Surface Magnetic Field Noise Measurements at Geneva Mineloop antenna, balun, filter, and analog tape...

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SURFACE MAGNETIC FIELD NOISE MEASUREMENTS AT GENEVA MINE

J. W. Adams W. 0 . Bensema N. C. Tomoeda

Electromagnetics Division Inst i tute for Basic Standards National Bureau of Standards Boulder, Colorado 80302

The views and conclusions contained in th is document should not be interpreted as necessarily represent ing the of f ic ia l policies or recommendat ions o f the Interior Department's Bureau o f Mines of t he U. S. Government.

June 1974

Prepared for U. S. Bureau of Mines Uni ted States Department of the In ter ior ~ i t t s b u r ~ ; Pennsylvania 15222 Working Fund Agreement HO 133005

U.S. DEPARTMENT OF COMMERCE, Frederick 6. Dent, Secretary

N A T I O N A L B U R E A U O F S T A N D A R D S Rtchard W Roberts D ~ r e ~ t o r

T h i s r e p o r t was p r e p a r e d by t h e N a t i o n a l Bureau o f S t a n d a r d s , B o u l d e r , C o l o r a d o , unde r USBM C o n t r a c t No. HO 133005. The c o n t r a c t was i n i t i a t e d u n d e r t h e Coal Mine H e a l t h and S a f e t y Resea rch Program. I t was a d m i n i s t e r e d u n d e r t h e t e c h n i c a l d i r e c t i o n o f t h e P i t t s b u r g h Mining and Resea rch C e n t e r w i t h Flr. Howard P a r k i n s o n and M r . Ha r ry a c t i n g a s t h e t e c h n i c a l p r o j e c t o f f i c e r s .

T h i s r e p o r t i s a summary o f t h e work comple ted a s p a r t o f t h i s c o n t r a c t d u r i n g t h e p e r i o d June 1973 t o June 1974. T h i s r e p o r t was s u b m i t t e d by t h e a u t h o r s i n September , 1974 .

CONTENTS

Page I n t r o d u c t i o n - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1

Measurement Sys t em- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2

E a r t h - I o n o s p h e r e Waveguide E f f e c t on P r o p a g a t e d N o i s e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3 Othe r Measured Data - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4

C o n c l u s i o n s - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5

Recommendat ions - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5

Acknowledgments - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5 Ref e r e n c e s - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 6 Appendix- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 34

LIST OF FIGURES

F i g u r e 1. F i e l d r e c o r d i n g s y s t e m - - - - - - - - - - - - - - - - - - - - - - - - 7

F i g u r e 2a. D i g i t i z i n g p a r t o f d a t a p r o c e s s i n g s y s t e m - - - - - 8

F i g u r e 2b. F a s t - F o u r i e r t r a n s f o r m p a r t o f d a t a p r o c e s s i n g s y s t e m - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 8

F i g u r e 3. Spec t rum o f t h e h o r i z o n t a l , E-W c o m p o n e n t - - - - - 9

F i g u r e 4 . Spec t rum o f t h e h o r i z o n t a l , N-S c o m p o n e n t - - - - - 10

F i g u r e 5 . Spec t rum o f magne t i c f i e l d s t r e n g t h v s . t i m e - - 11

F i g u r e 6 . Spec t rum o f m a g n e t i c f i e l d s t r e n g t h v s . t i m e - - 1 2

F i g u r e 7 . Map o f s u r f a c e o v e r Geneva Coal M i n e - - - - - - - - - - 1 3

F i g u r e 8 . Spec t rum o f s u r f a c e EM n o i s e a t L i l a F l a t s o v e r Geneva Mine - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 4

F i g u r e 9 . Spec t rum o f s u r f a c e EM n o i s e , n o r t h s i d e o f L i l a P o i n t - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 15

F i g u r e 1 0 . 10 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Overlook - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 16

LIST OF FIGURES (Con t inued )

F i g u r e 11. 10 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Overlook - - - - - - , - - - - . - - - - - - - - - - . - - - - - - - - - - - 1 7

F i g u r e 1 2 . 10 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - -, - - - - - - - - 1 8

F i g u r e 1 3 . 10 kHz s p e c t r u m o f s u r f a c e n o i s e a t L i l a Canyon O v e r l o o k - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19

F i g u r e 1 4 . 10 kHz s p e c t r u m o f s u r f a c e n o i s e a t L i l a Canyon Over look- - - - - - - - - - - - - - - - - , - - - - - - - - - - - - - - 2 0

F i g u r e 1 5 . 10 kHz s p e c t r u m o f s u r f a c e n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 1

F i g u r e 1 6 . 10 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 2

F i g u r e 1 8 . 10 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 24

F i g u r e 20 . 3 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 6

F i g u r e 2 1 . 3 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 7

F i g u r e 2 2 . 3 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 8

F i g u r e 23 . 3 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 29

F i g u r e 24. 3 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 30

F i g u r e . 25 . 3 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3 1

F i g u r e 26 . 3 kHz s p e c t r u m o f s u r f a c e EM n o i s e a t L i l a Canyon Over look - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 32

