IONOSPHERIC ABSORPTION OF HF RADIO WAVE IN VERTICAL PROPAGATION *

Iranian Journal of Scinc & Tchnology, Transaction A, Vol. 3, No. A4 Printd in Th Islamic Rpublic of Iran, 7 Shira Univrsity IONOSPHERIC ABSORPTION OF HF RADIO WAVE IN VERTICAL PROPAGATION * I. UNAL **, O. OZCAN AND. CANYILAZ Dpartmnt of Scinc Taching, Faculty of Education, Inonu Univ., 448 alatya, Turky Dpartmnt of Physics, Faculty of Scinc and Arts, Firat Univ., 369 Elaig, Turky Emails: iunal@inonu.du.tr, oocan@firat.du.tr, mcanyilma@firat.du.tr Abstract In this study, absorption of high frquncy radio wavs in th ionosphric plasma hav bn invstigatd. Th wav quation was obtaind in trms of ionosphric paramtrs. Th numrical valus of th absorption hav bn calculatd for 4 H, 4.5 H and 5 H wavs. Th ncssary paramtrs for calculation hav bn obtaind using an Intrnational Rfrnc Ionosphr (IRI) odl. Th altitudinal, diurnal, sasonal and th variations of absorption with frquncy hav bn xamind. Th calculations show that th highst absorption occurs in th D-rgion. Th absorption is highr in summr than in othr sasons and is maximum at daylight. In addition, absorption dcrass with th incras of frquncy. Kywords Ionosphr, HF wav, absorption. INTRODUCTION Ionosphr is vry important for radio communication. 3-3 H frquncis ar calld high frquncis (HF) and ths frquncis ar th biggst frquncis that ar rflctd from th ionosphr. Th most usful way to prform systmatic masurmnts in th ionosphr is to us HF wavs. Th thory of HF radio wavs in th ionosphric plasma startd with th formulations of th Applton-Lassn disprsion rlation in th lat 9s and bcam mor important in th scond half of th th cntury []. Th us of HF radio spctrum continus to grow for both civil and military purposs, dspit th widsprad introduction of satllit-basd communication systms. In particular, th HF band is vry important whn th communication systm is dstroyd by an unusual vnt, such as a major arthquak. For this rason, it is important to invstigat and undrstand th HF propagation charactristic in th ionosphr. Radio wavs show diffrnt bhaviors dpnding on thir frquncis, oscillation frquncy of th lctron and th rfractiv indx of th ionosphric plasma. Du to ths bhaviors th wav rflcts, rfracts or is absorbd by th ionosphr. Radio wavs in th ionosphr ar subjct to som attnuation bcaus th motions of th lctrons and ions ar dampd through collisions with othr particls [-7]. Th purpos of this study is to invstigat th absorption of th HF lctromagntic wav, which propagats vrtical in th ionosphr as a function of hight and ionosphric paramtrs. Th rfractiv indx of th ionosphr will b obtaind by solving th conductivity quation and disprsion rlation. Th variations in th absorption will b invstigatd from th imaginary part of th rfractiv indx.. ABSORPTION OF THE RADIO WAVES IN THE IONOSPHERIC PLASA A radio wav is givn by, Rcivd by th ditor Sptmbr 6, 5 and in final rvisd form ay, 8 Corrsponding author

