The Alouette II Satellite

8/7/2019 The Alouette II Satellite

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THE ALOUETTE I1 SA TELLITEG . L . Nelms, H.E . L a r r i n g t o n , J . S . Le l r o se an d T.X. Har tzDeferice 3e se ar ch Telecofimunicat ions E stab l ishm entCanada

I . McDiarnidNat ional Research Counci lCana da

L . H . E T 8Ce ,Goddsrd Space F l i g h t CenterNat iona l Aercnzu t i cs and Sgsce Adilzinist rat ionU.S.A.

The Alouet te I1 s a t e l l i t e was b u i l t by t h e Defence3 i e sea rch Telecomrun icat ions Es t a b l i sl?-ment, Canada, andlaanched on 29 November, 1 9 6 5 by the N at i o n a l A er o n au t i e sand Space Adm inis t ra t io n of the U . S . A . a s p a r t of a n i n t e r -n a t i o n a l s a t e l l i t e programme f o r t h e s t u d y of t h e h i g hztxosphere. The o r b i t a l p a r ame t e r s a r e :

apogee 2982 k i l o m e t e r sp erige e 502 k i l omet e r si n c l i n a t i o n 7 9.8" progradep e r i o d 1 2 1 . 4 minutess p i n 2 . 2 5 r ev o l u t i o n s p e r mi n u t e .

F or t h e f i r s t o r b i t p e ri ge e oc cu rre d a t 27 ' s ou th l a t i t u d ea nd t h e l a t i t u d e of pe ri ge e moved sou th 1.89' pe r day.s a t e l l i t e c u r r en t ly o pe ra te s on command f o r about 6 hoursp e r day, c o l l e c t i n g d a ta f r o m one o r more of t h e fo l l ow in gf i v e ex p e r i men t s :

The

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1.

2 .

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4.

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A t op s id e sounder , which measures the d i s t r ib u t i o nof e l e c t r o n s i n t h e t op s i de i o n o sp h er e a s af u n c t i o n of d i s ta n c e from t h e s a t e l l i t e ,A background ra di o nois e experime nt , whichmeasures t he n o i s e environrn-z r o m abou t0 . 2 t o 1 4 bic/s,A very-low frequency (VLF) experiment , whichmeasures r a d i o f requency emiss ions f r o m 50 t o3 0 , 0 0 0 cy c le s per second,An en er ge t i c p a r t i c l e experimen t , which measurest h e f l u x of e l e c t r o n s i j i t h energ ies above 40 Kev,250 Kev and 3 . 9 MeV, the f l u x of p ro to ns w i t hen e r g i e s abo ve 500 Kev, above 1 0 0 Mev and i nt h e r an g e 1 to 8 Mev, and which me asure sp r o to n s p e c t r a i n t h e r an ge 1 0 0 t o 6 0 0 hiev.An e l e c t r o s t a t i c p robe exper iment , wh ichmeasures e le ct r or l number de ns i ty and temp eraturea t two l o c a t i o n s n ea r t h e s a t e l l i t e s u r fa c e .

A s i s t e r s a t e l l i t e , E xp lo re r X X S was launched b yt h e same vehicle and i s i n n e a r l y t h e same o r b i t a s A l o u e tt e 11.On 2 9 January , 1 9 6 6 t h e t w o s a t e l l i t e s were 540 ki lornetersa p a r t and w ere s e p a r a t i n g a t a r a t e of 8 t o 9 l u l o m e t e r s p e rCI .:cAy.l Ex p l o r e r XXXI co n t a i n s i o n and e l e c t r o n p r ob es, ande n e l e c t r o s t a t i c probe i d e n t i c a l to t h e e l e c t r o s t a t i c probeso n A l o u e t t e 11.

