Use of raytracing in models to investigate ionospheric channel performance

Use o ay acing in models o in es iga e ionosphe ic channel pe o mance G. Mi o ´ Ama an e * , S.M. Radicella Ae omony and Radiop opaga ion Labo a o y, Abdus Salam ICTP, S ada Cos ie a 11, 34014 T ies e, I aly Abs ac The main pa ame e s ha cha ac e ize an ionosphe ic channel, equency, ele a ion angle, g oup pa h, g ound ange, and apogee ha e been ob ained by means o 2D ay acing p og am called abc ay03. The analysis has conside ed diffe en hou ly ionosphe ic con- di ions o ou quie days (25–28 Ma ch 2000) and fi e geog aphic loca ions dis ibu ed in he wo hemisphe es. Elec on densi y p ofiles define he selec ed ionosphe ic condi ions. Ray acing is un conside ing expe imen al elec on densi y p ofiles om manually scaled measu emen s ob ained wi h ionosondes. The esul ing adio p opaga ion pa ame e s a e compa ed wi h hose ob ained using he IRI and NeQuick models d i en by measu ed F2 peak alues. Keywo ds: Ray acing; Ionosphe e; Elec on densi y p ofiles 1. In oduc ion The 2-dimensional 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 has been con- side ed in p e ious ionosphe ic s udies (Moo head and Radicella, 1998; Mi o ´, 2000; Mi o ´e al., 2002). The ou - pu s ob ained wi h his compu ing echnique a e he main adio p opaga ion pa ame e s o he selec ed equency: ime delay o he signal a elling om he ansmi e o he ecei e ( ela ed o g oup pa h), eflec ion heigh o apogee, g ound ange, and ele a ion angle. A pa icula ionosphe ic condi ion is inse ed in o he ay acing p og am using a model o a measu ed elec on densi y p ofile. The elec on densi y p ofile models used o his analysis a e he In e na ional Re e ence Ionosphe e (IRI) (Bili za, 1990, 2001) and NeQuick (Radicella and Lei inge , 2001; Radicella e al., 2003). The aim o his pape is o illus a e he effec s o he di - e ences be ween hese models and he expe imen al elec- on densi y p ofiles on adio sys em ope a ions. Simila s udies ound in he bibliog aphy show he impo ance o hese effec s. Fo example, he impac o he F egion long- e m end on adio sys ems has been e alua ed by Cannon Paul e al. (2004). This ecen s udy uses an analy - ic ay acing echnique – SMART (No man and Cannon, 1997, 1999) – and elec on densi y p ofiles fi ed o CCIR coefficien s and he esul s show ha a 16 km d op in hmF2 can in oduce g ound ange changes o 100 km wi h la ge alues unde ce ain ci cums ances. The analysis p esen ed in his pape has been di ided in o wo pa s: (1) s udy o he main adio p opaga ion pa ame e s o he ou quie days analyzed a fi e iono- sonde s a ions; (2) s a is ical analysis o he diffe ences in ele a ion angle, apogee and g oup pa h be ween he wo models and expe imen al esul s. 2. Me hodology The expe imen al elec on densi y p ofiles we e p o- duced di ec ly om he manually scaled ionog ams by using he NHPC in e sion echnique (Huang and Reinisch, 1997). The model p ofiles ob ained wi h he NeQuick and * Co esponding au ho . E-mail add ess: mi oama an [email protected] (G. Mi o ´Ama an e). IRI models we e fi ed o oF2 and M3000F2 measu ed cha ac e is ics. The ay acing p og am conside s he dis ance be ween ansmi e and ecei e (D) and he elec on densi y p ofile as inpu s. The elec on densi y p ofile is loca ed a he ci - cui midpoin . Fo his s udy, he ansmi e – ecei e links ha e been selec ed along a me idian. The analyzed dis anc- es a e calcula ed by inc easing he la i ude in one deg ee s eps up o 1500 km. The