44 I. Unal / t al. E = E i( k r t ) () whr is th angular frquncy and k wav vctor and can b writtn as follows: k = n () c Whr n is th rfractiv indx and c is th spd of light in th fr spac. Th rfractiv indx of th ionosphric plasma is givn by [], n = μ + iχ (3) μ is th ral part of th rfractiv indx and affcts th phas vlocity. χ is th complx part and dtrmins th attnuation of th wav [8]. Using Eq. () and Eq. (3), Eq. () is obtaind as, i μr t χr c E = E c (4) Th χ trm is calld th κ absorption cofficint and this xprssion shows that th radio wav is c χr attnuatd by th trm of c and movs by th vlocity of c μ. For th calculation of th absorption, th rfractiv indx of th ionosphric plasma must b known... Rfractiv indx for ionosphric plasma At high frquncy, th ffct of ions can b nglctd [9]. If w tak th ambint magntic fild B in th vrtical dirction, th conductivity tnsor can b obtaind as follows [], σ σ = σ σ σ σ (5) in which longitudinal ( σ ), Pdrsn ( σ ) and Hall ( ) p ( ν i) ( ν i) σ conductivitis ar, σ ε p =, ( ν i) ε εpc σ = and σ = rspctivly. ε [ c + ] [ c + ( ν i) ] is th dilctric cofficint of th fr B spac, = N c is lctron gyro-frquncy, and p = is th plasma oscillation frquncy m mε whr is lctron charg, m is lctron mass and N is lctron dnsity. 3 ν = νi n in which T 6 3 6 / νi = N 59 + 4.8log x T and ν n = 5.4 NnT ar N th lctron-ion and th lctron-nutral collision frquncis, rspctivly []. If w solv th axwll curl Equations B E = (6) t Iranian Journal of Scinc & Tchnology, Trans. A, Volum 3, Numbr A4 Autumn 7

Ionosphric absorption of HF radio wav in vrtical propagation 45 by using th currnt dnsity [ J] [ σ] [ E] E B = μj + με (7) t =, th following Equation can b obtaind. E - n( n E) iσ n = I + E (8) ε in which I is unit matrix and σ is givn in Eq. (5). From Eq. (8) w can obtain, xx yx x xy yy y x E x y E y = E (9) Whr xx x = = yy y = n = iσ, ε x = y = xy = yx iσ =, ε iσ =, ε () Dt()= is th basic disprsion rlation. Th rfractiv indx n can b obtaind in trms of plasma paramtrs. From this dtrminant, th following Equation can b obtaind. Eq. () givs th following two roots of n. Whr Autumn 7 iσ iσ σ iσ σ n n + = () ε ε ε ε ε ( )( ) ( ) c c ν c + 4 ν ( )( ) ( ) + c c ν c + 4 ν n = A + ib () n = C + id (3) p A = + p, ν + ν + ν B = c c c + 4 ν ( ) ( ) ( ) p C = + p, ν + + ν + ν D = c c c + 4 ν ( ) ( ) ( ) On of thm is th lft-hand polarid wav (Eq. ()) and th othr is th right-hand polarid wav (Eq. (3))... Wav absorbing xprssion Th Eq. () and Eq. (3) show that th rfractiv indx n = ( μ + iχ) = lctron collisions ar allowd. Thn, th imaginary part (χ) of n is, Iranian Journal of Scinc & Tchnology, Trans. A, Volum 3, Numbr A4 A+iB bcoms complx if

46 I. Unal / t al. χ, ( A + B ) ± A = (4) If w us this xprssion of χ in Eq. (4), th wav Equation for th vrtical propagation is obtaind as follows, E = E i μ t c ± c ( A B ) + A (5) 3. NUERICAL ANALYSIS AND DISCUSSION According to th Eq. (5) total absorption for th vrtical propagation can b dfind as: Total rfl. ( A B ) + A ± ( A + B ) Absorption = d + d (6) ± c rfl. c A in which (8 km) is takn for th bginning of th ionosphr, and rfl. (n=) is th rflction hight (Fig. ). Fig.. Schmatic illustration of th vrtical HF radio wavs propagating through ionosphric plasma Th calculations of this Equation hav bn don for + sign at gographic coordinats of (38 O 4' E v 39 O 4' N). In addition, th calculations hav bn don for quit-solar activity days (th sunspot numbr is about ). Th amplitud of th wav is takn as V/m at. Calculations hav bn don for vry km from to rfl. W assumd that th wav rflctd at hight whr c p. Th usd ionosphric plasma paramtrs hav bn calculatd by using Intrnational Rfrnc Ionosphr (IRI) with th Intrnational Radio Consultativ Committ (CCIR) odl. Th calculations hav bn don for Jun, 3 Sptmbr and Dcmbr. Iranian Journal of Scinc & Tchnology, Trans. A, Volum 3, Numbr A4 Autumn 7

