A preliminary validation of the technique developed using the NeQuick ionospheric model and the «effective ionization parameter» Az, based on vertical total electron content data ingestion, was carried out in a previous study. The current study was performed to extend the analyzed conditions and confirm the results. The method to validate this technique is based on a comparison between hourly F2 peak values measured with Vertical Incidence (VI) soundings and those calculated with the new technique. Data corresponding to different hours and seasons (equinox, summer solstice, and winter solstice) during the period 2000-2003 (high and medium solar activity conditions) were compared for all available ionosonde stations. The results show a good agreement between foF2 and hmF2 values obtained with the new technique and measurements from vertical incidence soundings during quiet and storms conditions.European Community Fifth Framework Programm

Coïsson, Pierdavide

Miró Amarante, Gloria

Nava, Bruno

Radicella, Sandro María

Annals of Geophysics

A preliminary validation of the technique developed using the NeQuick ionospheric model and the «effective ionization
parameter» Az, based on vertical total electron content data ingestion, was carried out in a previous study. The
current study was performed to extend the analyzed conditions and confirm the results. The method to validate this
technique is based on a comparison between hourly F2 peak values measured with Vertical Incidence (VI) soundings
and those calculated with the new technique. Data corresponding to different hours and seasons (equinox, summer
solstice, and winter solstice) during the period 2000-2003 (high and medium solar activity conditions) were compared
for all available ionosonde stations. The results show a good agreement between foF2 and hmF2 values obtained with
the new technique and measurements from vertical incidence soundings during quiet and storms conditions

Miró Amarante, G.

Radicella, S. M.

Nava, B.

Coïsson, P.

Annals of Geophysics (INGV, Istituto Nazionale di Geofisica e Vulcanologia)

