I gA100 238 MCE AIR DEVELOPMENT CENTER GRIFFISS AFB NY F/G 20/14I I~ RADIO FIELD STRENGTH MEASUREMENTS IN DESERT TERRAIN NEAR YUM--ETC(U)

I DEC 8G J L HECKSCHER. C B KALAKOWSKY

SIICLASSIFIED RADC-TR0-359 N

UtV2ELs1;LADC-TE4O-359

December 1960

MF RADIO FIELD STRENGTH MEASUREMENTSIN DESERT TERRAIN NEAR YUMA, ARIZONA

Joh L ultcho DTICRager W. WhddenJU 618Eli J. Tichovoisky E E~

E

[APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

~ ROME AIR DEVELOPMENT CENTERAir Force Systems CommandGriffiss Air Force Base, New York 13441

8i6 ]5 150

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is releasable to the National Technical Information Service (NTIS). At NTIS

it will be releasable to the general public, including foreign nations.

RADC-TR-80-359 has been reviewed and is approved for publication.

APPROVED: J-- lfg

TERENCE J. ELKINS, Acting ChiefPropagation BranchElectromagnetic Sciences Division

APPROVED:

ALLAN C. SCHELL, ChiefElectromagnetic Sciences Division

FOR THE COMIMANDER:*-

JOHN P. HUSSActing Chief, Plans Office

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RADC-TR-80-359 P- z 34. TITLE (e1nd SubfirJ,) S TYPE OF REPORT & PERIOD COVERED

S IMF RADIO I'IELD ST -ENGTHMEASUR EMENTSIN DESEtRT TERRAIN NEAR YU1IA, ARIZONA In-house

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John L . leckscher Roger W. Whidden'Charles B.) Kalakowsky Eli J.,Tichovolskv r

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19 KEY *OROS -CI, nfnn -,,,r~o,,s e neIn enr d dfrif Iv hi,,, k ,br,

1\1 F propa~fati,)n

1 '" grolund waveM " r'.lio field strength

20 ABSTRACT r ,nrlnueo,,reeree it ne'Anoer1

Dnd Id$ntIh , I> ,r 5 , ,

.Th field strength of the 'omnler( ial 'atii bIIOaIdl(s! station KBIL" wasImreasured at several hundred locations in tile dsort soutleas, of 'urea,A r'izonato Sttdy MI" ground-\wmv propj!;IIti( o)o t IIhI. olesort \alleys andmw'untain ridges. Field strengths 10low I he surfac,, or the desert iloor were:npasureli in specialiv drilled holes I ohlIso'Lvo Oh pIIntralion IoI" AI" into thedesert soil. Idealizied propauation patni molliftls aro, sho"n to product elfectssimilar to the observ;itions.

DO OjAN7 1473 ntlassitwo

SFCURITV CLASSIFICAtION OF '.IS PAGE Ih,., P.I. Fnt rf

Acce5~fl Preface

We aprecatethe aiublo u~gotjos, hlpfl inormtion n iln

ooperation ~ ~ ~ ~ ~ ~ ~ ~ ~ Dj oftemtvidvdas h otiue otisefr.I atrlr

Wapreevusflint the daabeugion; hlplifomtin and willing olL.C(., SJ.,C'if

peatio Poets thee Caynividl whoinernt Resbated Doitisiefot.A In pa['rt ki uar

forr-iEL sug elds potseniesa the techiqu fo mearin raiowae. petaio thfk soil e to

K lemett i for his able assistanh e in preparing the illustrations.

'I Itis wor k was performied at the request of the Spare anid Mis sit r Svst ems

Orrgani zat ion (SAIlSO) under the sponsorship of' Robert lBarbergj, Capt. USA i-'