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The purpose of t h e dual l a u n c h i s to p e r m i t n e a r l ys imul taneous compar i sons between the da ta o bta ine d by th es ounde r, VLF and e l e c t r o s t a t i c p robe expe r imen t s i n A l ou e t t e I1m i . t h e p r o b es i n E x p lo r er X X X I , and to p r o v i d e i o n e nde l e c t r o n t e q e r a t u r e and i o n c o np os it io n da te a t t h e h e i g h tof the s a t e l l i t e for u se w i t h the sow-der da ta . S i n c e t h ed . i s t r l b u t i o n of e l e c t r on s betw een t h e peak of t h e F l a y e r o fthe ionosphere ( the he ight of t h e p e ak o f t h e F l a y e r r e r g e sfrom abou t 2 0 0 t o 500 k i l ome t e r s ) and th e s a t e l l i t e c an be

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d e t e r r i n e d from th e sounder records , use of this dat?, i nc o n j u n c t i o n w i th the data measured e t t h e s a t e l l i t e b y t h ep robes i s expec ted t o p1-ovid.e a g r e a t d e a l of in_formatior,zbou t t h e e n t i r e r eg i o n above t he peak 02 t h e F i a y e r . I nad d i t io n, comparisons can be made w i t h d a t a o b t a i n e d f ro mt h e A l o u e t t e I s a t e l l i t e (Uarren 1962; Warren 1963, b e l r o s em d 3arring-con 1 9 6 5 , 9 R T E r e p o r t , 1 9 6 6 ) launched on September2 9 , 1962, i n t o a 1000 k il om et ei - c i r c u l a r p o l a r o r b i t , r#:hichi s s t i l l prov i d i ng 1 to 2 hours of topside sounder, VLF,background r ad i o no i s e and e n er g e ti c p a r t i c l e data p e r dzji.The. To.pside Sounding Experiment :

The t o p s i d e s ou nd er i n A i o u e t t e I1 prov i des anave rage p u l s e power of about 300 w a t t s i n t o t h e a e r i a l s a ta p u ls e r e p e t i t i o n r a t e of 30 per second and puls e w i d t h of

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100 Fse c. The sounde r sweeps f r o m 0 . 2 t o 14.0 I ic/s, oncee;,rery SO seconds.Th.5 a e r i a l s u se d f o r t h e so un de r a r e two d i p o l e s , of l e c g t h2.20 f e e t and 7 5 T ee t t i p t o t i p .

It i s normal ly on f o r p e r i o d s o f 1 3 Il?irxtes .

A to ps id e sounder ionogram, take n 7v;lzzn the m t e l l i t ei y k i-A:RS a t a h e i g h t o f 900 -ki lometers , i s shown i n F i g . 1,

record was ob tai ne d when th e s a t e l l i t e was a t a h e i g h t of? v ~ p m x i r n z t e l y00 k il o n e te rs , nea r Bermuda. The axes of theionograms a r e apparent range ( t ime de lay ) i n kilcrnete-rs 2ndI"i:eclu.ency in Nc/s. The pul se re pe t i t i c r ! r a t e of 30 .puls?s2 ~ ; r econd provides 4800 k i l ome t e r s of appa ren t i-ange Lek.-cnsound-er t ra ns i7 i t t e r pu l ses . When t h e t e l e x e t r y t a F e s --?-epL-ocessed i n t o ionograms, a h e i g h t i n t e r v a l 02 2000 k i l o m e t e r s!.- ith 1 0 0 ki lorLeter app are nt range markers, o r of 4500 k i l o m e t e r s. .7" 1. - p 200 kilometer clarker 's i s u s u a l l y u s e d. To F r o v i d e

:ra.nid i d e n t i f i c a t i o n , t h e m arkers at x m l t i p l e s of 1000 k i l o n e t e r sart3 xade double the w i d t h of t he o t h e r ma rke rs . The Treqxencys;.reep r a t e c h a n g e s s h a r p l y a t 2.0 blc/s.0.1-5 Plc/s/sec below 2 .0 I\ic/s and 1 . 0 bic/s/sec above 2.0 l f C / s .1% slow srreep r a t e below 2 .0 l ic /s enEbles t h e f req uen cy ofphenomena on t h c ionograms t o be measured w i th an accui*ac.j of- - 2 Kc/s, o r t h r e e t i m e s t h e a c c u ra c y t h a t can be o b t a i ned

