17:15 〜 19:15
[PPS03-P16] Current Status of Ground-Based Optical Calibration for the DESTINY+ On-board Cameras
キーワード：DESTINY+、(3200)Phaethon、光学校正、カメラ
DESTINY+ (Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science) is a flyby exploration mission to the asteroid (3200) Phaethon. The on-board cameras of DESTINY+, TCAP (Telescopic CAmera for Phaethon. Panchromatic camera) and MCAP (Multiband CAmera for Phaethon. 4 bands; 425 nm, 550 nm, 700nm, 850nm), will observe Phaethon to understand the nature of a meteor shower' s parent body. The raw images captured by these cameras must be converted into scientifically meaningful data through optical calibration to enable scientific analysis of the images.
The images captured by the cameras are mainly expected to be calibrated following the correction steps: (1) Bias correction, (2) Dark correction, (3) Linearity correction, (4) Flat-field correction, (5) Sensitivity correction, (6) Distortion correction. Each calibration requires bias images that correct the offset level of the sensor, dark images that correct the dark component of the images, linearity-correction data that correct deviation from linear relation, flat-field images captured from a target with spatially uniform radiance, sensitivity-correction data that correlate the count value with radiance, and distortion images from which the distortion coefficients are determined.
The manufacture and performance validation of the TCAP engineering model (EM) has been completed. We obtained bias images, dark images, and linearity-correction data using a thermostatic chamber. Since these calibration data do not require or are not affected by an optical system, they were acquired before the optical system was attached (i.e., only with the image sensor). We also evaluated various performances of the image sensor from the data, including bias level, dark current, dark noise, readout noise, conversion gain, Photo Response Non-Uniformity (PRNU), full-well capacity, linearity, and dead pixels. All the sensor performances were confirmed to match the catalog values provided by the image sensor manufacturer and to satisfy the required specifications within the margin of error. The flat-field images and the sensitivity-correction data has been acquired after the completion of TCAP EM using an integrating sphere at Tsukuba Space Center, whose spectral radiance is spatially uniform and has been calibrated to absolute radiance values with high precision. The data acquisition with the EM also serves as a rehearsal for the data acquisition with the proto-flight model (PFM). Thus we could extract some issues of the measurement method for preparing for the precise calibration-data acquisition for PFM.
The manufacture and calibration-data acquisition of MCAP EM was completed over a year ago. We found intense stray light due to the prism separating the light into two sensors. Therefore, although the data acquisition was not necessarily suitable for precise calibration, it helped us confirm the measurement procedure, prepare the measurement jig, and identify issues related to the optical system and the data acquisition. The stray light problem was fixed in the design of the proto-flight model (PFM) of MCAP, and the PFM is currently being assembled. The bias images, dark images, and linearity-correction data for PFM were obtained in the thermostatic chamber before the attachment of the optical system. We also confirmed that the performances of all four sensors match the catalog values and satisfy the required specifications with those data. The environmental tests of MCAP PFM will be conducted, followed by the acquisition of calibration data. After that, we also plan to conduct meteorite imaging tests, using some spectra-known meteorite samples to confirm the multiband imaging performance.
The images captured by the cameras are mainly expected to be calibrated following the correction steps: (1) Bias correction, (2) Dark correction, (3) Linearity correction, (4) Flat-field correction, (5) Sensitivity correction, (6) Distortion correction. Each calibration requires bias images that correct the offset level of the sensor, dark images that correct the dark component of the images, linearity-correction data that correct deviation from linear relation, flat-field images captured from a target with spatially uniform radiance, sensitivity-correction data that correlate the count value with radiance, and distortion images from which the distortion coefficients are determined.
The manufacture and performance validation of the TCAP engineering model (EM) has been completed. We obtained bias images, dark images, and linearity-correction data using a thermostatic chamber. Since these calibration data do not require or are not affected by an optical system, they were acquired before the optical system was attached (i.e., only with the image sensor). We also evaluated various performances of the image sensor from the data, including bias level, dark current, dark noise, readout noise, conversion gain, Photo Response Non-Uniformity (PRNU), full-well capacity, linearity, and dead pixels. All the sensor performances were confirmed to match the catalog values provided by the image sensor manufacturer and to satisfy the required specifications within the margin of error. The flat-field images and the sensitivity-correction data has been acquired after the completion of TCAP EM using an integrating sphere at Tsukuba Space Center, whose spectral radiance is spatially uniform and has been calibrated to absolute radiance values with high precision. The data acquisition with the EM also serves as a rehearsal for the data acquisition with the proto-flight model (PFM). Thus we could extract some issues of the measurement method for preparing for the precise calibration-data acquisition for PFM.
The manufacture and calibration-data acquisition of MCAP EM was completed over a year ago. We found intense stray light due to the prism separating the light into two sensors. Therefore, although the data acquisition was not necessarily suitable for precise calibration, it helped us confirm the measurement procedure, prepare the measurement jig, and identify issues related to the optical system and the data acquisition. The stray light problem was fixed in the design of the proto-flight model (PFM) of MCAP, and the PFM is currently being assembled. The bias images, dark images, and linearity-correction data for PFM were obtained in the thermostatic chamber before the attachment of the optical system. We also confirmed that the performances of all four sensors match the catalog values and satisfy the required specifications with those data. The environmental tests of MCAP PFM will be conducted, followed by the acquisition of calibration data. After that, we also plan to conduct meteorite imaging tests, using some spectra-known meteorite samples to confirm the multiband imaging performance.