SAMISO) I NN I and the technical direction )f Mr. A1im Culhane , 'I IM

Contents

1. INTRODUCTION 7

2. EXPERIMENTAL PROCEDURE 8

3. FLAT EARTH PROPAGATION THEORY 8

4. RESULTS OF REGRESSION ANALYSIS 14

4. 1 Estimate of Conductivity 144. 2 Apparent Radiated Power 15

5. PROPAGATION OVER ROUGH, NON-HOMOGENEOUS TERRAIN 15

5. 1 Hufford's Integral Equation 155. 2 Numerical Solution for Special Cases 17

6. P!:;NETRATION BFLOW THE DESERT FLOOR 19

7. DISCUSSION AND CONCLUSIONS 19

REFERENCES 20

Illustrations

1. RADC Measurement Sites in the Yuma and Lechuguilla Deserts 9

2. Amplitude of the Propagation Factor 10

3. Southern Pacific RR (90 ° - 1000) Sector Path Profile (lower portion)and Signal Strength-Distance Product 11

5

* ~IMustrations

.. Mohaw~k \allc\ (1 000 107.) 1 l t Pakth I rofjlIe (lowetc' po I-it)1n)And S ignali St rength-D1isti tac 1'cuduct I1I

5. %% il1ton H ills ( 107. 50 - 1100) Sector P'ath Profilc (lower portion)afnd signal Str,,ngtt- Distance Product 12

O . CoYote I 'eak, (1I100 - 160 Sector Patti I rofilc (low er poretion)and Signal. Str cci-Iistance P'roduct 12

7.Sheep Mountain (1160 - 1200) Sector Path P~rofile (lower portion)and Signal Strength- )i-rtance Product 13

8. Tinajas Altas Mountains (1230 - 1370) Sector Path Profile(lower portion) and Signal Strength-Distance Product 13

9. Geornitry for the Integral Equation 16

*10. The Attenuation Function I W Ion the Surface of the R~idge Shown atthe Bottom of the Figure, for Two Values of Earth Conductivity 18

11. The Attenuation Function I %VI on the Surface of the InhomogeneousPath Shown at the Bottom of the Figure, for Trhree Values of ar 18

S

Tables

1. Estimated Effective Conductivit, 14

6

MF Radio Field Strength Measurementsin Desert Terrain Near Yuma, Arizona

I. INTRODUCTION

The possibility that a network of underground tunnels or silos containing the

NIX mobile missile might be constructed in the desert regions of the southwestern

United States has renewed interest in techniques for survivable communications

between buried terminals which may be up to 50 km apart in adjacent valleys sepa-

rated by high mountain ridges. One proposed method is to use an MVF radio link

with the transmitting and receiving antennas located on the underground mobile

launch control centers. The propagation path for such a link would include two seg-

ments through the trench wall and soil overburden in addition to that over the desert

terrain. Although Ml" propagation curves over homogeneous earth are readily

available, 14propagation anomalies caused by topographical and electrical irregu-

larities unique to the proposed MX sites need to be studied in situ.

(Received for publication 24 November 1980)

1. Terman, F. E. (1943) Radio Engineer's Handbook, McGraw-Hill, New York.

2. Walt. J. R. , and Campbell, L. L. (1953) Transmission curves for ground wavepropagation at low radio frequencies, Radio Physics Laboratory Report R-1,D~efence Research Telecommunications Establishment, Ottawa.

.3. International Radio Consultative Committee (C. C. 1. R. ) (1974) Propagto inNon-Ionized Media (Study Group 5). Vol. 5, XI1lth Plenary AssemblyGeneva,1974, International Teleco mmunication Union. Geneva, 1.975.

4. Reference Data for Radio Engineers. 4th ed. (1956) ITT Corp.., New York.p. 7 14 ff.

7

2. EXPERIMENTAL PROCEDURE

Between 11 September and 24 September 1977 personnel from Rome Air

Development Center (RADC/EEP) made field strength measurements of the Yuma,

Arizona broadcast station KBLU (560 kHz, I kW, omni-dizectional in the daytime)

at several hundred positions on Luke AF Bombing and Gunnery Range, a desert

region southeast of Yuma. At each site the surface magnetic field was measured

using a Radio Interference-Field Intensity Measuring Equipment, Singer lodel

NM-25T, with a shielded 15-in. -diameter loop antenna oriented for maximum

signal. At some of the sites the loop also was lowered 2 m into a hole drilled bya power auger to probe the radio wave attenuation with depth. The measurements

were conducted only during daylight hours to eliminate the necessity of correcting

for KBLU day-to-night antenna pattern changes and to minimize sky wave inter-

ference.

