为了提高FY－2C的定量化应用，监测遥感仪器的长期变化，为扫描辐射计设计了可见光星上定标器。可见光星上定标器包括工作原理、光机设计、试验方法和在轨定标数据推算。发射前定标试验利用平面镜将太阳引入辐射计星上定标装置，获取电信号和计数值；在轨后每天午夜辐射计获取太阳像并输出计数值。通过分析发射前后所获取的定标图像和数据，并结合两年多的在轨运行状况，检验辐射计可见通道的探测性能，以确定辐射计的运行状态，判断可见光通道的衰减，并作为定量应用的参考。

Multi-channel scan radiometer(MCSR)on FY-2C Satellite launched in October,2004 has been working in orbit for two years. In order to improve quantitative application and track long-term changes in the visible channel,an onboard calibrator using a small beam of sunlight as source is designed,which is fixed on the second mirror and made up of two plates,two prisms and a set of baffles. The calibrator including optical structures,ground-based tests and on-orbit parameters are concisely described. In pre-launch experiments a mirror is used to lead the sunbeam into the MCSR,but in-flight performances the instrument can get the sun signal every midnight. By analyzing and comparing the signals and images,differences between them can be corrected,channel performances such as attenuation can be acquired in time and data also can contribute to better calibration results.