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IONOSPHERIC REFLECT IONS AT ME DIUM FREQUENC I ES
A thesis present e d in par t ial fulfilment of the requirement s f or the degree of
Doc t or o f PhiL osophy in Physi c s at Massey University
RALPH ERNEST H ENDTLASS 1973
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Abst rac t
This thesis examines a possible explanat i on for s ome of the t ime variat ions of t he ni ght-t ime sky wave at distances between 80 and 160 km from l ow-medium-freque n c y transmit ters . I n the postulat e d model t hi s variat i on i s e xplained in t erms of i nt er ference between t h e s i gnal s trave l ling along many paths f r o m the transm i t t er t o t he r e c ei ver via a lower i onosphere disturbed by the passage of a duc t e d ac oust i c wave . A r i gor ous s olut i on t o this mod e l is not p ossible, but by using reasonable approx
i mati ons a solut ion i s obtained whi ch is suitable f or analysing experimental rec ords o f sky wave variati ons.
The s e experi mental r e c ords were obtained by using an i n t e r ferometer t e c hnique t o separat e the sky wave from t h e ground wave. Some extremely good agree ment was found between the ory and e xperiment showing t hat thi s c ould be a u s e ful t ec hnique for st udying duc t e d ac oustic waves . C ertainly s ome , at least , o f the variat i ons c ommonly observed in the night -t ime sky wave si gnal are c aused in this way .
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ACKNO'NT,EDG �MENTS
I am deeply grat e ful t o Mr. E. R . H odgson who
not only sugge s t e d thi s pr o j e c t , but als o gave free ly o f h i s t ime , �dvic e and enc ouragement. A ls o I w ould like t o thank Profe s s or N . F. Barber o f Vic t oria Uni ver s i t y o f We llingt on, for h i s valuable assistan c e.
I a l s o w i sh t o express my appr e c i at i on t o all
the t e chnical staff under Mr. D.M. Williams , and
espec ially Mr . L.G . Cran fi e l d , for the use o f their skil ls and t ime. The Universi t y Grant s C ommi t t e e als o assist e d with grant 70/143.
Finally I t hank Mrs . D. G . S t i c hbury for her pati en c e and ability t o turn my i lle gible wri t i ng int o orderly t yp e s cript.
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Index
Front ispi e c e Abstrac t
Ac knowledgement s I ndex
List o f figures, SECT I ON ONE :
1-1 1-2
1-2-1 1-2-2 1-2-3 1-3 1-4
S E CT I ON TWO:
2-1
2-2
2-2-1 2-2-2
2-2-3 2-2-4
I NTRODUCTION TO THIS WORK AN D A REVIEW OF EARLI�R NORK
This e xperiment , origin and out line .
A bri e f survey o f experimental t echniques for obs erving t he i onosphere betv1een 50 and 100 km . H.F . vert i c al i n c i denc e ground based s ounding t e c hni qu e s.
H . F . oblique incidenc e gr ound base d s ounding t e c hniques
L . F . ground based s oundin g t e chniques
The l ower night -time i onosphere at middl e latitude s .
A physical proc ess and a postula t e d matheroat i c a l model .
HATHEMATICAL SOLUTION OF
THF:
IDEALIZ.�D MODEL.
The de formation o f the i oni zation b oundary by t he passage of an ac oustic wave.
Fac t ors a f f e c ting t he r e c eived sky wave due t o t he perturbe d boundary.
Int erf e re nc e t erms .
The val i d i t y o f t he appr oxima ti on u s e d i n t he above s e c t i on.
The re fle c tion c oe f fi c i ent . The r e f l e c ting area .
