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DAASM PROJECT-HIGH LATITUDE AIRCRAFT HF PROPAGATION EXPERIMENT

Gary S. Sales, et al

Air Force Cambridge Research Laboratories Hanscom Air Force Base, Massachusetts

19 May 1975

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295108 lAFCRUTR-75-0290

ENVIRONMENTAL RESEARCH PAPERS, NO. 516

10

DAASM Project-High Latitude Aircraft o HF Propagation Experiment

GARY S. SALES JOHN I; VIDEBERG RAJAN VARAD

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IONOSPHERIC PHYSICS LABORATORY PROJECT 5631

AIR FORCE CAMBRIDGE RESEARCH LABORATORIES HANSCOM APB. MASSACHUSETTS 01731

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Gary S. Sales John I. Videherg Rajan Varad

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ia SUPPLEMENTARY NOTES

"Boston College

19 KEY WORDS 'Connnu. on ,„„.. ..d. ,1 n.c....r, „Ö Id.nUI, Cv Woe» "umb.r)

Over-the-horizon radar Arrival angle spectra High latitude ionosphere HP propagation Doppler frequency spectra

Coherence

20 ABSTRACT rConilnu. or „v.,,* .Id, II n.r....r> .nd ^tn,,!, hy Mori, numb.,}

The purpose of the DAASM project is to investigate the effects and Umita- tions caused^ the auroral and polar ionosphere on over-the-honzon HF prop- agation using a backscatter sounding system.

The technique measures and records the ^n^plex arnplitude of^m^ng

ticated software on a CDC-6600 computer at AFCRL. This process, Uoing

DO FO'" 1473 EDITION OF I NOV 65 IS OBSOLETE Unclassified SECURITY CLASSIFICATION Of THIS PAGE fWisn D.r. Enlmrmd)

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20. (Cont)

Fourier analysis techniques, provides output in the form of Doppler frequency vs arrival-angle "maps ' as well as roheronce maps. These maps are used to analyze effects of the irregular high-latitude ionosphere, such as Doppler fre- quency and arrr. ai-angle spreading of the signal, and the temporal and sparial coherence. Various antenna configurations and spacings, together with adap- tive processing techniques, permit optimization of he resolution and signal/ noise ratio of the various parameters being analyzod. Use is made of bistatic oblique ionograms and a special polar-model computer prediction program to compliment the analysis.

This report presents selected data and the initial results of the effects on forward propagation using the DAASM system in conjunction with a moving air- craft to provide signal Doppler and arrival-angle information. A KC-135 specially equipped for ionospheric research made six S-hour flights of up to 3000 km into the Arctic from Goose Ray.

Examples of data selected to illustrate particular propagation effects are presented, such as Doppler frequency spreading, arrival-angle spreading, multiple mode propagation causing deviation from predicted values of both' arrival-angles and Doppler frequencies, etc.

Two of the most serious problems indicated by the Goose Bay DAASM experiment, in terms of the operation of OTH radar systems, appear to be the effects of TID's and tilted ionospheres. Investigation of the problem is continuing and further results of the analysis will be presented in a forthcom- ing report.

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Preface

Arknowledgment is cxtrnded to Dr. VV. I'fistcr. now at Boston College, for

the conception of this effort based on his earlier ionospheric "drift" experiments

:,t AI-THI.. Appreciation is extended to William McComish and Hohert K. Houdrenu

of Boston College for their efforts in progra mining the software for the CDC-GÜOü,

and to the members of the Ionospheric Dvnamics Branch of AKCHI. for their sup-

port with the aircraft and some of the data processing. Appreciation is exU.nded

to Dr. T. Klkins, Chief, Ionospheric Radio Physics Branch, for his continuing en-

couragement and assistance in making this endeavor possible. A special word of

thanks is extended to Mrs. I.inda Cillingham for her efforts in typing the original

manuscript.

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1. INTRODUCTION

Contents

2. EXPERIMENT

2. 1 DA ASM 2. 2 Oblique lono^rarns 2.3 Flight Plans

3. ANALYTIC TECHNIQUES

3. 1 DA ASM 3. 1. 1 Power Spectra 3.1.2 Coherence 3. 1.3 DA ASM Maps

3.2 Oblique lonograms

4. RESULTS

4. 1 General 4. 2 Data Format

4. 2. 1 Aircraft Track - Geographical Coordinates 4. 2. 2 Aircraft Track - Auroral Oval Coordinates 4. 2. 3 DAASM Maps 4,2.4 Coherence Maps

4.3 Aircraft Data

5. CONCLUSIONS

REFERENCES

10

10 13 14

IS

15 17 18 19 23

24

24 26 26 28 30 36 ?7

37

103

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8.

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10.

Oblique lonogram. (Joose Bay, Flight 4-106, 15 ,Iul 1974: 1641 IT: 1240 km

Coherence vs Distance, Typical Plot (a) Frequency 11.22 MHz, Flight 4-142. 2253 1IT (b) Frequency 8.22 MHz, Flight 4-106, 1940 UT

DAASM Flight 4-058, 27 Keb 1074 (a) Aircraft Path !n Ceographic Coordinates on a

Polar GeomaKnelic Projection Range and Bearing vs Time of Aircraft from Coose Bay Aircraft Tracks Helati%'e to Auroral Oval (Q - 3),

in Geomagnetic Local Time and Latitude

DAASM Might 4-060. 1 Mar 1074 (a) Aircraft Path in Geographic Coordinates

on a Polar ffeomagnetic Projection (b) Range and Bearing vs Time of Aircraft from Goose Bay (c) Aircraft Tracks Relative to Auroral Oval (Q 3),

in Geomagnetic Local Time and Latitude

DAASM Flight 4-14 1, 21 May 1074 (a) Aircraft Path in Geographic Coordinates

on a Polar CieomaL'netic Projection (b) Range and Bearing vs Time of Aircraft from Goose Bay

(b) (c)

3),

Ctoose Bay 3).

(c) Aircraft Tracks Relative to Auroral Oval (Q in Geomagnetic Local Time and Latitude

DAASM Flight 4-142, 22 May 1074 (a) Aircraft Path in Geographic Coordinates

on a Polar CJeomagnetic Projection Range and Bearing vs Time of Aircraft from Aircraft Tracks Relative to Auroral Oval (Q

in Geomagnetic Local Time and Latitude

DAASM Flight 4-193, 12 ,lul 1974 (a) Aircraft Path in Geographic Coordinates

on a Polar Geomagnetic Projection (b) Hange and Bearing vs Time of Aircraft from Goose Bay (c) Aircraft Tracks Relative tc Auroral Oval (Q 3),

in Geomagnetic Local Time and Latitude

DAASM Flight 4-196. 15 .lul 1074 (a) Aircraft Path in Geographic Coordinates

on a Polar Geomagnetic Projection (b) Range and Bearing vs Time of Aircraft from Goose Bay (c) Aircraft Tracks Relative to Auroral Oval (Q - 3),

in Geomagnetic Local Time and Latitude Flight 4-058, 27 Feb 197 4

FT 2325; 2343; 0058 (a) DAASM Map (b) Doppler Coherence

Flight 4-060, 1 Mar 1074 UT 0303; 0348; 0610; 0701 (a) DAASM Map (li) Doppler Coherence

13

20 20

24 25

25

26 27

27

28 20

29

30 31

31

32 33

33

34 35

35

38-43

44-51

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lustrations

0238; 0251; 0305; 0336

11. Flight 4-141. 21 May 1974 UT 2325; 2332 (a) DAASM Map (b) Doppler Coherence

12. Flieht 4-142, 22 Mav 1974 UT 2153; 2253; 2342, 2355, (a) DAASM Map (b) IJoppler Coherence

13. Flight 4 -193, 12 Jul 1974 FT 1655; 1718; 1721; 1920; 1940; 1941; 1943 (a) DAASM Map (b) Doppler Coherence

14. Flight 4-196. 15 Jul 1974 UT 1641; 1940; 1941; 1942; 2038; 2100; 2130 (a) DAASM Map fb) Doppler Coherence

52-55

56-71

72-85

86-101

Tables

1. DAASM Arrays (Large)

2. Additional Sub-Arrays

3. DAASM Flights

4. Coherence Table

11

12

15

19

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; i DAASM Project-High Latitude

Aircraft HF Propagation Experiment

I

I. IN'TRODl CTION

A series of papers1 described a method of vertical ionospheric "drift" mea-

surements and analysis; using complex amplitude measurements at spaced re-

ceivers. This method o* analysis first Fourier analyzes the received signal at

each antenna into its Uoppler frequency components, md then for each Fourier

component, determines the angle of arrival using the spatial array of antennas.

This technique has been adapted into an oblique sounding system using a linear

array of antennas and designed to operate either on backscatter signals or signals

propagated from a similarly equipped aircraft in i forward-propagation mode. The

DAASM system (DAASM is an acronym for Doppler/Arrival Angle Spectral Mea-

surements) has operated at Goose May, Labrador (5.^20'N, (i0°20'\n for just one

and one-half years beginning full operation In January 1074.

(Received for publication If) May 1075)

1 Pfister W , et al (1068-75) Pulse Sounding with Closely Spaced lieceivers as as a Tool'for Measuring Atmospheric Motions and Kine Structure in the Ionosphere, nnr, rs irv„0 Vol.i; T^nvironmental Research Paper No. 295, Dec 1968 Vol.11, Environmental Research Paper No. r95, Dec 1968 Vol.111, Environmental Research Paper Nc. 317. Mar 1970 Vol. IV. Environmental Research Paper No. 329. Aug 1970 Vol V. Environmental l^esearch Paper No. 468. Eeb 1974 Vol. VI. Environmental Research Paper No. 470. Mar 1974 Vol. VII. Environment..1 Research Paper No. 506. Apr 1975 Vol. VIII. Environmental P.esearch Paper No. 507. Apr 1975

Preceding page blank

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The purpose of the DAASM program is to investigate the effects of the auroral

and polar ionosphere on a backscatter sounding system which a* the same time can

receive a forward-propagated signal from an airborne transmitter. The aircraft

used for these experiments was a Kr-135. specially equipped for ionospheric ex-

periments. The questions to be answered concerned the character of the received signals and are focussed on three main areas:

(al Angle of Arrival - The degree to which the signals from the aircraft is '

deviated from the known bearing to the aircraft and the amount of angular spread- ing associated with the particular path.

