ABSTRACT
No matter how well and sophisticated hyperspectral sensors are built and calibrated prior to launch, once on orbits they are subject to degrade with time, for example, due to exposure to space radiation, or thermal, mechanical, or electrical effects. In-flight calibration is to track the instrument behavior on orbit and monitor the development of the instrument performance and especially the radiometric and spectral properties over the entire mission life to ensure a high data quality for the scientific interpretation and operational uses. This chapter begins with the description of the rationale of onboard calibration, distinction of calibration and validation, as well as the relationship between spectral and radiometric calibrations. It reviews onboard calibration systems adopted by eight spaceborne sensors. It then systematically describes and compares onboard radiometric calibration techniques, including solar-based calibration, radiative source based calibration, vicarious calibration, and offset correction. After presenting the strategy of onboard spectral calibration, it provides a systematic description of onboard spectral calibration techniques, including using filtered spectral lines of quartz tungsten halogen lamps, monochromator, doped Spectralon diffuser, atmospheric/solar lines, light emitting diode (LED) spectral lines and etalon. Finally, three concept designs of onboard calibration systems are demonstrated.
