PROBING OF THE ARTIFICIAL HOLE IN THE IONOSPHERE WITH THE HF SKYWAVE RADAR

Transcription

1 PROBING OF THE ARTIFICIAL HOLE IN THE IONOSPHERE WITH THE HF SKYWAVE RADAR JIAO Pei-nan MA Tie-han XU Guo-liang LI Zong-qiang Zhang Xin-sheng XU Fei (China Researh Institute of Radiowave Propagation, Xinxiang, Henan, 4500 China ABSTRACT This paper explains the experiment that HF skywave radar probed the artifiial ionospheri hole, whih is aused by the flames of the roket vertially launhed and penetrated the ionosphere. After the roket had passed through the ionosphere, the minimum time-delay P min -f on the baksatter ionograms obviously appeared with wave and fousing stripes resulting from the irregular struture et. The results indiated that there was a low eletron density zone, the artifiially reated hole in the ionosphere along the propagation path. Under the asymmetry quasi-osine ionospheri hole model, the experimental P min -f was simulated with the tehnique of ray traing. It was dedued that the range size of the hole in ionosphere along the radar beams was some 57 km and the ritial frequeny of the enter was.6 MHz lower than the bakground ritial frequeny (MHz. The ionospheri environment 50km away from the launhing site was disturbed and the propagation veloity of the ionospheri disturbane was about 50m/s. Key words: HF baksatter propagation, artifiial ionospheri hole, HF sky-wave radar, - D ray traing Ⅰ INTRODUCTION On 4 May 97, the US Sientists observed the ionospheri effets of the launhing of the Spae Laboratory with the launhing roket of Saturn V by Faraday effet tehnique along the Atlanti Coast in the northern part of USA. They found that there were large quantity of eletron ompound in the ionosphere due to the spurt flames of the roket whih ontained large quantity of hydrogen and water moleules thus the artifiial ionospheri hole was formed whih had the eletron density muh lower than that of the bakground in range of about 000km []. In 980s three observations with vertial ionosphere sounding for the vertial launhing of large sized rokets penetrating the ionosphere in China showed that there were obvious desend of ionospheri ritial frequeny with the abnormality of the eho [,6]. We first observed the ionospheri effet with the HF skywave baksattering radar after the launhing of a large sized roket penetrating the ionosphere and obtained the expeted results. This was the first suessful observation of the artifiial ionospheri hole with suh radar. Under the asymmetry quasi-osine ionospheri hole model, the experimental P min -f urve was simulated to fit with the tehnique of ray traing. The range size of the hole in ionosphere and the propagation veloity of the ionospheri disturbane had also been dedued. Ⅱ DESIGN AND BASIS OF THE EXPERIMENT We have done the analysis with the

2 Report Doumentation Page Form Approved OMB No Publi reporting burden for the olletion of information is estimated to average hour per response, inluding the time for reviewing instrutions, searhing existing data soures, gathering and maintaining the data needed, and ompleting and reviewing the olletion of information. Send omments regarding this burden estimate or any other aspet of this olletion of information, inluding suggestions for reduing this burden, to Washington Headquarters Servies, Diretorate for Information Operations and Reports, 5 Jefferson Davis Highway, Suite 04, Arlington VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subjet to a penalty for failing to omply with a olletion of information if it does not display a urrently valid OMB ontrol number.. REPORT DATE 4 APR 005. REPORT TYPE N/A. DATES COVERED - 4. TITLE AND SUBTITLE Probing Of The Artifiial Hole In The Ionosphere With The Hf Skywave Radar 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5. PROGRAM ELEMENT NUMBER 6. AUTHOR(S 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S AND ADDRESS(ES China Researh Institute of Radiowave Propagation, Xinxiang, Henan, 4500 China 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S AND ADDRESS(ES 0. SPONSOR/MONITOR S ACRONYM(S. DISTRIBUTION/AVAILABILITY STATEMENT Approved for publi release, distribution unlimited. SPONSOR/MONITOR S REPORT NUMBER(S. SUPPLEMENTARY NOTES See also ADM00798, Proeedings of the International Conferene on Radar (RADAR 00 Held in Adelaide, Australia on -5 September ABSTRACT 5. SUBJECT TERMS 6. SECURITY CLASSIFICATION OF: 7. LIMITATION OF ABSTRACT UU a. REPORT unlassified b. ABSTRACT unlassified. THIS PAGE unlassified 8. NUMBER OF PAGES 5 9a. NAME OF RESPONSIBLE PERSON Standard Form 98 (Rev Presribed by ANSI Std Z9-8