SURFACE MAGNET1 C FIELD NOISE MEASUREMENTS

AT GENEVA MINE

by J . W . Adams, W.D. Bensema, N . C . Tomoeda

Measurements o f s u r f a c e magnetic f i e l d n o i s e were made a t v a r i o u s l o c a t i o n s o v e r t h e Geneva Coal Mine n e a r P r i c e , Utah , on June 1 2 , 1973. The l o c a t i o n s s e l e c t e d were on t h e s u r f a c e o v e r emergency l o c a t o r beacons underground a t d e p t h s between 350 meters (1150 f t .) and 488 meters (1600 f t .) . The s u r f a c e t e r r a i n where t h e s e measurements were made was mountainous, and a c c e s s was d i f f i c u l t . There were no power l i n e s w i t h i n s e v e r a l m i l e s , and t h e wea the r was c l e a r ; t h e r e f o r e , t h e magnetic n o i s e l e v e l s were about a s low a s w i l l normal ly o c c u r .

R e s u l t s o f measurements o f d i s t a n t s f e r i c s i n d i - c a t e r a t h e r s h a r p c u t o f f f r e q u e n c i e s below which b r o a d - band, impuls ive n o i s e i s a t t e n u a t e d . The mechanism o f p r o p a g a t i o n f o r t h i s n o i s e above t h e daytime c u t o f f f requency o f 3500 Hz and t h e n i g h t t i m e c u t o f f f requency o f 1700 Hz i s deduced t o b e a waveguide formed by t h e D o r E l a y e r s o f ionosphere a s an upper p l a n e and t h e e a r t h a s a lower p l a n e .

The measurement sys tems used a r e s i m i l a r t o t h o s e used e a r l i e r . The t e c h n i q u e i s t o r e c o r d broadband, ana log s i g n a l s , d i g i t i z e t h e d a t a , and use a f a s t - F o u r i e r t r a n s f o r m t o o b t a i n s p e c t r a l p l o t s . This t e c h - n ique i s nove l i n t h a t i t can measure s i m u l t a n e o u s l y a l l magnet ic f i e l d energy w i t h i n a l i m i t e d p o r t i o n o f t h e spectrum f o r a l i m i t e d t i m e , and , a f t e r p r o c e s s i n g , reproduce t h e e v e n t s o c c u r r i n g i n t h a t t ime i n t e r v a l i n g r e a t d e t a i l . Key words : E a r t h - ionosphere waveguide ; e l e c t r o m a g n e t i c n o i s e ; EM1 measurement t echn ique ; s f e r i c i n t e r f e r e n c e .

1 . 0 I n t r o d u c t i o n

Magnetic f i e l d s t r e n g t h measurements were made on June 1 2 ,

1973, o v e r t h e Geneva Coal Mine i n t h e Book C l i f f Mountain

Range e a s t o f P r i c e , Utah. The l o c a t i o n s s e l e c t e d were on

t h e s u r f a c e o v e r emergency l o c a t o r beacons underground a t

dep ths between 350 mete r s (1150 f t .) and 488 me te r s (1600 f t .) . The s u r f a c e t e r r a i n where t h e s e measurements were made was

mountainous, and access was d i f f i c u l t . There were no power

l i n e s w i t h i n s e v e r a l m i l e s , and t h e wea the r was c l e a r ; t h e r e -

f o r e , t h e magnet ic n o i s e l e v e l s were about as low as w i l l

no rmal ly o c c u r .

The pr imary purpose o f t h e measurements was t o de te rmine

s u r f a c e magnet ic f i e l d n o i s e l e v e l s s o t h a t performance o f

emergency s u b s u r f a c e l o c a t o r beacons o f t h e U.S. Bureau o f

Mines cou ld b e b e t t e r p r e d i c t e d . These emergency l o c a t o r

beacons a r e l o c a t e d many hundreds o f f e e t underground and

when a c t i v a t e d , g e n e r a t e magnet ic f i e l d s i n a p u l s e d - c a r r i e r ,

o n - o f f mode f o r s i g n a l i n g t o t h e s u r f a c e , u s u a l l y i n emer-

gency s i t u a t i o n s . They o p e r a t e a t f r e q u e n c i e s below 3 kHz

where s i g n a l a t t e n u a t i o n through t h e e a r t h i s r e l a t i v e l y low;

however, t h e beacon s i g n a l s a r e g r e a t l y a t t e n u a t e d by v a r i o u s

e f f e c t s , and s u r f a c e n o i s e becomes a l i m i t i n g f a c t o r .

