ANNALS OF GEOPHYSICS, VOL. 45, N. 1, Feb ua y 2002
201
Sho No e
Wo s cases o a one-hop
high equency link
Glo ia Mi ó (1), Beni o A. de la Mo ena (1), Sand o Ma ia Radicella (2)and Miguel He aiz (3)
(1) A mosphe ic Sounding S a ion «El A enosillo»,Na ional Ins i u e o Ae ospace Technology,
Magazón,Huel a,Spain
(2) Ae onomy and Radiop opaga ion Labo a o y,Abdus Salam ICTP,T ies e,I aly
(3) Depa men o Geophysics and Me eo ology,Facul y o Physics,Complu ense Uni e si y,Mad id,Spain
Abs ac
The cha ac e isa ion o a HF channel by means o mon hly elec on densi y p o iles can be complemen ed wi h
a de ailed s udy o adio p opaga ion «wo s cases» on si ua ions wi h ex emes condi ions o adiop opaga ion
o a gi en pe iod. These «wo s cases» co espond o condi ions ha can be iden i ied by means o cumula i e
dis ibu ions o he key pa ame e 0F2. This pape analyses he main pa ame e s o he HF channel: ime delay,
apogee, ele a ion angle and ansmission equency wi h mean and ex eme condi ions. The me hod used o
cha ac e ise he ionosphe ic channel is based on ay- acing echniques.
1. In oduc ion
An HF communica ion link is cha ac e ised
by he Maximum Usable F equency ha is he
limi abo e which he signal will no be e lec ed
by he ionosphe e unde medium condi ions.
Howe e , i is con enien o s udy all possible
condi ions. Fo his eason, an analysis o wo s
cases aimed a ex ending he esul s ob ained by
means o mon hly median condi ions o ex eme
ionosphe ic si ua ions.
The concep o wo s cases was in oduced
in ay acing echniques (Mi ó e al., 2000) o
ex end he channel cha ac e isa ion o ex eme
ionosphe ic si ua ions a om median condi ions
o HF links. Wo s cases selec ion was
pe o med using 0F2 h ough hou ly cumula i e
equency dis ibu ions.
The 2D ay acing echnique used (called
abc ay03), is based on he exp essions in oduced
by C o and Hoogasian (1968) and C o (1969)
and i has been conside ed in p e ious
ionosphe ic s udies (Moo head and Radicella,
1998; Mi ó, 2000). The ou pu s ob ained wi h
his compu ing echnique a e he main adio
p opaga ion pa ame e s: ime delay o he signal
a elling om he ansmi e o he ecei e ,
e lec ion heigh o apogee, ele a ion angle and
ansmission equency.
Mailing add ess: D . Glo ia Mi ó, A mosphe ic Sounding
S a ion «El A enosillo», Na ional Ins i u e o Ae ospace Tech-
nology, 21130 Magazón, Huel a, Spain; e-mail: mi [email p o ec ed]
Key wo ds ionosphe e
−
adio p opaga ion
−
wo s
cases
−
ay- acing
202
Glo ia Mi ó, Beni o A. de la Mo ena, Sand o Ma ia Radicella and Miguel He aiz
A pa icula ionosphe ic condi ion is in oduce
in he ay acing p og am using model o expe-
imen al elec on densi y p o iles.
2. Da a
As p e iously indica ed, he pa ame e 0F2
was used o pe o m he wo s cases selec ion
h ough hou ly cumula i e equency dis i-
bu ions. This s udy conside ed hou ly e ised 0F2
alues om he digisonde DGS256 si ua ed a
El A enosillo A mosphe ic S a ion and he 1993-
1997 pe iod. An a e age o 1826 alues was
a ailable o each 24 h and cu -o equencies
limi ing 1% o hese alues wi h ei he he lowes
o he highes equencies ha e been chosen as
wo s cases condi ions. Fo example, a 00 UT
hou s 1% o cases had 0F2 lowe han 2.4 MHz
and highe han 7.3 MHz. Once he wo s cases
selec ion has been done, he co esponding
elec on densi y p o iles a e in oduced in he ay
acing echnique.
3. Me hodology
A each hou , p o iles belonging o hese
uppe /lowe condi ions a e g ouped o calcula e
a mean uppe /lowe ex eme p o ile. This p o-
Fig. 1. Hou ly mon hly elec on densi y p o iles and he co esponding o uppe and lowe selec ion a El
A enosillo A mosphe ic Sounding S a ion.
203
Wo s cases o a one-hop high equency link
cedu e p o ides h ee mean p o iles pe hou :
uppe ex eme, lowe ex eme and hou ly mean
p o ile o all cases. These mean p o iles we e
ob ained ollowing he me hodology desc ibed
in Huang and Reinisch (1996). Figu e 1 shows
an example o such p o iles.
As has been no ed, he ionosphe ic condi ions
in he e lec ion poin necessa y o cha ac e ise
he HF channel a e in oduced by elec on densi y
p o iles. I is impo an o poin ou ha he
p o iles ob ained a e he wo s case selec ion
belong o one o he link ex emes, El A enosillo
S a ion.