3 tehnique of ray traing for the affetion of the minimum time delay (P min -f of the baksattering ionogram aused by the disturbed ionosphere [,4] and found that the bend flutuation of the P min -f in the ionospheri baksattering ionogram ould be aused by the small saled disturbane of the eletron density of ionosphere whih shape was relevant to the horizontal gradient of the ionosphere and its hanges. This had been verified by the observation of the annular solar elipse effet happened on Sept. 987 with the HF Sky-wave Radar. So, if the there was large quantity eletron ompound emerging in the ionosphere due to the roket flame thus auses the artifiial zone of low eletron density, then there should be bend flutuation of the P min -f in the ionospheri baksattering ionogram. When the hole was formed, there should be obvious horizontal positive and negative ionospheri setional gradient hanges and the orresponding turning point at P min / f 0 in ionospheri baksattering ionogram. So, the frequeny sweep baksattering ionogram was taken as the basi data for analysis. The beam azimuth of the probing radar was offset about 00km northwest from the launhing site in order try to obtain the information of sale, existent period and the horizontal disturbane veloity of the artifiial ionospheri hole. So, the beam was not pointed to the enter of the launhing site but interseted with edge of the imaginary hole. The HF radar was working in the auto-frequeny sweep mode with the sweeping range from 5-5MHz. The experimental reord was the baksattering frequeny sweeping ionogram P~f but the urves of minimum time delay P min -f have been analysed as a main data. On the launhing day, from 5 h 0 min to 9 h 00 min the ionosphere was observed twie every ten minutes, other time one every 0 minutes. Ⅲ THE OBSERVED DATA A. Flutuated P min -f of the HF baksatter ionogram The launhing time of roket was 6 h 0 min and the observed baksattering ionogram kept normal without flutuation till 7 h 05 min. From 7 h 05 min to 7 h 50 min, there appeared a lear bending in the minimum time delay P min -f between ~0MHz frequeny and in the distane region of km. At 7 h min the obvious flutuation reahed the maximum. And it was reovered to normal till 8 h 00 m to the shape of sunset and night. Fig. shows the variation of time sequene of P min -f in the baksattering ionogram after the launhing of the roket at 6 h 04 min. the dot line showing the non-flutuated minimum time delay as referene. Time sequene Fig. Variation of time sequene of P min -f in baksattering ionogram B. Abnormal additional traks in ionogram 6 min after the launhing of the roket, namely at 6 h 0 min, exept the quasi-vertial refletion eho in the quasi-vertial refletion zone in the ionogram, there emerged some abnormal additional traks (it is also alled branh traks whih was a little bit lower than the quasi-refleting trak in F layer with the virtual height of about 60km, and the refleting frequeny from MHz point out by the arrow in Fig. a. The strange traks

