Study of Average Hourly Variations of Radio Refractivity Variations across Some Selected Cities in Nigeria

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1 IOSR Journl of Applied Physics (IOSR-JAP) e-issn: Volume 7, Issue 6 Ver. I (Nov. - Dec. 15), PP Study of Averge Hourly Vritions of Rdio Refrctivity Vritions cross Some Selected Cities in Nigeri Bw Mus 1,2, Dr. Ayntunji B.G 1, Dr. Mi-Unguw H. 1, Dr. Gldnchi G.S.M. 2, nd Shmsuddeen Idris Mu zu 3 1 (Ntionl Spce Reserch nd Development Agency, Auj, Nigeri) 2 (Deprtment of physics, Byero University, Kno, Nigeri) 3 (Deprtment of physics Shrd University Knowledge prk III, greter Noid) Astrct: The results of the diurnl vrition of refrctivity sed on mesurement of tmospheric pressure, temperture nd reltive humidity mde cross some selected loctions within Nigeri, Yol (9 0 11' N, 12 0 ' E), Anyig (7 0 45' N, ' E), Lgos (6 0 27' N, ' E), nd Port-Hrcourt (4 0 48'N, 7 0 E), is presented in this study. The study utilized three yers of meteorologicl dt mesured from Jnury 10 to Decemer 13 using Vntge Pro 2 utomtic wether sttion instlled t ech loction. The verge hourly vritions of refrctivity in the dry seson is lrgely s result of the vritions of the wet component (humidity) while the verge dily vritions of surfce rdio refrctivity in the riny seson is s result of oth the vritions of the dry (pressure) nd wet (humidity) component of surfce rdio refrctivity. It lso oserved tht the vlues of surfce rdio refrctivity showed sesonl vritions with high vlue during riny seson nd low vlues during dry seson with n increse in the vlue of surfce rdio refrctivity from minimum vlue of out 242N-units t Anyig sttion to mximum vlue of out 384-N units t Lgos sttion. The diurnl vrition of refrctivity of the troposphere is function of locl meteorology s oserved from results otined from the study. Keywords: Refrctivity, Temperture, Atmospheric pressure, Reltive Humidity I. Introduction A rdio wves propgting through the erth tmosphere will experience pth ending due to inhomogeneous sptil distriution of the refrctive index of ir which cuses dverse effects such s multipth fding nd interference. These effect significntly impir rdio communiction, ero-spce, environmentl monitoring, disster forecsting e.t.c. Chnges of temperture, pressure nd humidity s well s clouds nd rin, influence the wy in which rdio wves propgte from one point to nother in the troposphere. This region exerts considerle influence on rdio wves t frequencies ove MHz, lthough this effect ecme significnt only t frequencies greter thn MHz especilly in the lower tmosphere (Hll, 1979.). The effect of meteorologicl vrile of pressure, temperture, nd reltive humidity on rdio wve propgtion t UHF nd microwves frequencies re nlyzed from the study rdio refrctive index derived from these three prmeters (Ben nd Dutton, 1966). Since these vriles vry considerly dily nd sesonlly especilly In the tropics, quntittive knowledge of refrctivity vritions is required in order to e le to design relile nd efficient rdio communiction (terrestril nd stellite) system. Although in rdio propgtion study, the troposphere is considered s dielectric medium. The vritions of the refrctive index of the troposphere re smll ut nonetheless ply n importnt role in rdio wve propgtion. The rdio refrctive index is defined s the rtio of the speed of propgtion of rdio energy in vcuum to the speed in specified medium (Ben nd Dutton, 1966; Segl, 1985). Due to the minute difference etween the vlue of refrctive index in the troposphere (out ) nd tht of free spce (n = 1.0) it is more convenient to refer vritions in refrctive index in terms of prmeter clled refrctivity N (Thyer, 1974), which is defined s the mesure of devition of refrctive index, n of ir from unity which is scled-up in prts per million to otin more menle figures. Thus, N is dimensionless quntity defined s mesured in N units (Hughes, 1998). Considering the importnce of rdio communiction to this genertion nd the fct tht there is lck or deth of ccurte dt of meteorologicl prmeters more especilly in tropicl region, this necessitte the cll y Interntionl Telecommuniction Union for meteorologicl dt nd mny west Africn reserchers hs contriuted to the development of this field, mong the contriutors to this field re; (Aytunji, et l. 11), (Okoro nd Ago,12), (Adediji, et l. 13), (Flodun nd Ajewle, 05), (Kolwole nd Owonui, 1982), (Kissssou, et l. 13), (Ali, et l. 11), (Adeyemi nd Kolwle, 1992), (Hughes, 1993), (Igwe nd Adimul, 09), (Owoli, et l. 19), (Kolwole, 1980), (Adediji nd Ajewle, 10). DOI: 10.97/ Pge