ansmi e – ecei e dis ance (D) was calcula ed using he exp ession D¼Reacos½sin kTsin kR þcos kTcos kRcosðuTuRÞ;ð1Þ whe e uand ka e longi ude and la i ude o he ansmi e (T) and he ecei e (R) and Re he adius o he Ea h (6370 km). The p og am abc ay03 was un o each dis ance and ionosphe ic condi ion (expe imen al and model elec on densi y p ofiles a he ci cui midpoin ). The main adio p opaga ion pa ame e s ( ime delay, apogee, and g ound ange) we e calcula ed in he equency ange o 1– 20 MHz (0.1 MHz s ep) and ele a ion angle sweep be ween 6 and 60 deg ees (0.1 deg ee s ep). The analysis was un o diffe en hou ly ionosphe ic condi ions (0, 6, 12, and 18 LT) o he ou quie days (25–28 Ma ch 2000) and o fi e geog aphic loca ions dis- ibu ed in he wo hemisphe es (Table 1). The selec ed pe iod co esponds o high sola ac i i y wi h daily sunspo numbe s g ea e han 155. 2.1. S udy o he main adio p opaga ion pa ame e s o he ou quie days analyzed a fi e ionosonde s a ions The fi s s udy ca ied ou using he ay acing esul s was he compa ison be ween he diffe en analyzed days. G ound ange, ime delay (o he equi alen g oup pa h), and apogee o each day (85–88 days o yea 2000) we e plo ed. The examples shown in Fig. 1 co espond o Mill- s one Hill and Ascension Island a a ansmission equen- cy o 12 MHz and 12:00 LT. The le panel shows he expe imen al elec on densi y p ofiles used as ionosphe ic condi ions a he midpoin . I can be seen in he case o Mills one Hill whe e he p ofiles ha e some a iabili y, he g oup pa h and ange show he bigges diffe ences in he egion be ween he E and F1 eflec ions. Howe e , he e a e no significan diffe - ences a Ascension Island. Fo he es o he ionosonde s a ions, he esul s show ha Ramey has a simila beha - io o he o he selec ed No he n Hemisphe e s a ion, Mills one Hill, and he esul s ob ained a Jicama ca and G ahams own, in he sou he n Hemisphe e, a e close o hose ound a Ascension Island. 2.2. S a is ical analysis o he diffe ences in ele a ion angle, apogee, and g oup pa h be ween model and expe imen al esul s A s a is ical analysis has been done compa ing he wo models (IRI and NeQuick) and he expe imen al esul s in ele a ion angle, apogee and g oup pa h. Table 2 shows he s a is ical esul s a Ramey o 00, 06, 12, and 18 LT co - esponding o NeQuick (NQ) and IRI. The numbe o cases (numbe ), a e age o absolu e diffe ences (A e age), s anda d de ia ion (S de ), median o absolu e diffe ences (Median), cases wi h posi i e diffe ences (>0), and cases wi h nega i e diffe ences (<0) we e calcula ed o ele a ion angle, apogee, and g oup pa h. The diffe ences shown o he g oup pa h a e ela i e (di ided by expe imen al al- ues) because o he wide ange conside ed. Fo he case o Ramey, he diffe ences show ha NQ o e es ima es he h ee pa ame e s o 06, 12, and 18 LT and IRI unde - es ima es hem o 00 and 12 LT. IRI is wo se han NQ o 00 LT wi h diffe ences a ound 4 deg ees in ele a ion angle, 63 km in apogee, and 4% in g oup pa h. NQ is wo se han IRI o 06, 12, and 18 LT wi h diffe ences a ound 4–5 deg ees in ele a ion angle, 26–32 km in apo- gee, and 4–5% in g oup pa h. The shadow panels (Table 2–6)inA e age ow co espond o he compa ison be ween he IRI and NeQuick models ( he la ges alue) and he shadow panels in posi i e (>0) and nega i e (<0) diffe ences ow show he o e es ima ion o unde es i- ma ion o each model. Fo he case o Mills one Hill (Table 3), he diffe ences show ha NQ o e es ima es he h ee pa ame e s and IRI unde es ima es