T h i s r a t e i s about

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---_-_>A;? I_^i ;? L*yr1 .a:. ' i-eLj:mcy ;::,ie?i sit:The very l o w f requency exper iment i s o c c z s i o n a l l y

c;zr2,zed s imul taneous ly t . i i th t h e t o p s i d e s ou nd er apd sh3,rest h e same broad-band te lemetry channel .prociuces mutual in t e r fe re nc e between th e t::o e x p e r i n e n t s ,'QUX f o r c e r t a i n s t u d i e s t h e p o t e n t i a l a dv an ta ge s o r t h e

T h i s mode of o p e r a t i o n

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cord!ined expe r i nen t ou t ve i gh t he d i s advan tages of t h e i n t e r -- , ~ ~ : ? c e?,--.-,- ( B e rr i ng t o n e t al. 1 9 6 5 ) . S o far l i t t l e of t h esir:xl-,kaneou.s ciata hzve been an zl ys ed . On se v e r a l p as se s.k.'L..,.-,-n -,.--.:-'LC,)., E t I-&:? I i o u s l a t i t u d e s , t h e VX' e;cpn,rircen-l i s

, . , -?:I- ? , L O ? ~ . Gn cze sy-ch p 2 - s ~ -ecor:'+- e v e r :\-cst~;:j.j-~.t5.e even t shown i n Fig . I. va s observed. Here a norrcaifL - s c t i ona l hop w h i s t l e r , i . e . , t h e d i sp e r se d e l e c t r o i n a p e t i ci;:FLi.lse t h a t has propagated upwards from a l i g h t n i n g d i s c h a r g et o t h e s a t e l l i t e , i s shown. A p ro to n v h i s t l e r ( G ur n et t, e t al.1965) and. t h e f i r s t h e li um w h i s t l e r ( G a rr i n gt o n , E e l r o s e a ndI . l ? - : k r , 1 9 6 6 ) th2.t has ev er been dete cte d a r e also i d e n t L f i e d .='.InL.- d i s p e r s i o n of t h e f r a c t i o n a l hop v h l s t l e r can be used t o:!ctzlrx5ne t h e tctal e l e c t r o n c o nt en t a l o n g t h e v h i s t l e r p a t h .L L A c f r e q u e n c y a t which the p r o t o z t r z c e s e p a r a t e s f ro m t Y - 9P:r x- l ion al hop Yihis t ler ( t h e cross-oveimf re qu en cy ) d e t e r x h e st,ne r e l a t i v e abundance of protons a t t he s a t e l l i t e h ei gh t ,-:~;XLleh e d i s pe rs io n i n th e t a i l of t h e t r a c e c an b e u s e dto $.=rive number de ns i t y of pro ton s at t h i s h e i g h t . The

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rsion of t h e h e l i u x w h i s t l e r c an b e used t o f i n d t h er,u:-!:ber de ns i t y of hel ium a t t h e s s t e l l i t e , an d t h e heliiiixc m s s - o v e r f r eq u e n cy i n a f u n c t i o n only of t h e r e l a t i v e2'm.nd.ances of t h e v ar io u s i o n c o n s t i t u e n t s . Thus assu.i:?ing-I'nnt t h e io no sp he re a t t h e s a t e l l i t e h e ig h t i s composeds o l n l y of e l ec t r on s , p ro tons , he lium io ns and oxygen io nsc2 sjL$:m,l such a s that showm i n Fig. 4 c o n t a i n s i n f o r i x at i c ni'i-om x h i c h t h e e l e c t r o n d e n s i t y a t t h e s z , " e l l l t e height a s:.?ell as t h e r e l a t i v e a nd a b s o l u t e a bu nd an ce s of t h e i o nC C n P i i t u e n t s ( L e r r i n g t o n , E e l r o s e e n d i b t h e r , 1 9 6 6 ) can beci2Cixced. I n a dd i t io n , s u f f i c i e n t i n f o r m t i o n i s a v a i l a b l e

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t o .orovide 2, check on t h e accurac2- of t h e t h e o ry and r!ie2,sure-neii ts u se d i n d e r iv i n g t h e 6 a ta .

