[P-EM11] Space Weather and Space Climate

[PEM11-P20] Long-Term Trend of bias current obtained from Himawari-8/SEDA-e observation

*Tsutomu Nagatsuma¹, Kaori Sakaguchi¹ (1.National Institute of Information and Communications Technology)

Keywords:High Energy Particles, Sensor Calibration, Sensor Degradation, Data Processing

Space environment data acquisition monitor (SEDA) onboard Himawari-8, a Japanese geostationary meteorological satellite, has been operating since Nov. 2014. So Himawari-8 has almost 9 years of observation at Japanese meridian of GEO. SEDA has two sensors. One is high energy electron sensor (SEDA-e) and the other is high energy proton sensor (SEDA-p). SEDA-e measures internal charging currents produced from high energy electrons (from 0.1 to 4.5 MeV) collected by 8 metal plates arranged in a stack. Electron fluxes are estimated from the charging currents in each plates. Since the charging currents are quite small, it needs to be amplified by operational amplifier. This means that bias current is contaminated as an offset of particle flux. Therefore, we need to remove the bias current effect. We use bias current model based on the pre-flight measurements for subtraction. The bias current model is a function of temperature of SEDA-e. This works well for the beginning of Himawari-8/SEDA observation. However, the background flux level tends to be increase as time goes on especially for higher energy channels. This suggests that the bias current tend to be increasing with time goes on. Using more than nine years of SEDA-e and its temperature data, long-term trend of bias current and its relationship with high energy particle environment will be discussed in our presentation.