hem o 00, 06, and 18 LT. NQ is wo se han IRI wi h diffe ences a ound 3–6 deg ees in ele a ion angle, 25–38 km in apogee, and 3–5% in g oup pa h. A Jicama ca (Table 4), he diffe ences show ha NQ o e es ima es he h ee pa ame e s and IRI unde es ima es hem o 00 and 06. IRI is wo se han NQ o 06 and 12 LT wi h diffe ences a ound 5–10 deg ees in ele a ion angle, 46– 80 km in apogee and 5–10% in g oup pa h. NQ is wo se han IRI o 00 and 18 LT wi h diffe ences a ound 3–6 deg ees in ele a ion angle, 20–51 km in apogee, and 2–6% in g oup pa h. The diffe ences ob ained o G ahams own (Table 5) show ha NQ o e es ima es he h ee pa ame e s o 06, 12, and 18 LT and IRI unde es ima es he h ee pa ame e s o 00, 06, and 18 LT. IRI is wo se han NQ o 00 LT wi h diffe ences a ound 5 deg ees in ele a- ion angle, 47 km in apogee, and 5% in g oup pa h. NQ Table 1 Geog aphic coo dina es, geomagne ic la i udes and modified dip la i udes o he selec ed ionosonde s a ions S a ion La . Long. La . Geomag. Modip Ascension Is 7.9 345.6 1.40 23.24 G ahams own 33.3 26.5 33.80 50.97 Jicama ca 12.0 283.2 0.68 0.65 Mills one H. 42.6 288.5 53.99 55.90 Ramey 18.5 292.9 29.89 42.48 is wo se han IRI o 12 LT wi h diffe ences a ound 6 deg ees in ele a ion angle, 41 km in apogee, and 5% in g oup pa h. Fo he case o Ascension Island (Table 6), he diffe - ences show ha NQ o e es ima es he ele a ion angle and g oup pa h o 06 and 18 LT and IRI unde es ima es he h ee pa ame e s. IRI is wo se han NQ o 12 LT wi h diffe ences a ound 4 deg ees in ele a ion angle, 25 km in apogee and 4% in g oup pa h. NQ is wo se han IRI o 06 and 18 LT wi h diffe ences a ound 3–5 deg ees in ele a ion angle, 28–30 km in apogee, and 3–6% in g oup pa h. Fig. 1. Range, g oup pa h, and apogee e sus ele a ion angle o each selec ed day ( igh panel) and he co esponding expe imen al elec on densi y p ofiles (le panel) o Mills one Hill and Ascension Island. Table 2 S a is ical esul s a Ramey o ele a ion angle, apogee and g oup pa h diffe ences co esponding o NeQuick (NQ) and IRI Table 3 S a is ical esul s a Mills one Hill o ele a ion angle, apogee and g oup pa h diffe ences co esponding o NeQuick (NQ) and IRI Table 4 S a is ical esul s a Jicama ca o ele a ion angle, apogee and g oup pa h diffe ences co esponding o NeQuick (NQ) and IRI Table 5 S a is ical esul s a G ahams own o ele a ion angle, apogee and g oup pa h diffe ences co esponding o NeQuick (NQ) and IRI 3. Conclusions The diffe ences in g oup pa h and ange ound in he compa ison be ween he ou quie days when eflec ion occu s in he F1 egion confi m p e ious esul s by he au ho s (Mi o e al., 2005). The F1 egion is c i ical o de e mine he main adio p opaga ion pa ame e s using ay acing h ough ionog am-de i ed elec on densi y p ofiles. In summa y, compa ing he ay acing h ough mea- su ed and modeled p ofiles leads o he ollowing conclu- sions (Table 7): (1) NQ o e es ima es he h ee pa ame e s, (2) IRI unde es ima es he h ee pa ame e s, and (3) NQ and IRI pe o mances o he h ee pa ame e s a e simila wi h diffe ences a ound 4 deg ees in ele a ion angle, 33 km in apogee, and 4% in g oup pa h. Acknowledgemen s The au ho s a e g a e ul o D . Moo head o Nep une Rada L d., Glousces e , U.K., o his help in unde s and- ing he ay- acing echnique, o he Cen e o A mosphe - ic Resea ch a Uni e si y o Massachuse s Lowell, USA, o da a and so wa e suppo and o he IRI and NeQuick g oups. Re e ences Bili za, D. 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