This principle focus of this study is the absolute radio metric calibrations of FORMOSAT-2 RSI imagery in orbit. There are two principal parts for achieving this calibration. The first is the assessment of the calibration site by examining atmospheric observations from ground stations and field measurements via ground-based radio metric instruments. After careful consideration based on the essential requirements for a suitable calibration site i.e., prevailing clear and clean atmosphere conditions over a wide, flat and near lambertian surface with high reflectance, the airport on Dongsha Island was considered to be an suitable site. The next phase is to de sign a scheme for the field campaign at the calibration site for radio metric calibration. Thus a synchronous experiment acquiring simultaneous measurements from the FORMOSAT-2 Remote Sensing Instrument (RSI) sensor and ground-based instruments was proposed and implemented for the period 16 to 19 September 2004. As a result, a set of reason able radio metric coefficients for the absolute radiance calibration of the RSI was successfully constructed via the radiative transfer code associated with the synchronous measurements in this study.