(b) Ooppler Frequency - The extent to which propagation in the auroral re-

dons deviates the expected Doppler frequency associated with the aircraft motion

and the amount of iv.^u.-n.-v wading thai ncrurs ,,n the signal.

(O Coherence - The temporal and spatial coherence of these aircraft signals

after propagation through the irregular auroral medium.

The basic concept of the DAASM system is to record on digital magnetic tape

the signal output of each antenna in the receiving array. This recorded data repre-

sents a two-dimensional description ,f the received wave field, that is. time and a

one-dimensional space (linear antenna arra- i. In the most simple approach, a

two-dimensional Fourier transform of this data set results in a Doppler frequency

vs arrival-angle description of the received signal. These transforms are accom-

plished at the AFC-HL computer facility after the tapes are returned from the Goose Hay site.

The sampled data is limited both in time and space because of the finite dura-

tion of the sample (32 sec) and the limited extent of the antenna array (910 m

maximum». The resulting Doppler frequency and arrival angle description of

the signal is thereby limited in resolution. This is particularly true of the spatial

dimension, and advanced processing techniques having been developed to improve the capability of the system in this area.

This report addresses the six aircraft missions carried out during 1074 and

an attempt is made to relate the observed character of the received signals to the

propagation mode and other geophysical factors which may affect the auroral iono- sphere.

2. KXPKRIMKiNT

2.1 [JAASM

The DAASM system as configured for the Goose Bay experiments measures

the received amplitude and phase of an arriving radio signal as a function of both

10

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time and spare, in order to accomplish this, an array of ;>m.'>ll receiving antennas

was erected in a linear configuration broadside to the required receiving direction.

In this case the horesight of the array at Cioose Bay, that is. the direction normal

to the length of the array, was magnetic l^orth, 328° T. In order to provide maxi-

mum flexibility in terms of spatial sampling, a complex antenna arrangement was 2 3

developed using a 20-eloment array. The DAASM electronic system' was de-

signed to use subsets of this array, consisting of either 12 or 6 elements. Each

subset has either a aniform spacing or a Minimum Redundancy Array (MHA),

The MHA piovides all spacings that are multiples of a basic spacing up to some

maximum spacing with the minimum number of antennas. In the DAASM system

the several antenna sub-array configurations available are briefly described in

the following table:

Table 1. DAASM Arrays (Large)

No. of Klements Min. Spacing Max. Spacing Remarks

Configuration Code

12

11

10 m

10 m

110 m

450 m

Uniform

MRA

5/0

5/4

The configuration code above is designated by the symbols T/A, where T

selects the frequency mode and sampling sequence and A selects the antenna se-

quence. As will be described later, the DAASM system was designed to operate

with pulsed transmissions at a 400 llz repetition frequency. The experiments

described in this report all involve measurements carried out in conjunction with

the transmitter on-board the KC-13S aircraft as a signal source flying to the

north of Goose Hay. Because of transmitter average power limitations on the

aircraft, pulse repetition frequency was limited to 200 H?.. This necessitated a

change in the Goose Bay antenna system. Five additional sub-arrays, each with

six elements, were devised. Table 2 describes these sub-arrays. All of the

arrays are included in the 20 antennas and are selectable by i-. single multiposition

switch in the DAASM system. Depending on the selected sub-array, the DAASM

system samples each antenna sequentially with each transmitted pulse. After

completing the sequence of 6 or 12 antennas, the cycle is repeated until 512

samples are acquired on each antenna of the selected array. In fact, the DAASM

system operates at any two si locted radio frequencies at the same time.

2. Richard, D.W. (1972) Twenty-Element Receive Array for the DAASM Ex- periment, Instrumentation Paper No. 178.

3. Bibl, K. (19731 Doppler/Angle of Arrival Spectral Measurement System, ArCRL-TR-73-0759.

11

mmm

time and space. In order to accomplish this, an array of small receiving antennas

was erected in a linear configuration broadside to the required receiving direction.

In this case the boresight of the array at (loose Bay, that is, the direction normal

to the length of the array, was magnetic North, 328° T. In order to provide maxi-

mum flexibility in terms of spatial sampling, a complex antenna arrangement was 2 3 developed using a 20-element array. The OAASM electronic system was de-

signed to use subsets of this array, consisting of either 12 or 6 elements. Each 2 subset has either a uniform spacing or a Minimum Redundancy Array (MRA).

The MRA provides all spacings that are multiples oT a basic spacing up to some

maximum spacing with the minimum number of antennas. In the OAASM system

the several antenna sub-array configurations available are briefly described in

the following table:

Table 1. DAASM Arrays (Large)

No. of Elements Min. Spacing Max. Spacing Remarks

Configuration Code

12

11

10 m

10 m

110 m

450 m

Uniform

M RA

5/0

5/4

The configuration code above is designated by the symbols T.'A, where T

selects the frequency mode and sampling sequence and A selects ehe antenna se-

quence. As will be described later, the DAASM svdtem was designed to operate

with pulsed transmissions at a 400 Hz repetition frequency. The experiments

described in this report all involve measurements carried out in conjunction with

the transmitter on-board the K.C-135 aircraft as a signal source flying to the

north of Goose Ray. Because of transmitter average power limitations on the

aircraft, pulse repetition frequency was limited to 200 Hz. This necessitated a

change in the Goose Bay antenna system. Five additional sub-arrays, each with

six elements, were devised. Table 2 describes these sub-arrays. All of the

arrays are included in the 20 antennas and are selectable by a single multiposition

switch in the DAASM system. Depending on the selected sub-array, the DAASM

system samples each antenna sequentially with each transmitted pulse. After

completing the sequence of 6 or 12 antennas, the cycle is repeated until 512

samples are acquired on each antenna of the selected array. In fact, the DAASM

system operates at any two selected radio frequencies at the same time.

2. Richard, D.W. (1972) Twenty-Element Receive Array for the DAASM Ex- periment, Instrumentation Paper No. 178.

3. Bibl AF

. K. (1973) Doppler/Angle of FCRL-TR-73-0759.

Arrival Spectral Measurement System,

11

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Table 2. Additional Sub-Arrays

No. of Elements Min. Spacing Max. Spacing Remarks

Configuration Code

6 10 m 50 m Uniform 7/0 6 20 m 100 m Uniform 7/2 6 20 m 320 m MRA (Approx) 7/4 6 30 m 720 m MRA (Approx) 7/6 6 70 m 910 m MRA (Approx) 7/7

The actual procedure is to cycle through the array the first time using the first

frequency, then a second time through the array using the second frequency. On

the third sampling sequence through the array, the first frequency is used again

and this cycling is repeated until the 512 time samples at each antenna and at each frequency have been recorded.

This technique results in a sampling rate of approximately 16 Hz per antenna, per frequency, and a 32 sec time sample when the system prf is 200 Hz.

The signals are recorded synchronously on digital magnetic tape from four

sampling gates delayed in time from the transmitter pulse by a selectable amount.

The output of the four gates is digitized with seven bits and then recorded. Each

sample is recorded in quadrature at the 100 kHz IF. For the experiments des-

cribed here, the delayed gates are set at the time of the arriving signals from the

aircraft which is equipped with a similar DAASM system and operates synchron- ously with Goose Bay.

The spatial (antenna array) and temporal samples form the two-dimensional

array which is used in the data analysis to generate the two-dimensional DAASM maps as described in detail in the next section.

The experiment described in this report consists of six aircraft missions

covering the period of December 1973 to July 1974. Each flight was approxi-

mately 8 hours in duration, and several different flight patterns were executed

flying out to distances of 3000 km to the north of Goose Bay. The details of

these plans will follow in Section 2.3 . Whenever obliquely propagated signals

from the aircraft were available, the delayed samplmg gates were made to coin-

cide with the received signal and the data digitized and recorded. Two frequen-

cies were selected for each half hour of the flight before take-off using the best

propagation predictions available. Iv general, each predicted frequency was

used for at least 1 hour. With the availability of real-time oblique ionograms

(Section 2.2) between aircraft and Goose Bay. the selection of operating frequency was often mad^ during the flight.

12

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2.2 Ohliqup lonopranis

In Novemb(;r 1973, it was decided to generate oblique stepped frequency iono •

grams between the KC-125 aircraft and the Goose Bay Ionospheric Observatory

during the same time that the routine backscatter ionogram was being made at

Goose Bay. Roth the Goose Bay and the aircraft sounding systems begin the

stepped frequency mode simultaneously and each records an oblique ionogram.

The frequency range is normally 6 to 16 MHz in 100 kHz steps and the ionogram

takes approximately 1 min (Figure 1). These ionograms, although instituted pri-

marily for the purpose of studying the propagation in the polar regions, have

played a major role in the DAASM experiment. First they have made possible

the real-time selection of the two operating frequencies. By agreement with the

operating personnel of both the ground station and the aircraft, and after inspection

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13.1 14.1 15.1 16.1

Figure 1. Oblique Ionogram, Goose Bay, Flight 4-196, 15 .lul 1974: 1641 UT: 1240 km

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of the oblique ionogram. certain specified changes are allowed at one end of the

path and the operator at the other end attempts to follow these changes. W.th the

two-way oblique ionograms. this real-time method has worked exceedingly well

and has resulted in frequency usage closer to the optimum than is possible usmg 4

predictive methods. The second benefit derived from the oblique ionogram has been in the post

analysis, specifically the possibility of making mode identifications. An important

part of the DAASM program is to relate the observed spectral character of the

fixed frequency maps to the propagation mode. It is through understanding this

relationship that techniques for improving OTH radar performance can be de-

veloped. 5 The oblique ionograms are made using the existing Digisonde 128 systems

located at Goose Bay and in the AFCRL KC-135 aircraft. The data is recorded

on digital magnetic tape as well as displayed on site in real time in the manner

used for all "Digisonde" data.

2.3 Flight Hans

For each of the six flights used for this report, a flight plan was developed

for use bv the aircraft navigator. The actual flight paths deviated only slightly

from the planned path, and in the subsequent description only the actual paths are

presented. The chosen paths were often a compromise between competing ob.iec-

tives Certain compromises in flight path were sometimes made to permit auro-

ral oval monitoring by other scientists involved in the airborne measurements

program. Each of the six night paths are presented in three different manners. The

first display for each flight shows the actual geographic location of the aircraft as

a function of time on a geomagnetic projection, while the second display shows

range and bearing of the aircraft from Goose Bay. The third display shows the

path of the aircraft in corrected geomagnetic time vs latitude. The auroral oval

for Q= 3 remains fixed in this coordinate system. This allows the user to see

the physical relationship between the aircraft. Goose Bay and the oval during the

Hight. These aircraft track maps are useful when interpreting the observed

propagation modes and DAASM maps.

