SURFACE MAGNETIC FIELD NOISE MEASUREMENTS AT GENEVA MINE J. W. Adams W. 0. Bensema N. C. Tomoeda Electromagnetics Division Institute for Basic Standards National Bureau of Standards Boulder, Colorado 80302 The views and conclusions contained in this document should not be interpreted as necessarily representing the official policies or recommendations of the Interior Department's Bureau of Mines of the U. S. Government. June 1974 Prepared for U. S. Bureau of Mines United States Department of the Interior ~ittsbur~; Pennsylvania 15222 Working Fund Agreement HO 133005 U.S. DEPARTMENT OF COMMERCE, Frederick 6. Dent, Secretary NATIONAL BUREAU OF STANDARDS Rtchard W Roberts D~re~tor
Transcript
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
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
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
iii
LIST OF FIGURES (Con t inued )
Page
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 7 . 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 3
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 1 9 . 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 5
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
F i g u r e 2 7 . 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 3
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
f
I
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
4
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
C
7 4
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
I
r +
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
- r
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
P P
cr 'A 13 -3. -I -3 - *)
z m zrn r N- O
-I 1:
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)
RlrlS
MhGM
ETIC
FIELD
STR
ENGT
H, H,
dB R
ELAT
IVE T
O ON
E I4I
CROA
MPER
E PE
R ME
TER,
FOR
DISCR
ETE
FREQ
UENC
IES; O
R
RhlS
CI\GF
;ETIC-
FIELD
-STfiE
NCTH
SP
ECTR
UM D
ENSIT
Y LE
VEL,
H,, dB
REL
ATIVE
TO
OiiE
tAICR
OAtilP
ERE-P
ER-M
ETER
PE
R m
z, F
OR B
ROAD
BAN
D NO
ISE
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
c ,
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
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
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 ,
where
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 ion- osphere 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
