摘要 在華衛一號上的電離層電漿電動儀( IPEI )之孔徑面上裝載有一個調節IPEI表面電位的裝置，稱為SENPOT。其作用在使IPEI探測儀的表面電位和外界電漿的電位相近，將探測儀表面電位對探測儀所要測量的帶電粒子流影響降至最低。其隨時間所調節的電位大小稱為SENPOT potential。我們可以利用此一SENPOT potential來觀察低軌道低緯度衛星體的表面充電效應( Spacecraft Surface Charging )和電離層環境的關係。 經由理論可以得知，低軌道低緯度的衛星，其表面電流主要來自外界電漿的電子流與離子流，而這部分又和電離層的環境息息相關。 藉由資料的分析可以發現，在不討論地磁效應和缺乏電子溫度的資料之下，低軌道衛星的探測儀表面電位和外界電漿電位之差異，和電離層離子濃度的相關性非常大。而在磁暴來臨時，離子溫度和漂移速度的劇烈變化，也會使得SENPOT potential產生短時間的明顯改變。 在太陽閃焰(solar flare)較為強烈的日子，往往會改變電離層環境，尤其是日落後的電離層離子濃度增加現象。這也會使得SENPOT potential跟著環境變化，產生日落後的極大值延後約1.8個小時，以及消退趨緩的現象。 Abstract The ionospheric plasma and electrodynamics instrument (IPEI) onboard the ROCSAT-1 satellite consists of four sensors and a sensors potential circuit (SENPOT) on its aperture plane. The SENPOT is designed for minimizing the potential between the plasma and the sensor’s aperture plane to prevent from the surface potential effect on the ionized particles. The modulated potential by SENPOT varying with time is called the SENPOT potential. In this thesis, we use the SENPOT potential data to investigate the relationship between the satellite surface charging and the environmental conditions at low latitude ionosphere. The surface current of the low-orbit and low-inclination spacecraft is dominated by ambient plasma current. Theoretically, SENPOT potential is strongly related to electron temperature. Unfortunately, ROCSAT-1 IPEI did not provide the in-situ measurements of electron temperature. However, by analyzing the other IPEI data we found that the SENPOT potential is strongly varying with the ion density. During the storm days, correlated violent changes were found among the ion temperature, ion drift velocity and the SENPOT potential. In the days when there were large solar flares, the ion density enhancements were frequently observed after the sunset hours. Similar changes with local time were found in the SENPOT potentials, with the peak SENPOT potential at about 1.8 hours after the local sunset. In addition, the fading of SENPOT potential is slower than that of the normal days.