2 . 0 Measurement Sys tem

The b l o c k diagram of t h e f i e l d r e c o r d i n g measurement s y s -

tem i s shown i n f i g u r e 1. I t c o n s i s t s o f a b a l a n c e d , s h i e l d e d

loop a n t e n n a , b a l u n , f i l t e r , and ana log t a p e r e c o r d e r . L a t e r

i n t h e l a b o r a t o r y , t h e ana log s i g n a l i s f i l t e r e d , d i g i t i z e d ,

f a s t F o u r i e r t r a n s f o r m e d , and p l o t t e d on m i c r o f i l m . See

f i g u r e 2 f o r t h e l a b o r a t o r y p r o c e s s i n g sys tem. This g i v e s an

o u t p u t p l o t of one component o f a b s o l u t e magnet ic f i e l d s t r e n g t h

v e r s u s f r equency- - a s p e c t r a l p l o t . The t r a n s f o r m may be

r e p e a t e d t o a l l o w t h r e e -d imens iona l p l o t s , where t ime i s t h e

a d d i t i o n a l v a r i a b l e .

Th i s sys tem i s d e s c r i b e d i n more d e t a i l i n t h e Robena

Mine r e p o r t [ I ] .

3 .0 E a r t h - I o n o s p h e r e Waveguide E f f e c t

on P ropaga ted Noise

During t h e t ime t h e measurements were b e i n g made, t h e r e

were no v i s i b l e thunder s to rms o r c l o u d s anywhere i n s i g h t ,

and h e n c e , t h e a tmospher i c n o i s e was l a r g e l y t h a t p r o p a g a t e d

from d i s t a n t s o u r c e s . During d a y l i g h t , s t r o n g s f e r i c s were

p r e s e n t , p r i m a r i l y above 3500 Hz, a s shown i n f i g u r e 3. A t

n i g h t , s f e r i c s came i n above 1700 H z , a s shown i n f i g u r e 4 .

A t h r e e - d i m e n s i o n a l view g iven i n f i g u r e 5 shows more d e t a i l

o f t h e dayt ime s t r u c t u r e . A s i m i l a r p l o t i n f i g u r e 6 shows

t h e n i g h t t i m e s t r u c t u r e . Note t h e 2500 Hz and 1900 Hz sub-

s u r f a c e c o a l mine beacon s i g n a l s i n f i g u r e 5 . The 1900 Hz

beacon i s a lmos t obscured by t h e a tmospher i c n o i s e a t n i g h t

( s e e f i g u r e 6 ) . N o t i c e t h e s h a r p c u t o f f o f n o i s e a t 1700 H z

a t n i g h t and t h e more g r a d u a l c u t o f f a t 3500 Hz d u r i n g t h e day .

I o n o s p h e r i c e f f e c t s on r a d i o t r a n s m i s s i o n have been w i d e l y

s t u d i e d f o r y e a r s , b u t t h e s e measurements w i t h t h i s new s y s t e m

show some f r e s h i n s i g h t s i n t o e a r t h - i o n o s p h e r e waveguide

phenomena. A d r a m a t i c and s h a r p i n c r e a s e i n a t t e n u a t i o n o f

p r o p a g a t e d a t m o s p h e r i c n o i s e a t f r e q u e n c i e s below t h e waveguide

c u t o f f f r equency ( a s mentioned above) has been o b s e r v e d . About

t e n dB o f s i g n a l - t o - n o i s e r a t i o may be g a i n e d by o p e r a t i n g a t

a f r equency below t h e waveguide c u t o f f f r equency r a t h e r t h a n

above t h e c u t o f f , a s shown by t h e one example i n f i g u r e 6 .

The p~o_bab_~e_p_r-opa~ation .- mechanism i s a p a r a l l e l p l a t e waveguide formed by t h e D o r E l a y e r s o f t h e i o n o s p h e r e and

t h e e a r t h . The TE o r TM modes a r e e x c i t e d between t h e

p a r a l l e l p l a n e s and have a c u t o f f f r equency o f

where c i s t h e v e l o c i t y o f l i g h t , and a i s t h e s p a c i n g between

t h e p l a t e s 121.

I f a = 88 km, f c = 1704 Hz, 3408 Hz, . . . . I f t h e D

l a y e r i s a b o u t 50 km above t h e e a r t h , and i f t h e E l a y e r i s

a b o u t 100 km h i g h [ 3 ] , t h e c u t o f f f r e q u e n c i e s c a l c u l a t e d a r e

a p p r o x i m a t e l y c o r r e c t . The h e i g h t o f maximum i o n o s p h e r i c

d e n s i t y may v a r y somewhat, and may n o t be t h e e x a c t d i s t a n c e

needed f o r t h i s model. T h i s phenomenon s h o u l d b e f u r t h e r

i n v e s t i g a t e d , a s i t r e l a t e s d i r e c t l y t o what f r e q u e n c i e s t h a t

s h o u l d b e u s e d f o r t h e emergency l o c a t o r b e a c o n s .

4 .0 O t h e r Measured Da ta

A map o f t h e s u r f a c e i s shown i n f i g u r e 7 . No i se a t

l o c a t i o n B 1 , 463 m e t e r s (1520 f e e t ) o v e r t h e 1900 Hz b e a c o n ,

i s shown i n f i g u r e 8 . No i se a t l o c a t i o n C 1 , 442 m e t e r s

(1450 f e e t ) o v e r a 1700 H z b e a c o n , i s shown i n f i g u r e 9 .