The extended h i gh f requenc y coverage of the...l i i o u e t t e Ii VLF r e c e i v e r has p e r r L t t e d the c l .e tect io9 c!f_ - - . . . ,7 fyc;; se~;ey&l- groufiC; ' oa , sed $I,LI' -,y,-.ns!:7;;;cer:;. I:?- -k t , i rT 5 t h e s i g n s i s fror.1 one such +~-a;~s; ; i i t~~ers , ~ : e see11 7 . t- 3 . "fl-equ.encies of 1 7 . 6 and 18.2 Kc/s.o n t h e p r o p a ga t i on of VLF waves r i i t h in the ionosphere c2nb e o b t a i n ed f ro m s t u d y i n g t h e r eg i o n s i n i:;'nich such s ig i -a ls

Considerable inTorTi?ation

+,,iL--a observed . Also shown i n t h i s f i g u r e i s n o i se v i t h az'i?.?..:-p lovrer cut- off freq uen cy t h z t has bee i? t r i ggered b y a: , j n i s t l e r .Lhat t h e lower cu t -o f f f r equency of such no i se i s the_ - I t has been suggested. (E ri c e and SrxLth 1964)-.

r hybrid. resonence of t h e p l a s ~ ~t t h e s a t e l l i t e h e ig ht ,.I- \-\, +he f a c t s t o d at e seen t o suppoi-t t h i s hj rpothesis( X r r i n g t o n , Cel rose and Melrns, 196 5) . For th e o r'oi -t of

Alo1xette I1 the lo : . rer hybr id resonance f requency lies betweenhundred c yc le s and 20 ICc/s, and the resonance fL"reqv.ency

:.1.'1 be .vi thin t h e p as s b zn d of t h e A l o u e t t e I1 VLF' r e c e i v e r ,T!hei-ie\rer n o i s e su ch as t h a t shovm i n t h e f i g s r e OCCUI'S. S k ? C ?

. - -_, ._Lihis resonance frequencL- i s r e l a te d t o t h e l o c d elec'crofi5 e n s i t y and. t he ion co inpos i t i on , t h i s phenomena provides jrets i lo ther source of inf or im t ion on t h e c o n s t i t u t i o n of thei 3.csp h e r e .r ,---L tle 3ackground Radio Noise E,.cncrir?zl?t:

Tine AGC voltage f orn t he swep t-f equency sounderr c c e i v e r i s moni tored a l l t h e t i me thc?,t t h e t o p si d e soui?der-

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is opera t ing . These d-ata provide a measure of t h e backgroundrn,?.io n o is e l e v e l a t t h e s a t e l l i t e 2 s a f u n c t i o n cf Trequenc;::;,'l,n~n t h e s7:eep rang e of abou t 0 . 2 t o 14 $!ic/s.I , . x 8 experinlent Fs vzr:; s i x i l a r t o o n e c a r r i e d i n t h e~ ~ . ~ - ~ ~ . ~ % ~ pL s a t e l l r t e ( sz r t : ,< ' 1,014a,,i964-5, 1

.-:1 2 E s s e n t i a l l y. . . -

. .c, 112 - c i ~ s ; lAeszn~ qd-jp;clepAt .:-;;,?p? -pa,nge ;",as teen I ~ ~ - ~ P ~ Z . ~2.'" .

- , - 7 i I - t hh e r e s u l t t h a t d a t a can be o b t a i n e d a t s i g n i f i c a n t l : 7iLoT.':er f r e q u e n c i e s .