The measurement sites were accurately located in almost every case by

choosing positions near the numerous USGS markers found alongside Jeep trails.

The sites are shown in Figure 1, along with the location of the KBLU transmitting

antenna in downtown Yuma. The distribution of the markers was such that no series

of measurements was strictly aligned along a radial path from KI3L.U. However,

six sectors were chosen within which the terrain could be characterized reasonably

well by a single profile, thus providing a convenient way to group and display the

data. Dashed lines are used in Figure I to show the sector boundaries. A repre-

sentative path profile, corrected for the standard tropospheric refractive index

gradient (4/3 earth radius), was constructed for each sector using USGS maps.

3. FLAT EARTII PROPAGATION TIIEORY

Over a flat, homogeneous, and well-conducting earth the vertical electric field

strength-distance product is given by

. x 300 f . ifpe) (Volts) (I)

where P is the effective radiated power in kW,

l(p) = 1 - i i'pe " e e1, fe (i

5. Reference Data for Radio Engineers, 5th ed. , (1957) ITT Corp., New Yorkp 74 1 ff.

8

0

:0000

I7 INI!0I. 0

0 ,0

~0

0 0,,

0E

0

and

wkxPe = 1P 0 •

I (pe) is the Sommerfeld propagation factor, pe is the numerical distance,

= 8. 854 X 10- 12 ./m, Le is the radian frequency, a is the surface conductivity0

(Siemens/meter) and kx is the distance in wavelengths. Eq. (1) can also be expressed

log I E " x log IfF log 300 ,. (2)

where log = log 1 0 . 1 FI is plotted as a function of pe on a logarithmic scale in

Figurc 2. For numerical distances of the order of unity or less,

log I1. - -0. 183 pe 1 (3)

At 560 kllz, Eq. (3) is valid for distances out to at least 50 km if C= 0. 01 S/m and

to 100 km fore = 0.02 S/rn. Combining Eqs. (2) and (3),

0.09 15 c klog E" x! - 0 x + log 300 VP-. (4)

Equation (4) is in the standard form v mx + b, where, upon the application of

linear regression analysis to the measured iE" xl data, the slope

i = -0.0915 o (5)a

yields an estimate for u, and the v-intercept

b = log 3 00 T (6)

indicates an apparent radiated power

U.O

0o.5- oq IFI.-O.183 IPelQFigure 2. Amplitude of the

-F (Peiiv/9F e eerfc(P ) Propagation Factor00(

1 i where PsCOW"

fa 01 2

EFFECTIVE NUMERICAL DISTANCE IPel

10

sm- oRADC MEASUREMENTSe KOLU DATA SHEET

2002 3.GdB aoo 00~ 00

00 0 o0 Figure 3. SouthernPacific( RR (20 - !W0

10 Sector Path Profile(lower portion) andSignal Strength -DistanceProduct

4-

VI 0

(1000 a a0. 0 Scoioc ath rofle (owe porion

-4_

'II L 4j_ 1

400

4 0 6 0 . 0 0 % 0F g r 4 o a k V l e0D(100 0.5)Sco

10 ahSrflL(oeUprin

an1inl1tegh Dsac

500- oRADC MEASUREMENTS

400

0-j 300 __- _

o . 200-0'-0.02 5dB

S00 00 0 FigUre 5. "ellton Hills00 ~ ( 107. 5 - 110' ) Sector

0 b 0 Path Profile (lower portion)100 __ and Signal Strength -Distance

P rod uct

=j

3000 oRD ESUEET2220300- 0L

20

00 0 (10 11)SetrPt

100 100Sg alSr n th Dsa c

300 (90

01

i.di --- RADC MEASUREMENTS

200-002

15 dB O. 0

(0

00 ~ tot Iigt c07 Shevep NMountainwj SOL 0 (116 -120 ') SetrPath

0 Protii. (Nmvfr portion) and6 0 h Signal Strenqth -lDitance1' odUct

40

3000 42 :) ~

AW-

200 '1m)'0

0KBLU

400F F0 o RAOC MEASUREMENT300-A a KBLU DATA SHEET

00 0

-J0

000 Seto Pathr.fil

00

>20

15d

W~ 104

4. RESULTS OF REGRESSION ANALYSIS

4.1 Estimate of Conductivity

The upper portions of Figures 3 to 8 show measured values of IE" xl on a

logarithmic scale vs distance from the KBLU antenna. The lower portions are

corresponding terrain profiles which reveal long flat path segments occasionally

interrupted by relatively steep ridges. The effective conductivity of these flat seg-

ments was estimated by fitting a regression line to selected data points not too close

to the mountain ridges, and then using Eq. (5) to estimate a. The regression line

is shown in the figures as a solid line, and the o estimates are given in Table 1.