A l l t h e r e m a i n i n g f i g u r e s a r e o f n o i s e a t l o c a t i o n A l ,

1150 f e e t o v e r a 2500 Hz b e a c o n ,

F i g u r e s 10 t h r o u g h 1 8 show s p e c t r a o f d a y , t w i l i g h t , and

n i g h t n o i s e t o 10 kHz. F i g u r e 1 3 shows a d i s t a n t s f e r i c .

F i g u r e s 19 t h r o u g h 27 show expanded s p e c t r a o f d a y ,

t w i l i g h t , and n i g h t n o i s e . These s p e c t r a a r e v a l i d from

100 Hz t o 3 kHz.

Da ta i n f i g u r e s 8 t h r o u g h 27 i s a b s o l u t e and h a s an u n c e r -

t a i n t y o f + 1 dB [ I ] . T h i s u n c e r t a i n t y o n l y a p p l i e s o v e r t h e

f o l l o w i n g f r e q u e n c y r a n g e s : f i g u r e s 8 and 9 , 300 Hz t o

2600 Hz; f i g u r e s 10 t h r o u g h 1 8 , 560 Hz t o 10 kHz; f i g u r e s 19

t h r o u g h 2 7 , 100 H z t o 3 kHz. See s e c t i o n 9 . 0 , Appendix, f o r

t h e code key t o u s e i n d e t e r m i n i n g t h e meaning o f t h e numbers

i n t h e h e a d e r b l o c k a t t h e t o p o f e a c h s p e c t r u m . The r e s o l u -

t i o n bandwidth i s g i v e n on t h e o r d i n a t e o f t h e p l o t s .

5.0 Conclus ions

The s u r f a c e n o i s e a t a remote s i t e , away from p o w e r l i n e s ,

w i l l n o t be f r e e o f power l ine harmonics ; t h e i r ampl i tudes w i l l

b e reduced.

The e a r t h - i o n o s p h e r e may p r o v i d e a waveguide t o p r o p a -

g a t e d i s t a n t n o i s e , p a r t i c u l a r l y above 3500 H z d u r i n g t h e day

and above 1700 H z a t n i g h t . These f r e q u e n c i e s a r e v a l i d o n l y

d u r i n g t h e p e r i o d covered by t h e s e measurements, a s i o n o s p h e r i c

phenomena a r e q u i t e t ime , g e o g r a p h i c a l l y , and s e a s o n a l l y

dependent .

6.0 Recommendat i o n s

These l i m i t e d r e s u l t s i n d i c a t e t h a t emergency l o c a t o r

beacon f r e q u e n c i e s shou ld be s e l e c t e d below 1700 H z and b e -

tween harmonics o f t h e 60 Hz power l ine f requency .

A d d i t i o n a l measurements shou ld b e made o v e r a d i u r n a l

c y c l e and d u r i n g each o f t h e f o u r s e a s o n s . Higher g a i n b a l u n s

and /o r a m p l i f i e r s shou ld be used t o lower sys tem n o i s e .

7 . 0 Acknowledgments

Ed Niesen a s s i s t e d w i t h t h e f i e l d work, Winston S c o t t

a s s i s t e d w i t h t h e d a t a p r o c e s s i n g , and Sharon Foote and

J a n e t Becker performed t y p i n g s e r v i c e s .

David S t e r n s a t t h e U n i v e r s i t y o f Colorado a s s i s t e d w i t h

d i g i t i z i n g d a t a .

Car l F i s h e r and Ruben Mayes o f Westinghouse Georesearch

Labora to ry made ar rangements w i t h M r . Watson o f Geneva Mine

o f U.S. S t e e l Co. F i s h e r and Mayes a s s i s t e d i n s p e c i f y i n g

l o c a t i o n s , f r e q u e n c i e s , and overburden w i t h r e s p e c t t o

emergency l o c a t o r beacons .

Frank Cowley and Lorne Matheson o f t h e N a t i o n a l Oceanic

and Atmospheric A d m i n i s t r a t i o n a s s i s t e d w i t h computer s o f t w a r e

and d a t a p r o c e s s i n g .

8 . 0 Refe rences

Bensema, W . D . , M. Kanda, and J . W . Adams, " E l e c t r o m a g n e t i c

Noise i n Robena No. 4 Mine," NBS T e c h n i c a l Note 654,

A p r i l 1974.

Ramo and Whinnery, " F i e l d s and Waves i n Modern Radio"

(John Wiley 6 S o n s , I n c . , New York, New York, Second

E d i t i o n , p . 328, p . 335, e t c . , 1959) .

Terman, " E l e c t r o n i c and Radio Engineer ing" (McGraw-

H i l l Book Co. , I n c . , New York, New York, F o u r t h E d i t i o n ,

p . 825 , 826, 1 9 5 5 ) .