321ANNALS  OF  GEOPHYSICS, VOL.  48, N.  2, April  2005Key  words electron density model – vertical inci-dence ionograms – ionospheric data ingestion1. IntroductionOne of the most unpredictable sources of er-ror for single frequency satellite navigation andpositioning systems is due to the ionosphere. Agood knowledge of the behavior of the ionos-pheric regions is essential to obtain a better rep-resentation of parameters like the Total ElectronContent (TEC) which is directly proportional tothe time delay of electromagnetic signals. A technique to reconstruct the spatial andtemporal structure of the electron concentrationin the ionosphere has been developed using theNeQuick ionospheric electron density modeldriven by an «effective ionization parameter»called Az (Nava et al., 2003). NeQuick is aquick-run model for ionospheric applicationsdeveloped at The Abdus Salam ICTP in Trieste(Italy) and the University of Graz (Austria). Ithas been used by the European Space Agency -ESA satellite navigation and positioning pro-grams and adopted by Recommendation P.531-6 of the ITU-R (International Telecommunica-tion Union, Radiocommunication sector) (nowsuperseded by P.531-7; ITU, 2001). Az values are determined minimizing the dif-ferences between experimental and modeled ver-tical TEC global maps. The result is a global gridof Az values for a specific condition which al-lows us to calculate with the NeQuick model theelectron density at any point in the ionosphereincluding the F2 peak parameters values. The aim of this paper is to compare these cal-culated F2 peak values with independent and si-multaneous global observations in order to vali-date the technique. These measurements, the criti-Validation of a method for ionosphericelectron density reconstruction by means of vertical incidence data during quiet and storm periodsGloria Miró Amarante, Sandro M. Radicella, Bruno Nava and Pierdavide CoïssonThe Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste (Italy)AbstractA preliminary validation of the technique developed using the NeQuick ionospheric model and the «effective ion-ization parameter» Az, based on vertical total electron content data ingestion, was carried out in a previous study. Thecurrent study was performed to extend the analyzed conditions and confirm the results. The method to validate thistechnique is based on a comparison between hourly F2 peak values measured with Vertical Incidence (VI) soundingsand those calculated with the new technique. Data corresponding to different hours and seasons (equinox, summersolstice, and winter solstice) during the period 2000-2003 (high and medium solar activity conditions) were comparedfor all available ionosonde stations. The results show a good agreement between foF2 and hmF2 values obtained withthe new technique and measurements from vertical incidence soundings during quiet and storms conditions.Mailing address: Dr. Gloria Miró Amarante, The Ab-dus Salam International Centre for Theoretical Physics(ICTP), Strada Costiera 11, 34014 Trieste (Italy); e-mail:amarante@ictp.it322Gloria Miró Amarante, Sandro M. Radicella, Bruno Nava and Pierdavide Coïssoncal frequency in the F2 region (foF2) and the heightof the maximum of ionization (hmF2), are ob-tained experimentally from ground-based verticalionospheric sounders located around the world.A preliminary validation was done (MiróAmarante et al., 2003) using data correspon-ding to four quiet days in the year 2002 (highsolar activity conditions). The main results andconclusions of this analysis will be included inthis paper.2. Ionospheric parameters measured with vertical incidence soundingsThe DIDbase software developed by LowellUniversity lets us extract ionograms from a net-work of digisondes distributed around theworld. This possibility allows manual scaling ofthe available ionograms to measure the real val-ues of the main ionospheric parameters (criticalfrequency, height, Ionospheric Total ElectronContent - ITEC: Huang and Reinisch, 2001).The analysis has been done for differentconditions summarized in table I. For each pe-riod, all the available ionospheric stations wereselected (fig. 1). The number of locations variesfrom 13 during the period of March 2000 up to27 for the 3rd of June 2002.The manual scaling of the ionograms (al-most 8300 ionograms) was done for each con-sidered case and foF2 and hmF2 were extractedto be compared with the reconstructed values.3. Ionospheric parameters calculated with the reconstruction techniqueTwo global grids corresponding to foF2 andhmF2 were obtained from the NeQuick modeldriven by the «effective ionization parameter»Az. This parameter is calculated by means of thetechnique described in Nava et al. (2003) in sucha way that the differences between experimentaland NeQuick model vertical TEC are minimum.The experimental vertical TEC maps used for theminimization are generated with two differenttechniques. The first is the one developed byCODE (Centre for Orbits DEterminations,http://www.cx.unibe.ch/aiub/ionosphere.html)with two hour intervals and the second one wasgenerated by the University of La Plata, Argenti-na with one hour intervals (Meza et al., 2002;and Brunini et al., 2004).The calculated F2 peak values at the avail-able digisonde locations (fig. 1) are extractedFig. 