4 had appeared three times in the ionogram obtained in the vertial sounding station 50 km away from the launhing site when the roket penetrating the ionosphere []. and the time were 54s, 64s, 90s respetively. a b Fig. a The abnormal traks in ionogram at 6 h 0 min, b the fous stripe of the irregular in ionogram at 6 h min (point out by the arrow. the white line is the alulated value of P min -f with the ionospheri hole model C. Fous-strips of irregular in ionogram After 7 h 4 min there were fous-strips of the irregular in the baksattering ionogram along the oblique range of 000 km. The fous strips of the irregular in the baksattering at 6 h min as shown by the arrow in Fig.b Ⅳ ANALYSIS AND DISCUSSION A. Model of artifiial ionospheri hole In order to study the artifiial ionospheri hole with the tehnique of fitting of two-dimensional ray traing, a model of asymmetri quasi-osine hole of the variation of eletron density with height and the distane of geoentri angle θ was onsidered, if it ould be simply expressed with the ritial frequeny, it should be f ( θ r rm N (, = e r θ 80.6 rm rb f ( θ f f = (0 xθ f Cos(πR( θ V / λ V < θ V (0 xθ f f Cos(πR ( θ V / λ V < θ V f (0 xθ θ V»òθ > V πr f x λ πr f df ( x θ = λ x Sin (πr ( θ V / λ Sin (πr ( θ V / λ V < θ V θ V»òθ > V V < θ V Where v, v, v are the geoentri angle positions (rad of the front, enter and the bak alulated from the radar station. f (0 the ritial frequeny(mhz of the top side of the radar station. x is the bakground negative gradient of the ritial frequeny (MHz/rad. (λ λ / is the disturbed range (km of the ionosphere in the refleting area along the diretion of radar beam. f is the flutuation amplitude of the ritial frequeny of the hole (MHz/rad. r m, r b, are the height of maximum eletron density and the bottom height in ionosphere alulated from the geo-enter respetively. The model was at about θ = v, v, v and f (θ and the value of first order differential oeffiient respetively as: df ( V df ( V f ( ν = f ( ν = f (0 xν, = = x; df ( V df ( V f ( ν = f ( ν = f (0 xν f, = = x; df ( V df ( V f ( ν = f ( ν f (0 xν, = = x; It an be seen from the above that, f (θ and its differential oeffiient at the joint point θ = v, v, v are suessive, beause the vertial distribution of eletron density is also suessive. where,

5 B. Parameters of artifiial ionospheri hole With the tehnique of two-dimension ray traing and in the model of the above stated ionospheri model of asymmetri quasi-osine hole, the P min -f of the ionogram at 7 h 0 min was simulated. It shows that model below with the parameters of the ionospheri hole, the alulated value of P min -f has good agreement with that of the experimental data. The parameters of the ionospheri hole model were: r b =6570km, r m =6700km, f (0 =.4MHz, x= -5MHz/rad, f = -.MHz/rad, λ =764.4km λ =8.km V =0.05rad, V =0.095rad, V =0.5rad, so, the maximum disturbing amplitude of the ritial frequeny was.6mhz lower than the bakground ritial frequeny and the width of the disturbed zone along the deteting path was 57.km. Fig. shows the profile of the eletron density of the ionosphere of the model F (the variation of the ionospheri eletron density with θ and the trae of the minimum time delay P min vs all frequenies at7 h 0 min. In fig. ray a, b, j is orresponding P min at frequeny, 4, 4MHz respetively. Fig. At 7 h 0 min the P min of model of asymmetri quasi-osine hole simulate by ray traing Beause the ray was offset 00 km from the launhing site, the above parameters are not the parameters of the artifiial ionospheri hole, but that of the tangential setion of the radar ray around the edge of the hole. Therefore, aording to the relative geometri positions of the radar ray and the launhing site, it was deduted that ionosphere 50 km away from the launhing site had also been disturbed by the roket flame. In other words if assume the artifiial ionospheri hole is a irular hole, then the size of hole was dedued about 700km. It is a pity that the parameters of the ionospheri hole is not approved beause of the lak of the vertial sounding data from the diretions of eastward or northeastward from the launhing site. C. Existent duration of hole and propagation veloity of the disturbane The HF baksattering ionogram shows that the ionosphere along the diretion of radar beam (00 km away from the launhing site was disturbed 60 minutes after the launhing and the deduted propagation veloity of the disturbane is 50.5m/s. The apparent ionospheri disturbane along the diretion of radar beam lasted more than 40 minutes. Considering the fat that the ionospheri disturbane above the launhing site lasted two hours and ten minutes, whih was shown by the data obtained by a vertial ionospheri sounder near the launhing site, it an be deduted that the Maximum time of the disturbed zone aused by the roket flames 7 h min namely, 79 minutes after the launhing of the roket and the ionosphere 50 km away from the launhing site was also disturbed. Later, the edge of the Maximum disturbed zone began to reombine gradually, and the ionosphere along the diretion of radar beam reovered after 7 minutes. Then the disturbed area ontinually narrowing till 8 h 6 min the reovery of the ionosphere above the launhing site. The whole ourse lasted minutes. D. Explanation of the energy fous strips of irregular There was obvious horizontal gradient along the diretion of radar beam beause of the existene of the low eletron density area.