I OSCILLOSCOPE I LOOP ANTENNA, I SENSITIVE AXIS VERTICAL

1' - I BALUN

SIMILAR TO 3 , BUT WlTH ANTENNA SENSITIVE AXlS HORIZONTAL, E - W SIMILAR TO 3 , BUT WlTH ANTENNA SENSITIVE AXlS HORIZONTAL, N - S o

25 kHz

AN ALU ti TAPE RECORDER

CHANNEL

F i g u r e 1. Field Recording System

3 FILTER t .

ONE CHANNEL AT A TIME

CHANNEL 3

ANALOG TAPE 5 ,

RECORDER

F i g u r e 2a. D i g i t i z i n g p a r t of d a t a p r o c e s s i n g system

lGl T A L TAPE

F i g u r e 2b. F a s t - F o u r i e r t r a n s £ orm p a r t of d a t a p r o c e s s i n g system

MICROFILM OUTPUT

DIGITAL COMPUTER

WJO ccn rn w

- I 421 onrn UWI -DO (n<w 4-4-

2%: I mob nzr rn II m -cm n;o I m-ns

D -no mrno

3 (nDW xmo 002 ztrn ;L rn Z 4 Cn 4 orno

z n w rn m$s D C, moz oorn < b rnt-2

n w 3 ~n n 02 - ~rnm

RMS MAGNETIC FIELD STRENGTH, H, dB RELATIVE TO ONE MICROAMPERE PER METER, FOR DISCRETE FREQUENCIES; OR

RMS MAGNETIC-FIELD-STRENGTH SPECTRUM DENSITY LEVEL, Hd, dB RELATIVE TO ONE MICROAMPERE-PER-METER PER JRTL, FOR BROAD BAND NOISE

RMS MAGNETIC FIELD STRENGTH, H, dB RELATIVE TO ONE MICROAMPERE PER METER, FOR DISCRETE FREQUENCIES; OR

RMS MAGNETIC-FIELD-STRENGTH SPECTRUM DEtiSITI LEVEL, Hd, dB RELATIVE TO ONE MICROAMPERE-PER-METER PER mz, FOR BROAD BAND NOISE

WW m mmo o n m won PW-I

G; - S 5 S: $h)-I

h) I w m 2 3

2x8 'A 0 a mc- W N

wcno z-5 2 * -4 - r 00.

Z-IZ I m-m >on 2 Z 0

-Imz cn C 0 n w mnz W * z -n-I n m M 0

B n n m 5 2 mm0 v 0 om nm+ nz-

m n rn c mx-n r - oom xor

cr 'A 13 -3. -I -3 - *)

z m zrn r N- O

Figure 5 Spectrum of magnetic f i e l d s t r e n g t h vs . t i m e . Antenna placed on su r f ace of ground above Geneva Coal Mine, a t . "Lost-Miner Beacon" pu l se s showing a t 2500 Hz are from a t r a n s m i t t e r beacon s t r a i g h t down 351 meters (1150 f e e t ) . Pulses a t 1900 Hz a r e from a t r a n s m i t t e r 0.8 k i l ome te r s (1/2 mi le ) away under 463 meters (1520 f e e t ) of overburden. X

F i g u r e 6

S o e c t r u m o f m a g n e t i c f i e l d s t r e n g t h v s . t i m e . A n t e n n a

laced nn s u r f a c e o f g r o u n d a b o v e G e n e v a C o a l M i n e ,

i n . " L o s t - M i n e r B e a c q n " p u l s e s a t 2 5 0 0 H z c a n

s t i l l b e s e e n b u t t h o s e a t 1900 H z a r e r a r t i a l l y o b s c u r e d

b y t h e a t m o s ~ h e r i c p u l s e s ( I i g h t n i n g s t a t i c ) p r q n a g a t i n g

i n f r ~ m o v e r t h e h o r i z o n . T h i s p l o t s h r l w s t h a t b y p l a c i n g

t r a n s m i t t e r f r e q u e n c y b e l ~ w 1600 H z , a t m o s p h e r i c

i n t e r f e r e n c e c a n b e r e a u c e d a t l e a s t 10 d B , a f a c t n r

q f 10 t q I r e d u c t i ~ n i n n o w e r .

Geneva Coal Mine Entrance

Figure 7 Map of su r f ace over Geneva Coal Mine.

Location Overburden Beacon Frequency Code (Hz)

IES; O

;ETIC-

-STfiE

H,, dB

OAtilP

0 625 1,250 1,875 2,500 FREQUENCY

Figure 9 spectrum of s u r f a c e C I I n o i s e , n o r t h s i d e of L i l a P o i n t , o v e r c'eneva Mine, Loca t ion C1 on F igu re 7. 1700 llz bencoq t h r o ~ , . , ' . 442 me te r s (1450 f t . ) o f overhurden i s n o t v i q i b l e . Antenna s e n s i t i v e a x i s was v e r t i c a l . Daytime, June 1 2 , 1973.