Assuming the data is normally distributed about the regression line, we can assign

confidence limits 6 to the calculated values of o. The results of choosing a 95 percent

interval are shown in the last column of Table 1. Evidently only the 100 ° - 107. 50

sector contained enough data over a sufficiently long and flat range to permit a

reasonably accurate estimate for (j, which was 0.022 S/r. This value is somewhat

higher than the 0. 01 S/m estimated by Morgan' or the 0. 008 S/m estimated by the

FCC. 8

Some of the data scatter within the flat segments was due to the fact that the

measurements were not along radial paths, and each data point within a given

sector actually represents propagation over a slightly different path. Additional

perturbations were produced by local anomalies such as ore deposits, faults, power

and telephone lines, and railroads, as well as by focussing, diffraction, and multi-

path effects.

Table 1. Estimated Effective Conductivity

Sector No. Data Correlation Est or 95% Conf. Limits(Degreesl Points Coefficient [S/mr [S/m

90 100 24 0.39 0.023

100 107.5 44 0.70 0.022 0.016 - 0.033

107.5 - 110 19 0.42 0.029 *

110 - 116 21 0.22 0.026 *

116 - 120 6 0.22 0.030 *

123 - 137 20 0.52 0.023 0.011 -0. 122

The data scatter was too great to permit an accurate determination of 0.

(Due to the number of references cited above, they will not be listed here. SeeH.'terences, page 20.

14

-4.2 Apparenit Radiated Power

In Figurc-c s Ito 8the dashed lines plot I -,E x If ron Eq. (4) for aIl:,t - Ot 4

conductivitY 0. 02 S / i from i 560 kli z t ransmrtitter r'adii-irlg I kWk. Re(g rI . s ion

analYsis on HAlK mecasu red data over path ,;eginrents wi cre no(, rIoIunt:,inl 'ida'uts

interposed betwee(n the t ransmaitter and observer (for example, F'igu res 7 and( 1)

Yields v'-intercepts displced approximate-lY 1. 6 (11B below the equi.Al t I k\\ IoI rac: IA

alIote. This discrepancy% could be due to the NI- 251' cAlibration, since- J, - x d;. t!

Supplied by KIAL is consistently,. higher- than the RAD I)'neasuremnents;. ( )it the otler

hand, beyvond the Gila Mountains (F"igu res 3 through 6) the reg ression lines ire dis -

placed fromt 3 to 5 dIB below the nominal 1 k\% value. Ibhis reduction in :ippa rent

radiated power can be interpreted as the effect of the nmountain ridge in extracting

ene-rgy front the propagating ground wave.

The losses may be due to scattering by the terrain clevaition changes 'tnd/or

to increased absorption by a pooch~ conducting path segment, but neither mehanisnm

can be adequately treated by flat eu rth theorY. Indeed for' certain paths the signal

strength drops byv as mrch as 15 d13 behind the ruounta in r-idges (F**igures 6 znd i) and

then exhibits a recovery effect with dist:nce. Sireh ai variationl req riice's tile Muore

comrprehensive theory which follows in the next section.

.. PROPAGATION OVER ROUJGH, NON-IIOVIOGEN EOI S TERR AI N

5. 1 liii ibrds hIn ICral EIi~iiit im

( 'alculartions of the effects of irregular te rrain (can be made viai a one- dimen-

sionAt integrail equaition derived by I lufford. 9 i s Eq. ( 1 1) in the nota tion of

u~igur.'( 9 is

x

WVW ) I f F W(s) -f(s) - d~s

Where W is thle attenuration funerio f11or the Hecrtz pxtenrial. III termis of the vortical

oerctric field, an apprroximoate expression Ior k is

x x-0 F:

9. Hf~rfioro, G. A. (1952) An inregral equar ion approach to tiii' probtlemo of wNavepropagation over an irreg Ular terraini, Quart. J. AppI. Math. 9:39 1-404.