I n g e ne re l a p o r t i o n of t h e r eco rc ! n ea r t h eupl2e_r end of th e sweep range c on ta ins in t e r f e r i n g t r e n s -z i s s i o n s t h a t propagate u p f roni the ground above thef'rc!c:uenc:- o r ~.71?;ich he ionosphere i s a ~hiel?. S i 1 5 2 - ~ ~ r l - y ,k c e r e i s ev i d en ce t h a t a p o r t i o n of t h e low end of t h eI-equeric;F r m g e , below t he e le c t r o n gyrofrequer,c:: z l s o i scontaminated b y ground t r ansm iss ions . Ee tveen the se .two

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- - L A . t s ,, .~, novever, i t i s p o s s i b l e t o i d e n t i f y a t leas ' i thefnllovsing main types of no is e 'and. t o get det , z i i l ed cpan t i t a t ive

-- ,.Lc, on +;hen:11.) g a la c t i c no i se , 7:hich exceeds th e r ece , ive- no i se

( 2 )l e v e l a , t Trequencies S r e a t e r t h an ab o u t 0.3 ~: i c / s ,no i se e in i s s ions t h a t aspear t o S e g e a e r a t e d r 5 t h i ni o no s ph e r e: t h e s e o c c ur i n t h e f re q u e n c y r an gebetween th e e l e c t ro n gyro f requency , f and theupper h:Tbi*id f requerxy, f T, anda bove t h e g a l a c t i c n o i s e l e v e l a n d w hic h e xt e nddoicn i n frecydenc:v t o a l o w e r l i m i t of about0 . 6 I.ic/s:hav e be en i d e n - t i f i e d i n t h e r e c o r d s b u t o t h e r

H'(5) s o l a r n o i s e e m is si on s , w hic h e p p ea r s p o r a d i c a l l y

t o da te 2 nui?-her of Type Iii bu. r s t s

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c.,;/pes of s o l a r n o i s e h a v e c o t y e t b e e n f'ounGa t t h e s e sai;ie low f r e q u e n c i e s .

y>Lep*d;-pose cf thz encr-- gLa-'- iAC 92"-ct,icic ez,periT,;,?nt-:Je s%a+n,d rcnnrr7nt +---,--BurLLLi*L b ~ ~ l l l ~,s f o l l o t i s : (1) t o proviiie

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" t i c f i e l d of s o l a r and cosfi5c ray p a r t i c l e s , and. (3)--.. i u , L ~ ~ e t i c, ?.. field a s a r e s u l t o f i t s i n t e r x t i o n v i t h tkc ssiari.;i??ci.

The experiment, rjhich i s an iiqi2roved version ofwii3 flown i n A l o u e t t e I, consists of s e v e n d i f f e r e n t countersc a >z b l e of d e t e c t i n g e l e c t r o n s x i t h e n e r g i e s above 40 Kev,253 Ilev and 3 . 9 Kev 2nd protons c2bove 500 Kev, i n the ronge-: 0 8 biev and ebove 1 0 0 Fev and oI" iiiessuring proton s p e c t r a-: - -"',,a p y " y a__.__ _ " _ _ - _5- 130 t o SO0 Fiev. : dos t of tke C e t e c t o r s 2,i-e? % r ~ c t i o n a l ,h?at i s theL rileasu.re i n t e n s i t i e s i n a smal lr x g 3 of a n g l e s about a givelz d ir e c t i o n !ihich i s determined; . r S _ t h r e s p e c t t o t h e d i r e c t i o n of t h e e a r t h ' s m ag ne tic f i e l d-a:;,- i:!zgnetometers on board the s a t e l l i t e . fit t h e t lme of: . :ri t ing 8.11 d e t e c t o r s are operating normal ly .

'The e;q)eririient i s cap,?,ble of 2 t i m e r e s o l u t i o ncf about l / 8 of a second although i n most of t h e a n a l y s i sc o u n ti n g r a t e s a v er ag ed i n 1 second and 4 second intervElsiJ2.11 be used .