1. Observing sites available for the periods ana-lyzed.Table I. List of selected periods for the validationof the reconstruction method.Day Month Year Ap Dst Sunspotnumber25 03 2000 8 −9 18526 03 2000 3 −1 17027 03 2000 4 1 15528 03 2000 4 1 16915 04 2002 6 −8 13803 06 2002 10 −21 13311 10 2002 6 −38 12125 11 2002 15 −46 5619 11 2003 12 −179 7020 11 2003 150 −152 9021 11 2003 42 −76 9722 11 2003 30 −63 8323 11 2003 22 −38 109323Validation of a method for ionospheric electron density reconstruction by means of vertical incidence datafrom these two global grids by interpolationsince the Az maps have a grid spacing of 2.5° inlatitude and 5° in longitude.4. Comparison between measured and calculated peak valuesAs an example, the critical frequency foF2 andthe maximum height hmF2 for Millstone Hill(middle latitude Northern Hemisphere) and Gra-hamstown (middle latitude Southern Hemi-sphere) are shown in fig. 2a-d (quiet period) andfig. 3a-d (storm period). Calculated F2 peak val-ues using CODE (foF2CODE) and La Plata(foF2LAPLATA) vertical TEC maps are plottedtogether with the experimental ones (foF2SAO,obtained with Sao-Explorer, http://ulcar.uml.edu/SAO-X/SAO-X.html).The figures show a good agreement betweenboth foF2 data sets (foF2CODE-foF2SAO andfoF2LAPLATA-foF2SAO) during quiet condi-tions while the differences between calculatedand experimental values increase for geomagnet-ic disturbed conditions. The results are consider-ably worse in the case of hmF2. However, this isnot surprising. NeQuick uses the CCIR (ITU-R)maps for foF2 and M(3000)F2 and an internalmap for foE to calculate hmF2 by means of Du-deney’s form of the Bradley and Dudeney (1973)formula (see Dudeney, 1983) which works quitewell for average (monthly median) conditionsbut can give larger errors in individual cases.Minimizing differences in electron content alsomeans some minimization for foF2 but hmF2 isnot affected. The height error of true heightanalysis of ionograms can also be quite large.The left panel of fig. 4 presents the scatterplot of foF2 (F2 peak electron density) recon-structed with the NeQuick model against thecorresponding foF2 ionosonde measurements forquiet periods (2000 and 2002). This exampleFig. 2a-d. foF2 (a) and hmF2 (c) for Millstone Hill (middle latitude Northern Hemisphere); foF2 (b) and hmF2 (d)for Grahamstown (middle latitude Southern Hemisphere), during March 2000 (quiet period).bc daFig. 4. Linear regression fitting for reconstructed and experimental foF2 during quiet (left) and storm (right) con-ditions.324Gloria Miró Amarante, Sandro M. Radicella, Bruno Nava and Pierdavide CoïssonFig. 3a-d. foF2 (a) and hmF2 (c) for Millstone Hill (middle latitude Northern Hemisphere); foF2 (b) and hmF2 (d)for Grahamstown (middle latitude Southern Hemisphere), during November 2003 (storm period).corresponds to CODE experimental verticalTEC maps. The scatter plot shows a high degreeof correlation between the two independent es-timates of foF2. The line drawn corresponds tothe best-fit line. Examination of the intercept ofthe best-fit line shows that on average thefoF2NeQuick values exceed those from digison-des by ∼1.16 MHz during quiet period. Theac db325Validation of a method for ionospheric electron density reconstruction by means of vertical incidence datastorm conditions are also shown on the rightpanel in fig. 4. This example corresponds to 20thNovember 2003 (Ap index=150) and shows howthe agreement between both data sets is also ob-tained for a very disturbed day. It is important topoint out that this storm occurred under middlesolar activity conditions (sunspot number = 90)and the analysis was done considering togetherall the ionospheric effects (positive and negativestorms) distributed around the world.The selected data are classified to create dis-tributions with different conditions of solar ac-tivity, vertical TEC mapping technique and qui-et or storm periods. The results of the linear re-gression fitting corresponding to each distribu-tion are summarized in tables II and III for foF2and hmF2 respectively. The correlation coefficients R make clear thedifference in accuracy for reconstruction of foF2and hmF2. In the case of the critical frequencythe correlation coefficient is approximately 0.90which means that the fitting between both dataset is excellent. However this value does not ex-ceed 0.70 for the peak height possibly for thereasons indicated above when discussing the re-sults shown in figs. 2a-d and 3a-d. The foF2 re-construction is also good during the studiedstorm period with values higher than 0.86. Itmust be noted that regardless of the actual val-ues of the correlation coefficient all the resultsindicate a very high statistical significance.The comparison between the two verticalTEC mapping techniques (CODE and La Plata)does not show a clear dependence on the tech-Table III. Linear regression fitting results for hmF2 (hmF2NeQuick=A∗hmF2Ionosonde+B; R is the correlationcoefficient and N the number of selected data).hmF2 (km) La Plata CODEPeriod A B R N A B R NCalm 2000 0.34 187.7 0.53 1094 0.35 183.9 0.48 5462002 No data 0.55 128.6 0.60 52919.11.2003 0.75 70.0 0.70 325 0.72 72.5 0.68 16520.11.2003 0.62 129.4 0.50 279 0.56 141.9 0.46 140Storm period 21.11.2003 0.72 90.1 0.50 242 0.80 68.2 0.52 11322.11.2003 0.76 80.1 0.66 324 0.72 83.1 0.67 16423.11.2003 0.72 90.2 0.68 323 0.62 113.3 0.66 156Table II. Linear regression fitting results for foF2 ( foF2NeQuick=A∗ foF2Ionosonde+B; R is the correlation co-efficient and N the number of selected data).foF2 (MHz) La Plata CODEPeriod A B R N A B R NCalm 2000 0.98 0.20 0.89 1096 1.01 −0.10 0.91 5472002 No data 0.94 1.44 0.91 93619.11.2003 0.90 −0.06 0.91 469 0.96 −0.04 0.93 24120.11.2003 0.96 0.12 0.89 402 1.00 0.24 0.89 204Storm period 21.11.2003 0.76 0.74 0.86 379 0.79 0.98 0.87 18122.11.2003 0.91 0.17 0.88 463 0.96 0.23 0.89 23223.11.2003 0.86 0.48 0.89 457 0.92 0.53 0.90 225326Gloria Miró Amarante, Sandro M. Radicella, Bruno Nava and Pierdavide Coïssonnique of the vertical TEC map used to derive Azvalues. The number of points corresponding toLa Plata technique is higher because these mapsare obtained hourly. The dependence on solar activity is only no-ticeable for hmF2 where the fitting improveswhen solar activity decreases. However, furtheranalysis considering low solar activity andstorm conditions under very high solar activityshould be done in the future.5. ConclusionsThe comparison of F2 peak values generat-ed by the new technique of 3D reconstructionof the electron density and the correspondingvertical incidence ionosonde data covering awide area of different geographical, seasonaland hourly conditions indicates that:– The critical frequency of the F2 layershows a very good agreement between both datasets during high and middle solar activity quietperiods.