4 Barehausen. A. F.. et al (196-9) Predicting Lonß Term Operational Param- l. b„rgnausen, _. _r'pni]encv sky.Wave Telecommunications äystemsrESSA

eters of High Frequency 5ky-V Tech. HepoH EHL UO-m-Vb.

Bibl. K.. et al(1970) Digital Interpreting Goniometrie Ionospheric Sounder. AFCRL-7 1-0002.

14

^,..^,.iJJi..^JJ.V>.;J^./*:lJl-.lr-:;<.M,J.i^K^.,Wi^^

IP.

The six flights used in th is report are detailed in the following table:

Table 3. DA ASM Flights

DA ASM No. Date Take-Off (UT) Landing (UT)

DM 4-050 27 Keb 1974 1900 034 2 DM 4-060 1 Mar 1974 2355 0829 DM 4-141 21 May 1974 174 3 0220 DM 4-142 22 .May 1974 203 2 0457 DM 4-193 12.Iul 1974 1440 2250 DM 4-196 15 .lui 1974 1440 2236

i. ANALYTIC TF.C.llMyi KS

3.1 DAASM

As stated in the introduction, the purpose of tho DAASM proiect is to provide

. description of the character of radio signals arriv-ng from a point source through

a relatively disturbed ionospheric medium. Fn order to provide such a description

the approach chosen is to devise a signal power density estimate as a function of two

vanables. Doppler frequency. w. and wave number, k. associated with arrival angle

1 ho power as n function of th.se two variables results from the two-

dimensional transforms of the recorded amplitude data in space and time, that is

x and t. The DAASM system at Goose Hay utilizes a one-dimensional linear

az.muthal arrival angle. The data is ambiguous with respect to the elevation angle of the source or sources.

Three methods of estimating the power density function are described T le

three methods arose from the various antenna configurations available with the

DAASM system. The third method is the only one used for all th- data presented

here, even though it is relatively time consuming on the computer because it in- volves matrix inversion.

As a general introduction to the analytic techniques used here, a short des- cription of the basic approach is given.

If the time samples are understood to constitute one dimension and the spa-

tial samples to be the second dimension, then the two-dimensional Fourier trans-

forms yields the Doppler frequency/wavenumber power density (FWPD) spectrum

Thus, if A.(a)) and Am{Wl denote the discrete complex Fourier spectral line

at Doppler frequency, co at antennas J and m respectively, then the cross spec- trum between the antennas is given by:

15

■■4t^mA mumiiäm^ü

^^WjiVlgf.''.^"'"''"."'-'''^'^!1!111!.1 i.'i1 m[ ilM.iiiiliiiNiiiiMiiiiiipiiiiiiiiiiMH ^IIIHIII PIIII| I FiiiiiBi^iiiiif III|IIIPIIII HIM ||i nil MHIIIM , MH

S. (w) = A.iu) • Av (co) .l171 .1 rn

In general, a smoothed version of cross-spectral estimates S. (w) is always used. The estimated FWPD spectrum is defined bv

- N N

P(W,k^ = E T. W W S. (u)) • expik- (r.-? ) j=l m=l J m Jm J m (1)

where N is the total number of antennas, i^'s are the vector distances from

some arbitrary origin, k is the wavenumber vector, ind the W's are suitable weights imposed on the i antenna.

In a report, different methods of spectral analysis to extract Doppler fre-

quency, phase and coherence information are described in detail. It was found

that the frequency-averaging technique provided a very efficient and reliable

means of cross-spectral estimation, and only the frequency-averaging technique

of estimating the cross-spectra is used in all of the data involved here. Once the

cross-spectra have been estimated, the spatial component of the FWPD spectrum

can be estimated by several methods. The three methods of wavenumber analysis

can be delineated in terms of the choice of the weights W. and are: (1) The Fast

Fourier Frequency-Wavenumber Analysis or the Conventional Analysis, which is

most useful for an initial diagnostic scan in the frequency-wavenumber iw-k) space.

Wavenumber sidelobe characteristics can be varied by proper choice of weights

for the different cross-spectral terms; however, the resolution is relatively poor.

(2) The minimum redundancy version of the conventional method is only applicable

to the data from a strict minimum redundancy configuration of the antennas.

(3) The adaptive method using the maximum likelihood principle offers high reso-

lution in spatial characteristics and is applicable to any arbitrary antenna config-

uration. Unlike the other two methods, this method assigns adaptive weights to

the different cross-spectral terms depending on the azimuthal look-angle and the spatial characteristics of interference and nois.e.

The part of the analysis and computation common to all three methods is the

determination of a suitable cross-spectral estimate between any given pair of antennas.

The recorded data, 512 points per subcase for each antenna, consists of two

sets of 256 equally-spaced complex-valued time samples displaced from each

other by a ratio ß = 25 . Fach 256 sample set could be used for processing; how-

ever, it is practical to treat only the middle 128 samples in each set in order to

1. Pfister, W. , et al (1975) Pulse Sounding with Closely Spaced Receivers as a Tool for Measuring Atm^hinc Motions and Fine Structure in the lono- sPhere' Vol. VII, Environmental Hesearch Paper No. 50ti, April 1575

16

i;SaAi&Ku.a&*,i;s»;>K»;^lA>^i.n.MÄv~,i;.K.^^

^jpHim^wp^if^

allow for adjustment of range gates and frequency before processing the datn.

Thus, the sets consisting of 128 samples in each subcase are immediately trans-

formed into the frequency domain via a Fast Fourier Transform. The resulting

128 complex-valued discrete Fourier spectrum spans a basic Doppler frequency

range of 8 Hz. It is possible to either combine or interlace the resulting two sets

of Fourier spectra. If the Fourier spectra are aligned, the signal-to-nois1: ratio

can be improved but the basic Doppler frequency range is still 8 Hz. If the two

sets are interlaced, the Doppler frequency range can b« doubled to IG Hz without

any improvement in the signal-to-noise ratio.

In tne case of signals transmitted hv the aircraft, the basic range of 8 Hz is

sufficient. Hackscatter signals often occupy a band wider than 8 Hz, in which case

interlacing proves to be very useful. In any case, the combined or interlaced

Fourier spectra form the starting point for further data processing.

Three types of output have been designed. These consist of (1) power spectra,

(2) coherence spectra, and (3* maps -if Doppler frequency vs arrival angle called

DAASM maps.

3. 1. 1 POWER SPFCTRA

Power spectra are calculated for each antenna by taking the product of each

Fourier spectral line with its own complex conjugate. Of course, the Fourier

spectra are normalized in each channel so that the total power in each channel

equals unity. That is, if g represents the unnormalized m frequency line,

then the normalized Fourier spectrum is simply

/

g m

Vl/;^ The power spectra are smoothed by the frequency-averaging technique over

seven frequencies concurrently with the operation of evaluating the product of the

Fourier spectra. This feature enables the cross-spectra to be estimated In an

identical way merely by inserting the Fourier spectra of the appropriate pair of

antennas. The [fower spectra and the cross-spectra are different only in a mat-

ter of the antennas involved.

The power spectra thus obtained are pk tted on a standard format of logarith-

mically-scaled numbers ranging from 0 to 15 which corresponds to a linear

scale from 0 to 9P . The exact equation defining the scales is

1. Pf ister, W. , et al (197 5) Pulse Sounding with Closely Spaced Receivers as a Tool for Measuring Atmospheric Motions and Fine Structure in the lono- sphere. Vol. VH, Environmental Research Paper No. 506, April 1075.

17

«^.■..■.w..«^,A.-;.,;,.. ■,„i',i.,.s,-«>i.,j' . -, >>;™,1^.;iv,i.,..1.^^;;„/,,,WJ.x.;ii„s^«v-..,;«.t.x,..^,!,^,;:'»,,.,^v.....,t^-^'A-i:Ji:..;- ,.-„..^:.,.i,vfca.-,,,;,;;.; :•„,■.. ., -. .,-,. w..„^,>:ii, ;./:■;.:..-LU^J!

mmm^mf^^^' ^«pas^si^BR®i^?p!!«SS5BS^

Plog = 2+71oglOPIin

= 2 -> I',.

s 1', '' 100 lin

lin

where P]og is the printed output integer and P^ is thr, v:lhle of the nornialized

power lor the i ; requencv designed to have :. maximum of 100 .

P. ii n 256

I i=l

25 (i

I he power spectral outputs provide the basis for selection of data segments

smtable for the more complex and time consuming P(W. k) analvsis. The data

consists of subcases where each subcase has four different range gates and two

carrier frequencies. Therefore, for the six antenna configurations there will be 4!i channels of power spectra for each subcase.

■■i. 1. 2 COHKRKXCK

Coherence spectra between the ivth ■■—■ "-- -th

by the equation: and the n channels (antenna) is defined

C'OlKw) i = mn| pr

Smn(w) I

th

V^mm(w)-Snn^

WherCth

Smn '^ is ^ smoothed cross spectrum at Doopler frequency OJ between

■■■nd n channels and S^co) would be the power spectrum ,,f the mth el annel ,t

.3 clear that the coherence is „ number which lies between 0 and 1 . This linear

range is converted to an inverse hyperbolic tangent scale and multiplied bv a suit-

able scale factor to provide the printed output numbers for the data in Section 4

The following table shows the relationship between coherence value and output

numbers. The coherence spectra are plotted for each available distance between

the various pai s of antennas in order of increasing distance. Since the coherence

.s only available at specified distances, the plots are backfilled at intermediate

distances with the same value. It was found that the raw coherence thus plotted

appeared sometimes to be a discontinuous function of distance instead of a mono-

ton.cally decreasing function. Therefore, three successive subcases have been

averaged for each distance at each Uoppler frequency to provide a much smoother

p.cture and thus improve the statistical confidence limits which depend on the

sample size. A least-square linear fit is plotted for a sample of these data in I* igure 2.