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Auto rmt ic da ta p rocess ing equ ipcen t f o r man i m n o r tm t p a r t of t h e e xp er ime nt s i n c e a o r e t h a n 1 0 d a t a

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p ~ , f r , t s er moqth a re ob ta ined and i t i s n e ce s sa ry t o p l o tL L l of t n z s e i n t h e i n i t i a l p a r t of t h e m a l y s i s . The: L L ~rom th e teleiactr :; t s p e s a r e f i r s t t r a n s f z r r e d t o,. 1- , .t a l !:fi@e-~ilc t a p e and t h e pi*ocessing i s done o n e n I.:;,si)c.oj?z;;iter. ,IlI


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sweep o u t t h e a mbient p a r t i c l e s i n i t s p z t h .The two p ro be s a r e use d i n d e p e n d e c t l g m 6r c o ~ - i z n t i a l l y . A r-eyecting sa.wtootln voltz-ge i s cipplic:d t o

. . ,-, - P O ~ ST;;P;~~I> s us e , a;;< T;>I,? ye .c.4-j;i:;s ~ : ~ ~ - ~ - ~ ~ L f ;, ;> -, i y q o r t a n t i n a s z t e l l i t e ha ving 2-11 e x t ~ r ~?-02g n te n na i n which l a r g e v o l t a g e s 2 r e i n du c e 6 b y t h e i rhigh v e l o c i t y throu.gh t h e g eo ms gn etic f i e l d . The s a t e l l i t e sp o t e n t i a l c a n b e resolved when i t l i e s be tx ee n -10 voltsc?xd +2 volts.must be appl ied to dr ive the p robe t o t h e plasma potentic7.1.Th e gross n a t u r e of th e i o n and el e c t r o n Vrake can bed e r i v e d by o b se r v i n g t h e r o l l r,: ,odul~~'~iol?f i o n ande l e c t r o n c u r r e n ts as the probes pass b eh in d t h e s a t e l l i t e .

T h i s i s done by n o t i n g t h e v o l t a g e w hich

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References :--1..,7

- e-..L, I45,6.7.8.9 ,

io.

11.12.

13.7 dA .-.15.16.

1 7 .

18.

- .:. ':arren, E.S., 1962, Can, 5 , Ph;,s. do, 1692,' ' , 9 9.-'? 1% 3 , iTature 197, 4 E5 ?,,;-??lrose, J,s.D3TE F,eport No. 1159-1 ( I n P r e s s ) , 1966.~ockwood, G . E. K . , 1963, Can. J. Phys. 41, 1 9 0 .C a l v e r t , IJ. and Goe, G . E . , 1963, J . G . R . -8, 6113.Lockvood, G.E.K. , 1965, Can. J, Phys. 63, 291.3 a r r i n g t o n , R.E. and E e l r o s e , J.S. , 1963 , ILTa'cure E, 51.B u r n e t t , D . A . , Shawhan, S . D . , E r i c e , N . M . , and Snk t h , R.L,,1955, J. Geophys. Res., 7 0 , 1665.Garr ing ton , 8.E. , Ee l ros e , J.S. a ~ d zther, !.!,E., NatlJ-re(1x2 Press).S r i c e , N . N . and S n i t h , R . L . , 1964, Nature 203, 926.Ba r r i ng t on , R . E . , Ee l ros e , J .S . and r\Telms, G.L . , 1 9 6 5 ,J. Geophys. Bes., 70, 647.H a r t z , T.R., 1964, Ann. d 'Ast rophysique 27, 823.-i!artz, T.Z. , 1364 , Ann. dffistro~ h::siq'Je 27, 831.E a r t z , T.Z., 1964, i iature 203, 173.Brace, L.H., Spe nce r, i(.IJ. and Cc lg arn o, A . , 1 9 6 5 , P l a n e tSpace S c i . , l3, 647.Spencer, N . V . , Brace, L . H . , Cerignan, G.R. , Taeusch, D.fi . ,and Niernann, H,, 1965, J . Geophgs. Re s . 70, 1, 2665.Brace, L.H., and Reddy, 6.81. , 1965 , J. Geophys. Res. 70,23, 5783.

