Gallium Fixed-point Blackbody Radiation Source for Calibration of Sea Surface Temperature Radiometer

A gallium fixed-point blackbody infrared radiation source is designed to calibrate the sea surface temperature radiometer. Due to the fact that the sea surface temperature radiometer requires additional regular calibration data before and after deployment to monitor the performance characteristics of the instrument, water bath blackbodies and ammonia heat pipe blackbodies are commonly used internationally for calibration. However, water bath blackbodies are greatly affected by atmospheric pressure, and ammonia heat pipe blackbodies are large in volume and difficult to transport. Therefore, a gallium blackbody is designed for the calibration of sea surface temperature radiometers. Firstly, the structure and working principle of a gallium fixed-point blackbody radiation source are introduced. The simulation software, which is based on the Monte Carlo algorithm, then simulate the emissivity of STEEP321 blackbodies and conducted experiments to measure the emissivity. The source of emissivity uncertainty is discussed. Experiments on phase transformation reproducibility of gallium under electric heating and water- bath heating are carried out and the effect of electric heating power on phase transformation reproducibility of gallium is discussed. Finally, the measurement experiment of ISAR thermometer radiometer is carried out to verify the blackbody. The results show that the emissivity is better than 0.998 8, and the emissivity measured by the radiation method is in good agreement with the theoretical simulation results, and the measurement repeatability(standard deviation)reaches 0.1%. The results show that the reproducibility of phase change temperature table is better than +/- 0.03 K. The difference between ISAR and FLUKE 1524 measurements of the temperature near the blackbody cavity is within +/- 0.15 K. The blackbody is developed successfully and can be used to calibrate the sea surface temperature radiometer after modification, and it can provide calibration sources for the development of sea surface temperature measurement equipment with independent intellectual property rights. The theoretical calculation of emissivity is high, but the actual measurement of emissivity is lower than the theory for the following reasons:the ratio of black body cavity length to opening diameter is not large enough, and the uncertainty in the measurement process of emissivity. The craft used for the fixed-point container is generally to spray polytetrafluoroethylene film on its surface. Thicker polytetrafluoroethylene cylinder and polytetrafluoroethylene sleeve are installed with gallium fixed point, which greatly avoids the pollution caused by direct contact of metal when the sprayed polytetrafluoroethylene film is relatively thin.