, 246, and 280 kIn,respectively, to the east of the transmitter. The pulse reflection data recorded at those sites at 1015 UT,when the solar zenith angle was about 86 degrees, is given in Figure 26. In the three traces of Figure26a, two skywave pulses are seen, which are clearly separated from an earlier arriving groundwavepulse. The first skywave (labeled C in each tract) is presumed to have been reflected from a C-layer inthe lower ionosphere, whereas the second, much stronger. skywave is presumed to have been reflectedfrom D-region ionization produced by Lyman-c radiation from the sun. Based on the arrival times ofthe early skywave reflections and the path lengths over which the observations were made it isestirated that the effective height of the C-layer that produced the reflections was 67 km.

Figure 26b shows effective plane-wave reflection coefficients derived from the C-layerreflections. The coefficients provide estimates of the reflection properties of the C-layer as a functionof frequency and incidence angle, which can then be used to infer a conducting-slab model of the layer.

6. Rasmussen. J.E., Kossey, P.A., and Lewis, EA (1980) Evidence of an ionospheric reflecting layerbelow the classical D region, J. Geophys. Res. 85: 3037-3044.

7. Bain, W.C. and Kossey, P.A- (1987) Characteristics of a reflecting layer below the classical Dregion" J. Geophys. Res. 92: 12,443-12.444.

80

19 MAY 1980140 00001980 -

191980

03 0000030TIM0 -- SL

Figur 2.Dt bandatCo0 hwngWa elcin(cicle ara)fo liue elwteNra -ein

17 MAY 181

17 MAY 1980 1015 UT' X =86"

- _ 280km - CANASVIEIRAS 7 CANASVIEIRAS

C

24"Cm C OCAMIORIU

CAMBORIU

180km - TIM80 -

C

TIM 80

Figure 26. Data Recorded on 17 May (Day 138) 1980 at Timbo. Gamboriu and Canasvieiras.

a. Normal Skywave Data Showing Weak Reflections below the Normal D-Region (C).b. Normal Reflection Coefficients Derived fr-im the "C' Protions of the Received Skywaves.

82

As described by Kossey and Lewis 8, an estimate of the thickness of the slab can be obtained fromthe frequencies at which the relative nulls occur in the reflection coefficients. The magnitudes of thereflection coefficients are then used in determining an effective conductivity of the slab. From thedata of Figure 26b, it was estimated that a 10-ki thick slab, having a uniform conductivity of 10 -7

Siemens/m, could describe the ionization (phenomenologically) that produced the C-layer reflections.This model contrasts with a more strongly ionized, 6-km thick slab, located at 60 km altitude that wasinferred from earlier pulse reflection measurements at a mid-latitude location in the United States 7.

If the low altitude reflections that were observed in Brazil did indeed come from a layerproduce/d by cosmic rays. it is not too surprising that its features might differ appreciably from thoseobserved at higher latitudes. This follows, qualitatively at least, from consideration of thegeomagnetic field conditions. In Brazil, the measurements were made where the geomagnetic field hada dip-angle of only about 15 degrees; that is, the field was almost horizontal. It is surmised that '.henearly horizontal geomagnetic field produces a shielding effect to charged particles, thus reducing theability of the cosmic rays to penetrate deeply into the lower atmosphere. At higher latitudes, wherethe geomagnetic field has a much larger dip-angle, such shielding effects are expected to be very muchweaker. For example, at the mid-latitude location where the pulse reflection data were used to infer arelatively strongly ionized, 6-ki thick layer, at 60 km altitude, the dip-angle of the geomagnetic fieldwas almost 70 degrees.

Too little appropriate data were acquired during the experiments in B.azil to attempt tocharacterize the nature of the C-layer at low latitudes. The limited data that were obtained, however,provide useful information on how future experiments might be designed to better exploit the pulsereflection technique for investigating the C-layer. For example, the data of Figure 26 illustrate thatthe lengths of the propagation paths in such experiments should be carefully chosen. If the path is tooshort, (that is, the incidence angle of the pulses on the layer is too steep) the reflections may be tooweak to be clearly discerned. For example, the C-layer reflection observed in Timbo. 180 km from thetransmitter, was almost too weak to be measured: while in Canasvieiras, at a distance of 280 km, itwas relatively strong, and easily measured. On the other hand, at Canasvieiras, there was very littleseparation between the groundwave, C-layer and D-region pulse reflections, owing to the relativelylong propagation path. At the intermediate distance of 246 km, at Camboriu, however, there wasample separation between the observed pulses, and the amplitude of the C-layer reflection wasrelatively strong.