,.J - .. m N.. .... n.9 i l "l. \ 7 .') _I

P' u . ,

- s c.. I : C - - c ;, i ,n L C C t l 3 : , A - I < " Y - .: - YI

3 - L o o m > E C U . i

27 g.2; U Y i h u m - c m ::":- o r -

V K m r r N '- .a C - 32:. i '" 5 c ,=

+ c -5:

ISION QNV0 OY3I0 10j ' z w 13d M13W-83d-313dWVOIW l?lO 01 3AIlV13I 0P "H ' 13h31 AllSN30 Wn1133dS H13N311S-0131j-3113N3V~I SWI

I 0 ' ~313~3n0313 313I3S10 I O i '1313~ I 3 d 313dWV0131N 310 0 1 3 A l l V B I UP 'H 'HL3N311S 0131j 3113N3V11 SWI

FREQUENCY, Hz

Figure 12 I n kHz spectrum ~f surfncc E!! noise a t Li la Csnvon nvrrlook. nvvr Ienrva Vine. I.antlxrn A 1 m Ficfrre 7. 2509 Ilr hcaron thr<-up.l~ 151 meter* (1150 It.) ol ovrrburden Lx r l e n r l v v i s i b l e . ,\l!r(.nl.a w . n s i t i v e a x i s was vertical. Nighttine. 10:11 p .m. , .It,nv 1 2 . 1471.

3SION ONVB QVOMB 'd04"-& 113d 4313#-113d-343dNV0431 3N0 0 1 3h l lV134 BP "H '13A31 AllSNIO NnY133dS H13N3YlS-O131~-3113N3YM SW11

a C ' I I c i .- .. 0 4 c u i

U C U U O C m . 4 o V - " U 5 " - - ' . &,:=

0 .- r e z - 3-. . L : . -- U * .- V S C p . > 3

n o U u ; C > - w - w N ; u - = r A ' L L C O

3 C C C ? W > - L 1

M0 '~313~3nMM~ 313M3SIO 104 '1313~ M3d 3M3dWVOM31W 3NO 01 3AllVlId 8P ' H ' ~ 1 3 ~ 3 8 1 ~ 0131j 3113N3VW SWM

2 4 8 " - - L CI Oi " .. > c n D c -

c u r z. 5 2 7 d '2 . u c " $ - 0 - 4 L >? - - a

U .A . m li, w c ? rn 5 G .4 - c - c '2 w C d U G C rJ .A 0 U U N L rn .d a u ~

0 0 0 A .c

0 . m u 13 E C

2 2 : ; u X I - u rc m v 3 > 4 L G > ? C , - .>;: .- -

. * L . I U F C C

C z r , d Ci 4 -

3SION QNVfi QVOMfl 104 ' z w M 3 d M313W-M3d-3M3dWVOM3l\q 3NO 0 1 3AIlY13M flP ' P ~ ' 1 3 ~ 3 1 AllSN30 WnM133dS H13N3MlS-Q13\4-3113N3VPI SWM

MO 'S313N3n03M4 313M3SIQ M04 'M313!4 M3d 3M3dWV0131W 3N0 0 1 3AllV13d BP 'H 'H13NIMlS Q1314 3113N3VW SWM

0 m " z-

- g ."

2 t. 0 C? >"

.. m r--

5 C . c c 2 m p 2 : ' - - . .. ., 7 z s ::; i r .-

N :. c C 4 . 5 - - C 3 2 C Y

2 .- L. - L - A m - 3 D d

0 :- . s

m T . . . _ *

., -- c c , r w C C :- L

-: . - - u < - = e s : c - L + n c a . r - c_ 3 C a: c ; ; r L - -

c - : : C . v. PI - c " Y I 8 . 4

> U i U

- - - ..! r = o - C L C c :. ; z .. I-.. r.,

0 m \C ' *- 4

ar ! $4 3 M

..J v ::

:: t o * N % . , " . - . .. . . ., f.

r - C N- L

" N . m,, U) -..

r r . . 0 ,) .-.. u ~ r . ?

c" . J . ,

-.. 8 <" . .,

.,.. . . ,. .' .... . . . . , . . . <. . ... 11 ",.. 0 ;: U .. ., .... ' ... m

m . .... U ..< ? <o -. '.h7 L-J

,, 1 .'. rr ', YJ z ,--- ,,

ZN'O N 0 .. II ' I

-0, * :.; " "f . m ,, o: w * -m $J :.; v - N "0

-3 :: n . P I N & - . m

I, - . ' .. . - ., " :::

N -.- ln .. .. m.. 0

- "a .. - - < 9

. . , > - I .

su .a . ,

I 2 0 0 2040 20 I 30.000 I I I . 0 0 : 9 3 1 ' 3 / ' 3 ' 1 56 1 1 54 1‘ . I 95 .003 -1 38.111 0 10 .001 D OLaOLL Z L I Y C > l 43O:E 58 79 0 0 73Go:n c o r r . r e c : -4: t o : con,: : : 2 . L

C-22 RG=10000;-40dB' 3G= : ii= : 52 005+003 , : 3086 : 336+::2.

