| The thermal infrared imager(TIRI)is the main payload of CASEarth satellite,which can achieve a resolution of 30 m and a width of 300 km through whisk broom with line array in the 505 km orbit,and is currently the thermal infrared payload with the largest width resolution ratio in China.Once launched into orbit,CASEarth,will provide high-resolution thermal infrared remote sensing data for the detection of human activities,economic development,pollution(water,soil and air pollution)monitoring and ecological function assessment,water resources and arable land census.High-precision radiometric calibration is the key to the quantitative application of remote sensing data.The calibration accuracy of the TIRI is affected by the radiometric calibration model,calibration frequency,instrument temperature,detector stability,measurement accuracy of calibration source such as blackbody,instrument sensitivity and other factors.This research is carried out from three aspects,multi-parameter joint extremum optimization design,low-frequency calibration model,and on-orbit high-precision solution method for the whisk broom thermal infrared load.The main contents and innovations are as follows:1.Aiming at the problem of limited integration time of whisk broom camera,a multi-parameter joint optimization model,such as responsivity,instrument temperature and dark current,is established in this paper.Incorporate engineering constraints,and the optimization of parameters such as temperatures of instrument,integration capacitance,integration time and optical aperture are set.Besides,for the large field of view optical system where the low temperature exit pupil does not match the cold stop,a multi-component temperature grid simulation model is established to optimize the stray radiation of the instrument,so that the ratio of the instrument's internal thermal radiation to the 300 K blackbody signal is less than0.214(8-10.5?m)?0.204(10.3-11.3?m)?0.563(11.5-12.5?m),which is similar to the ratio of Landsat 8 TIRS.In the realization of 300 km width,30 m high resolution,the noise equivalent temperature difference of the instrument is better than 0.08 K.2.The whisk broom with long line array of TIRI needs to adjust satellite attitude to view deep space.The observation of deep space can quantitative measure background response.In view of the problem that frequent radiometric calibration affects the effective use of time of the TIRI,this paper proposes a high frequency of background response prediction method based on the temperatures of instruments and a low frequency calibration model based on instrument stability evaluation is established.The on-orbit radiometric calibration is viewing fixed temperature blackbody every scan and viewing deep space every two weeks.Besides the above normalized radiometric calibration methods,we introduce stars and the moon as calibration sources for cross-calibration,the iterative optimization of calibration frequency can be further realized in orbit.This method has been verified by other satellites.3.CASEarth thermal infrared imager adopts a three-band integrated filter,a four-stage TDI and 2000 pixels long line array.For the four-stage TDI detector,a four-stage TDI pixel selection method based on multi-temperature point traversal is proposed,and the noise equivalent temperature difference of the three bands can be increased by 13.14%,7.30% and 9.36%,respectively.For spectral transmittance,non-uniformity of blackbody temperature,affected the accuracy of radiometric calibration parameters,ground measurements and analysis methods are established.We put forward the low frequency time efficient calibration calculating method,and verify the validity of the method through the ground vacuum low temperature radiometric calibration test.The laboratory radiometric calibration uncertainty is less than or equal to 0.500 K. |
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