5.7 Unusual Moving High Altitude Nighttime Reflections

Often at night unusual, moving, reflections were observed coming from regions well above thealtitudes normally associated with the VLF/LF pulse reflections. The reflections tended to begin at ahigh altitude around 0200 UT and, in most cases, drifted downward over a period of 6-8 hr beforedisappearing during the sunrise transition period. Sometimes, however, the reflections began to driftupward again, about 2 hr before sunrise. These moving reflections can be easily seen in many of the

8. Kossey, P.A. and Lewis, E.A. (1981) The Reflection Properties of Conducting Slabs, RADC-TR-80-371, ADA098940.

83

quasi 3-dimensional displays of reflection data given in this report. A five-day sample of such data isgiven in Figure 27. It is hoped that future research will provide the necessary analyses to characterize

these unusual nighttime reflections and the ionization processes that produce them.

6. ELECTRON DENSITY MODELS OF THE LOWER IONOSPHERE

Phenomenological models of the lower ionosphere can be derived from steep-incidence VLF/LFreflection data using mathematical inversion techniques such as those summarized by Sechrist9 .

Under normal ionospheric conditions this is not an easy task, since the polarization rotation effects

of the geomagnetic field cannot usually be ignored. In addition, there is a question as to theuniqueness of models derived from reflection data. Nevertheless, since the VLF/LF reflection

properties are very sensitive to electron densities below about 90 km at night, and below 75 km during

the day, such data provide an important means for developing and validating models of the lower

ionosphere.

Figure 28 shows electron-density models of the low latitude Ionosphere in Brazil, derived from

the pulse reflection data. The models were obtained using a trial-and-error approach, which employedfull-wave and iterative computational techniques. In doing this, data from all nine of the receiving

sites, were Included so that the derived models were made to produce computational results consistent

with a large number and variety of experimental data.

The technique involved the choice and refinement of trial electron density models of the lower

ionosphere that served as inputs to a full-wave computational program, used to calculate theoreticalvalues of VLF/LF reflection coefficients and effective heights of reflection, across a wide frequency

band. The calculated values were then compared to those derived from the experimental data, and the

differences between them were used as the basis for adjusting the trial electron density profiles.Finally, for each electron density model a root-mean-square (RMS) error was determined from the

theoretical (computer) and experimental values. As such, the RMS errors provided a means for

comparing the various electron density models under consideration.

Based on the strong tendency for the experimental values of the reflection coefficients to

decrease monotonically with increasing frequency. trial electron-density profiles were chosen that

varied exponentially with altitude. Figure 28 shows the noon and midnight electron-density models,

having the smallest RMS errors, that were obtained from the numerous exponential models that were

tested. In the notation of Wait and Spies 10, which is often used to characterize such models, the noonmodel is described by a 3 = 0.43 km- 1 and a h = 70 kin, and the midnight model by 0 = 0.8 km-1 and h =

83 km. For the noon model, the average RMS error between the calculated and experimental values for

the magnitudes of the normal reflection coefficients was 1.4 dB over the 15-50 kHz band and averaged

over the nine receiving locations in Brazil. The corresponding RMS error in the effective heights ofreflection was 1.2 km. For the midnight model, the RMS errors were 1.8 dB and 1.0 km, respectively,

9. Sechrist. C.F. (1974) Comparison of techniques for measuement of D region electron densities.Radio Sci. 9: 137-149.

10. Wait, J.R. and Spies, K.P. (1964) Characteristics of the earth-ionosphere waveguide for VLF radiowaves, Nat. Bur. Stds., Tech. Note 300.

84

29 MAY 1980150 0000 -_

1200 *

28 MAY 1980 ?~

1200_

27 MAY 1980 -

148 0000 -__ '

1200

26 MAY 198047 0000-

200 ~ ~ I y ~ ~

25 MAY 1980 ~--146 0000

1200-

24 MAY 1980145 0000 -

00o 060 300 400 50TIME -. LSECONDS

Figure 27. Data Obtained at Camboriu Showing Moving Reflections (circled areas)

During the Nighttime coming from Relatively High Altitudes above the D-Region.