15

provided W is slowly varying. The quantity

f(s i /4 kx r 2 ] ik(r r 2 r 0 )

where & is the (normalized) surface impedance

6 i e

p

II

T sa 10

Figure 9. Geometry for the Integral Equation.s and x are the horizontal distances of thescattering point Q and the observer P,respectively, from the source T. a- is. the slopeof r 2 , p is the terrain slope at Q, and L is aunit vector at Q normal to the terrain

The factor r 2/an takes into account the terrain slope and the aspect angle with

respect to the observer. As may be seen from Figure 9,

ar 2

=z sin (S-a)

where 0 is the terrain slope and (Y is the slope of r 2 .

For gently undulating terrain with gradual inhomogeneitics, the functions \N(s)

and f(s) are slowly varying. T1o the extent that W and f can be represented as con-

stants within arbitrarily small intervals ,s = s -n an approximate solutionof Eq. (7) is

W n, zI- _ " , n r nI n(8)n

where W is a constant value for W over the nth interval, f is a constant valuefor r over the same interval and

s f in sin -n Sn

-1 s -)

16

5.2 Numerical Solution for Special Cases

Equation (8) was solved numerically via a CDC 6600 computer for several

cases. In Figure 10 the results of including a Gaussian-shaped ridge

G(x) : hexp -9 (xb )29

on an otherwise flat, homogeneous earth are shown for t-vo values of conductivity.

In Eq. (9). G(x) is the terrain elevation, h is the ridge height ai x= b and w is the

ridge width measured at G (x) h/ 10. This form corresponds to the model chosen10

by Berry. The attenuation function W at fi rst decreases at the flat earth rate,

and then increases to a maximurn just before the crest of the ridge. Behind the

ridge there is a minimum, and then a partial recovery with increasing distance

from the source.

Figure 11 illustrates the perturbation in IWI caused by a 6 km wide segment

of conductivity a s , centered at 30 km, in an otherwise homogeneous flat path of

conductivity 0. 02 S/in. Such a path represents the much poorer conductivity ex-

pected in the mountain ridges. W I follows the flat earth attenuation rate out to

the beginning of the segment, and then, depending on the selected value for 0 ss

decreases more or less rapidly until the far edge of the segment is reached. As in

the case of the ridge, I vI partially recovers as the distance from the inhomo-

geneity increases. (The abrupt conductivity change in this model does not satisfy

the conditions under which Eq. (8) was derived, so the results are not valid inthe

immediate vicinity of the edges of the segment. ) A comparison of Figures 10 and 11

with 7 and 8 seems to show that the effect of a segment of poor conductivity more

closely matches the observed I E' xI variation than the elevation effect. The models

demonstrate that irregularities in both profile and earth conductivity play significant

roles in determining the propagation of llF over ridges.

10. Berry, L.A. (1967) Radio propagation over a Gaussian-shaped ridge, IEEETrans. Antennas Propag. AP-15(No. 5):701-702.

11. FAO-Unesco, Soil Map of the World, Vol. II, Unesco-Paris, 1974.

17

_ 1.0-FLAT EARTN.0..02

0.8- E .15

- 0.8.....

-FLAT EAR H , 0

0.6- Figure 10. TJhe Attenuation* I unction Wi I n the Surface

f thel R idge Shown at the

0.4L---L-I ottoro or the VIglire. forIwo Values of EarthCond Uct ivi ty

3000K--

x -000

LO 001-ASIA IG AT x-*32

1000

40 s0 so-2joX(kmn)

T_ ,4 Figure 11 lhe AttenuationF.,tin )nl the Surfaceof the Inhomogeneous PathShown at the Bottomn of the

0.2- Figure. for Three Valuesof a

S1000 Cma ('.02

(7-.0O2 40 a)

