Automated information technology for ionosphere monitoring of low-orbit navigation satellite signals

Transcription

1 Automated nformaton technology for onosphere montorng of low-orbt navgaton satellte sgnals Alexander Romanov, Sergey Trusov and Alexey Romanov Federal State Untary Enterprse Russan Insttute of Space Devce Engneerng (FSUE RISDE ), Moscow, Russa E-mal: Introducton In the last couple of decades onospherc rado tomography by navgaton low earth orbt satellte sgnal methods has been ntensvely evaluated. Ths knd of tomography conssts of the synchronous regstraton of one satellte sgnal by a number of recevng statons and s followed by an onosphere electron content dstrbuton reconstructon based on a set of ntegral values (sgnal phase delay). Settng recevers along a satellte pass allows us to obtan heght lattude onosphere cross-sectons. The horzontal sze of such sectons s commonly a few thousand klometres, and the vertcal sze s about 1000 km. The frst rado tomography experments were processed about 0 years ago (Kuntsyn and Tereshchenko, 001) and the theoretcal part has been well nvestgated, but the approaches to data acquston and processng have been less well studed. Usually the tme gap between satellte sgnal regstraton at the recevng statons and the end of thematc data processng s weeks, or even months. The man reason for such a tme delay n most modern tomography systems s because manual procedures are used n the process of acqurng and processng data whch constrans the speed of the nformaton beng transmtted to the recever. Consequently, data processng requrng vsual analyss or qualtatve assessment for decson makng needs to be modfed to reduce output tme. At the same tme, t s necessary to organze the hgh-speed data acquston. The process of tomography data acquston and processng conssts of several stages: (1) data acquston from the recevng statons, () analyss of data characterstcs, (3) dfferent transformatons necesstatng decson makng, and (4) reconstructon of problem solvng qualty assessments. Thus, t s necessary to develop an automated system of the tomography data acquston and processng n order to ncrease the capablty of the data recevng operaton. The automated onospherc tomography data processng technque, the processng center and data acquston recevng staton nteracton algorthm and the specal software for nformaton acquston, processng, storng and representng are needed to develop such a system. The automated onospherc tomography data processng technque The technque s based on the phase-dfference tomography method (Kuntsyn and Tereshchenko, 001). The technque parameters were obtaned as a result of numerc modelng carred out for the geometry of the recevng statons network, located on Sakhaln Island. The network conssts of three recevng statons spaced about 50 km apart. The technque conssts of three stages: 1. Useful sgnals allocated from data are receved from the statons on the bass of emprcally obtaned boundary condtons (dsperson of the dfferental phase values n runnng average wndow N = 10 s less than 1 and the length of the sgnal part s longer than 60 s).. The systematzaton of the exstng data s realzed by rado soundng sessons. The data belongng to one sesson are characterzed by a common satellte dentfer and the tme dfference between regsterng data on the recevng statons of the chan s less than 35 mn. 3. The hgh-frequency sgnal component (greater than 0.1 Hz) s elmnated and then the phase dervatve wth respect to tme s calculated. The data are decmated and only every eghth measurement s used for further research. 4. The orbt satellte locaton row s calculated usng the SGP4 orbt model (Kelso, 1996) for the satellte communcaton sesson accordng to the procedure of sgnal decmaton. Thus, the satellte PICES Scentfc Report No

2 locaton s calculated for every conformed measurement from the data fles. 5. The redundant data for tomography task solvng are rejected as soon as the locatons of the rado sgnals n the area of nterest are defned. For example, t s necessary to dscard part of the receved ntal data from the southern staton f the smallest satellte lattudes, fxed for t, are the smallest for all the tomography chan statons. It s also necessary to reject the data of the southern staton f the satellte lattudes characterzng ths nformaton are also less than the mnmum lattudes for the northern statons. The analogous but opposte condtons are used for cullng data of the northern statons. 6. The projectng operator matrx s formed on the bass of the sgnals path locatons and peceplanar approxmaton functon for the grd dmensons 50 5 km and 1000 km heght. The vertcal grd sze s defned by the current sesson geometry. 7. An optmal ntal guess s pcked up by formng the fnte set of the model electron concentraton dstrbutons and by correspondence analyss of the ntegral measurements calculated on ther (model dstrbuton sets) bass to expermental data. 8. The lnear equaton system (SLE) s formed usng the created projectng operator matrx, the ntal guess and measurement vectors Ax = b. The SLE solvng procedure s realzed by the algebrac reconstructon technque (ART) wth the relaxaton teraton algorthm. The teraton procedure ends f the velocty of the SLE rght part of the reconstructon error change becomes less than 0.001, otherwse, t wll end after 50 teratons. Thus, the electron concentraton reconstructon s completed as soon as the values n regular grd nodes are calculated. Consequently, the numercal parameters of every stage of the proposed technque were formalzed and defned as a result of our research. The specal software for automated onospherc tomography operatve data processng was developed. Remote recevng staton network admnstraton The task of operatve data transfer s solved by means of recevng statons connected to the Internet. The transfer tme of the data from one satellte communcaton sesson (0 Kb) s 14 s, wth a typcal connecton speed of 18 Kb/s to a local Internet provder. It s necessary to provde the recevng staton wth an actual schedule of satellte rado vsblty sessons used. The proposed decson s based on the satellte orbt parameters, and the rado vsblty zone calculaton on the bass of the SGP4 model. If the communcaton sesson s nvsble even for one recevng staton n the tomography chan, the records of satellte communcaton sessons need to be culled after the communcaton schedule s formed. Thus, the fles wth the communcaton schedule are formed n the way represented above to transmt to the recevng staton. The remote control problem s solved by checkng the accessblty of the recever statons va the Internet and analyzng the retreved log fles perodcally. The proposed approaches were realzed n the algorthm consstng of three procedures: the calculaton of the satellte rado vsblty zone, schedules, new data recevng, and recevng staton admnstraton. The executon of the procedure s determned by the task manager n accordance wth pre-defned rules. The task manager works permanently and checks the schedule perodcally. If the current tme corresponds to the tme of some procedural executon, the specal process n charge for ths procedure s ntated. Specal software for onospherc tomography data acquston and processng To automate tomography data processng, t s necessary to solve a number of supplementary tasks such as ballstc data acquston and managng the studes of the data processng. Specal software was developed to solve the whole spectrum of the onospherc tomography system data processng problems revealed above. The specal software structure conssts of functonal segments n charge of acqurng, processng, storng and representng nformaton, and management and admnstraton of the acquston and processng nformaton processes (Fg. 1). The basc functonalty of each segment s provded wth the executon of one, or more often, several program modules. A user web-nterface allows the user to access data processng results and manage the acquston and processng data procedures nteractvely usng any computer wth an Internet connecton (Fg. ). 04 PICES Scentfc Report No. 36

