非球对称电离层掩星反演技术
摘要
2006年4月,中国台湾和美国合作的COSMIC卫星星座的发射成功,为反演电离层掩星提供了大量的观测资料。电离层中的不规则体和电离层的扰动,对卫星通讯、短波通讯和卫星导航定位,产生重要影响。无线电波在地球电离层中的传播容易发生色散、吸收和折射等效应。现有的研究表明,通过电离层(电子含量或电子密度)的异常扰动有可能探求地震前兆信息。对电离层的认识和探测,发展相应的预报业务,具有重要的应用价值和科学意义。
本文讨论了传统的电离层掩星反演以及其它反演方法,本文的结构如下:
1、简要地介绍了无线电掩星技术的发展状况、电离层结构及研究现状
2、通过COSMIC掩星电离层观测资料L1和L2的相位组合,可以得到总电子含量TEC;再利用非掩星侧的辅助观测数据来校正TEC,以消除LEO卫星轨道高度以上的TEC;然后在电子密度局部球对称假设和信号直线传播近似下,利用Abel积分变换得到电子密度垂直廓线。
3、Abel变换反演电离层方法是在球对称假设下进行的。电离层的非球对称分布给电离层电子密度反演带来误差。本文探讨了非球对称电离层反演方法,讨论了这些方法的可行性。
4、介绍独立研发的电离层掩星反演软件,给出文件输入、文件输出接口。
5、对本文工作做了简要总结和展望
A constellation of six satellites, called COSMIC, was launched on 15 April 2006 from Vandenberg Air Force Base, California. And lots of ionospheric occultation data were provided from the COSMIC satellites. In the Earth’s ionosphere, radio wave propagation prone happen reflection, scattering, refraction and absorption. Ionospheric disturbances and irregularities can affect short-wave communications, satellite communications and satellite navigation. Therefore, there is very important to search the ionosphere.
This thesis discusses the traditional inversion of ionospheric occultation and other inversion methods. The main works can be summarized as following:
1. This thesis briefly describes the development of the Ionospheric Radio Occultation (IRO) technique, the structure and the current situation of the ionospheric.
2. The relative total electron content TEC is obtained through the combination of COSMIC radio occultation ionosphreic measurements L1 and L2 phase; The TEC data are then calibrated by non-occultation observation data on the auxiliary side to remove portion of TEC above the LEO orbit altitude; The electron density profile can be retrieved from TEC by Abel integral transformation, with a spherically symmetric assumption of electron density and an approximation of signal straight-line propagation.
3. The Abel inversion based on a spherical symmetry of the ionospheric electron density distribution is a traditional method for inversion of ionospheric occultation. However, the real ionosphere is not strictly spherical symmetry, which can cause error in inversion process of ionospheric occultation data. To reduce the error, this thesis discusses the other inversion methods, focusing on the feasibility of these methods.
4. This thesis introduces the ourselves researching software of the inversion of ionospheric occultation, including input files and out files.
5. Make a brief summary of the results.
本文讨论了传统的电离层掩星反演以及其它反演方法,本文的结构如下:
1、简要地介绍了无线电掩星技术的发展状况、电离层结构及研究现状
2、通过COSMIC掩星电离层观测资料L1和L2的相位组合,可以得到总电子含量TEC;再利用非掩星侧的辅助观测数据来校正TEC,以消除LEO卫星轨道高度以上的TEC;然后在电子密度局部球对称假设和信号直线传播近似下,利用Abel积分变换得到电子密度垂直廓线。
3、Abel变换反演电离层方法是在球对称假设下进行的。电离层的非球对称分布给电离层电子密度反演带来误差。本文探讨了非球对称电离层反演方法,讨论了这些方法的可行性。
4、介绍独立研发的电离层掩星反演软件,给出文件输入、文件输出接口。
5、对本文工作做了简要总结和展望
A constellation of six satellites, called COSMIC, was launched on 15 April 2006 from Vandenberg Air Force Base, California. And lots of ionospheric occultation data were provided from the COSMIC satellites. In the Earth’s ionosphere, radio wave propagation prone happen reflection, scattering, refraction and absorption. Ionospheric disturbances and irregularities can affect short-wave communications, satellite communications and satellite navigation. Therefore, there is very important to search the ionosphere.