– This agreement is also good for the No-vember 2003 storm considering together all theionospheric effects (positive and negative stormeffects) distributed around the world. – The hmF2 parameter shows a worseagreement than foF2 values and the worst resultshave been found for high solar activity.– The results obtained are not dependenton the technique of the vertical TEC maps used,CODE and La Plata.Therefore, it has been demonstrated that thenew technique can be used to build scenariosthat reproduce global ionospheric conditions ina realistic way.AcknowledgementsThe Aeronomy and Radiopropagation Labo-ratory group of The Abdus Salam InternationalCentre for Theoretical Physics is grateful to theUniversity of La Plata for providing their verti-cal TEC maps and to the ionospheric groups(Lowell University (U.S.A.), National Observa-tory of Athens (Greece), Radio Research Labo-ratory (Sinpil Seolsung Ichon Kyunggi, Repub-lic of Korea), Rhodes University (Grahamstown,South Africa), Communications Research Labo-ratory (Tokyo, Japan), Rutherford AppletonLaboratory (Chilton, United Kingdom), IstitutoNazionale di Geofisica e Vulcanologia (Rome,Italy), INTA (Huelva, Spain), Ebro Observatory(Spain), CASLEO (San Juan, Argentina)) fromwhom we received data used in this study. Oneof the authors (G.M.A.) also wants to thank tothe Marie Curie Fellowship of the EuropeanCommunity Fifth Framework Programme undercontract No. HPMF-CI-2002-01867 for support-ing this research. REFERENCESBRADLEY, P.A. and J.R. DUDENEY (1973): A simple modelof the vertical distribution of electron concentration inthe ionosphere, J. Atmos. Terr. Phys., 35, 2131-2146.BRUNINI, C., A. MEZA, F. AZPILICUETA, A. VAN ZELE, M.GENDE and A. DIAZ (2004): A new ionosphere moni-toring technology based on GPS, Astrophys. SpaceSci., 290 (3), 415-429.DUDENEY, J.R. (1983): The accuracy of simple methods fordetermining the height of the maximum electron con-centration of the F2-layer from scaled ionosphericcharacteristics, J. Atmos. Terr. Phys., 45, 629-640.HUANG, X. and B.W. REINISCH (2001): Vertical electroncontent from ionograms in real time, Radio Sci., 36 (2),335-342. ITU (2001): Ionospheric propagation data and predictionmethods required for the design of satellite servicesand systems ionosphere characteristics, Recommenda-tion P.531-6, approved in 2001-02, managed by ITU-RStudy Group SG3 (version 6 superseded in 2004 byversion 7).MEZA, A., C.A. BRUNINI and A. KLAEUSBERG (2002): Glob-al behaviour of the ionosphere electron density usingGPS observations, Adv. Space Res., 30 (2), 307-312.MIRÓ AMARANTE, G., S.M. RADICELLA, B. NAVA and P.COÏSSON (2003): Validation of a new method for ionos-pheric electron density reconstruction by means of ver-tical incidence data, in Proceedings of ‘AtmosphericRemote Sensing using Satellite navigation Systems’,Special Symposium of the URSI Joint Working Group,Matera (FG), Italy, 335-342.NAVA, B., P. COÏSSON, G. MIRÓ AMARANTE and S.M. RADI-CELLA (2003): A new model assisted method for iono-sphere electron density reconstruction, in Proceedingsof ‘Atmospheric Remote Sensing using Satellite navi-gation Systems’, Special Symposium of the URSI JointWorking Group, Matera (FG), Italy, 343-348.(received October 18, 2004;accepted March 19, 2005)

English

Validation of a method for ionospheric electron density reconstruction by means of vertical incidence data during quiet and storm periods

idUS. Depósito de Investigación Universidad de Sevilla

A preliminary validation of the technique developed using the NeQuick ionospheric model and the «effective ionization&#13; parameter» Az, based on vertical total electron content data ingestion, was carried out in a previous study. The&#13; current study was performed to extend the analyzed conditions and confirm the results. The method to validate this&#13; technique is based on a comparison between hourly F2 peak values measured with Vertical Incidence (VI) soundings&#13; and those calculated with the new technique. Data corresponding to different hours and seasons (equinox, summer&#13; solstice, and winter solstice) during the period 2000-2003 (high and medium solar activity conditions) were compared&#13; for all available ionosonde stations. The results show a good agreement between foF2 and hmF2 values obtained with&#13; the new technique and measurements from vertical incidence soundings during quiet and storms conditions

P. Coïsson

B. Nava

S. M. Radicella

G. Miró Amarante

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Validation of a method for ionospheric electron density reconstruction by means of vertical incidence data during quiet and storm periods

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Annals of Geophysics (INGV, Istituto Nazionale di Geofisica e Vulcanologia)

idUS. Depósito de Investigación Universidad de Sevilla

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