3 where F s the ntal value and F ~ s the reconstructed one. Results showed that the errors of the model dstrbuton reconstructon, descrbng the dsturbed onosphere state (the exstence of the rregulartes and the horzontal gradent of electron concentraton), are characterzed by δ = 0.08 and δ m = 0.10 and become less wth the regulatng of the onosphere structure. Experment Results Fg. 1 Flowchart of specal software developed for onospherc tomography data acquston and processng. Informaton storage n the system conssts of managng nformaton acquston and processng from a set of tomography chans realzed wth the provson for further possble enlargement of the recevng system segment. Ths approach s based on specal metadata structure usage where each recevng staton s characterzed by the set of the herarchcal and geographcal characterstcs, and allows the system to work wth a sngle tomography chan as a set element. Numercal Modelng Results The reconstructon of the onosphere electron concentraton model dstrbuton was carred out by developng specal software accordng to condtons dentcal to real experment geometry descrbed n Romanov et al. (008) for thematc processng qualty assessment. The reconstructon errors were obtaned by calculatng the dscrepancy between ntal and reconstructed functons, and defned by the followng relatons (Kuntsyn and Tereshchenko, 001): δ = ( F F ~ ) F max F F ~ δ m =, max F ; Expermental research on the qualty of the developed system of onospherc tomography data acquston and processng was carred out usng real onospherc tomography data from statons located on Sakhaln Island. The system of onospherc tomography data acquston and processng workng results are the heght lattude dstrbuton of electron concentraton (Fg. 3). Fgure 4 represents the results of the comparson between the data from the onosonde n Wakkana cty (Hokkado Island, Japan), located approxmately n 150 km to the south of Yuzhno- Sakhalnsk cty (Sakhaln Island, Russa) and the nformaton reconstructed wth the ad of the specally developed software. The onosonde data were provded by WDC for Ionosphere, Tokyo, Natonal Insttute of Informaton and Communcatons Technology. Data from the reconstructon of 90 onosphere states were used: 50 were receved n summer perod of 007 (July August) and 40 n January 008. The maxmum values of onosphere electron concentraton n the regon of the onosonde locaton were recalculated to the crtcal frequency fof terms for the further comparson. Good agreement was shown, wth a mean dscrepancy of 15% and δ = Maxmum dscrepances of 41% and 46% were obtaned for two reconstructons. The correlaton raton for two data rows was 84% (R = 0.84). These results are n good accordance wth qualty assessments of the onosphere tomography reconstructons represented n ndependent research (δ = ) (Kuntsyn et al., 007). However, t s necessary to note that ndependent assessments were obtaned usng the phase dfference tomography approach, but wthout any automaton technque. PICES Scentfc Report No

4 The correspondence of these results shows that the new technque proposed n ths research allows us to automatcally reconstruct the electron concentraton dstrbuton n the onosphere wth typcal accuracy as for the phase dfference tomography approach. The operatonal speed of the onospherc tomography reconstructon usng ths system s 5 15 mn. The speed of ths automated data acquston and processng has no analogue n Russa, and has not yelded the best foregn samples. Fg. The structure of onospherc tomography data acquston and processng automated system. Fg. 3 Electron concentraton dstrbuton on July 9, 007, 0:30 (local tme) on Sakhaln Island. 06 PICES Scentfc Report No. 36

5 A remote network management algorthm was developed whch allows tasks to be solved automatcally for onospherc tomography data acquston, dataware and workablty admnstraton of the recevng statons. The specal software for automated onospherc phase dfference tomography data acquston and processng was developed. It allows the reconstructon of the onosphere vertcal electron concentraton dstrbuton n 5 15 mn after the satellte communcaton sesson ends. Fg. 4 The scatter plot of the values of crtcal frequency (fof calculated from tomography reconstructon and measured by onosonde n Wakkana (Hokkado Island, Japan). Conclusons In the current research, the followng results were acheved. The technque of automated onospherc tomography data processng was developed. The automated onosphere reconstructon has an accuracy about 15%. References Kelso, T.S Real-world benchmarkng. Satellte Tmes 3 (November/December): Kuntsyn, V.E. and Tereshchenko, E.D Ionosphere Tomography. Sprnger, Berln. Kuntsyn, V.E., Tereshchenko, E.D. and Anreeva E.S Ionosphere Radotomography. 336 pp. (n Russan). Romanov, A.A., Trusov, S.V., Romanov, A.A. et al., 008. Researchng of onosphere dsturbances on phase-dfference tomography method at Russan Far East regon. Earth Remote Sensng : 14 0 (n Russan). PICES Scentfc Report No