18

6. IPEN ETRATION IELOW r TIlE I)ESERT FLOOR

Attenuation of M fields with depth in homogeneous, well-conducting soil is

described by

- V/ P -.iy/6lIt It _ s

where II is the magnitude of the field at the surface, y is the depth below the sur-0

face and 6 is the depth of penetration or skin depth. Attenuation measurements ofs

tne magnetic fields penetrating the desert soil were made by lowering a loop an-

tenna into 18-in. diameter holes drilled approximately 6-ft deep by a commercial

power auger, and recording the decibels change from the surface reading. An

effective skin depth was then calculated via

6s =8.69 vIt 10 d B ] - If[ dB] (10)

A total of 30 holes were drilled at various locations as indicated in Figure 1. The

relative attenuation was read to within about ± 0. 25 dB on the NMI-25T panel meter,

and the depth was measured accurately. The average skin depth calculated was

28. 25 ft with a standard deviation of 13. 01) ft.

7. DISCUSSION AND CONCLUSIONS

The data in this report can be used to estimate total propagation path loss for

a point-to-point communication link between terminals buried in the desert south-

east of Yuma and separated by mountain ridges. The desert valley soils have rela-

tively high apparent conductivity, with a correspondingly low attenuation of propa-

gating MF radio waves. The mountain ridges can have a large effect which depends

on the location of the terminal. The mountains can be modeled to predict the

attenuation, but good accuracy requires that both the terrain profile and the ground

constants be known. An overburden of desert soil will result in additional loss.

The measurements and portions of the modeling work in this report were pre-

sented to an MX C 3 working group at a technical interchange meeting at Norton AFB,

California on 14 December 1977.

19

References

1. Terman, F.E. (1943) Radio Engineer's Handbook, McGraw-Hill, New York.

2. Wait, J. 1., and Campbell, L. L. (1953) Transmission curves for ground wavepropagation at low radio frequencies, Radio Physics Laboratory Report R-1.Defence Rebcarch Telecommunications Establishment, Ottawa.

3. International Radio Consultative Committee (C. C. I. R.) (1974) Propagation inNon-Ionized Media (Study Group 5), Vol. 5, XIIIth Plenary Assembly, Geneva,1974, International Telecommunication Union, Geneva, 1975.

4. Reference Data for Radio Engineers, 4th ed. (1956), ITT Corp., New York,

p. 7 14 ff.

5. Reference Data for Radio Engineers, 5th ed. (1957) ITT Cprl., New York,p 741 ff.

6. Kreyszig, E. (1972) Advanced Engineering Mathematics, 3rd ed., Ch. 19,Wiley, New York.

7. Morgan, R. R. (1968) World-Wide VLF Effective Conductivity Map, WestinghouseReport 80133F-1, Westinghouse Electric Corp. , Environmental Science andTechnology Dept., 13ou]der, Colorado.

8. Fine, H. (1954) An effective ground conductivity map for continental United States,Proc. IRE 42:1405-1408.

9. Hufford, G. A. (1952) An integral equation approach to the problem of wavepropagation over an irregular terrain, Quart. J. Appl. Math. .a9391-404.

10. Berry, L.A. (1967) Radio propagation over a Gaussian-shaped ridge, IEEETrans. Antennas Propag. AP-15(No. 5):701-702.

S11. FAO-Unesco, Soil Map of the World, Vol. I, Unesco-Paris, 1974.

20

MISONOf

Rcmte Air Development CenterRAVC ptaA and execwteA )tAeowch, devetopment, te~t andAetected acqui~ition p4ogitam in Auppo~t oj Command, ContotComtxuicationA and in-te~igence (C3 1 I activitieA. Technicaxand enginemiung *6uppo'ut w.Lthin a4ea6 oj techniWa competence"6 p'tovided to ES?) fto9'wm O~e4 (PO4) and otit pi ES?)etement6. The p~incipat technicat rr&L6ion a~eaA atecommniwcatioml, etectomagnetic guidance and cont't, aux-veLuance o6 94tound and aeLo,6pace object;, inteLtgenee datacottection and handLing, in~o.'maton Aya-tem -technotogy,iono.6pheAxc p4opagation, .6otjd ztamte 6cienceA, mtcAowavephq4ZicA and etecftonic 4eViabiti-ty, maintainabifity andcompatbdaiy.

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