( v)
ii iii
"iv
v,vi,vii viii , ix
1 1
3 4 5 6 7 12
16
16
22 22
27
30 32
2 -3 Fac tors a f f e c t i ng the rec eived sky wave due to the experiment al
arrangement . 37
2-4 The range over which r e c eivable group
re flec t ions c an o c c ur . 39
2 - 5 The ext ent ion to a cont inuous c urve o f exp e c t e d sky wave amplit ude versus
group po sitio n . 4 0
2-6 The extention o f the proc eeding work in thi9 s e ct io n to an arbitary length
acoust i c group . 42
SECTION THREE : A DESCRIPT I ON OF EXPERIM�NTAL M�THOD . 43
3-1 The aerial syst e m . 43
3 -2 R e j e c t io n of the ground wave . 4 5
3 -3 R e j e c t ion o f the sky wave . 4 5
3-4 3-5
Limi t a t ions o f t he automa t i c sky wave
re j ec t ion c ircuitary . 49
An out lin e o f pract ical c ircuit details . 50
3-6 Experimental rout ine . 52
SECTION FOUR: RESULTS, CONCLUSIONS AND SUGGEST I ONS . 54
4 - 1 Result s o f early work . 54
4 -2 The d e t e rminat ion o f paramet e rs from
records made using a high c hart spee d . 58 4 -3 -1 Reco gni t ion o f s i gni f i c ant event s from 4 -3 -2
4-4 4-5
A PPENDIX ON E:
high spe e d records . 61
Result s obtained from hi gh spe e d records .
Co mparison with other experiment s . Conc lusion and sugges t ions for fut ure re sear ch .
TH"I� PR� DICT I ON OF THE S KY NAVE SIGNAL TO BE EXPECTED FROH i\N
64 69
70
ACOUSTIC 'VAVB GROUP OF i\RBI TARY LENGTH· 74 ( vi )
APPEN DIX TtVO : APPENDIX THREE :
RE FERENCES :
S I MPLIFI E D C IRCUIT DIAGRAMS F LO� CHA�T F OR CALCULATING THE EXPECTED S KY WAVE AMPLITUDE US ING THE T HEORY OF S :!;CTION T�VO.
( vii )
76
8 1 82
List o f Figure s
Figure i : Experim ent al, mid-latit ude, night -time
e le c t ro n density distr ibutions . 10 F i gure i i Mid-lat i t ude , night -tim e e l e ctron density
distribution as a fun c t ion of solar
zenith angle . 1 0
Figure iii :· The geom e try o f the idealized mode l . 23
Fi gure iv : 28
F i gure v : 28
Fi gure vi : 28
F i gure vii : The rat io o f the specular r efle c t ion area to any one o f t he non-specular re fle c t io n areas plot t e d as functions of the dis tanc e of the wave group from the t ransm i t t er and the total aerial e xt e nt .
Fi gure viii The value of B r e quired for s i gnals r e f l e c t e d from posit ion x to arri ve at the r e c eiver plott e d as a func tion o f x, and the pos sible range o f
36
r e fl e c t ion point s as a func t ion o f L/A. 39 Figure ix A block diagram o f the syst em u s e d in
this experiment . 44
Figure x The po lar r esponse o f the aerial s ys t em
when set up for ground wave reje c t io n. 47 Fi gure xi The polar response o f t he aerial sys t em
when s e t to re j ec t s i gnals with an
angle o f arrival o f 60°. 47
Figure xii The addit ions r e quire d to t he syst em shown in figure i x to enable that
sys t em to hunt for the sky wave . 48 Figure xiii A typical night's r e cord.- 55 Figure xiv : Recor ds showing exampl e s o f false
i ndi c a t io n of angle o f arri val and examples of t he mo notonic varia t ion
in the nngle o f arrival . 57
Figure xv : A plot o f L vs t::.x •
Figure xvi : A s e t o f theo r e t i c al curves o f sky wave amplitude vs gr oup position.
Figure xvi A h i s to gram of t he o c c urrence o f d e t e c t e d values o f L in a total popula t ion o f 82 .
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59 62
64
Figure xviii An example of the good agreement between theory and experiment obtained by using successive
approximation to get a best fit. 65 Figure xix The angle of arrival of an observed
sky wave compared with the theoretical
values obtained from a computed curve. 66 Figure xx Theoretical sky wave amplitude vs position
curves for both 570kHz and 6 60 kHz .. 68 Figure xxi Simplified circuit diagrams. 79 Simplified circuit diagrams, continued. 80
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