The solar irradiance monitor (SIM), with the design accuracy of 5%, used to monitor the secular changes of the
total solar irradiance on FY-3 satellite, takes the sun-scanning measurement method on-orbit. Compared to the
sun-tracking measurement method, this method simplifies the structure and cuts the cost, but the measuring accuracy is
affected by the sun-synchronous orbit, sunlight incidence angle and the installing angle of the SIM in the satellite.
Through the ground calibration experiment, studies on the affection of different sunlight incidence angles to the
measurement accuracy. First, by the satellite tool kit (STK) simulation software, simulates the orbital parameters of the
sun-synchronous satellite, and calculates the Sun ascension and declination at any time. By the orbit coordinate
transformation matrix gets the components of the Sun vectors to the axes of the satellite, and base on the components
designs the field of view and the installing angles of the SIM. Then, designs and completes the calibration experiment to
calibrate the affection of the incidence angles. Selecting 11 different angles between the sunlight and the satellite X-axis,
measures the total solar irradiance by the SIM at each angle, and compares to the irradiances of the SIAR reference
radiometers, and gets the coefficient curves of the three channels of the SIM. Finally, by the quadratic fitting, gets the
correction equations on the incidence angles: 5 2 3
R1 5.71x10-5α2 - 2.453 10-5 α2 1.0302, R2 = 2.84×10-5α2-1.965x10-3α+1.0314 and R3 =1.72x10-5α2-4.184x10-4α+0.9946. The equations will improve the on-orbit measurement accuracy of the solar
irradiance, and are very important to the on-orbit data processing after the satellite launched.