18

.■...■■.^■-.■..,. .■..,. .....i....,>..-.-..,.-v..^..., :,.;-.. ..,..1 - ■. ... -.■..■■-...., »-^l-^■■■■■■-^■■^■^■M^.livH^ T .. ..,..r...-i|..r,.,h....- .,-..... -, .i , ... . , ■ |lY-niK^Wmijfiltoli^f.a

■WV

mmMmwmmmmmmmmmmmm ^vvs**^^

^y^KWi^gmm^mmm^^ i'tv"**^&^!^m

■■.-■!, '■- t" i : TjlVSf-.".^^'^.^-^'^,

Table 4. Coherence Table

Coherence Printed Number

s0. 30 0 0. 31 1 0. 56 2 0.74 3 0. 86 4 0. 02 5 0. 96 6 0. 98 7

>0. 99 8 through 15

The coherence spectra are primarily useful in determining the maximum use-

ful aperture as a function of operating frequency and the signal propagation mode.

3. 1.3 UAASM MAPS

DA ASM maps consist of plots of power density vs Doppler frequency and

wavenumber which, in turn, is simply related to the azimuthal angle of arrival.

3. 1.3. 1 Rartlett Estimate

A particularly efficient algorithm to calculate the (w-k) spectra is achieved

if the weights in Eq. (1) are chosen to correspond to a triangular taper function

anc will be referred to as Fast Frequency-Wavenumber analysis or the general- ized Bartlett estimate.

In such a case, the individual cross-spectral terms need not be separately

calculated. The separate Fourier spectra from each antenna output can be used

directly, and frequency smoothing can be applied in the final step. The details of

the algorithm are as follows:

Let IAJMI exp i 0.M represent the Fourier spectral line at frequency W

from the jth antenna. Then the cross-spectrum between the jth and mth antennas is

S. (w) = .im A,(üJ)

.1 ! Arrl<

w> I exp j (0,

and the (w-k) spectrum

N N piu.k) = r T

.)= 1 m= 1 S.mM exp -jik. (r.-rm)| (2)

where k is the wavenumber.

19

^^^^;^-wa^a.i&la

ip^ppppip^pq^i

12

;0 FLIGHT 142

100 200 300 400 500 DISTANCE (m)

600 700

0.99 UJ u z UJ

0.96 K I O o

0.86

0.56

0 800

(a) Krequency 11.22 MHz, Flight 4-142, 225.3 t'T

0.99

100 200 300 400 500 600 700 DISTANCE (m)

(b) Frequency 8.22 \'lHz, Flight 4-196, 1940 UT

Figure 2. Coherence vs Distance, Typical Plot

20

.,■,,.:/.,.„ fr'furTi-a'ffiliitiat'luiia ^atfll^jIMjgjffljg^lga^aiii^^

- a

in m m«m\\mmaammmm3mmssim!ms*,tm:i

Eq.(2) can be written alternately as I

P(W,k) = E |A.(W) | exp i |0.(W) - k • r. .1=1

Z? IA (0!) I exr m=l

. exp j-i(5 (w) - k • r | m r / m m (3)

The subscripts j and m can be replaced by a single subscript n m-j, and

the double summation can be replaced by a singlfe summation. Thus,

I N

, O A (w) exp i 0 («) - k • r P(u.k) = n=l

(4)

Eq. (4' can be computed much faster than Eq. (3). -> _>

P(a), kl is calculated at as many points as desired in k, say with increments -»

Ak. Each successive point in k can be computed from the previously computed

point by simple complex multiplication because exp i (k 4 A:,) = exp ik • exp i Ak .

This step is common to all three approaches of (üJ-k) spectra1 calculations and

saves considerable computer memory and time.

Since frequency smoothing is independent of the operations of k , a set of

weights W(cü) is calculated using P(üJ,O) for each W, and each P(a),k) is multi-

plied by the appropriate W(a)) to yield Piw.k), the frequency smoothed estimate.

The relation between the wavenumber k and the direction of arrival 0 measured

from boresight for the case of a linear array is given by

2 7rf sin

where k is now a scalar, f the operating carrier frequency, and c the velocity

of light.

3. 1.3.2 Banning Estimate (Minimum Redundancy Version)

The minimum redundancy array version can be treated as a special case of

the general equation for the (w-k) spectra given by Eq. (1). It is. assumed, of

course, that a certain number of consecutive multiples of the basic antenna spacing

are available by suitably placing the different antennas. Distances beyond the

largest consecutive multiple are considered as having zero weight; that is, their

contribution to the (w-k) spectra is zero. The non-zero weights decrease as a co-

sine squared function with distance. In addition, the self-spectral term is assigned

a weight of 0.5 , so that the expression for the (w-k) spectrum can be w-itten as

21

«i^rf/^,.,.. .^...^..^.^.^..„^„.^^...antiiw^-t-.^

.!*pg?ww*^p^«i^ mmn

P(a),k) 2So

L. T W iSl exp i(k-d;) (5)

./here SQ rorresponds to the self term and S^ is the rrnss-spectral term corre-

sponding to the pair of antennas separated by a distance 'I' I. is the largest suc-

cessive multiple of the basic spacine and W. is the weight given by the cosine-

squared function. It is well known that 'he cosine-squared weights result in good

sidelobe suppression. It can be showiiJ that for 6 antennas only 13 consecutive

multiples are possible, and for 11 antennas the corresponding number is 45. A

similar configuration for more than 11 antennas is not known at the present time.

Kach spacing occurs only once, and hence the name "minimum redundancy" for the

array. Only those cross-spectral terms corresponding to the multiples of the

basic spacing need be calculated. Thus, for 1 1 antennas, 45 of 66 possible terms

are available. The applied weights are almost optimal for the configuration and

there is excellent sidelobe suppression. If the carrier frequency is chosen such

that the basic spacing is a half-wave length or smaller, then there will be no grat- ing lobes.

3.1.3.3 Maximum Likelihood Kstimate

The third approach to (w-k) spectral estimation employs an adaptive scheme

to generate the set nr weights in the filter given by Eq. (1) Instead of using a

fixed set of weights for all k, the adaptive scheme allows icr the set of weights to

be varied depending on the particular k as well as the chara-ter of the signal,

that is, interference and noise. In other words, the set of weights is dictated by

the data sample available, subject to the constraints that a unit plane wave signal

travelling with a given wav^number k = ko (arriving from the direction towards

which the antenna beam is pointed), is passed undisturbed through the spatial filter,

but everything else for which k = ko (arriving from other directions) is rejected in

an optimal manner. Thus, the true spectrum is reproduced with high resolution

and not smeared, which normally occurs as a result of the convolution between

the true spectrum and the particular array pattern. This choice of constraints re-

salts in a convenient mathematical formulation. It is only necessary to calculate

the inverse of the matrix of cross-spectral terms for each Doppler frequency of

interest in order to furnish the optimal set of weights automatically adapted to

each k for a given data sample. The cc.mputational procedure is set forth in the following steps.

The normali'/ed input Fourier spectra from the various antennas is converted

to cross-spectral estimates S. («) by any one of several spectral estimation pro-

cedures^ in this case by frequency averaging and smoothing with seven frequencies.

6. Moffet, A.T. (1968) IEEE Transactions on Antennas and Propagation AP-16 (No.2hl72. " -*-**

22

,M„^:. ..;.;, . ... .:-..- ,.,.. i -.v.,;.-.;..,.,.. ■■„-;-..,„.^.^ .,.■....-.,;:..,.^^,.^^.w-,.^^^;Jl;.,■■:,.,:...Ji^^,^^^,<,;1.,,i,>.».tii.:.A..-!V...-.,., ,.. ......■;.... j tä^m^ii^uaaaaMäi^^^

m^mmmmmwm^^m ww&mpmwm ^mwm^mmmm^vmv,-mf^«wi''>iim^»^^

■:\i*y^^,^:^-^'—^"' &■

Subscripts j and m refer to the antennas in question. Next, an NX N ••matrix of

cross-spectral estimates fS(w)] is organized at each OJ, where N is the total num-

ber of antennas. Not all NX N terms need be evaluated since S. (w) = S* .(u). jm mj '

where the asterisk denotes complex ccnjugation. The sum of the diagonal elements

in the matrix is stored as a measure of total power at anv jriven Hoppler frequency

and used later for renormaliz.ation. The matrix itself is normalizeti by replacing 1/2

each element S (w) / S aj)/[S (to) ^^W» . a step which ensures sensor

equalization. The normalized cross-spectral matrix for Doppler frequency co is

then inverted. The elements of the inverted matrix are used in the equation for

(oj-k) spectra

P(w, k) N N

m-1 n= 1

■1

jm' exp i k • (r

-1 (6)

It is seen that the weights W. and the cross-spectral elements [Kq.(l)] together

a^e replaced by the corresponding inverted matrix elements and the reciprocal is

taken to yield the high-resolution (ai-k) power density estimate. The increments

over k are calculated in a chain sequence from the various values in the same

manner as indicated before. The final step is to restore relative power levels at

the different Doppler frequencies. First, the values of P(tü,k) are summed over

all k and the normalised values of P(a;,k) are obtained by simply dividing by this

sum. Next, the normalized P(cü,k) are multiplied by the sum of the diagonal ele-

ments of the original cross-spectral matrix which have been stored as indicated

before. Thus, the renormalized P(w. k) are obtained with an appropriate scale

factor and are recorded on magnetic tape for later printouts (see Section 4.2.3).

S.2 Oblique lono^runis

During the six flights, the oblique ionograms have been scaled for both mode

availability and frequency. The oblique ionograms are taken, ore every 5 min,

which represents a considerable effort. The results are used to provide the iden-

tification necessary to relate the DAASM maps with propagation mode Another

aid to mode identification is the Polar Model ITS-78 program.7 The polar model

program has been modified for use with aircraft to Goose Bay propagation paths,

that is, where one end of the propagation path is continuously changing. A syn-

thesized ionogram is calculated from this program and compared with the measured

one.

The calculated and measured oblique ionograms together provide a reasonably

reliable method of mode identification.

7. Elkins, T..I. (19731 An Empirical Model of the Polar Ionosphere. Survey in Geophysics, No. 26T; ~~~

23

»f^yi^ffiimfiw^rtfiiffiff^^

rvr-"^--'-^^/^^!;^;;)^^.^^

4. RESULTS

4.1 General

The results of the aircraft meesurements will be presented in sequential sec-

tions with each night as a complete package. The detailed analysis of the DAASM

data will be presented in a subsequent report, and here only data will be presented

to illustrate the character of the aircraft signals propagated over auroral paths.

