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As wide-field scanning solar irradiance monitors (SIMs) on the FY-3(01) satellite and FY-3(02) satellite have short measuring time and low accuracy, the high precision sun-tracking measurement of the SIM on the FY-3(03) satellite was explored. Firstly, the sun-tracking accuracy and the rotation angle of the SIM were analyzed, the field of view, frequency and the resolution of the Digital Sun Sensor (DSS) were tested and determined, and the on-orbit image irradiance of the DSS was calibrated. In order to eliminate the jitter tracking, the relationship between the control interval and the tracking accuracy was analyzed, and the ideal control interval was determined to be 500 ms. The experiment on ground and on-orbit show that the sun-tracking accuracy of SIM is better than 0.1, the pitch on-orbit tracking accuracy, yaw on-orbit tracking accuracy are 0.029 and 0.025, respectively, and the original TSI value measured successfully by the SIM is 1353.1 W/m2. Moreover, the DSS shows an accurate sun pointing and reliable sun-tracking control, by which the measurement time of TSI is increased significantly. The experiment shows that the SIM on the FY-3(03) satellite implements the sun-tracking measurement on the sun synchronous satellite, and the tracking accuracy is about 10 times that of the similar payload CPD on International Space Station (ISS).

Solar Irradiance Monitor(SIM) on the FY-3C satellite was designed to be a Small-field-of-view Radiometer(SFoV-R) with a precise solar pointing system to decrease the measurement uncertainty derived from the wide field-of-view of SIM on FY-3A and FY-3B satellites.To obtain the measurement uncertainty derived from the SFoV-R,the field-of-view of SFoV-R on FY-3C satellite determined by a view-limiting aperture and a precision aperture was calculated.Based on this field-of-view,a theoretical change curve of the measured irradiance incidence angle was achieved.Then,an actual measurement of the change curves was performed.The result indicates that the relative deviation on an average between the theoretical and measured change curves is 1%-2%,which is close to the limit accuracy of the measuring installation and proves the veracity of the calculated values for field-of-view.The correction term of radiation exchange between space and the radiometer is estimated to be 2.023 W/m2 based on the calculated field-of-view.Experiments show that the standard deviation of this correction term can be neglected compared to the requirement of solar irradiance measurement accuracy.