Ionosphric absorption of HF radio wav in vrtical propagation 47 Th variations of th amplitud with hight for 5 H is shown in Fig.. As is sn from th Figur, th maximum absorption occurs in th ionosphric D and E-rgion. In th F v F rgion wav absorption is smallr than th D and E-rgion. This is an accptd rsult, as th nutral dnsity is biggr than th lctron dnsity at low altituds during daytim (Tabl ). So, th total absorption bcoms maximum as lctron collision frquncy incrass [-4]. Amplitud (V/m)..9.7.5.3 7 9 3 5 7 9 9 7 5 3 9.6.5.4.3. 7 Amplitud (V/m) Altitud (km) Altitud (km) (a) (b) Fig.. Th variation of th amplitud attnuation with hight for 5 H. ( Dcmbr at. LT, a: Up to rflction point, b: Thn th rflction) h (km) Tabl. Th variations of th nutral and lctron dnsitis, lctron collision frquncy and absorption cofficint with hight ( Dcmbr at. LT) N n (par./m 3 ) N (l./m 3 ) ν (s - ) κ (m - ) 8 5.8E+ 3.8E+8 5.9E+6 6.66E-6 85.77E+ 7.66E+8.77E+6 4.66E-6 9 7.5E+9 8.3E+9 7.6E+5.E-5 95.88E+9 3.49E+.88E+5 3.6E-5.6E+9 6.57E+.9E+5 3.5E-5 5 4.78E+8 9.48E+ 4.85E+4.83E-5.E+8 9.83E+.9E+4 8.59E-6 5.E+8 9.8E+.9E+4 4.E-6 5.46E+7 8.88E+ 6.E+3.3E-6 5 3.9E+7 9.66E+ 4.5E+3.56E-6 3.3E+7.E+.86E+3.6E-6 35.37E+7.3E+.3E+3 8.89E-7 4 9.8E+6.6E+.66E+3 7.6E-7 45 7.3E+6.9E+.34E+3 5.98E-7 5 5.6E+6.3E+.E+3 5.5E-7 55 4.44E+6.7E+ 9.34E+ 4.56E-7 6 3.58E+6.3E+ 8.5E+ 4.6E-7 65.93E+6.3E+ 7.7E+ 3.95E-7 7.44E+6.57E+ 6.54E+ 4.65E-7 75.5E+6.99E+ 6.8E+ 6.3E-7 8.74E+6.44E+ 6.9E+ 8.57E-7 85.49E+6.87E+ 5.9E+.8E-6 9.8E+6 3.7E+ 5.73E+.7E-6 95.E+6 3.6E+ 5.53E+.96E-6 9.69E+5 3.9E+ 5.3E+ --- Th diurnal and sasonal variations of th amplitud for thr diffrnt frquncis (4 H, 4.5 H, 5 H) ar givn in Fig. 3. Somtims ths frquncis pass through th ionosphr. As sn in th Figurs, th 5 H wav dos not rflct at night bcaus th critical frquncy at h m F (f F) is Autumn 7 Iranian Journal of Scinc & Tchnology, Trans. A, Volum 3, Numbr A4

48 I. Unal / t al. approximatly 5 H. Th total absorption has bn dcrasing with th frquncy incras, much gratr in summr than wintr. Similar rsults hav bn obtaind by Singr t al. [5]. Th diurnal variation of total absorption is rlatd to th variation of th lctron dnsity which is givn in Fig. 4. As is sn, for Dcmbr, lctron dnsity is lss than Jun and 3 Sptmbr. Howvr, th wav amplitud at Dcmbr is highr than th othr sasons. So, whn th lctron dnsity is at maximum, th total absorption has bn incrasing. Incrmnts in th absorption during th daytim is also rlatd to th incras of th lctron tmpratur [6]. Howvr, according to th IRI odl, th sasonal lctron tmpratur variations ar vry small, so th sasonal variations of absorption mainly dpnd on th lctron dnsity variations. Ths rsults ar abl to guid usrs for xprimntal studis, spcially ionosphr propping tchnology such as ionosonda HF frquncy..8 (a) Amplitud (V/m).6.4. 4 H 4.5 H 5 H 6 8 4 6 8 4 Local Tim (hour) Amplitud (V/m).8.6.4. 4 H 4.5 H 5 H (b) 6 7 8 9 3 4 5 6 7 8 9 Local Tim (hour).5 Amplitud (V/m).4.3. 4 H 4.5 H 5 H (c). 8 9 3 4 5 6 7 Local Tim (hour) Fig. 3. Th diurnal variations of th total absorption during th wav path (a: Jun, b: 3 Sptmbr, c: Dcmbr) Iranian Journal of Scinc & Tchnology, Trans. A, Volum 3, Numbr A4 Autumn 7