2 Study of Averge Hourly Vritions of Rdio Refrctivity Vritions cross Some Selected Cities This study presents the results of verge dily nd sesonl vritions of surfce rdio refrctivity derived from the computtion of tmospheric pressure, temperture nd reltive humidity using recommendtion ITU-R 453 (ITU, 12). II. Study Are Nigeri lies etween ltitude 4 0 N nd 14 0 N nd longitude 2 0 E nd 15 0 E respectively with totl re of 923,768 squre kilometers. The countryis locted etween the Equtor nd the Tropic of Cncer. Theltitude of Nigeriflls within the tropicl zone ut the climtic conditions re not entirely tropicl in nture. The climtic condition vries in most prts of the country, in the north the climtic condition is rid nd to the south there is n equtoril type of climte. The wether condition cn e generlly chrcterized into wet seson, from April to Octoer; dry seson, from Novemer to Mrch in the north nd wet seson, from Mrch to Octoer; dry seson, from Novemer to Ferury in the south. III. Relevnt Theory Electromgnetic wves propgting in the troposphere re refrcted nd scttered y vritions in the rdio refrctive index n. Recll tht the electromgnetic field of plne wve propgting in medium of constnt refrctive index, n, hs spce, r, nd time, t, vrition given y: E(r, t) = E 0 exp[i(nk 0. r ωt)] 1 Where ω = 2π frequency nd k0 is vector norml to the wve front with mgnitude equl to the free spce wve numer (= 2π/wvelength). In the troposphere, the refrctive index is not constnt. At microwve frequencies, however, it vries slowly on the scle of wvelength. In this cse it is still possile to write: E(r,t) E 0 exp[i(n(r)k 0. r ωt)] 2 Although the mgnitude of E(r,t) will in generl vry with position. The vlue nd vritions of n(r) re fundmentl to understnding the wy in which electromgnetic wves propgte through the troposphere. The rdio refrctive index of the troposphere is due to the moleculr constituents of the ir, principlly nitrogen, oxygen, cron dioxide nd wter vpour. The vlue of n devites from unity ecuse of the polrisility of these molecules due to the incident electromgnetic field, nd quntum mechnicl moleculr resonnces. (Brcly, 1996). According to ITU-R (12), the tmospheric refrctive index, n, cn e computed y using: N = n Where N is rdio refrctivity expressed y with the dry term of rdio refrctivity given y: 4 nd the wet term given y N wet = e T 2, where: P is tmospheric pressure (hp) e is wter vpor pressure (hp) nd T is solute temperture (K) This expression my e used for ll rdio frequencies (for frequencies up to GHz; the error is less thn 0.5%) for representtive profiles of temperture, pressure nd wter vpour pressure (Bin et. l. 1997) The wter vpor pressure, e, cn e clculted from reltive humidity s Where e s is defined s e s = EF exp t t d t + c And: EF wter = P t 2 Where e s is the wter vpour prtil pressure, t is temperture in Celsius, H is the humidity, nd constnts for wter re =6.1121, =18.678, c = nd d = 234.5(ITU-R, 12). DOI: 10.97/ Pge

3 PRESSURE(hp) PRESSURE(hp) REFRACTIVITY(N- UNIT) TEMPERTURE(0C) Study of Averge Hourly Vritions of Rdio Refrctivity Vritions cross Some Selected Cities IV. Methodology And Instrumenttion The indirect method of mesuring refrctivity ws employed in this study. Surfce vlues of pressure (hp), Temperture ( o C), nd Reltive humidity (%) were extrcted from mesurements mde using Dvis Vntge pro2 utomtic wether sttion instlled t the ground surfce t Lgos (6 0 27' N, ' E) Lgos Stte, Port-Hrcourt (4 0 48'N, 7 0 E) Rivers Stte, Anyig (7 0 45' N, ' E) Kogi Stte nd Yol (9 0 11' N, 12 0 ' E) Yol Stte. The wether sttions hve five minutes integrtion time. Dt collected from Jnury 11 to Decemer 13 were verged over ech hour to give twenty four dt point representing diurnl vritions for ech dy. The hourly dt for ech dy is further verged to give dt point for the dy nd verge ws tken over the month to give dt point for ech month which ws used to determine the monthly vritions for ech yer. The corresponding months for ech yer of the three yers under study were then verged to give the verge sesonl vritions for the period under study. The dt were used to compute the surfce rdio refrctivity V. Figures c d Fig. 1 To 1d Averge Hourly Vritions Of Surfce Rdio Refrctivity, Temperture, Humidity And Pressure For Dry Seson Over Lgos From 11 To e f G h Fig. 1e To 1h Averge Dily Vritions Of Surfce Rdio Refrctivity, Temperture, Humidity And Pressure For Riny Seson Over Lgos From 11 To 13 DOI: 10.97/ Pge

