Investigation of Thermal Response Model for Solar Irradiance Absolute Radiometer

Abstract

Solar Irradiance Absolute Radiometer (SIAR) is a cavity-type electrical substitution radiometer for transferring the World Radiance Reference (WRR). In order to shorten the measurement period, and ensure the measurement precision, the cavity temperature response model is experimentally investigated and corrected. The thermodynamic equation of cavity temperature is solved. Based on the analysis of non-equivalent in optical and electrical heating, the cavity temperature response model is corrected to a double exponential form. The simulation result analyzes the origin of the temperature pulse. A new characteristic parameter, named as non-equivalent response time, is proposed and measured. The cavity temperature response characteristic of SIAR is improved by the compensation of the temperature pulse. Comparison experiment results illustrate that the temperature pulse can be compensated by inserting a delay time, and the cavity temperature response model is simplified to a single exponential form. Thus, SIAR with large thermal time constant can adopt shorter measurement period, meanwhile measurement precision is 0.07%. The investigation of non-equivalent response time is important for the radiant calibration of SIAR. This correction method can also be used to optimize the on-orbit calibration method of Total Solar Irradiance Monitor (TSIM).