This thesis discusses the traditional inversion of ionospheric occultation and other inversion methods. The main works can be summarized as following:
1. This thesis briefly describes the development of the Ionospheric Radio Occultation (IRO) technique, the structure and the current situation of the ionospheric.
2. The relative total electron content TEC is obtained through the combination of COSMIC radio occultation ionosphreic measurements L1 and L2 phase; The TEC data are then calibrated by non-occultation observation data on the auxiliary side to remove portion of TEC above the LEO orbit altitude; The electron density profile can be retrieved from TEC by Abel integral transformation, with a spherically symmetric assumption of electron density and an approximation of signal straight-line propagation.
3. The Abel inversion based on a spherical symmetry of the ionospheric electron density distribution is a traditional method for inversion of ionospheric occultation. However, the real ionosphere is not strictly spherical symmetry, which can cause error in inversion process of ionospheric occultation data. To reduce the error, this thesis discusses the other inversion methods, focusing on the feasibility of these methods.
4. This thesis introduces the ourselves researching software of the inversion of ionospheric occultation, including input files and out files.
5. Make a brief summary of the results.
引文
[1] Escudero, A., A. C. Schlesier, A. Rius, et al., Ionospheric tomography using ?rsted GPS measurements– Preliminary results [J], Physics and Chemistry of the Earth Part a-Solid Earth and Geodesy, 26(3), 173-176, 2001.
[2] Larsen, G. B., S. Syndergaard, P. Hoeg, et al., Single frequency processing of ?rsted GPS radio occultation measurements [J], GPS Solutions, 9(2), 144-155, 2005.
[3] Jakowski, N., A. Wehrenpfennig, S. Heise, et al., GPS radio occultation measurements of the ionosphere from CHAMP: Early results [J], Geophys. Res. L., 29(10), 2002.
[4] Wickert, J., C. Reigber, G. Beyerle, et al., Atmosphere sounding by GPS radio occultation: First results from CHAMP [J], Geophys. Res. L., 28(17), 3263-3266, 2001.
[5] Liou, Y. A., A. G. Pavelyev, J. Wickert, et al., Analysis of atmospheric and ionospheric structures using the GPS/MET and CHAMP radio occultation database [J]: a methodological review, GPS Solutions, 9(2), 122-143, 2005.
[6] Garcia-Fernandez, M., M. Hernandez-Pajares, J. M. Juan, et al., Performance of the improved Abel transform to estimate electron density profiles from GPS occultation data [J], GPS Solution, 9(2), 105-110, 2005.
[7] Gobiet, A. and G. Kirchengast, Advancements of Global Navigation Satellite System radio occultation retrieval in the upper stratosphere for optimal climate monitoring utility [J], JGR-Atmospheres, 109(D24), 2004.
[8] Hajj, G. A., C. O. Ao, B. A. Iijima, et al., CHAMP and SAC-C atmospheric occultation results and intercomparisons [J], JGR-Atmospheres, 109(D6), 2004.
[9] Schmidt, T., S. Heise. J. Wickert, et al., GPS radio occultation with CHAMP and SAC-C: global monitoring of thermal tropopause parameters [J], Atmospheric Chemistry and Physics, 5, 1473-1488, 2005
[10] Straus, P. R., Ionospheric climatology derived from GPS occultation observations made by the ionospheric occultation experiment [J], Advances in Space Research, 39(5), 793-802, 2007.
[11] Yunck, T. P., C.-H., Liu, R. Ware, A history of GPS sounding [J], Terr. Atmos. Oceanic Sci., 11, 2000.
[12] Han, S. C., C. K. Shum, C. Jekeli, et al., Improved estimation of terrestrial water storage changes from GRACE [J], Geophys. Res. L., 32(7), 2005.
[13] Wickert, J., G. Beyerle, R. Konig, et al., GPS radio occultation with CHAMP and GRACE: A first look at a new and promising satellite configuration for global atmospheric sounding [J], Ann.Geophys., 23(3), 653-658, 2005.
[14] Lin, C. H., J. Y. Li, T. W. Fang, et al., Motions of the equatorial ionization anomaly crests imaged by FORMOSAT-3/COSMIC [J], Geophys. Res. L., 34(19). 2007b.
[15] Liou, Y. A., A. G. Pavelyev, S. F. Liu, et al., FORMOSAT-3/COSMIC GPS radio occultaion mission: Preliminary results [J], IEEE Trans. Geosci. & Remote Sensing, 45(11), 3813-3826, 2007.