4 PRESSURE(hp ) PRESSURE(hp) Study of Averge Hourly Vritions of Rdio Refrctivity Vritions cross Some Selected Cities c d Fig. 2 To 2d AVERAGE DAILY VARIATIONS OF SURFACE RADIO REFRACTIVITY, TEMPERATURE, HUMIDITY AND PRESSURE FOR DRY SEASON OVER PORT-HARCOURT FROM 11 TO e g h Fig. 2 To 2h Averge Dily Vritions Of Surfce Rdio Refrctivity, Temperture, Humidity And Pressure For Riny Seson Over Port-Hrcourt From 11 To f DOI: 10.97/ Pge

5 REFRACTIVITY (N UNIT) PRESSURE(hp) TEMPERATURE(0 C) PRESSURE(hp) Study of Averge Hourly Vritions of Rdio Refrctivity Vritions cross Some Selected Cities c d Fig. 3 To 3d Averge Dily Vritions Of Surfce Rdio Refrctivity, Temperture, Humidity And Pressure For Dry Seson Over Anyig From 11 To e f g h Fig. 3 To 3d Averge Dily Vritions Of Surfce Rdio Refrctivity, Temperture, Humidity And Pressure For Riny Seson Over Anyig From 11 To T(hrs) Fig. 4 And 4 Averge Dily Vritions Of Surfce Rdio Refrctivity, For Dry And Riny Seson Over Yol From 11 To 13 VI. Results And Discussions Averge Hourly Vritions Of Refrctivity Fig. 1 to Fig. 1h depictsthe verge hourly vritions of surfce rdio refrctivity, Temperture, reltive humidity, nd pressure over Lgos for dry nd riny seson. Fig. 1 represent the surfce rdio refrctivity, shows strong dependence on the wet term (Humidity) of refrctivity with high vlues in the morning nd lte in the evening nd low vlues in the dy time. This is ttriuted to the response of the erth to DOI: 10.97/ Pge

6 Study of Averge Hourly Vritions of Rdio Refrctivity Vritions cross Some Selected Cities solr insoltion which is the mjor force ehind the wether condition oserved. The solr insoltion cuses the temperture to e high nd humidity low during the dy. The highest vlue is 377 N-units nd the lowest vlue is 366 N-units. The verge dily vritions of surfce refrctivity over Lgos for riny seson is depicted in Fig. 1e, shows mximum in the fternoon with sudden rise pre-noon nd sudden drop just t the noon. The mximum vlue is out 386 N-unit which occur etween the 11:00hr locl time nd 12:00hr locl time units nd the lowest vlue is out 378 N-unit. To determine the mjor force driving the vritions in riny seson, the signture of refrctivity vrition is compred with tht of temperture, humidity, nd pressure s depicted in Fig. 1f, 1g nd 1h respectively. Fig. 1f depicts the vritions of temperture over Lgos which shows low vlues in the morning nd lte evening with high vlues during the dy. Fig. 1g depicts the vritions of Humidity, these vritions followed opposite trend s expected with high vlues in the morning nd lte evening. Fig. 1g depicts profile of Pressure; it showed pttern tht is lmost synchronous with refrctivity vritions. Therefore the dry component (pressure) is mjor force driven diurnl vritions of refrctivity over Lgos during riny seson. The diurnl vritions of refrctivity, temperture, reltive humidity nd pressure over Port-Hrcourt for dry nd riny seson is depicted in Fig. 2 to Fig. 2h respectively. Fig. 2 showed tht the refrctivity vlue in dry seson is high in the erly morning nd lte evening with mximum vlue of 356N-units nd low during the dy with minimum vlue of out 351 N-units etween the 14:00hr LT nd the 15:00hr LT. This is in greement with wht is expected when the refrctivity vritions is een driven y the wet term. Fig. 2e depicts the diurnl vritions of surfce refrctivity for riny seson, showed sudden rise prenoon nd sudden drop post noon. The mximum vlue of 357 N-unit ws oserved round the noon. To understnd the min force driven the vrition in riny seson, Fig. 2f, 2g nd 2h represent the profile of