Abstract
TRISHNA is an Indian-French cooperative mission to be launched in 2025. Its principal focus will be on evapo-transpiration, ecosystem stress, and coastal oceans sea surface temperature. The satellite will host two payloads: one instrument in the VSWIR range – 7 bands from 485 to 1600 nm under ISRO’s responsibility, and one instrument in the TIR range – 4 bands from 8.5 to 11.5 μm. The resolution of both instruments is 57m at nadir and their swath is about 1000 km. TRISHNA’s TIR and VSWIR instruments will be extensively calibrated and characterized in on-ground facilities to ensure that their performance will meet the specifications throughout TRISHNA’s lifetime. Yet, the operation in space after the launch and during several years can lead to different behaviors as the ones expected from ground calibration, justifying a validation and if necessary a calibration of some parameters of the ground processing. The TRISHNA TIR instrument radiometric performances rely on an on-board calibration device (blackbody) and cold space viewing. Some so-called vicarious calibration methods are being developed in the TIR using natural targets in order to validate and monitor the calibration performed using the blackbody, and to potentially be used as a backup in case of hardware failure. These natural targets include the oceans, the Moon, snow deserts in Antarctica or Greenland and instrumented sites. The TRISHNA VSWIR instrument on the other hand will not benefit from an on-board calibration and will exclusively rely on vicarious calibration. CNES has experience in vicarious calibration in the VSWIR and will use some methods which have been already proven for other sensors (Rayleigh scattering, deserts, clouds, Moon and instrumented sites). The presentation will focus on the description of the radiometric calibration strategy and the associated methods.
TRISHNA In-orbit Radiometric Calibration
TRISHNA is an Indian-French cooperative mission to be launched in 2025. Its principal focus will be on evapo-transpiration, ecosystem stress, and coastal oceans sea surface temperature. The satellite will host two payloads: one instrument in the VSWIR range – 7 bands from 485 to 1600 nm under ISRO’s responsibility, and one instrument in the TIR range – 4 bands from 8.5 to 11.5 μm. The resolution of both instruments is 57m at nadir and their swath is about 1000 km. TRISHNA’s TIR and VSWIR instruments will be extensively calibrated and characterized in on-ground facilities to ensure that their performance will meet the specifications throughout TRISHNA’s lifetime. Yet, the operation in space after the launch and during several years can lead to different behaviors as the ones expected from ground calibration, justifying a validation and if necessary a calibration of some parameters of the ground processing. The TRISHNA TIR instrument radiometric performances rely on an on-board calibration device (blackbody) and cold space viewing. Some so-called vicarious calibration methods are being developed in the TIR using natural targets in order to validate and monitor the calibration performed using the blackbody, and to potentially be used as a backup in case of hardware failure. These natural targets include the oceans, the Moon, snow deserts in Antarctica or Greenland and instrumented sites. The TRISHNA VSWIR instrument on the other hand will not benefit from an on-board calibration and will exclusively rely on vicarious calibration. CNES has experience in vicarious calibration in the VSWIR and will use some methods which have been already proven for other sensors (Rayleigh scattering, deserts, clouds, Moon and instrumented sites). The presentation will focus on the description of the radiometric calibration strategy and the associated methods.