6 At this time, usually, the uniqueness harateristis of the extremum of the time delay P vs angle in the baksattering ionogram obtained from the stratified homogeneity model, had been damaged to form two multi extremum of the omplex urves or more [5]. Therefore, the time delay orresponding to the points of extremum would not be the minimum time delay. And near the points of extremum dp/dα = 0, the flux of the ray within the angle or the unit time inreased, so the energy outside of these time delays foused. From this, it is known that among these extremums, the one orresponding to the minimum time delay was the minimum time delay. Otherwise, it was the time delay of foused energy. Time delays of the foused energy at different frequenies formed the foused strips on the ionogram. So, foused strips were the important harateristis of the baksattered ionogram of the disturbed ionosphere. fond and trae the target like roket from the launhing of the roket till the roket enter the ionosphere by the HF sky-wave radar. Ⅴ CONCLUSIONS The analysis of the experimental data shows that it is feasible to probe the artifiial ionospheri hole with HF Baksatter Radar. As the first experiment for suh purpose it was also a suessful one. And it was also feasible and reasonable for the dedution of the parameters of the low eletron density zone of the ionosphere with the tehnique of fitting of two-dimensional ray traing and the experimental data under the model of asymmetri quasi-osine hole. The target harateristi of the roket shows that it is possible to fond and traed the target like roket from the launhing of the roket till the roket to enter the ionosphere by the HF sky-wave radar. E. The Target Charateristi of the Roket Researhes show [7] that the radar ross setion of the roket body is determined by its physial dimension whih exists in the resonane range in the HF band. But the radar ross setion of the roket flame varies with the height in HF band and the maximum value of RCS reahes 40dB. The spetrum analysis shows that eho of the roket has the harateristis of double peak spread, namely the ombination of spetrums of the roket body and that of the flame. The latter usually has wider spreading in spetrum. If the roket turns off without flame, it is very diffiult for the HF Sky-wave radar to find the roket target. However, the artifiial ionospheri hole due to the ionospheri eletron ombined by the large quantity of neutral moleular aused by the roket flame that makes desending of the eletron density an be fond by the HF sky-wave radar. Therefore it is possible to Referenes ( Mendllo M. and G. S. Hawkins, Siene, 975, 87, pp. 4. ( ZHANG Ran-fang, Modifiation of Ionoshpere by Roket Exhaust, Proeeding of ISSP 86, Beijing, China, 986, pp ( JIAO Pei-nan, Ionoshpere Undulations During the Annular Elipse of Sep.,987, Chinese J. of Geophysis (in English, 990, (, pp (4 JIAO Pei-nan, Chinese Journal of Radio Siene (in Chinese, 990, 5 (, pp (5 CI Jia-ai and JIAO Pe-inan, Journal of Spae Siene (in Chinese, 99, (, pp (6 WANG Jie, Corretion for Atmospheri Refrative Error of Radio wave (in Chinese, Publishing House of NDI,999, pp.7-9, (7 CHEN Yu-hun and Le Zi-hua, Proeeding of IEE 4 th International Conferene on Antenna and Propagation (London, 988, pp Contat to pnjiao@publi.xxptt.ha.n