Temperture, Humidity nd Pressure respectively. The Temperture profile showed lowest vlue round 6:00hr LT efore grdully rise to mximum vlue round 15:00hr LT. The vrition of Humidity followed opposite trend s expected with high vlue round 6:00hr LT nd minimum round 15:00hr LT. The pressure profile showed minimum vlue y 6:00LT nd grdully increse to first mximum vlue t noon efore sudden increse to its pek vlue t 15:00 LT. The pek vlue of refrctivity out this time s shown in Fig. 2e is ttriuted to the pressure vritions (dry term) while sudden drop post noon is s result of increse in temperture which led to the decrese in Humidity nd consequently the refrctivity. Therefore, the vritions refrctivity during the rest of the dy re ttriuted to the wet term. The verge dily vritions of rdio refrctivity, temperture, reltive humidity nd pressure for riny nd dry sesons over Anyig is depicted in Fig. 3 to Fig. 3h respective. Fig. 3 depicts the refrctivity vritions for dry seson over Anyig, showed sudden rised to rech pek vlue of 267 N-unit round 8:00hr LT to 9:00hr LT nd grdul decresed to reched minimum vlue of 238 N-unit round 16:00 LT nd 17:00 LT. To show tht the refrctivity vritions in dry seson is likely driven y dry component. Fig. 3d depicts pressure profile, shows mximum t 9:00 LT nd minimum vlue t 17:00 LT. Therefore, the pressure profile shows lmost synchronous pttern of vritions with refrctivity vrition depicted in Fig. 3. This confirms tht dry component (pressure) is the min driving force for refrctivity vrition t Anyig for dry seson. Fig. 3e shows tht in riny seson the refrctivity is high (356N-units to 358N-units) in the erly nd lte hours of the dy. It grdully drops from 10:00hr locl time nd rech minimum of 353 N-units round 13:00hr efore grdully risen till the end of the dy. Therefore, wet term is driven the refrctivity vritions in riny seson, while dry term is responsile for the vritions in dry seson. The diurnl vritions of refrctivity, temperture, reltive humidity nd pressure for riny nd dry sesons over Yol is depicted in Fig. 4 nd Fig. 4 respectively. The two profiles show low vlues in the dy nd high vlues in the morning nd evening. The highest vlue for riny seson is out 363 N-units nd the lowest vlue is 356 N-units while the highest vlue for dry seson is 284 N-units nd the lowest vlue is 271 N- units. The diurnl vritions of refrctivity over Yol showed consistency with wht is expected of humidity vritions nd therefore it is ttriuted to the wet term for oth sesons. The results otined from the study shows tht the verge hourly vritions of surfce rdio refrctivity in dry seson is mjorly driven y the wet term (Humidity) t Lgos, Port-Hrcourt nd Yol sttions, while, the dry component (pressure) is the mjor driving force the vritions t Anyig during the sme seson. The results lso show tht in riny seson, dry component (pressure) is the mjor force ehind the vritions t Lgos nd Port-Hrcourt while the wet term (Humidity) is the mjor cuse of surfce rdio refrctivity vritions t Anyig nd Yol. This result lso shows tht the surfce rdio refrctivity vritions do not lwys depend on the wet term (humidity) only s reported y Adeyemi nd Kolwole (1992) ut is in greement with the findings of Ayntunji et l (11) which shows tht the diurnl vrition of refrctivity depends on locl meteorology s determine y the locl topogrphy. DOI: 10.97/ Pge

7 Study of Averge Hourly Vritions of Rdio Refrctivity Vritions cross Some Selected Cities VII. Conclusion In-situ mesurement of temperture, pressure nd humidity were crried out t surfce of Anyig, Yol, Lgos nd Port-Hrcourt for period of three yers. The dt from these sttions were employed to determine the diurnl vrition of rdio refrctivity t the sttions under study using ITU-R Model. The mjor findings of this study re s follows: - The verge hourly vrition of refrctivity in the dry seson is lrgely s result of the vritions of the wet (Humidity) component of refrctivity while the verge vritions of refrctivity in the riny seson is s result of oth the vritions of the wet (Humidity) nd dry (Pressure) components of refrctivity. - Hourly or Diurnl vrition of refrctivity depend on locl meteorology s dictted y the topogrphy. - Refrctivity