FREQUENCY, Hz

I2 0 0 2 0 1 1 20 I 1OtOOO 2 44 .000 0 9 / 1 9 / 1 3 : I 5 9 57 1, 47 . F 1 9 5 - 0 0 1 6 91.001 0 004000 0 OO+OOC 2 0 1300D 4 1 0 0 1 W

62 79 0 0 '3Go1n c o r r . . r c c . : - 4 0 r o t c o n 9 t . z !2.4 " 2 -

,=% C=22 RG;IOO@C1-4OdB! EG= 0 FG= AG= 52

2 2s 33 - n q rr 52 % 3 2 2 . I

, 000+003 , 3.3086 . 5 236.022,

zGg g - e.

- J m ICi.

" * x .:

2 % . -0

a "-1 7?

>- - , '.z

, ., L

0 625 1,250 1,875 2,509 3,125

FREQUENCY, Hz

3Sl011 CIiVB UVOMR MOJ'z& 1% M313W-13d-3M3dW10bJIPI 3113 0 1 3AllV13M 0P "H '13A31 AlISNjU WnM13JdS H13R3MlS-U1311-"J13H3Y! SWti

MO 'S313N3nD3~3 31383S10 U01 ' 8 1 3 1 1 B d 313dWVOM31W 3N0 0 1 3hllV131 EP 'H ' ~ 1 3 1 3 i i l S 01314 3113N$VI4 SWM

FREQUENCY, Hz

3SION QNVU UVO1U 104 'I& bbd M13W-13d-313dWV0131W IN0 01 3Al lV131 UP "H '13h31 AlISN30 Wn1133dS H13N311S-013lJ-3113N3Y~ SWM

MO !S3\3N3n0313 31313SIQ 104 'N313W Y3d 3MdWV013lW 3N0 0 1 3A11V131 1P ' H 'Hl3N3MlS Q1314 3113N3VW SW1

9 .0 Appendix

Decoding o f Spec t rum C a p t i o n s

Spec t rum c a p t i o n s a r e g e n e r a l l y o r g a n i z e d i n t o t h e f o l -

l owing fo rma t : L

F i r s t l i n e : MP NDT NZS NDA NPO RC DF d a t e , t i m e , f r a m e , s e r i a l ,

MP = Two's power o f l e n g t h o f F o u r i e r t r a n s f o r m , example ,

2MP where MP = 1 2

N D T = D e t r e n d i n g o p t i o n , example, 0 ( d c removed)

NZS = R e s t a r t s p e c t r a l a v e r a g e a f t e r o u t p u t , example , 0

( r e s t a r t e d )

NDA = Data segment advance i n c r e m e n t , example , 2048

NPO = Number o f s p e c t r a ave raged between o u t p u t c a l l s ,

example , 20

RC = I n t e g r a t i o n t i m e i n s econds p e r s p e c t r a , example , 0 .168

DF = R e s o l u t i o n bandwid th , s p e c t r a l e s t i m a t e s p a c i n g i n

h e r t z , example , 62 .5

Date = Date o f computer p r o c e s s i n g , example , 03 /21/73

Time = Time o f computer p r o c e s s i n g , example , 15 :06:34

Frame= Frame s e t number, example , 10

S e r i a l = Fi lm frame s e r i a l number, example, 42.

Second l i n e : DTA DA(1) DA(2) DA(3) NSA NRP NPP, where

DTA = D e t r e n d i n g f i l t e r p a r a m e t e r a , example , 0 .00195

DA(1) = D e t r e n d i n g f i l t e r a v e r a g e , K = l , example , 59.4

DA(2) = D e t r e n d i n g f i l t e r a v e r a g e , K = 2 , example , 0

DA(3) = D e t r e n d i n g f i l t e r a v e r a g e , K=3, example , 0

NSA = Number o f pe r iodograms a v e r a g e d , example , 20

NRP = Number o f d a t a p o i n t s p r o c e s s e d s i n c e s p e c t r u m

i n i t i a l i z a t i o n , example , 43008

NPP = Number o f d a t a p o i n t s p r o c e s s e d s i n c e d a t a i n i t i a l -

i z a t i o n , example , 43008.

T h i r d l i n e : RUN, SESSION, MONTH, DAY, YEAR Gain c o r r . , r e c . =

t o t . c o n s t r . = , where

Run and S e s s i o n = t h e t i t l e of t h e p o r t r a y e d frame i d e n t i f y i n g

t h e d i g i t i z i n g s e s s i o n and run number,

example , 2 1 8 3

Month, Day, Year = d a t e d a t a were r e c o r d e d i n t h e mine ,

example , 8 25 73

Gain c o r r . r e c . = r e c e i v e r g a i n c o r r e c t i o n , example , - 6

t o t . c o n s t . = c o n s t a n t g a i n c o r r e c t i o n o f e n t i r e s y s t e m ,

example , 46 . 4

F o u r t h l i n e : C = , PG = , DG = , FG = , AG = , where

C = c o r r e c t i o n c u r v e used w i t h d a t a , example , 25

RG = r e c e i v e r g a i n and accompanying c o r r e c t i o n i n dB added t o

t h e d a t a , example , 200 ( - 6 dB)

DG = d i g i t i z e r g a i n , example , 0

FG = f i l t e r g a i n i n dB, o f t e n rounded t o n e a r e s t s i n g l e d i g i t ,

example , 0

AG = a b s o l u t e g a i n c o r r e c t i o n added t o d a t a , example , 52