[16] Schreiner, W., C. Rocken, S. Sokolovskiy, et al., Estimates of the precision of GPS radio occultations from the COSMIC/FORMOSAT-3 mission [J], Geophys. Res. L., 34(4), 2007.
[17] Sokolovskiy, S. V., C. Rocken, D. H. Lenschow, et al., Observing the moist troposphere with radio occultation signals from COSMIC [J], Geophys. Res. L., 34(18), 2007.
[18] Wang, K. Y. and S. C. Lin, First continuous GPS soundings of temperature structure over Antarctic winter from FORMOSAT-3/COSMIC constellation [J], Geophys. Res. L., 34(12), 2007.
[19] Gorbunov, M. E. and K. B. Lauritsen, Analysis of wave fields by Fourier integral operators and their application for radio occultations [J], Radio Sci., 39(4), 2004.
[20] Jensen, A. S., M. S. Lohmann, H. H. Benzon, et al., Full spectrum inversion of radio occultation signals [J], Radio Sci., 38(3), 2003.
[21] Karayel, E. T. and D. P. Hinson, Sub-Fresnel-scale vertical resolution in atmospheric profiles from radio occultation [J], Radio Sci., 32(2), 411-423, 1997.
[22] Wang, X. and D. R. Lu, Comparative analysis of inversion methods of retrieving atmospheric profiles with GPS occultation measurements [J], Chinese Journal of Geophysics-Chinese Edition, 50(2), 346-353, 2007.
[23] Garcia-Fernandez, M., M. Hernandez-Pajares, M. Juan, et al., Improvement of ionospheric electron density estimation with GPS/MET occultations using Abel inversion and VTEC information [J], JGR-Space Physics, 108(A9), 2003.
[24] Hajj, G. A., R. Ibanez-Meier, E. R. Kursinski, et al., Imaging the ionoshpere with the Global Positioning System [J], Int. J. Imaging Sys. & Tech., 5(2), 174-184, 1994.
[25] Tsai, L. C. and W. H. Tsai, Improvement of GPS/MET ionospheric profiling and validation using the Chung-Li ionosonde measurements and the IRI model [J], Terr. Atmos. Oceanic Sci., 15(4), 589-607, 2004.
[26]杜起飞,孙越强,刘正廷,等,GPS掩星探测天线相位中心的校准[J],空间科学学报,26(6),487-490,2006.
[27] Zeng, Z., X. Hu and X. J. Zhang, Applying artificial neural network to the short-term prediction of electron density structure using GPS occultation data [J], Geophys. Res. L., 29(9), 2002.
[28]胡雄,张训械,吴小成,等,山基GPS掩星观测实验及其反演原理[J],地球物理学报,49(1),22-27,2006.
[29] Hu, X., X. C. Wu, X. Y. Gong, et al., An introduction of mountain-based GPS radio occultation experiments in China [J], Advances in Space Research, 10(42), 1723-1729, 2008.
[30]宫晓艳,胡雄,吴小成,等,雾灵山GPS掩星观测事件统计分析[J],应用气象学报,19(3),2008.
[31]胡雄,曾桢,张训械,等,大气GPS掩星观测反演方法[J],地球物理学报,48(4),768-774,2005.
[32]王鑫,吕达仁,GPS无线电掩星技术反演大气参数方法对比[J],地球物理学报,50(2),346-353,2007.
[33]吴小成,胡雄,张训械,等,电离层GPS掩星观测改正TEC反演方法[J],地球物理学报,49(2),328-334,2006.
[34]宫晓艳,胡雄,吴小成,等,大气掩星反演误差特性初步分析[J],地球物理学报,50(4),1017-1029,2007.
[35] Syndergaard S., On the ionospheric calibration in GPS occultation measurements [J], Radio Sci., 35(3), 865-883, 2000.
[36] Schreiner, W. S., S. V. Sokolovskiy, C. Rocken, et al., Analysis and validation of GPS/LEO radio occultation data in the ionosphere [J], Radio Sci., 34(4), 949-966, 1999.
[37] Beyerle, G., T. Schmidt, G. Michalak, et al., GPS radio occultation with GRACE: Atmospheric profiling utilizing the zero difference technique [J], Geophys. Res. L., 32(13), 2005a.
