风云三号气象卫星红外分光计在轨交叉定标精度监测系统

为了满足定量遥感对红外探测仪器定标精度监测的需求,采用风云三号气象卫星红外分光计(IRAS)与国际基准红外高光谱探测仪器进行交叉比对的方法,建立了FY-3C气象卫星红外分光计与高光谱仪器IASI的在轨交叉定标精度监测系统.通过对2014年一年的IRAS观测数据的定标精度监测和分析,结果显示,IRAS与IASI的相关系数均在0.98以上,通道1和18的定标偏差最大,分别为-3.7 K和2.1 K,通道9和16也有超过1K的偏差,其他通道的平均偏差均在1 K以内.地表观测通道8、9、18、19、20由于受卫星观测时空变化频繁的影响偏差标准差较大,在1.5~3 K左右,其他通道观测误差稳定性较好,均在1.5 K以内.通道2、3、4,10~13的定标偏差随目标亮温变化趋势不明显,通道14~20定标偏差随目标亮温变化趋势最强,最低和最高目标亮温对应的定标偏差之间的差别最大可达到5 K.定标偏差的时间序列分析表明大部分通道的定标偏差在一年的时间内保持稳定,变化幅度不超过0.3 K;通道15、19、20的定标偏差变化幅度约为1 K,通道1、14、16、17、18定标偏差一年的变化范围达到2~4 K.总之,在轨交叉定标精度监测系统为实时监测定标精度的变化提供了有效工具,为诊断仪器性能和改进定标方案提供了参考依据.

Platform for monitoring accuracy of on orbit cross calibration: Infrared Atmospheric Sounder onboard FY-3 satellite

For quantitative remote sensing, instrument calibration precision should be monitored from time to time. To monitor the accuracy of cross calibration of FY-3C satellite Infrared Atmospheric Sounder(IRAS), a platform was set up based on a cross comparison of IRAS with standard infrared high spectral resolution instruments- Infrared Atmospheric Sounding Interferometer (IASI). Calibration precision monitoring analysis using IRAS data in the year of 2014 shows results as the following. For all the 20 infrared channels the correlation coefficients of IRAS with IASI were above 0.98. The mean bias for most channels are less than 1K except that channels 9 and 16 are nearly 1.4 K and channels 1 and 18 are larger than 2 K. The standard deviation for most channels is less than 1.5 K, while for surface sounding bands of 8, 9, 18, 19, and 20, it ranges from 1.5 to 3 K. The latter is probably due to that the channels which detect atmosphere of near boundary layer were more susceptible to the time and location differences. The calibration bias variation trend with target brightness temperature was flat for channel 2, 3, 4, 10 to 13, while an obvious trend can be seen for channels of 14 to 20 and the difference between maximum bias and minimum bias can reach 5 K. Time series analysis of calibration bias indicates that for most channels the calibration bias were stable in one year and the variation magnitude was less than 0.3 K. It is about 1 K for channel 15, 19, and 20. The calibration bias variation reached 2 to 4 K in one year for channel 1, 14, 16, 17, 18. In a word, IRAS cross calibration accuracy monitoring system provide a tool for real time monitoring of calibration precision change.