85

i/ COLLISION FREQUENCY/SEC105 104 I05 106 007 08 109

rJ' 11,, 1 liiilii , 1,,111 1 n I , , I,1111I I I lit111 I I'li

110--COLLISION FREQUENCY PROFILE

100-

90.

-80- •~ *.........-

I- BETA=O.8kni' ,h a 83km-70-

60 BETA=O.43km-, h -70km ".

50 - -

40-30 ' 0 1 1 I I 1 11 1 3ill I 1 111[11 4 I II 1 I I IIIIId 5 1 IIIIIIu

10o 102 10 10 o 105 0

Ne, ELECTRON DENSITY/ cm 3

Figure 28. Electron Density Profiles of Low Latitude Ionosphere Derived from

the VLF/LF Reflection Data Gathered During this Series of Measurements.

86

determined from data over an even wider frequency band of 15-65 kHz. The agreements between the

experimental and calculated values for the two models are very good, based on earlier experiences with

developing such phenomenological models of the ionosphere for example, Lewis et a12 .

7. SUMMARY

Observations of VLF/LF pulse reflections from the lower ionosphere, acquired at a relatively low

geomagnetic latitude in Brazil, have been presented. In addition, the use of the data to determine

effective heights of reflection and to provide a measure of the plane-wave reflection coefficients of the

iorir-,, L.e, derived from such data, were discussed. Although the models are phenomenological, and

not :-.athematically unique, they should be useful as inputs in longwave propagation prediction codes.More generally, the VLF/LF reflection data given in this report should be useful for validating other

electron density models of the lower ionosphere, such as those derived from long path VLF/LFradiowave observations or from theoretical considerations of the chemistry of the low latitudeatmosphere; that is, such models should have VLF/LF reflection properties that are consistent with

experimental data such as the data described in this report.

Other reflection data acquired during the experiments require further study to characterize their

properties and to identify the processes that may be responsible for them. These include weak daytimereflections from layers below the classical D-region, seen during sunrise periods and moving

reflections from altitudes well above those normally expected with VLF/LF waves, observed from time

to time, at night.

87

87

References

1. Rasmussen, J.E., Lewis, EA, Kossey. PA., Reginaldo Dos Santos, Edsel De Freitas Coutinho,Kahler, R.C., and Klemetti, W.I. (1975) Low Frequency Wave-Reflection Properties of theEquatorial Ionosphere, AFCRL-TR-75-0615, AD A025 111.

2. Lewis, E.A., Rasmussen, J.E., and Kossey, P.A. (1973) Measurements of ionospheric reflectivityfrom 6 to 35 kHz, J. Geophys. Res. 78: 3903-3912.

3. Kossey, PA., Turtle, J.P., Pagliarulo, RP., Klemetti, W.I., and Rasmussen, J.E. (1983) VLFreflection properties of the normal and disturbed polar ionosphere in northern Greenland.Radio Sd. 18: 907-916.

4. Bracewell, R.N., Budden, K.G., Ratcliffe, JA, Straker, T.W., and Weekes, K. (1951) Theionospheric propagation of low- and very-low-frequency radio waves over distances less than1000 km. Proc. Inst. Electr. Eng. 98(111), 221-236.

5. Crombie, D.D. (1958) Differences between E-W and W-E propagation of VLF signals over longdistances, J. Atmos. Terr. Phys. 12: 110.

6. Rasmussen, J.E., Kossey, P.A., and Lewis EA (1980) Evidence of an ionospheric reflecting layerbelow the classical D region, J. Geophy,. Res. 85: 3037-3044.

7. Bain, W.C. and Kossey, P.A. (1987) Characteristics of a reflecting layer below the classical Dregion" J. Geophys. Res. 92: 12,443-12,444.

8. Kossey, PA. and Lewis, E.A. (1981) The Reflection Properties of Conducting Slabs. RADC-TR-80-37 1, ADA098940.

9. Sechrist, C.F. (1974) Comparison of techniques for measurement of D region electron densities,Radio ScL 9: 137-149.

10. Wait, J.R and Spies, K.P. (1964) Characteristics of the earth-ionosphere waveguide for VLF radiowaves, Nat. Bur. Stds., Tech. Note 300.

89 ¢ 1 ;. . - --rnment ITint F. Off cc' - t-7 7

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