Within each flight section, the different types of display will be indicated. Fig-

ures 3(a), (b), (c) through 8(a), (b), (c) for Flights 4-058, 4-060, 4-141, 4-142.

4-193, and 4-196 are concerned with the aircraft track and propagation paths.

A limited quantity of data is presented here, varying from eight maps for

Flight 4-196 to two maps for Flight 4-14 1. These maps are given in Figures 9(a)

and (b) through 14(a) and (b). The maps were selected to illustrate certain general

(a) Aircraft Path in Geographic Coordinates on a Polar Geomagnetic Projection Figure 3. DAASM Flight. 4-058, 27 Feb 1974

24

Ijaagaaiayflii^ ■'■■'■-"----t-

mmmm

■ j1

Z800

2600

2400

2200

2000

1 1800 -

S 1600 z 4 "■ 1400 t- u, S 1200 o

4 1000

800

600

400

200

0

BEARING

RANGE

19 20 21 22 23 UT

00 01 02

BS

290

300

310

320

330

340

350 §

«I

10 g a:

03 04

20

30

40

50

60

70

(b) Range and Bearing vs Time of Aircraft from Goose Bay

16,

2100

2048UT 204e !

„t\2IOO / / 0000 oj K- ^oofaaoa^ooio

.0100 AIRCRAFT TRACK

• 08

■or

POSITIONS OF GOOSE BAY

(c) Aircraft Tracks Relative Oomagnetic Local Time

Figure 3. DAASM Flight 4-058. 27 Feb 1974

cks Relative to Auroral Oval (Q ^ 3), Focal Time and Latitude

in

25

:r*:a*^:,ü-,A~JS*t^

mmmmmmmmmmimmmm^^mwmm

features of the observed behavior and special events. For each time selected, the

maps are included for both Doppler/Arrival Anple and Doppler Frequency/Coher-

ence Distance. This results in a rather complete description of the received sig-

nals. The details of the for.nat for this map data will be eiven in Sections 4.2.3

and 4.2.4. For each flight, the maps will begin with Figure n(.i) for Doppler/

Arrival Angle and Figure 3(b) for Doppler/Coherence Distance maps. Fach figure

will consist of all the maps for that Right identified by time and arranged sequentially.

The map data for each flight is supplementedby thegeographical and auroral oval plots of the aircraft track. The auroral oval aircraft track shows the relative posi-

tion of the aircraft, Ctoose Bay, and the auroral oval at all times during the flight.

4.2 Data Formal

4. 2. 1 AIRCRAFT TRACK - GEOGRAPHICAL COORDINATFS

Using the KC-135 aircraft navigator log, the position of the aircraft at each

observation time is plotted in geographic coordinates in Figures 3(a) through 8(a)

for each flight on a polar projection of the Farth. Along the track are indicated the

hourly positions. In order to make some of the more complicated flight paths clear

and for use in analysis of the DAASM maps. Figure 2(b) is a plot of range and

bearing of the aircraft measured from Goose Hay as a function of time.

(a) Aircraft Path in Geographic Coordinates on a Polar Geomagnetic Projection

Figure 4. DAASM Flight 4-060, 1 Mar 1974

26

^^■'■'- ■ ■■-■■■ -■■■ ..^-- ..-:.. ...-..-:■.-.^^..^^. - MtaajaaaaisiiiiidiäiaiayititeaBBäit^i BB aaatBC aa& a a:, i,^, „ ^ < u^uu ...^■,v^..i.u^,^il.^.^^^^.^,,i.«i„^.,„.,i,;A:w;.^Jjai^^:i^^^A!^?.i^i^U:fcä^

2800 -

2600 -

2400 -

2200 -

2000 -

I 1800 -

u 1600 z < ^ 1400

£ 1200 u

< 1000

800

600

400

200

0

BEARING

RANGE

BS

23 00 01 02 03 04 UT

05 06 07 08

(b) Ranije and Hearint; vs Time of Aircraft from Coose Bay

14 10

TO'

0035U

0400

POSITIONS OF GOOSE BAY

(c) Aircraft Tracks Relative to Auroral Oval (Q = 3), in r;eoniaf,metic Local Time and Latitude

Figure 4. DAASM Flight 4-OCO, 1 Mar 1974

27

290

300

510

320

330

340

350

0

10

20

30

40

50

60

70 09

- i i-if -III-I- iV -Vi iV;--TVrii- ■-,-?'rt--|iH-- niiiiiiiiiiiAViiiin;^ ■ i -f --''i IwMWiiin^nTiiitivfrtV^^

1

I I

4. 2. 2 AIRCRAFT TRACK - AURORAL OVAL COORDINATES

In order to see the relationship between the aircraft position and the auroral

oval as a function time during the flight, a second plot of aircraft position in geo-

magnetic latitude against corrected geomagnetic time, in polar form, is shown in

Figures 3(c) through 8(c). In this coordinate system, the auroral oval remains

fixed while the receiving site at Goose Ray circles at constant geomagnetic lati-

tude, .I)3.30N, and is shown at hourly positions. In Figure 3(c), the one-hop and

two-hop reflection points are indicated for the aircraft to Goose Bay at 0000 UT.

The points labelled 1 and 3 are the two-hop reflection points, and the point

labelled 2 is the one-hop reflection point. It is obvious from Figure 3(c) that the

one-hop reflection point lies within the oval near the poleward edge while for the

two-hop mode, one reflection point lies in the polar cap and the second reflection

lies within the oval. This information will be useful for one interpretation of the

DAASAI maps.

■ X5?

(a) Aircraft Path in Geographic Coordinates on a Polar Geomagnetic Projection

Figure 5. DAASM Flight 4-141, 21 May 1974

28

SSÜjÜSÜsl :':-',^i..^.i.vA\»\;..^j>.^^.j-..r.^/^i;ii.v^v,;.a^^

(h) Hanpo and Hearing vs Time of Aircraft from (loose Hay

2000

2100

2200 \

OG

POSITIONS OF GOOSE BAY

0200 — (A. 0220J'

(c) \ircraft Tracks Relative to Auroral Oval (Q= 3), in Geomagnetic Local Time and Latitude Figures. DAASM Flight 4-141, 21 May 1974

■.;.(''': '.-i.^&iMMiaöU*** ̂ jifiA^aaM^täd^^a^ttifeaflfiä^^

•&^$imshm^m>m**'!<**' iW!pBpiW|BJPglPP!>fPBpTOPH|8

4. 2.3 DAASM Maps

At any selected time and range, a DAASM map is generated according to the

technique described in Section 3. 1.3.3. These maps, for each of the two selected

operating radio frequencies, represent the Doppler frequency vs arrival-angle

spectrum of the aircraft signal. The two operating frequencies are displayed one

above the other, and the abscissa is the Doppler frequency in 1 Hz steps about a

chosen center frequency indicated in the legend attached to each map. The total

Doppler frequency range is always 8 Hz for the maps included in this report. The

ordinate scale represents the arrival angle, linear in wave number, measured

from boresight (0°) to i 90° at the end of «ach map. The arrival-angle scale is

repeated twice; once for each radio frequency. The first frequency listed corre-

sponds to the lower map. Using a special printing system,' the presented maps have a dynamic range

of approximately 22 dB with the difference between adjacent numbers equal to

(a) Aircraft Path in Geographic Coordinates on a Polar Geomagnetic Projection

Figure 6. DAASM Flight 4-142, 22 May 1974

30

■'■^ ■■ -- ■ .■....■ ,.;..,.. :■.:.:■ .■ ,.;. ^... . ^.Q. .,M .t-^;: ,.--.^.^1^,^ .^^

(g^lipPflf^flll^U^JSlW^PT*^ rrXJvmtW y^.'^,^.^prmT^:.r.^-y!J7»r^'.^ r?rrT7yr^z^^:^^?rrvr,

2800 -

2600 -

2400 -

2 200 -

2000 -

F IB00 ,_ BEARING \ -

- \

o 1600 2 <3 a 1400

2 1200 u X 5 1000

^,

-

800 - RANGE */

600 -

400 -

200 -

0 U i 20

(I)) Range and Hearing vs Time of Aircraft from (loose Hay

2100

2200

2056 UT fx2IOO

2300

POSITIONS OF GOOSE BAY

(c> Aircraft Tracks Relative to Auroral Oval (Q = 3), in deomagneUc Local Time and Latitude

Figure 6. DAASM Flight 4-142, 22 May 1974

31

üife>iA^,*Ä.K-:,^^

WlijfBBp^P^

1.5 dB. The numbering system is designed so that the larger num'.ers (numbers

range from 0 to 15) appear more dense, giving a visual appearance of increasing

blackness near the peaks of the signal. For example. Figure 9(a) (UT 2343) shows

the DAASM map for aircraft signals at 8.2 and 6.6 MHz over a distance of 1960km.

The DAASM map in this case was generated using a rather small array with an

aperture of 50 m (see Section 2.1). For frequency 1, 8.2 MHz, the received power

is very close to boresight, 0°, and at a Doppler frequency of -5.4 Hz. The raw

Fourier spectra were smoothed over seven frequencies, and the small antenna

aperture results in a minimum width of the displayed signal of the order shown.

For other maps where the large antenna arrays were used, narrower angular

(a) Aircraft Path in Geographic Coordinates on a Polar Geomagnetic Projection

Figure 7. DAASM Flight 4-193, 12 ,Iul 1974

1. Pfister, W. , et al (1975) Pulse Sou.iding with Closely Spaced Receivers as a Tool for Measuring Atmospheric Motions and Fine Structure in the lono- sphere. Vol. VII, Enivornmental Research Paper No. 506, April 1975. Tc si

32

aa&jwatjaaBaii^^

|flflj!((gBB^?'i&r'B*r?P^ 11 II I IHIHlHTMHHMBmr

v.

i

■■v

19 UT

BS

20 21 22 23 00

(bl Hange and Rearing vs Time of Aircraft from (loose Mav

290

300

310

320

330

340

35C

0

10

20

30

40

50

60

70

tu m

I ■ y ■'

■,,;■

i f

POSITIONS OF GOOSE BAY 1600 .ISOSUT

2000 J , 2000,

2100

2200\ ^2100 12200

2250

1600/ 70' /-AIRCRAFT TRACK

(c) Aircraft Tracks Relative to Aurora] Oval (Q= H), in Cieomagnetic, Local Time and Latitude

Figure 7. DAASM Flight 4-103, 12.lullfi74

33

USiiiSsl*ai£jj3&jliSsjllgS^ „^■^^■.i.^^^.-.^-^u.

r'??7T^y^W37^^*V:r<?^~^'!^"^:'^ ^^^v-r,?^^^»v^T"-,^~^ .^'^Ä?i^l^w^^-r!77';v^'^;T-^''-"7

spectra are often observed. Caution must be exercised in interpreting the ob-

served angular spreading until the specific antenna array is taken into account.