._l . L - 4 L A , E.S., -c,nd S a r r i n g t o n , R . L . , 1 9 5 3 , Nature G, 651.

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7j i g u r e 2:

F i g u r e 3:

F i w r e 4:

An A lo ue tt e I1 t ops ide sounder ionogran recordedvhen t h e s a t e l l i t e x as n e a r Bernucia, E t c ,n Zl t i t udeof 900 ! + J ~ ; : L ~ ~ ~ ~ s .?leT;C?.~-~C;JSr e f l e c t L c ~ r s i . e sc u i-,-e 17 , u ~ ~ - ~ i ~ l e d .- , . - .

The Z-wave pla sma fr eq ue nc y a t t h e s z z e l l i t e ,The 0-xave plasma frequency a t t h e s a t e l l i t e ,The X-Twa-ge p l a sn a f r equ en cy a t t h e s a t e l l i t e ,

fZS, o ccu r s a t X = 1 + Yf,:, o c c u r s a t X = 11 Uf-.S,- o c c u r s a t X = 1 - YThe j?lasma sp ikes observed a t t h e s a t e l l i t , e o cc ur

a t %he f o l l o w i n g f r e q u e n c i e s :f r J J t h e e l ec t r on g :j ro lrequency, O C C U ~ Sa t Y = 3.f,,,, t h e plasna f r equency , occurs a t X = 1f T , t h e upper hybr id f r equency , occ urs a t X = 1 - 1n-fH, t h e m u l t i p l e s o f t h e e l ec t r o n g y r o f r eq u en cy ,

-1.

2

12 5 n1 L _ _ _ _ ^ _occur a t Y = -An A l o u e t t e Ii to ps id e sou.r.der ionogram re co rd edvhen t h e s a t e l l i t e vxs near Eermuda, a t an a l t i t u d eof 2802 k i l o me t e r s .An A lo ue tt e I1 topside sounder ionogram recordedwhen t h e s a t e l l i t e 1;ras n ea r S an t i ag o , C h i l e , a tan a l t i t u d e of 555 k i l o me t e r s .A VLF spectrogram, shoirring 2- pro ton and he l iumw h i s t l e r . The lower p a r t of t k igu-re i s t h eac t u a l sp ec t r o g r am o b t a i n ed f ro n a sona-graphs pe ctr um m a l y s e r .d l l u s t r a t e s t h e i de a l i z ed form of th es e whisclers .

The upper p a r t of th e f i,gure

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F i g u r e 5: A Rqrspanll spec t rogran , shcvaing signals frornAlsoL,F t r a n s r f i t t e r s a t 17.5 and 1 8 . 2 Rc/s.

i l l u s t r a t e d i s a band o f l o x e r k y b r i d resonancen o i s e a t abo-dt 5 Kc/s. that hes been ti-lg;ered 3)-t h e ~:rhi.st!.er echo of -:he f r a c t i o n z l - h o p ~ ~ h L s t l . e ra p p e a r in g a t 3.5 seconds.P r t c h a n g le d i s t r i b u t i o n s o b t ai n e d d ur i ng twop a s s e s on day 335 (Dec. 2, 1 9 6 5 ) . I n one spinp e r i o d e a c h p i t c h a ng le i s s2,mpled twice andt h e open ancl c l o s e d c i r c l e s e ac h r e f e r t o ah a l f pe ri d.A re ;?ea t ing sawtooth vo l ta ge (Va ) i s a p p l i e dt o e ac h c y l i n d r i c a l e l e c t r o s t a t i c p ro be an dt h e c u r r e n t t o e ac h c o l i e c t o r I s masured . b ya m u l ti - ra n g e c u r r e n t d e t e c t o r ( I ) . Only oneof t he p robes i s shown he r e ,

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F i , y r e 7 :

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