Research Of On-orbit Radiometric Calibration Of Direct Solar Viewing

On-orbit calibration technology is an effective mean to ensure the quantitative application of remote sensors.At present,the on-orbit calibration technology based on the diffuser has become mature,MODIS with an accuracy of 2%?4%is recognized as the highest level.However,climate change prediction and on-orbit cross-calibration research need higher accuracy,due to its own reflection characteristics the diffuser limits the calibration accuracy further improved.In order to satisfy the needs of scientific research,the international proposed the on-orbit radiometric calibration of direct solar viewing.It avoids the uncertainly of on-orbit calibration due to degeneration of the diffuser,it is possible to make the calibration accuracy to get an order of magnitude of the upgrade.Aiming at the direct observation of the sun,the new radiometric calibration method was discussed,at the same time its overall technology program has been designed.According to the characteristics of the observation target during the calibration process,methods of attenuating the sunlight was designed,moreover the measure of the attenuation factor was included.Firstly,the radiance of the typical observation targets which includes solar,lunar and earth was calculated,and it obtained that on-orbit calibration of direct solar viewing based on attenuating five orders of magnitude to the sunlight by analyzing and comparing the results.Then according to the required attenuation times,two ways which included combination attenuation methods and perforated plate were studied.The combination attenuation methods used decreasing optical entrance aperture size,shorting detector integration time and inserting attenuating filters to collectively provide the level of attenuation,and the perforated plate achieved the objective by both blockage and diffraction.Next,three attenuation factors belonged to combination attenuation methods were experimented respectively,and the actual attenuation ratio was measured.The result of combination attenuation methods could achieve 5 orders of magnitude,meet the requirements of on-orbit calibration of the direct observation of the sun.Finally,the progress and shortcoming of the study were summarized,and direction of the next research had been given.