vlues computed for the loctions under study increses from out 242 N- units t Anyig northern Nigeri to 384 N-units t Lgos southern Nigeri. From the forementioned findings, the following re some of the pplictions of this reserch work. - The knowledge of meteorologicl prmeters otined in this study cn e useful when plnning frequency reuse in the loctions. - The surfce rdio refrctivity dt otined in this study will provide rdio engineers with dequte informtion relevnt for the design of communiction systems in the loctions. - It will serve s importnt prmeter in determining the coverge nd qulity of VHF, UHF nd microwve signls in the loctions. Acknowledgements The uthors will like to cknowledge NASRDA, Center for Atmospheric Reserch under the project, Tropospheric Dt Acquisition Network (TRODAN) ndcentre for Bsic Spce Science, University of Nigeri, Nsukk for providing the dtse for this study. References [1] Ali, S., Mlik, S. A., Alimgeer, K. S., Khn, K. S. nd Ali, R. L., (11). Sttisticl estimtion of tropospheric rdio refrctivity derived from 10 yers meteorologicl dt, Journl of tmospheric nd solr-terrestril physics, Vol. 77, pp [2] Adediji, A. T. nd Ajewole, M. O., (10). Microwve Anomlous Propgtion (AP) Mesurement over Akure South-Western Nigeri, Journl of tmospheric nd solr-terrestril physics, vol. 72, pp [3] Adediji, A. T., Ajewole, M. O. nd Flodun, S. E., (11). Distriution of rdio refrctivity grdient nd effective erth rdius fctor (k-fctor) over Akure, South Western Nigeri, Journl of tmospheric nd solr-terrestril physics, vol. 73, pp [4] Adediji, A. T., Mhmod, I. nd Mndeep, J. S., (13). Vrition of rdio field strength nd rdio horizon distnce over three sttions in Nigeri, Journl of tmospheric nd solr-terrestril physics, vol. 109, pp 1-6 [5] Aytunji, B. G. nd Okeke, P. N., (11). Diurnl nd sesonl vrition of surfce refrctivity over Nigeri, Progress in electromgnetic Reserch B, vol., pp [6] Aytunji, B. G., Okeke, P. N. nd Urm, J.O., (11). Sesonl vrition of surfce refrctivity over Nigeri, Advnces in spce Reserch vol. 48, pp [7] Adeyemi, R. A. nd Kolwole, L. B., (1992). Sesonl nd Diurnl Vritions of Surfce Refrctivity in Akure, South-Western Nigeri, Unpulished M.Sc Thesis, deprtment of Physics, Federl University of Technology, Akure, Nigeri. [8] Ben, B. R., Dutton, E. J., (1966). Rdio Meteorology, Dover Edition, New York, USA, 1. [9] Bin, S. M., Young, G. S. nd Crton, J. A., (1997). A new model of the ocenic evportion duct, Journl of Applied Meteorology, Vol. 36, pp [10] Flodun, S. E. nd Ajewole, M.O., (05). Rdio refrctive index in the lowest m lyer of the troposphere in Akure, Southwestern Journl of tmospheric nd solr-terrestril Physics, Vol. 68, Pp [11] Hughes, K. A., (1993). Rdio Propgtion Dt from Tropicl Regions: A Brief Review of seminr on Rdio Propgtion in Tropicl Regions, An unpulished lecture note presented t Centre for Theoreticl Physics, Trieste (Itly). [12] ITU R., (12). The refrctive index: its formul nd refrctivity dt, Recommendtion 3/1, ITU-R, Pp [13] Igwe K.C. nd Adimul, I. A., (09). Vrition of surfce rdio refrctivity nd rdio refrctive index grdient in su-shel, Nigeri journl of spce reserch, vol. 6, pp s [14] Kissssou, S.,Lenouo, A., Tchwou, C., Lopez, P. nd Gye, A. T., (14). Climtology of rdr nomlous propgtion over West Afric, Journl of tmospheric nd solr-terrestril physics. [15] Kolwole, L. B., (1980). Climtologicl Vrition of Surfce Refrctivity in Nigeri, Nigeri Institute of Physics, Vol. 4, Pp [16] Kolwole, L. B., nd Owonui, J. J., (1982). The Surfce Rdio Refrctivity Over Afric, Nigerin Journl of Science, Vol. 16, Nos. 1 & 2, Pp [17] Owoli, I. E. nd Willims, V. A., (19). Surfce Rdio Refrctivity Pttern in Nigeri nd Southern Cmeroon, Journl of West Africn Science Assocition, Vol., No. 1, Pp 3-17 [18] Okoro, O. N. nd Ago, G. A., (12). The effect of vrition of meteorologicl prmeters on tropospheric rdio refrctivity for minn, Glol journls inc., (USA). [19] Segl, B., (1985). Mesurement of tropospheric refrctive index relevnt to the study of nomlous microwve propgtion- review nd recommendtions, CRC Report No [] Thyer, G. D., (1974). An improved eqution for rdio refrctive index of ir, Rdio Science, Vol. 9, No. 10, Pp DOI: 10.97/ Pge