[38] Eshleman, V. R., G. L. Tyler, G. E. Wood, et al., Radio science with Voyager 1 at Jupiter: preliminary profiles of the atmosphere and ionosphere [J], Science, 204, 976-978, 1979.
[39] Fjeldbo, G., V. R. Eshleman, The atmosphere of Mars analyzed by integral inversion of the Mariner IV occultation data [J], Planet Space Sci., 16, 1035-1059, 1968.
[40] Fjeldbo, G., A. J. Kliore, V. R. Eshleman, The neutral atmosphere of the Venus as studied with the Mariner V radio occultation experiments [J], Astron. J., 76, 123-140, 1971.
[41] Hajj, G. A., L. J. Romans, Ionospheric electron density profiles obtained with theGlobal Positioning System: Results from the GPS/MET experiment [J], Radio Sci., 33(1), 175-190, 1998.
[42] Kuo, Y.-H., X. Zou, W. Huang, The impact of GPS data on the prediction of an extratropical cyclone: An observing system simulation experiment [J], J. Dyn. Atmos. Ocean, 27, 439-470, 1997.
[43] Kursinski, E. R., G. A. Hajj, J. T. Schofield, et al., Observing earth’s atmosphere with radio occultation measurements using the Global Positioning System [J], J. Geophys. Res., 102(D19), 23429-23465, 1997.
[44] Lindal, G. F., Atmosphere of Neptune [J], Astronom. J., 103, 976-982, 1992.
[45] Ogawa, T., Radar Observations of Ionospheric irregularities at Syowa Station, Antarctica: A brief Overview [J]. Ann. Geophys., 14, 1454-1461, 1996.
[46] Rius, A., G. Ruffini, A. Romeo, Analysis of ionospheric electron density distribution from GPS/MET occultations [J], IEEE Trans. Geosci. & Remote Sensing, 36, 383-394, 1998.
[47] Rocken, C., R. Anthes, M. Exner, et al., Analysis and validation of GPS/MET data in the neutral atmosphere [J], J. Geophys. Res., 102(D25), 29849-29866, 1997.
[48] Steiner, A. K., G. Kirchengast, H. P. Ladreiter, Inversion, error analysis, and validation of GPS/MET occultation data [J], Ann.Geophys., 17, 122-138, 1999.
[49] Tyler, G. L., D. N. Sweetnam, J. D. Anderson, et al., Voyager 2 radio science observations of the Uranian System: atmosphere, rings, and satellites [J], Science, 233, 79-84, 1986.
[50] Ware, R., M. Exner, D. Feng, M. Gorbunov, et al., GPS sounding of the atmosphere from Low Earth Orbit: Preliminary Results [J], Bull. Am. Meteorol. Soc., 77, 19-40, 1996.
[51] Zhang D. H., K. Igarashi, X. Zuo, et al., The Observation of Large Scale Travelling Ionospheric Disturbances Based on GPS Network [J]. Chinese Journal of Geophysics, 45(4), 469-475, 2002.
[52]刘振兴,等,太空物理学[M],哈尔滨:哈尔滨工业大学出版社,2005.
[53]熊年禄,唐存琛,李行健,电离层物理概论[M],武汉:武汉大学出版社,1999.
[54]张训械,曾桢,胡雄,等,电离层水平不均匀性对无线电掩星资料反演的影响[J],地球物理学报,45,1-6,2002.
[55]曾桢,胡雄,张训械,无线电掩星和激光雷达观测结果比较[J],空间科学学报,21(2),165-171,2001.
[2] Larsen, G. B., S. Syndergaard, P. Hoeg, et al., Single frequency processing of ?rsted GPS radio occultation measurements [J], GPS Solutions, 9(2), 144-155, 2005.
[3] Jakowski, N., A. Wehrenpfennig, S. Heise, et al., GPS radio occultation measurements of the ionosphere from CHAMP: Early results [J], Geophys. Res. L., 29(10), 2002.
[4] Wickert, J., C. Reigber, G. Beyerle, et al., Atmosphere sounding by GPS radio occultation: First results from CHAMP [J], Geophys. Res. L., 28(17), 3263-3266, 2001.
[5] Liou, Y. A., A. G. Pavelyev, J. Wickert, et al., Analysis of atmospheric and ionospheric structures using the GPS/MET and CHAMP radio occultation database [J]: a methodological review, GPS Solutions, 9(2), 122-143, 2005.