Ionosphric absorption of HF radio wav in vrtical propagation 49 Elctron Dnsity (l/m 3 ) 5.E+ 4.5E+ 4.E+ 3.5E+ 3.E+.5E+.E+.5E+.E+ 5.E+ Jun 3 Sptmbr Dcmbr 4 6 8 4 6 8 4 Local Tim (hour) Fig. 4. Th diurnal and sasonal variations of th lctron dnsity at h m F REFERENCES. Suchy, K. (). Thory of high-frquncy (HF) radio wavs in th scond half of th th cntury. J. of Atmos. and Solar-Trr. Phys. 6, 683-687.. Ratcliff, J. A. (959). Th magnto-ionic thory and its applications to th ionosphr. Cambridg Univrsity Prss. 3. Buddn, K. G. (985). Th propagation of radio wavs. Cambridg Univrsity Prss. 4. Oyinloy, J. O. (988). Equatorial HF radio wav absorption masurmnts and th IRI. J. of Atmos. and Trr. Phys. 5, 59-5. 5. Lastovicka, J., Boska, J. & Bursova, D. (993). Digital masurmnts of LF radio wav absorption in th lowr ionosphr and infrrd gravity wav activity. Annals Gophysica., 937-946. 6. Blova, E. G., Pashin, A. B. & Lyatsky, W. B. (995). Passag of a powrful HF radio wav through th lowr ionosphr as a function of initial lctron dnsity profils. J. of Atmos. and Trr. Phys. 37, 65-7. 7. ishin, E. V. & Atamaniuk, B. (995). Radio wav turbulnt absorption du to lctron bam injction in th ionosphr. J. of Atmos. and Trr. Phys. 57, 93-99. 8. organ, A. D. (969). agnto-ionic ffcts in polarisation and absorption. AGARD Confrnc Procdings (3-5). England: Tchnivision Srvics Slough. 9. İnan, U. S. & İnan, A. S. (). Elctromagntic wavs. USA: Prntic Hall Inc.. Aydoğdu,. & Öcan, O. (996). Effct of magntic dclination on rfractiv indx and wav polariation cofficints of lctromagntic wavs in mid-latitud ionosphr. Indian J. of Radio & Spac Phys. 5, 63-7.. Rishbth, H. & Garriott, O. K. (969). Introduction to ionosphric physics. Acadmic Prss.. Fjr, J. A. (955). Th intraction of pulsd radio wavs in th ionosphr. J. of Atmos. and Trr. Phys. 7, 3-33. 3. Kopka, H. & öllr, H. G. (969). Calculation of th fild strngth of a radio transmission for givn lctron dnsity and collision frquncy profils. AGARD Confrnc Procdings (9-8). England: Tchnivision Srvics Slough. 4. Frguson, B. G. & cnamara, L. F. (986). Calculation of HF absorption using th Intrnational Rfrnc Ionosphr. J. of Atmos. and Trr. Phys. 48(), 4-49. 5. Singr, W., Taubnhim, J. & Brmr, J. (98). A tst of IRI lowr ionosphr modls by comparison with radio propagation data. J. of Atmos. and Trr. Phys. 4, 4-48. 6. Nishino,., Yamagishi, H., Stauning, P., Rosnbrg, T. J. & Holtt, J. A. (997). Location, spatial scal and motion of radio wav absorption in th cusp-latitud ionosphr obsrvd by imaging riomtrs. J. of Atmos. and Solar-Trr. Phys. 59(8), 93-94. Autumn 7 Iranian Journal of Scinc & Tchnology, Trans. A, Volum 3, Numbr A4