The hulk of the data in this report was taken using the 7/6 configuration with an

aperture of 7 20 m allowing relatively high angular resolution.

Kxamples of narrow angular spectra using the 7/6 array are shown in Fig-

ure 13(a) (IT IMO). Here the angular width is as small as ; nv observed for sig-

nals propagated in the Arctic ionosphere. The Doppler frequency spreading is

also minimal, ( ..-'sistent with the Doppler frequency smoothing. The relatively

high amplitude at other' arrival angles for the same Doppler frequency as the air-

craft signal results from the sidelobes generated by the "Maximum Likelihood"

processing (Section 3,1.3.3). In this case, the sidelobes are some 15 dB below

the peak. This is acceptable considering the relatively few antennas (six) usec' in

these samples. The sidelohe level suppression depends critically on the numl-.'r

(a) Aircraft Path in Geographic Coordinate;- on a Polar Geomagnetic Projection

figure 8. DAASM Plight 4 - 106. 15.11111074

34

m&ia M. li UA I «ii -■-■■■ li ■■■ • H i .-..„.. .J.«^..i^Mialj,.^<vv .-.....-T..,- ■:..■,-„..i^. .VJ .:... ,:. ... ,■ . . .,.- .::.,■ :..-, . .,.^ ,.■,.....,...,■■:.■.,,..:....., _.i,i^^^ .■i=~^-,^L-M^^^^^i,i,^^„iL^i^

W&^^my^m^^mtnmx^mmmim^^iismisimmsmissesm ((«ira^wipsrtweBsÄi'Wr't'W;^/ ■" ■ ■ ■■.^f^^m^xsn^T^Mm

I

23 00

BS

01

290

300

310

320

330

340

350 $

0

10

20

30

40

50

60

70

(b) Range and Bearing vs Time of Aircraft from Goose Bay

POSITIONS OF l7nn „. GOOSE BAY\ "yr

.„^ I5I6U.T

2000

2100

»2200

2200\/ 1 2236

(c^ Aircraft Tracks Relative to Auroral Oval (Q=3), in Geomagnetic Local Time and Latitude

Figure 8. DAASM Flight 4-196, 15 .lul 1974

35

■Bjatflfe /^J.!... .,- :. .^.Ss:**.^*^. *M^*^:. . ^..>^..-.V.^t..^ ...*■•,>*. ^4sX^^-^.^^.U<r^^ -...^^iL-.A.l-^^r-.V-^-.ri.^^^.J^.h-A^/^..^..^'-... „/..^.^ : ^.......... ■\:^!^,: ..^i.^ i:***^^^; Lt i iiiirf.lgii

ou.i,*iiii*m>K#*-"

of antennas used in the analysis. All data processed for this report used six

antenna arrays. The resulting high sidelobe level often makes it difficult to iden-

tify the aircraft signal; however, the MI.M always results in t^e largest power

(highest number^ at the correct signal.

4. 2.4 roilKHKNCi: MAI'S

The coherence between pairs of antennas within the array is defined as the

magnitude of the cross-spectra (Section 3.1.2). i-or each Doppler frequency line

in the spectra the coherence is calculated for all the pairs of antennas, that is,

all spacines available in the selected antenna array. The coherence map {Fig-

ures n(b) through 14(b) displays the coherence level plotted for each Doppler fre-

quency vs distance. Kach distance line in the coherence map represents 10 meters

spacing up to a maximum of OfiO meters. The maximum distance and the available

intermediate distances depends again on the antenna configuration chosen.

Tor example, the commonly used 7/6 antenna array uses six antennas with

physical spacings of 30, fiO, 100, 200, and 330 meters giving 15 possible spacings

of 30, GO, 100, 160, 200, 230. 260, 290, 330, 360, 300, 430, 490, 690, and 720

meters. All of these spacings are used for coherency calculations and for plotting

purposes. The coherence for distances less than 30 meters is set equal to C'OH

(30 m) and the coherence for distances of 40 and 50 meters is set eaual to C'OH

{60 m). This back-filling continues up to the largest available distance; in this

case 720 meters. Between 720 meters and 960 meters, the end of the graph, no

data are available, l-'or the filled arrays, configuration 5/0, 7/0, and 7/2, the

largest spacing is in general less than 100 meters and the coherence data of little

value, though these coherence maps are included for completeness.

Two typical examples are discussed here for general information. The first

example chosen illustrates high coherence across the entire large array and the second coherence which becomes small after only a short distance across 1he array.

The actual computer-printed data is shown in Figures 12(b) (l.T 2253) and 14(b)

(IT 1940). The upper half of Figure 12(b) (FT 2253) shows a strong line at approx-

imately -H Hz Hoppler frequency where the coherence remains relatively high

above the background noise level out to the maximum distance of 720 meters. The

lower half of Figure 14(b) (FT 1940) shows a strong line at +5 Hz with a rapidly

decreasing coherence as the antenna spacing increases. The coherence is a rela-

tively noisy statistical parameter ' resulting in fluctuations which make the

8. Jenkins, Cl. M. , and Watts, 0.0. (1968) Spectral Analysis and its Applications, Holden-Day, pp 374-411.

1. Pfister, \V, , et al (1975) Pulse Sounding with Closfcly Spaced Receivers as a Tool for Measuring Atmospheric Motions and Fine Structure in the lono1

sphere, Vol.V'II, Fnvironmental Research Paper No. 506.

36

^iA;;:j>wkK.^ui.,,.i^:,-.»,^,^^i^

mm^mmm^mm^^m^mmm mWm^^mmm^^mrn^^^^w!^^.

■;:,H'T,yFü ,B9<EöiWStw*«e ■ :-i'.c'iws^^;f',^^^'->f,^''Wvh>^^*>^^.*-,Ä«^^^/^r^*f^rr^^va;t^.^">»r*^A'<*' .^.^^■^^»y^Äf ^J0TC>10>^ •*.i^''-"'"'^■'"'tH''';{ L

simple concept of monotonically decreasing coherence with distance appear to be

violated. Figure 2 shows the least square linear fit to the above illustrated data.

For Flight 4-142 it 2253 UT, an antenna separation of approximately 1450 meters

would be required for the coherence to decrease to a value of 0.56, while for

Might 4-196 at 1040 UT. the distance required for the coherence to decrease to

0.56 is approximately 500 meters. As will be shown in subsequent reports, this

difference in behavior can be related to the propagation mode; that is, the E-modes

having high spatial coherence and F-modes relatively shorter coherence distances.

1.:! Aircral'l Dala

The data consists of compilation of samples of data selected from six air-

craft missions (Figures 3 through 14).

-«SW»MäSS®S8 -.fl

.-,. C.ONCi.l SIONS

The nucleus of this report comprises compilation of samples of data taken

from six aircraft missions each lasting approximately 8 hours. This selection

process is meant to illustrate several features that are common to the propagation

of radio signals from a small source, basically point-to-point propagation in the

auroral ionosphere. At this point, it is necessary to recognize the fact that these

aircraft signals are often spread both in Doppler frequency and azimuthal arrival

angle. Spreading sometimes occurs in only one of these two dimensions. For

example, spreading occurs in Doppler frequency and not in arrival angle as can

be seen in Figure 14(a) at 2038 UT. There are times when multiple modes are

set up which have different Doppler frequencies and arrival angles than that ex-

pected from the known aircraft speed and direction, A good examf'e of many

modes set up simultaneously is shown in Figure 13a at 1719 UT, Here several

modes are established at the same time, very likely due to the passage of a

travelline ionospheric disturbance. Another very common feature is reflection

from a tilted ionosphere which alters the arrival angle by several degrees.

The two most serious problems encountered in the DAASIU experiment at

Goose Bay, in terms of the operation of an over-the-horizon radar system ap-

pears to be TID's and tilted ionospheres. How much of the occurrence of these

features can be ascribed to propagation across the auror? oval needs to be in-

vestigated. For this purpose similar measurements at mid-latitude should be

undertaken. The relationship between the observations cataloged here and ionospheric

conditions and propagation modes will be presented in a subsequent report.

11

37

j^aaij^iaaaaaWA-aaiM^^

-i......u..J-J_-,n„v„-,,«1/.lia

mmmmmmmmmmmmmmm

1 1 1 1 1 I i 900W 1

i 1 FREQUENCY 2

1 w 45°- — UJ ^ 30°- — Q: o ^ 1=,° Q 15 - -

UJ -' 0° o u

2 <

15° - _ _i < > 30°- _ cc K < 45°- -

90° E

90°W

„45° - -

o-1

UJ 30°- _ LLI

cc o 15° - _ UJ Q

~ 0° UJ U

_J

'J 2 15°- — <

■-1 30°- < >

^45° - — tr <

90° E IFREQUENCY 1 r I 1 |

-4 -3 -2 -1 1 1 1

■ TCD +l +2 +3 + / %

FREQUENCY DOPPLER FREQUENCY (Hz)

a DAASM Map

DATE-- ?:?;-74,058' TIME (UTI- 2325

FREQI IMHzl ■8-212

FREQ2lfliH2i -- --|ai- RANGE (Km) I7I0 AZIMUTH ideg.) 328T

ANT. CONFIGURATION - 7/l

CENTER FREOIHzl "6

Figure 0, Flight 4-058, 27 Feb 1074, UT 2325

38

gltfiiifflVT- tr- 'itf ■■r^rin'WiVti>tnitYViitl^iiirai^teMllin-»rtft<tMifitilr^

■KHBKmVUil V^-^^iTi-r-*^-*"^"'