[6] Garcia-Fernandez, M., M. Hernandez-Pajares, J. M. Juan, et al., Performance of the improved Abel transform to estimate electron density profiles from GPS occultation data [J], GPS Solution, 9(2), 105-110, 2005.
[7] Gobiet, A. and G. Kirchengast, Advancements of Global Navigation Satellite System radio occultation retrieval in the upper stratosphere for optimal climate monitoring utility [J], JGR-Atmospheres, 109(D24), 2004.
[8] Hajj, G. A., C. O. Ao, B. A. Iijima, et al., CHAMP and SAC-C atmospheric occultation results and intercomparisons [J], JGR-Atmospheres, 109(D6), 2004.
[9] Schmidt, T., S. Heise. J. Wickert, et al., GPS radio occultation with CHAMP and SAC-C: global monitoring of thermal tropopause parameters [J], Atmospheric Chemistry and Physics, 5, 1473-1488, 2005
[10] Straus, P. R., Ionospheric climatology derived from GPS occultation observations made by the ionospheric occultation experiment [J], Advances in Space Research, 39(5), 793-802, 2007.
[11] Yunck, T. P., C.-H., Liu, R. Ware, A history of GPS sounding [J], Terr. Atmos. Oceanic Sci., 11, 2000.
[12] Han, S. C., C. K. Shum, C. Jekeli, et al., Improved estimation of terrestrial water storage changes from GRACE [J], Geophys. Res. L., 32(7), 2005.
[13] Wickert, J., G. Beyerle, R. Konig, et al., GPS radio occultation with CHAMP and GRACE: A first look at a new and promising satellite configuration for global atmospheric sounding [J], Ann.Geophys., 23(3), 653-658, 2005.
[14] Lin, C. H., J. Y. Li, T. W. Fang, et al., Motions of the equatorial ionization anomaly crests imaged by FORMOSAT-3/COSMIC [J], Geophys. Res. L., 34(19). 2007b.
[15] Liou, Y. A., A. G. Pavelyev, S. F. Liu, et al., FORMOSAT-3/COSMIC GPS radio occultaion mission: Preliminary results [J], IEEE Trans. Geosci. & Remote Sensing, 45(11), 3813-3826, 2007.
[16] Schreiner, W., C. Rocken, S. Sokolovskiy, et al., Estimates of the precision of GPS radio occultations from the COSMIC/FORMOSAT-3 mission [J], Geophys. Res. L., 34(4), 2007.
[17] Sokolovskiy, S. V., C. Rocken, D. H. Lenschow, et al., Observing the moist troposphere with radio occultation signals from COSMIC [J], Geophys. Res. L., 34(18), 2007.
[18] Wang, K. Y. and S. C. Lin, First continuous GPS soundings of temperature structure over Antarctic winter from FORMOSAT-3/COSMIC constellation [J], Geophys. Res. L., 34(12), 2007.
[19] Gorbunov, M. E. and K. B. Lauritsen, Analysis of wave fields by Fourier integral operators and their application for radio occultations [J], Radio Sci., 39(4), 2004.
[20] Jensen, A. S., M. S. Lohmann, H. H. Benzon, et al., Full spectrum inversion of radio occultation signals [J], Radio Sci., 38(3), 2003.
[21] Karayel, E. T. and D. P. Hinson, Sub-Fresnel-scale vertical resolution in atmospheric profiles from radio occultation [J], Radio Sci., 32(2), 411-423, 1997.
[22] Wang, X. and D. R. Lu, Comparative analysis of inversion methods of retrieving atmospheric profiles with GPS occultation measurements [J], Chinese Journal of Geophysics-Chinese Edition, 50(2), 346-353, 2007.
[23] Garcia-Fernandez, M., M. Hernandez-Pajares, M. Juan, et al., Improvement of ionospheric electron density estimation with GPS/MET occultations using Abel inversion and VTEC information [J], JGR-Space Physics, 108(A9), 2003.
[24] Hajj, G. A., R. Ibanez-Meier, E. R. Kursinski, et al., Imaging the ionoshpere with the Global Positioning System [J], Int. J. Imaging Sys. & Tech., 5(2), 174-184, 1994.
