| 其他摘要 | With further development of space remote sensing and constant improvement of requirement on quantitative application of remote sensing data, high precision calibration of space-borne sensor is increasingly more necessary and important. The calibration is the premise of remote sensing products quantitative application. Reliability，breadth and depth of application of remote sensing data depend largely on accuracy of calibration. The calibration is to establish a quantitative relationship between the sensor output digital signal and the corresponding radiation of targets. space-borne sensor calibration includes laboratory calibration and on-orbit calibration. Although laboratory calibration were carried out before space-borne sensor’s launching, the calibrated performance of the instrument would be certain changes over time because of the impact of harsh space environment and conditions inconsistency between on-orbit operation and laboratory calibration. In order to correct and calibrate the impact, on-orbit calibration is required for space-borne sensor. For high-precision imaging spectrometer, the spectral and polarization properties are directly related to its radiometric calibration accuracy. So, on the basis of theoretical analysis and development studies on-orbit calibration of both domestic and foreign space -based sensor, for FY-3 (02) ultraviolet hyperspectral ozone spectrometer characteristics, the research on on-orbit spectral calibration, on-orbit polarization correction and on-orbit radiometric calibration were carried out. The first part of this paper is about on-orbit spectral calibration. On the basis of summarizing the current spectral calibration methods, a new high accuracy on-orbit spectral calibration method has been introduced. According to the principles of spectrometer slit function effect on target spectrum detection，a high resolution target spectrum was used to convolve with instrument’s slit function. The convolved results were matched with corrected spectrum measured by instrument. The spectral variation was determined by minimizing matching error, then, the on-orbit spectral calibration was finished. By this method, on-orbit spectral calibration of FY-3B ultraviolet ozone vertical spectrometer was made. And the result was validated by standard spectrum of on-board mercury lamp. Under the condition of elimination the influence of instrument itself, the calibration accuracy could reach ±0.01nm, which meet the requirements of ultraviolet hyperspectral ozone spectrometer. The feasibility the high-accuracy on-orbit spectral calibration was verified. The second part of this paper is about on-orbit polarization correction. Firstly, polarization properties of atmospheric scattering spectra were introduced and polarization sensitivity of space-borne spectrometers was presented using Mueller matrix calculus. The effect of polarization on measurement data of space-borne spectrometers was analyzed. Two methods were introduced to minimize the effect, depolarizer and polarization correction. But, for ultraviolet hyperspectral ozone spectrometer, the depolarizer scheme could not meet the requirements. So, polarization correction was employed. According to the polarization correction theory, ground polarization calibration of space-borne spectrometers and on-orbit polarization measurement of incident light were made to complete polarization correction. In terms of ground polarization calibration of space-borne spectrometers, a high precision method (overdetermined equation method) was proposed. And according to the method, a measuring system of instrument polarization characteristics was established in the laboratory. The main error sources of overdetermined equation method and polarization measurement system were analyzed and correction method was given. Polarization properties of limb ultraviolet imaging spectrometer were calibrated with the overdetermined equation method and polarization measurement system. According to uncertainty analysis, the calibration accuracy was up to 1.53%. In terms of on-orbit polarization measurement of incident light, the basic scheme and some improvement program were set for ultraviolet hyperspectral ozone spectrometer.And the related principle experiment was carried out by joint use of two early prototypes in XX project. The results showed that the accuracy of the polarization measurement scheme could be up to 2.0%. Finally, the effect of the ground polarization errors and on-orbit polarization measurement errors on the polarization correction accuracy was analyzed. It was showed that polarization effect on ultraviolet hyperspectral ozone spectrometer by use of the on-orbit polarization correction was reduced to less than 2%, which meet the requirements of the instrument on-orbit polarization index.The last part of this paper is about on-orbit radiometric calibration. On the basis of summarizing the current radiometric calibration methods, a combination calibration plan of "sun + diffuser" absolute calibration and fixed moon’s observation relative calibration was applied for ultraviolet hyperspectral ozone spectrometer. The specific implementation and algorithms of the calibration plan were described. Finally, the accuracy of on-orbit radiometric calibration scheme was analyzed, and it was showed that the calibration uncertainty was about 4.2%, which meet the on-orbit requirements. The reliability and accuracy of remote sensing data were guaranteed, and a useful reference was provided for subsequent space-borne sensors on-orbit calibration. |
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