M

I

er Lü _i

CL Q. O Q

+ 4 r-

+ 3-

+ 2 -

+ I -

CENTER FREQUENCY

■2 _

-3

-4 + 4

+ 3 -

+ 2 -

^ CENTER

^ FREQUENCY

Q. O -| — Q

"2 —

"3 -

0

h

T-

60 -1 1 1 320 480 640

DISTANCE [Ml

8 00 960

OJ

>- o

UJ D

O

LÜ

et

o

UJ

O Lü CE

b. Coherence

Figure 9. Flight 4-058, 27 Feb 1974, UT 2325

39

u.. ■.,.....■.,.,.j n^. ■^...l „„■■.h-.iiimj-- ■- ..■-.:..-w.;>jL-.t...^-.- J.....-.^.....-- ^—.^-H.^.^....,. ..--,.■■■-■ ■.,*..^M:.,^,.±-..iu:^:*,-,^.:i,X.-m**Ji

m I ft^fW.WaftSa^ 'm~&$rmtx>tf!toi

90oW

W 45°- UJ

^ 30°- o

S 15°-

ÜJ

15°

< > 30°-

% 45°-

90° E

90oW

_ 45° -

uj 30°- UJ Q: w 15° _ UJ Q

0°

o 15° -

-J 30°- <

< 90° E

-r 4

[FREQUENCY 2

[FREQUENCY I

CENTER FREQUENCY

+ I + 2 + 3 + 4

DOPPLER FREQUENCY (Hz)

a. DA ASM Map

DATE - 2-;|7-74 (058)

FREQKMHz)—- 8-'!2

FREQ 2 (MHz) "• -2

RANGE (Km) I960

AZIMUTH (deg.) 328T

ANT. CONFIGURATION-7'0

CENTER FREO (Hz) ^

Figure 0. Flight 4-058, 27 Feb 1974. FT 2343

40

r in iiiii iMfflilniiiiifiliiiifiMiifiiiiltiilfifteffi^^ KtrttlitTTir-y-^- "--'■-,l

mmmmmmm^mmm^msm^^^^^^

60 320 480 640 DISTANCE [M]

800 960

b. Coherence

Figure 9. Flight 4-058, 27 Feb 1974. UT 2343

41

.■.■-^. ^..■■-u.^^...^.,..:-.......^.^.^.^-.^,^^^^..^,^.^^ m&mm

PiPPPPftitiPMIW^^

1 1 1 1 l 1 1 gCwl- iFREOUENCY 2

1 w 45°- — UJ w 30°- — tr o Q 1 0 — -

u -J n" o u

z <

15°- — _i < > 30°- - cc

^ 45°- -

90° E

900W

_450 - -

^ uj 30°- — UJ CE o 15° - _ u Q

~ n" UJ u

_J <^ 2 15°- — <

-J 30r- __ < > 0:45" — er <

90° E FREQUENCY 1 1 1 1 j

-4 -3 -2 -1 1 1 1

TCD +1 +2 +3 + 4 FREQUENCY

DOPPLER FREQUENCY (Hz)

a DA ASM Map

DATE T1ME(UTI—- FREQ I IMHz) ■ FREQ 2 (MHz) RANGE (Km) —

2-P7-74 (058) .'." 0058 ...8.22 „662 ... 1830

AZIMUTH (deq.l 328T

ANT. CONFIGURATION - m

CENTER FREQ(H2l +6

i

Figure 9. Flight 4-058, 27 Feb 1974, LFT 0058

4?

a&aaamaadailail^^

mmmmm mmmm^^w

i_ + 4 f

+ 3-

+ 2-

X

cr LL)

_I Q. Q. O Q

CENTER FREQUENCY

■2 _

"3

"4 + 4

+ 3

+ 2 - M X

+ I —

CENTER

FREQUENCY

"3 -

0

r

60 320 480 640

DISTANCE TM]

8 00 -i- 960

> O z. LÜ

O

Lü

cc U.

> u z Lü D O UJ cr LL.

b. Coherence innre H. Flight 4-058, 27 I-'eh 1074, UT 0058

4.-3

ivrAtuiU--',^-» •-•^■-■■.'■ijr-f,j'4^^wmtofe r.lfil^M^r^^riMiiyiiMr"NnirtT^miiiMMVf^^^^"-;^

QSSISfflll&mimsmsmmiwiiwNmmmsmm

mmmmm- wsmmmimmimmmmmmz^' WfigWWlfc. -.«»ByWrtTOtlWBWWUVWiWKWliWI t.VU»wi»c-A^.J-.,— i-^.-

90°W

U1 45°- UJ u 30°- It o UJ Q 15°-

UJ _J 0° o 2 <

IS"- -I < > 30°- a: n- < 45° _

90oE

90oW

_45° -

uj 30°- ÜJ

o 15° _ UJ Q

Ul _l

z 15° - <

-J 30°-

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90oE [ -r 4

"[FREQUENCY 2

•3

[FREQUENCY I

CENTER FREQUENCY

+ I + k + 3 + 4

DOPPLER FREQUENCY (Hz)

a DA ASM Map

DATE ..3-1-74 1060) TIME (UT) 0303

FREQI (MHz)— I3-22

FREQ 2 1MHz)— '1-22 RANGE (Km) 1900 AZIMUTH (deg.) 352T ANT. CONFIGURATION-7'2

CENTER FREO(Hz) "8

Figure 10. Flight 4-060, 1 Mar 1974, UT 0303

44

juaattiaaa i .-■-.. ■..■■■■. ■■■■■■'-■■ ^■- -■■.■. i^aiiki^iatiaa&aaaaifl^^

| 1 1 1 1 1 + 4 T~

+ 3" -

+ 2 - - ,—^ r-j

X + 1 - i—

cc

n

CFNTFR

FREQUENCY t

Q. O "I - Q

-2 _ L_

-3

-4 + 4

+ 3 -

+ 2 -

+ I -

CENTER

FREQUENCY

■2 —

-3 -

-^ IJL 0

h

160 320 480 640

DISTANCE [Ml

—1 f— 800 960

u

o UJ

cc u.

LÜ D O UJ cc

b.Coherence

igtiro 10. Flight 4-060, 1 Mar 1074, UT 0303

4 5

ü^y*-ti----,i^,MW,t~:>^<w^^^^^

i,5~-jSili V^fglll^fljitiQ/ifi^^ '.S._l. 1 „ - - .,.,.......,..,. -..,-»™ra-.-»—f i-*rvr*=nn-«r,V.SH.-SK :■

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to 45°- u UJ 30°- ir o UJ Q 15°-

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15° -

0°-

13 z 15° - <

-1 30°-

E45°-

< 90° E i

iFREQUEMCY 2

FREQUENCY I T

+ 2 ! CENTER +l

FREQUENCY D0PPLER FREQUENCY (Hz)

a. DAASM Map

Figure 10. Hight 4-060, 1 Mar 1974, UT

+ 3 + 4

DATE._ __.. 3-1-74 (060)

TIME(UT) -O,34®, FREQI (MHz)- • f*" FREQ 2 (MHz) - ''• ^ RANGE (Km)-— ™° AZIMUTH (deg.) *5T

ANT. CONFIGURATION- 7'Z

CENTER FREQ (Hz) "8

0348

4G

I , Li±l i B. ! ■ ■ ■ ■ ■ - I ■,■■,.■. ■.,:-.■. :■-■■■■ - ■■■ -• ^-n.,. .„■,.■„■ .v.._.,■■■.,.-. ,,., ., .....^;,..;-,^., ... ....■■..,. .....i..,. ..:.-.~.^w-■^^^^^W^;..K^.V^^^J^>^rtrtVia?i^aliiiK1i^^

§mmm* ^m^mw^mßm^w^ !9ä}R9>ttKEa]amfaWf*WV£AxtA. '-'ri.-tr.MKithin*-i-Kr-,raT1-^r.T-«i-3ir1,.^.tr(tv^„arft.^^1,, '■•S>»Sry^^rt.v»f.-vtu'

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+ 4

+ 3-

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V

CENTER

FREQUENCr

■2 _

-3

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+ 3

- +2 - X

+ I -

CENTER

Q_ FREQUENCY

8 -'-

-3 -

"4 1* —r 0 160

I

\-

r

L

320 480 640

DISTANCE [Ml

800 960

*

o

LÜ

o UJ

>- u 21 UJ

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I ■■3

I ■;5

b.Coherence

i-'igure 10. l'"light 4-060, 1 Mar 1974, UT 034 8

47

^^.^■^■...^...^...^^^.^^.^^^■..■^►^S^^UA^A;.^^^.^^.^ ^^^w^^rf.^twaiBal

mmmmmmmmm. m^m^m^m^m^mm^^^m^mm. •am&fiHfV ■ ■aiT/.^wfTV"?»^

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45°-

30°-

15°-

0°

15°-

30°-

^ 45°-

90° E

90oW

_ 45° -

uj 30°- UJ a: o 15° - UJ Q

Ul 0°-

0

z 15° <

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545o_

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-I

."■.iiitil.:.

■;;4'

CENTER FREQUENCY

+ I

[FREQUENCY 2

JFREQUENCY T

+ 2 t

+ 3 + 4

DOPPLER FREQUENCY (Hz)

a. DAASM Map

DATE 3-1-74(060) TIME(UT)— — Oö'O FREQI (MHz) '3.22 FREQ2(fViHz) 11.22 RANGE (Km) 1590 AZIMUTH (deg.) -3511 ANT. CONFIGURATION -7/7

CENTER FREQ (Hz) +9

Figure 10. Flight 4-060, 1 Mar 1974. UT0610

48

^■J;;.fa.a,..:'.,v,a.,j.,-^,.,...,.„,^<,^t..^...:...-.,.y,..M^t..l- ...VV. .^ ;./.;:■ ^,..J..^C,;<-..tf..-,^.A>,:^..,^;.i^^

iW^jWTrnvT^-w^fSJtfreOT^^ V^ ^•^r-'-^'-:';':^-.'r>:

ft;

1 + 4 T

+ 3-

+ 2-

U! _J CL Q. O Q

CENTER FREQUENCY

"3

"4 + 4

+ 3 -

+ 2 -

+ I —

W CENTER _l CL 0. O Q

FREQUENCY

-2 -

"3 -

-4

0

h-

L

T 160

T 320 480 640

DISTANCE [Ml

T

CM

>- U z UJ D

o UJ

DC U.