[25] Tsai, L. C. and W. H. Tsai, Improvement of GPS/MET ionospheric profiling and validation using the Chung-Li ionosonde measurements and the IRI model [J], Terr. Atmos. Oceanic Sci., 15(4), 589-607, 2004.
[26]杜起飞,孙越强,刘正廷,等,GPS掩星探测天线相位中心的校准[J],空间科学学报,26(6),487-490,2006.
[27] Zeng, Z., X. Hu and X. J. Zhang, Applying artificial neural network to the short-term prediction of electron density structure using GPS occultation data [J], Geophys. Res. L., 29(9), 2002.
[28]胡雄,张训械,吴小成,等,山基GPS掩星观测实验及其反演原理[J],地球物理学报,49(1),22-27,2006.
[29] Hu, X., X. C. Wu, X. Y. Gong, et al., An introduction of mountain-based GPS radio occultation experiments in China [J], Advances in Space Research, 10(42), 1723-1729, 2008.
[30]宫晓艳,胡雄,吴小成,等,雾灵山GPS掩星观测事件统计分析[J],应用气象学报,19(3),2008.
[31]胡雄,曾桢,张训械,等,大气GPS掩星观测反演方法[J],地球物理学报,48(4),768-774,2005.
[32]王鑫,吕达仁,GPS无线电掩星技术反演大气参数方法对比[J],地球物理学报,50(2),346-353,2007.
[33]吴小成,胡雄,张训械,等,电离层GPS掩星观测改正TEC反演方法[J],地球物理学报,49(2),328-334,2006.
[34]宫晓艳,胡雄,吴小成,等,大气掩星反演误差特性初步分析[J],地球物理学报,50(4),1017-1029,2007.
[35] Syndergaard S., On the ionospheric calibration in GPS occultation measurements [J], Radio Sci., 35(3), 865-883, 2000.
[36] Schreiner, W. S., S. V. Sokolovskiy, C. Rocken, et al., Analysis and validation of GPS/LEO radio occultation data in the ionosphere [J], Radio Sci., 34(4), 949-966, 1999.
[37] Beyerle, G., T. Schmidt, G. Michalak, et al., GPS radio occultation with GRACE: Atmospheric profiling utilizing the zero difference technique [J], Geophys. Res. L., 32(13), 2005a.
[38] Eshleman, V. R., G. L. Tyler, G. E. Wood, et al., Radio science with Voyager 1 at Jupiter: preliminary profiles of the atmosphere and ionosphere [J], Science, 204, 976-978, 1979.
[39] Fjeldbo, G., V. R. Eshleman, The atmosphere of Mars analyzed by integral inversion of the Mariner IV occultation data [J], Planet Space Sci., 16, 1035-1059, 1968.
[40] Fjeldbo, G., A. J. Kliore, V. R. Eshleman, The neutral atmosphere of the Venus as studied with the Mariner V radio occultation experiments [J], Astron. J., 76, 123-140, 1971.
[41] Hajj, G. A., L. J. Romans, Ionospheric electron density profiles obtained with theGlobal Positioning System: Results from the GPS/MET experiment [J], Radio Sci., 33(1), 175-190, 1998.
[42] Kuo, Y.-H., X. Zou, W. Huang, The impact of GPS data on the prediction of an extratropical cyclone: An observing system simulation experiment [J], J. Dyn. Atmos. Ocean, 27, 439-470, 1997.
[43] Kursinski, E. R., G. A. Hajj, J. T. Schofield, et al., Observing earth’s atmosphere with radio occultation measurements using the Global Positioning System [J], J. Geophys. Res., 102(D19), 23429-23465, 1997.
[44] Lindal, G. F., Atmosphere of Neptune [J], Astronom. J., 103, 976-982, 1992.
[45] Ogawa, T., Radar Observations of Ionospheric irregularities at Syowa Station, Antarctica: A brief Overview [J]. Ann. Geophys., 14, 1454-1461, 1996.
[46] Rius, A., G. Ruffini, A. Romeo, Analysis of ionospheric electron density distribution from GPS/MET occultations [J], IEEE Trans. Geosci. & Remote Sensing, 36, 383-394, 1998.
[47] Rocken, C., R. Anthes, M. Exner, et al., Analysis and validation of GPS/MET data in the neutral atmosphere [J], J. Geophys. Res., 102(D25), 29849-29866, 1997.
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