Experimental Research on the Temperature Characterization of a Miniature Phase Change Cells in the Blackbody for the On-Orbit Radiometric Calibration of Thermal Infrared Sensors

For on-orbit radiometric calibration of infrared (IR) satellite instruments, we have developed a blackbody source whose temperature can be accurately determined by use of miniature phase change cells to provide fixed points. The temperatures and reproducibility of six phase change cells containing H2O, Ga & x2013;Sn alloy, Ga & x2013;Zn alloy, phenyl salicylate (PS), succinonitrile, and Ga were accurately determined by the measurement of the phase change plateaux. The points were measured using the quasiadiabatic vacuum measurement system, which was developed by the National Institute of Metrology, China. The reproducibility time span of the Ga fixed point was as long as six years. Results indicated that the reproducibility values of multiple phase-change run-off point temperatures of H2O, Ga & x2013;Sn alloy, Ga & x2013;Zn alloy, PS, succinonitrile, and Ga were 2.0, 3.6, 1.5, 3.5, 2.9, and 3.1 mK, respectively. Furthermore, a strong linear relation was observed between the heating power and the run-off temperature. With decreasing heating power, the temperature of the plateau decreased and approached the defined fixed-point value. All simulation results of the miniature fixed points were consistent with the experimental data.