11:00 AM - 1:00 PM
[PPS03-P08] Radiometric calibration plan for thermal infrared imager TIRI onboard Hera mission
ESA’s Hera mission will explore a binary S-type asteroid Didymos. JAXA develops a thermal infrared imager TIRI onboard Hera spacecraft. TIRI consists of an uncooled micro-bolometer array of 1024 x 768 pixels, optics with a field of view of 13.3 x 10.0 degrees, 7 filters including wide bandpass covering 8-14 μm wavelength and 6 narrow bands at 7.8, 8.6, 9.6 10.6, 11.6, and 13.1 μm. The scientific goals of TIRI are to reveal the thermophysical properties and infrared spectral properties of the S-type asteroid, as well as an artificial crater on its moon Dimorphos formed by the spacecraft impact via the DART mission.
In 2022, both the engineering model (EM) and flight model (FM) of TIRI will be delivered from the manufacturer. In this presentation, we focus on the laboratory-based radiometric calibration test. This calibration test constructs the calibration curves for all pixels, which relate to the target radiance and digital outputs. Furthermore, based on our experience of Hayabusa2’s thermal infrared imager TIR, the bolometer output varies with the target size in the image even if the target temperature is the same (so-called size-of-source effect). Therefore, we should investigate this effect quantitatively.
TIRI calibration instruments consist of a vacuum chamber with a germanium window, a gimbal installing TIRI, and 3 measurement targets (large cold target, blackbody furnace, and infrared collimator). The cold target enables to control the temperature from the room temperature down to 150 K using a Stirling chiller. On the other hand, calibration at the hotter temperature (from room temperature up to 450 K) is performed using the blackbody furnace. To evaluate the size-of-source effect, we use an infrared collimator and a blackbody with several sizes of filter holes. Compiling these data, we will construct the conversion factors to the radiance (or brightness temperature) for each pixel and filter in terms of the target temperature, target size, and instrument temperature.
In 2022, both the engineering model (EM) and flight model (FM) of TIRI will be delivered from the manufacturer. In this presentation, we focus on the laboratory-based radiometric calibration test. This calibration test constructs the calibration curves for all pixels, which relate to the target radiance and digital outputs. Furthermore, based on our experience of Hayabusa2’s thermal infrared imager TIR, the bolometer output varies with the target size in the image even if the target temperature is the same (so-called size-of-source effect). Therefore, we should investigate this effect quantitatively.
TIRI calibration instruments consist of a vacuum chamber with a germanium window, a gimbal installing TIRI, and 3 measurement targets (large cold target, blackbody furnace, and infrared collimator). The cold target enables to control the temperature from the room temperature down to 150 K using a Stirling chiller. On the other hand, calibration at the hotter temperature (from room temperature up to 450 K) is performed using the blackbody furnace. To evaluate the size-of-source effect, we use an infrared collimator and a blackbody with several sizes of filter holes. Compiling these data, we will construct the conversion factors to the radiance (or brightness temperature) for each pixel and filter in terms of the target temperature, target size, and instrument temperature.