F i f t h l i n e : Top of S c a l e , S t a n d a r d E r r o r , S p e c t r a l Peak , where

Top of S c a l e = l a r g e s t s c a l e mark ing f o r computer drawn 4 g r a p h , example , 1 .000+004 (1 .0 x 10 )

S t a n d a r d E r r o r = s t a n d a r d e r r o r of c u r v e , example , 0 .3162

S p e c t r a l Peak = l a r g e s t s p e c t r a l peak o b s e r v e d , example ,

4 .108+003 (4 .108 x l o 3 )

I I 1 4. 1'ITL.E AND SIJ13Tll'l.l 15. Pub l i ca t ion I l a t r I

U.S. DEPT. O F COMM.

BIBLIOGRAPHIC DATA S H E E T

SURFACE MAGNETIC-FIELD NOISE MEASUREMENTS AT GENEVA MINE 6. Performing Organization C o d e

1. l'UI3I.I(:A?'lON OH K f I ' O K 1 ' NO.

NBSIR 7 4 - 3 6 9

J. W. Adams, W. D. Bensema, N. C. Tomoeda 9. PERFORMING ORGANIZATION NAME AND ADDRESS 110. Projecr /Task/Work Unit No.

7. AU'SHOR(S)

NATIONAL BUREAU O F STANDARDS, Boulder Labs DEPARTMENT O F COMMERCE WASHINGTON, D.C. 20234

2. Gov't Accc-ssion No.

276.55 8. Performine Orean. Reoort No.

'12. Sponsor ing Organizat ion Name and Complete Addrr-sx (Street, C i ty , S t a t e , Z I P )

U. S. Bureau of Mines P i t t s b u r g h Mining and Safety Research Center 4800 Forbes Avenue

3. Rec ip i en t ' s Acccss ion No. 1

Covered

16. ABSTRACT (A 200-word o r l e s s f ac tua l summary of m o s t s ign i f i can t information. If document i nc ludes a s ign i f i can t b ibl iography o r l i t e r a tu re su rvey , ment ion i t here . )

Measurements of s u r f a c e magnetic f i e l d n o i s e were made a t va r ious l o c a t i o n s over the Geneva Coal Mine near P r i c e , Utah, on June 12, 1973. The loca t ions s e l e c t e d were on the su r face over emergency l o c a t o r beacons underground a t depths between 350 meters (1150 f t . ) and 488 meters (1600 f t . ) . The sur face t e r r a i n where these measurements were made was mountainous, and access was d i f f i c u l t . There were no power l i n e s wi thin s e v e r a l mi les , and t h e weather was c l e a r ; the re fore , t h e magnetic n o i s e l e v e l s were about as low a s w i l l normally occur.

Resu l t s of measurements of d i s t a n t s f e r i c s i n d i c a t e r a t h e r sharp cutoff f requencies below which broadband, impulsive noise i s a t tenuated. The mechanism of propagation f o r t h i s n o i s e above t h e daytime cutoff frequency of 3500 Hz and the night t ime cu to f f frequency of 1700 Hz is deduced t o be a waveguide formed by the D o r E l a y e r s of ionosphere as an upper plane and the e a r t h as a lower plane.

The measurement systems used a r e s i m i l a r t o those used earlier. The technique is t o record broadband, analog s i g n a l s , d i g i t i z e the da ta , and use a fas t -Four ier trans- form t o o b t a i n s p e c t r a l p l o t s . This technique i s novel i n t h a t i t can measure simultaneously a l l magnetic f i e l d energy wi th in a l i m i t e d por t ion of the spectrum f o r a l i m i t e d time, and, a f t e r processing, reproduce the even t s occurr ing i n t h a t time i n t e r v a l i n g r e a t d e t a i l .

17. KEY WORDS (s ix to twe lve en t r i e s ; a lphabe t i ca l order; c a p i t a l i z e on ly fhe f i rs t l e t t e r of t h e f i r s t k e y word u n l e s s a p rope r name; separated by semicolons) Ear th-ionosphere waveguide ; elect romagnet ic no i se ; EM1

measurement technique; s f e r i c i n t e r f e r e n c e .

I LZ For Off ic ia l Dis t r ibut ion. Do Not R e l e a s e to NTlS

I CZ Order From Sup. of Doc., U.S. Government P r in t ing Of f i ce Washington, D.C. 20402. SD Cat. No. C 1 3

21. NO. O F P A G E S 18. AVAILARILITY &- Unlimited

( UNCLASSIFIED I 1 19. SECURITY CLASS

( T H I S R E P O R T )

20. SECURITY CLASS 122. P r i c e 1 Order From Nat ional T e c h n i c a l Informnrion Se rv ice (NTIS) Spr ingf ie ld , Virginia 221 51 UNCLASSIFIED

WM. USCOMM-DC 29042-P74

Surface Magnetic Field Noise Measurements at Geneva Mineloop antenna, balun, filter, and analog tape...

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