卡西尼號磁力計用以量測土星周圍的磁場強度與方向。在本論文中，我們使用介於2005年一月至2009年十二月之間，卡西尼號與土星距離小於8倍土星半徑的磁力計觀測資料。首先我們扣除背景磁場得到磁場擾動，再篩選出頻率接近水族離子迴旋頻率的訊號，並判斷其偏極，確認其為離子迴旋波後再進一步分析它們在土星磁層的空間與強度分佈，我們發現離子迴旋波大多分佈在小於6倍土星半徑的低緯度區域。從高緯度區域 (2008年資料) 測量到的迴旋波頻率我們推測波源的位置在赤道附近，而且離子迴旋波是沿著磁場傳播。我們發現水族離子迴旋波也可能出現在大於6倍土星半徑的區域。最後，在假設離子為冷環分布(cold ring distribution)的條件下，我們也推導了離子迴旋波的不穩定條件並且與觀測資料作比較。

The magnetometer (MAG) on the Cassini satellite measures the strength and direction of the magnetic field in the Saturn magnetosphere. In this research, we use MAG data when the distance between Cassini and Saturn is smaller than 8RS from 2005 January to 2009 December. First, we remove the background magnetic field, then pick up the magnetic perturbation signals with frequencies near the water group ion gyro-frequencies and determine their polarization to identify that they are water group ion cyclotron waves which are left-hand circularly polarized. Furthermore, we determine the spatial and intensity distributions of the water group ion waves in the Saturn magnetosphere. We find that the source region of water group ion cyclotron waves is mostly in the low latitude regions near the equator inside 6RS radial distance and the ion cyclotron waves propagate along magnetic field line to higher latitude region (in 2008 data). However, we also find that some water group ion cyclotron waves may appear outside 6RS region. Finally, by assuming that the water group ions have a cold ring distribution, we have derived the instability condition of ion cyclotron waves and compare with observed wave and plasma data.

Andre, N., M. Blanc, S. Maurice, et al. (2008), Identification of Saturn's magnetospheric regions and associated plasma processes: Synopsis of Cassini observations during orbit insertion, Rev. Geophys., 46, RG4008.
Barbosa, D. D. (1993), Theory and observations of electromagnetic ion cyclotron waves in Saturn’s inner magnetosphere, J. Geophys. Res., 98, 9345–9350.
Blanco-Cano, X. (2004), Wave generation in moon-satellite interactions, Adv. Space Res., 33, 2078– 2091.
Belenkaya, E.S., I. I. Alexeev, V. V. Kalagaev, M. S. Blohhina (2006), Definition of Saturn’s magnetospheric model parameters for the Pioneer 11 flyby, Ann. Geophys., 24, 1145–1156.
Chou, M. and C. Z. Cheng (2010), Modeling of Saturn’s magnetosphere during Voyager 1 and Voyager 2 encounters, J. Geophys., 115, A08202, doi:10.1029/2009JA015124
Cowee, M. M., N. Omidi, C. T. Russell, X. Blanco-Cano, and R. L. Tokar (2009), Determining ion production rates near Saturn’s extended neutral cloud from ion cyclotron wave amplitudes, J. Geophys. Res., 114, A04219, doi:10.1029/2008JA013664.
Dougherty, M. K., N. Achilleos, N. Andre, C. S. Arridge, A. Balogh, C. Bertucci, M. E. Burton, S. W. H. Cowley, G. Erdos, G. Giampieri, K.-H. Glassmeier, K. K. Khurana, J. Leisner, F. M. Neubauer, C. T. Russell, E. J. Smith, D. J. Southwood, B. T. Tsurutani (2005), Cassini Magnetometer Observations During Saturn Orbit Insertion, Science, 307, 1266.
Gombosi, T. I., and A. P. Ingersoll (2010), Saturn: Atmosphere, Ionosphere, and Magnetosphere, Science, 327, 1476, doi: 10.1126/science.1179119.
Huddleston, D. E., R. J. Strangeway, J. Warnecke, C. T. Russell, and M. G. Kivelson (1998), Ion cyclotron waves in the Io torus: Wave dispersion, free energy analysis, and SO2+ source rate estimates, J. Geophys. Res., 103, 19,887–19,889.
Jia, Y.‐D., C. T. Russell, K. K. Khurana, J. S. Leisner, Y. J. Ma, and M. K. Dougherty (2010), Time‐varying magnetospheric environment near Enceladus as seen by the Cassini magnetometer, Geophys. Res. Lett., 37, L09203, doi:10.1029/2010GL042948.
Kivelson, M. G. (2005), The current systems of the Jovian magnetosphere and ionosphere and predictions for Saturn, in The Outer Planets and their Moons, Space Sciences Series of ISSI, 19, 299-318, doi: 10.1007/1-4020-4038-5_16.
Leisner, J. S., C. T. Russell, M. K. Dougherty, X. Blanco-Cano, R. J. Strangeway, and C. Bertucci (2006), Ion cyclotron waves in Saturn’s E ring: Initial Cassini observations, Geophys. Res. Lett., 33, L11101, doi:10.1029/2005GL024875.
Martinez, C. (2005), Cassini Discovers Saturn's Dynamic Clouds Run Deep, (http:/ /www. nasa. gov/ mission_pages/ cassini/ whycassini/cassini-090505-clouds. html). NASA. Retrieved 2007-04-29.
Mauk, B. H.; D. C. Hamilton,; T. W. Hill, et. al. (2009), Fundamental Plasma Processes in Saturn’s Magnetosphere, Saturn from Cassini-Huygens, M. K. Dougherty, L. W. Esposito, and S. M. Krimigis (Eds.), pp. 281-331, Springer, Dordrecht.
Press, W. H., S. A. Teukolsky, W. T. Vetterling (1992), Numerical Recipes in C. Cambridge University Press, Cambridge New York Port Chester Melbourne Sydney.
Rodríguez-Martínez, M., X. Blanco-Cano, C. T. Russell, J. S. Leisner, R. J. Wilson, and M. K. Dougherty (2010), Harmonic growth of ion-cyclotron waves in Saturn's magnetosphere, J. Geophys. Res., 115, A09207, 13 pp., doi:10.1029/2009JA015000.
Russell, C.T. (1993), Planetary Magnetospheres, Reports Progress Phys., 56: 687–732.
Russell, C. T., J. S. Leisner, C. S. Arridge, M. K. Dougherty, and X. Blanco-Cano (2009), Nature of magnetic fluctuations in Saturn’s middle magnetosphere, J. Geophys. Res., 111, A12205, doi:10.1029/2006JA011921.
Smith, E. J., and B. T. Tsurutani (1983), Saturn’s magnetosphere: Observations of ion cyclotron waves near the Dione L shell, J. Geophys. Res., 88, 7831– 7836.
Reference Websites:MAG measurements: http://www.nasa.gov/externalflash/135_splash/index.html