Abstract
Japan Aerospace Exploration Agency (JAXA) operates integrating spheres (barium-sulfate-coated, gold-coated, and PTFEcoated) at Tsukuba Space Center for radiometric calibration in the visible and short-wave infrared spectral bands, and several JAXA missions have utilized these spheres for the ground calibration test of their onboard sensors. The bariumsulfate- coated integrating sphere has the largest aperture diameter (36 cm), and it has been employed for calibration of satellite-borne cameras (e.g., PLANET-C, Hayabusa-2). However, the spatial uniformity of this sphere has gradually deteriorated due to long-term aging of the barium sulfate coating, after more than two decades of operation. Although its performance is periodically evaluated and correction factors are applied to compensate for spatial non-uniformity, the increasing magnitude of the compensation introduces additional uncertainty, thereby degrading radiometric calibration accuracy. Furthermore, since it is equipped only with halogen lamps, the achievable radiance in the wavelength region below 400 nm does not meet the standard radiance requirements for Earth-observation missions, even with all the halogen lamps on. This limitation poses a significant challenge for future Earth-observation missions requiring the shortwavelength bands for aerosol identification and ocean color monitoring.
Hence, we introduced a large-size barium-sulfate-coated integrating sphere equipped with LED and halogen lamps in 2025. The sphere has a diameter of 1 m and an exit port diameter of 40 cm, and multiple halogen lamps with different wattages are installed in a triad configuration. In addition, dedicated LED light source modules are also installed to enhance radiance output and improve spectral performance and stability in the wavelength band around 400 nm. The radiance level can be adjusted not only by turning the lamps on or off, but also by using built-in attenuators attached to the front of the lamps. Following the installation at Tsukuba Space Center, performance evaluations (spatial uniformity, angular uniformity, radiance stability, repeatability, etc.) were conducted using the established procedures. The results show that it achieves both high radiance around 400 nm and good uniformity, compared with the currently used integrating sphere. This presentation reports the performance evaluation results, along with the future operational procedures for maintaining traceability to primary standards at the National Institute of Advanced Industrial Science and Technology (AIST).
Initial Operation Results of a Barium-Sulfate-Coated Integrating Sphere Equipped with LED and Halogen Lamps
Japan Aerospace Exploration Agency (JAXA) operates integrating spheres (barium-sulfate-coated, gold-coated, and PTFEcoated) at Tsukuba Space Center for radiometric calibration in the visible and short-wave infrared spectral bands, and several JAXA missions have utilized these spheres for the ground calibration test of their onboard sensors. The bariumsulfate- coated integrating sphere has the largest aperture diameter (36 cm), and it has been employed for calibration of satellite-borne cameras (e.g., PLANET-C, Hayabusa-2). However, the spatial uniformity of this sphere has gradually deteriorated due to long-term aging of the barium sulfate coating, after more than two decades of operation. Although its performance is periodically evaluated and correction factors are applied to compensate for spatial non-uniformity, the increasing magnitude of the compensation introduces additional uncertainty, thereby degrading radiometric calibration accuracy. Furthermore, since it is equipped only with halogen lamps, the achievable radiance in the wavelength region below 400 nm does not meet the standard radiance requirements for Earth-observation missions, even with all the halogen lamps on. This limitation poses a significant challenge for future Earth-observation missions requiring the shortwavelength bands for aerosol identification and ocean color monitoring.
Hence, we introduced a large-size barium-sulfate-coated integrating sphere equipped with LED and halogen lamps in 2025. The sphere has a diameter of 1 m and an exit port diameter of 40 cm, and multiple halogen lamps with different wattages are installed in a triad configuration. In addition, dedicated LED light source modules are also installed to enhance radiance output and improve spectral performance and stability in the wavelength band around 400 nm. The radiance level can be adjusted not only by turning the lamps on or off, but also by using built-in attenuators attached to the front of the lamps. Following the installation at Tsukuba Space Center, performance evaluations (spatial uniformity, angular uniformity, radiance stability, repeatability, etc.) were conducted using the established procedures. The results show that it achieves both high radiance around 400 nm and good uniformity, compared with the currently used integrating sphere. This presentation reports the performance evaluation results, along with the future operational procedures for maintaining traceability to primary standards at the National Institute of Advanced Industrial Science and Technology (AIST).