>- u

o UJ cr

800 960

4

■,:■-

if I •I

b.Coherence

Figure 10. Flight 4-060, 1 Mar 1974, UT 0610

40

feaihjfajKIHgtgljggjjliai^^ mmm

|IU^JIMl^^Wi,^W'W«i*W*f^^

1 1 1 1 I I i

90°W I FREQUENCY 2

^ 45°- — UJ UJ 30°- — cr e3

e l50- -

UJ _J no o u

2 <

15° - — _j

< > 30°- Q:

cc < 45°- —

90° E

9C°W

_ 45° - -

^ UJ 30°- — LU cr o 15° - _. UJ Q

~ 0° UJ U

_i

13 2 15° - — <

-1 30°- < > £45° - _ cr <

90° E ' FREQUENCY 1 I i 1 | 1 1 I

-2 CENTER

FREQUENCY

DOPPLER FREQUENCY (Hz)

a. DA ASM Map

+ 2 + 3 + 4

DATE TIME (UT)- FREOI (MHzl

3-!-74 (060) "0701 .13.22

FRE0 2(MHzl "-^ RANGE (Km) 930

AZIMUTH Idea.) 349T

7/7 ANT. CONFIGURATION - '" CENTER FREO(Hz) .-f?

Kigure 10. l-light 4-0fJ0, 1 Mar 1974. IT 0701

3 0

MltoiBat^^^^

UMMÜPHP f5*WA^5ipV^7^'MWr'>P^^rf^\^^'^;^i^ret¥!V3i

m i

I + 4 A

+ 3-

+ 2-

Lü CENTER FREQUENCY

"I -

-2 _

3 -

-4 + 4

+ 3

~ +2 - tsl X

tr ÜJ _j CL Q. O Q

+ I —

CENTER FREQUENCY

-2 -

-3

"4

h"

T 60

T

% >- u z: tu

o ÜJ er

LU

O UJ cc U-

320 4 80 640

DISTANCE [Ml

800 960

■ft

'■1 1

i

b. Coherence

Figure 10. Flight 4-060, 1 Mar 1974. UT 0701

51

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DATE 5-21-74(141) TIME (UTI "" FREQI (MHz) 8-22

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l-'lRiire 11. I'light 4-141, 21 May 1074, VI 2325

r,2

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Figure 11. Flight 4-141. 21 May 1974. UT 2325

53

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Figure 11. Flight 4-141, 21 May 1974

+ 2 + 3 + 4

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Figure 11. Flight 4-141, 21 May 1974, FT 2332

55

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Figure 12. Flight 4-142, 22 May 1974, [JT 2153

56

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ifrurc 12. Flight 4-142. 22 May 1!>74. UT 2153

57

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DATE —- TIME (UT) FREQI (MHz) — FREQ 2 (MHz) — RANGE (Km) —• AZIMUTH (deg. I ANT. CONFIGURATION

5-22-74 (1421 "2253

13.22 11.22 1440 349T

.7/6

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'igure 12. Flight 4-142, 22 May 1974. UT 2253

58

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uro 12. Flight 4-142, 22 May 1974, UT 2253

59

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DATE-- -l^;Um

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Figure 12. Flight 4-142, 22 May 1974, UT 2342

60

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b.Coherence

ure 12. Flight 4-142. 22 May 1074, !'T 2342

61

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DATE 5-22-74(142) TIME(UT) 2355 FREQKMHz) 8-22 FREQ2(MHzl — 11-22 RANGE (Km) 2270 AZIMUTH (deg.) 354T ANT. CONFIGURATION - 7/6

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Figure 12. Flight 4-142, 22 May 1074, UT 2355

62

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6 3

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DATE ■ TIME(UTI FREQI (MHz)-— 8-22

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5-22-74 (142) 0238

"igure 12. [•'light 4-142, 22 May 1974, UT 0238

64

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Figure 12. Flight 4-142, 22 May 1974, UT 0238

65

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DATE TIMEIUTI FREQ I (MHz) FRE0 2IMHZI RANGE (Kml AZIMUTH (deq. I ANT. CONFIGURATION - 7/6

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Figure 12. Flight 4-142, 22 May 1974. LIT 0251

66

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Figure 12. Flight 4-142. 22 May 1974, UT 0251

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DATE —- TIME (UTI FREQ I IMHzl

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Figure 12. light 4-1-12, 22 May 1374. IT 0305

68

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Figure 12. Flight 4-142. 22 May 1974. UT 0305

69

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DATE 5-22-74(142) TIME lUT) 0336

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lrigure 12. Flight 4-142, 22 May 1974, UT 0336

70

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b. Coherence igure 12. Flight 4-142, 22 May 1074, UT 0336

71

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Figure 13. Flight 4-193, 12,Iul 1974, UT 1655

72

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■igure 13. Might 4-103. 12 .lul 1074, UT 1655

7 3

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DATE 7-12-74(193) TIME (UTI - — 1718 FREOKMHz) 13.22 FREQ 2 (MHz) - — 11.22 RANGE (Km) 1680 AZIMUtH(deg.) - OOOT ANT. CONFIGURATION-7'0

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Figure 13, Flight 4-193, 12.lul 1974. LIT 171!

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.■ifiurel3. Flight 4-103. 12,1011074. IJT1718 l'iß

75

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DATE 7-12-74(193)

TIME (UTI l721

FREQI (MHz) l3-22

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"igure 13. Flight 4-133, 12 ,lul 1974, UT 1721

76

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Figure 13. Flight 4-Jfl3. 12 ,lul 1974, UT 1721

77

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figure 13. Flight 4-103. ,2.IU] ,c,74,

78

DATE — 7-l2-74 (193) TIME(UT)— \m FREQI (MHz)- .8.22 FRE0 2(MHz) 6.62 RANGE (Km) 1440 AZIMUTH (deg.) OOOT ANT. CONFIGURATION-7'6

CENTER FREO (Hz) +5

UT 1920

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ure 13. Flight 4-103, 12 .lul 1074. UT 1020

7 9

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DATE TIME (UTI—- — FREQ I (MHZ) FRE0 2(MHz) RANGE (Km) AZIMUTH (deg. I ANT. CONFIGURATION CENTER FREQ (Hz) -—

7-12-74 (193) "'1940 ..8.22

6.62 1150

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Figure 13. Flight 4-193, 12,lul 1974, UT 1940

81

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DATE H2-M.I93) TIME IUTI m

FREOI (MHz) 8-Z2

FRE0 2(MHzl 6-62

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\fTure 13. Flight 4-103, l'i.lul 1P74, UT 1041

82

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b. Coherence

"igure 13. Flight 4-103, 12,lull974, UT 194 ]

(13

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T FREQUENCY I

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i + 3 + 4

7-12-74 (193) DATE — —" ,0,3 TIME(UT) 'w/ FREQKMHz) °'" FREQ2IMHZ) - -^ RANGE (Km) ™ AZIMUTH (deg.) ^,'1

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i^ure 13. Might 4-193. 12 ,Iul U'74. VT 1943

84

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Figure 13. Flight 4-193. 12 .lul 1974, UT 1943

85

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ipiire 14. Flight 4-196, 15.lul 1974,

r + 2

r + 3 + 4

ÜATE--- -•l7;l^74,l96,

TIME (UTI l641

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ligure 14. Flight 4-inC, 15 .lul 1974, l!T 1641

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Figure 14. Flight 4-196, 15 Jul 1974, UT 1940

88

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igure 14. I'ljght 4-19(3, IS.Iul 1974. I'T 1940

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[)AT[ 7-15-74(1961 TIME (UTl — 1940 FREQI (MH2I - 8.22 FR[0 2(MHzl 11.22 RANGE (Kml 1950 AZIMUTH Ideg. I 353T ANT. CONFIGURATION - 7/6

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Figure 14. Flight 4-106. 15.1»: 1!174. UT 1040

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DATE-- (7:l?-74,l96)

TIME IUTI — m

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Tigure 14. Flight 4-106, IS.Iul 1974. L'T 1941

92

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igure 14. Flight 4-1OG. 15 .lul 1074, UT 1041

93

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DATE- 7-15-74(196) TIME (UTI- — 1942 FREOI (MHz) 8.22 FREQ2(MHz) - 6.02 RANGE (Km) 1950 AZIMUTH (deg. I 353T ANT. CONFIGURATION - 7/6 CENTER FREO (Hz) +7

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Figure 14. Flight 4-196. 15 Jul 1974, UT 1942

95

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Figure 14. Flight 4-196. 15 Jul 1974, LIT 2038

97

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a. DA ASM Map

DATE 7-15-74(196)

TIMEIUT1 2|30 FREQI (MHz) 8.22 FREQ2(MHz) 6-02

RANGE (Km) ol0

AZIMUTH (deg.l 350T

ANT. CONFIGURATION -'//6

CENTER FREO(Hz) +4

iMgure 14. Flight 4-196, 15 .lul 1974, UT 2130

100

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DISTANCE M

b. Coherence igurc 14. Flight 4-1%, 15.1ull074. UT21^0

101

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References

Pfister, W. , et al (196»-75) Pulse- Sounding with Closely Spaced Receivers as as a Tool for Measuring Atmospheric Molions and Fine Structure in the Ionosphere, Vol.1. Environmental Research Paper No. 2P5, Dec 1968

Environmental Research Paper No. 295, Dec 1968 Environmental Research Paper No. 317, Mar 1970 Environmental Research Paper No. 329, Aug 1970 Environmental Research Paper No. 468. Feb 1974 Environmental Research Paper No. 470, Mar 1974 Environmental Research Paper No. 506, Apr 1975 Environmental Research Paper No. 507, Apr 1975

Vol. II, Vol. Ill, Vol. IV, Vol. V. Vol. VI, Vol. VII. Vol. V!!i,

2. Richard, D.W. (1972) Twenty-Element Receive Array for the DAASM Ex- periment, Instrumentation Paper No, 176.

3. Ribl, K. (1973) Doppler/Angle of Arrival Spectral Measurement System, AFCRL-TR-73-0759.

4. Rarghausen, A. F. , et al (1969) Predicting Long Term Operational P»J"-n- eters of High Frequency Sky-Wive Telecommunications Systems, ESSA Tech. Report ERL 1 lu-Vl'S-'/H.

5. Bibl, K. , et al (1970) Digital Interpreting Goniometrie Ionospheric Sounder, AFCRE-7 1-0002.

6. Moffet, A.T. (1968) IEEE Transactions on Antennas and Propagation AP-16 (No. 2):172.

7. Elkins. T. I. (1973) An Empirical Model of the Polar Ionosphere, Survey in Geophysics. No. 2ST.

8. Jenkins, G. M,. and Watts, D.G. (1968) Spectral Analysis and Its Applications, Holden-Day, pp 374-411.

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