Howe e , he pa icula link be ween El
A enosillo and Eb o Obse a o io is si ua ed a
Fig. 2. Oblique ionog ams ob ained by abc ay03 p og am co esponding o uppe , lowe and mean condi-
ions.
midla i udes. The e o e, communica ions wi h a
ange close o 785 km co espond o one iono-
sphe ic hop wi h E (E mode) o F (Fmode).
Mo eo e , he ionosphe ic condi ions a he
e lec ion poin which is loca ed a ound he mid-
dle poin in his speci ic link, can be app oxima e
o da a om one o he ex emes, ansmi e o
ecei e (Mi ó, 2000).
Using he h ee mean p o iles a each hou
( ig. 1), ionosphe ic condi ions a e in oduced in
he abc ay03 p og am o de i e a each 24 h
he adio p opaga ion pa ame e s: ansmis-
sion
equencies, ele a ion angles, ime delays
and apogees unde ex eme and s anda d
si ua ions.
204
Glo ia Mi ó, Beni o A. de la Mo ena, Sand o Ma ia Radicella and Miguel He aiz
4. Resul s
The dis ibu ion o he g oup pa h P’ (p o-
po ional o ime delay) e sus he ansmission
equency gi es wha is known as an oblique
ionog am. Figu e 2 displays syn he ic oblique
ionog ams ob ained wi h he ay acing echni-
que co esponding o some o he 24 h s udied.
Di e ences be ween he h ee condi ions (uppe
ex eme, lowe ex eme and mean) can be clea ly
seen mainly a F2 heigh s.
F om he HF communica ion sys ems poin
o iew, he main p oblem is o ind ou he ex-
is ence o low 0F2 on low elec on densi y a-
lues. This si ua ion is c i ical because his
phenom-
enon educes he Maximum Usable F equency
and he communica ion equency band becomes
na owe han ha om mean and uppe condi-
ions ( ig. 2). Fo his eason, special a en ion
has been paid o he numbe o cases in which
he signal a i es a he ecei e in spi e o he
na owing o he equency ange o igina ed by
low elec on densi y condi ions. Resul s a e
summa ised in able I. As can be seen, only
dayligh s hou s (8:00 UT - 18:00 UT) p o ide
an accep able pe cen age o si ua ions in which
a link is es ablished unde all condi ions. As
expec ed, mos o hese signals belong o E
modes ha do no appea du ing he es o he
hou s. In gene al, i he daily ansmission is
done wi h a equency be ween 6 and 8 MHz,
he signal will each he ecei e unde ex emes
and mean si ua ions.
This s udy indica es ha he cha ac e isa ion
ob ained using ionosphe ic mean condi ions can
be applied in mos si ua ions. Only some cases
Table I. Numbe o lowe condi ions cases which a i e a he ecei e .
Hou (UT) To al Lowe % E Mode % E Mode F Mode % F Mode
0:00 4 1 25 0 0 1 100
1:00 3 1 33 0 0 1 100
2:00 4 1 25 0 0 1 100
3:00 4 1 25 0 0 1 100
4:00 4 1 25 0 0 1 100
5:00 7 1 14 0 0 1 100
6:00 7 0 0 0000
7:00 16 2 13 1 50 1 50
8:00 23 15 65 11 73 4 27
9:00 24 18 75 13 72 5 28
10:00 26 20 77 17 85 3 15
11:00 28 19 68 17 89 2 11
12:00 30 21 70 16 76 5 24
13:00 28 20 71 17 85 3 15
14:00 27 20 74 16 80 4 20
15:00 27 18 67 15 83 3 17
16:00 28 16 57 11 69 5 31
17:00 27 12 44 5 42 7 58
18:00 24 6 25 2 33 4 67
19:00 19 2 11 0 0 2 100
20:00 15 2 13 0 0 2 100
21:00 11 2 18 0 0 2 100
22:00 6 1 17 0 0 1 100
23:00 6 1 17 0 0 1 100
205
Wo s cases o a one-hop high equency link
du ing nigh hou s can p esen p oblems i he
ansmission equency used is nea he Maxi-mum
Usable F equency because in hese condi ions, he
signal will no be e lec ed by he low ionosphe ic
elec on densi y p esen in i s ay pa h.
5. Conclusions
The main conclusion eached in his pape
can be summa ised as ollows:
– In gene al, he cha ac e isa ion ob ained
by means o mon hly elec on densi y p o iles
(Mi ó, 2000) could be applied e en wi h ex eme
ionosphe ic condi ions. The main p oblem can
appea du ing nigh ime o ansmission
equencies close o he Maximum Usable
F equency.
Acknowledgemen s
The au ho s a e g a e ul o D . Moo head o
Nep une Rada L d., Glouces e U.K., o his
help in unde s anding he ay acing echnique,
abc ay03. This wo k has been possible hanks
o inancial suppo g an ed by he Na ional
Ins i u e o Ae ospace Technology (INTA).
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