风云三号D星(FY-3D)于2017年11月15日成功发射, 搭载了国内第一颗自主研制的极轨红外高光谱大气探测仪(High-spectral Resolution Infrared Atmospheric Sounder, HIRAS), 数据将在数值天气预报、大气温/湿廓线反演、大气成分探测等方面得到广泛应用。为满足高精度的探测能力需求, HIRAS的光谱分辨率达到0.625 cm-1, 辐射定标精度要求达到1.0 K, 光谱定标精度要求达到10×10-6, 均为目前国内星载红外仪器最高精度指标。由于光谱频率的精确性会直接影响辐射精度, 红外干涉仪器在数据应用之前必须进行光谱定标精度的精确评估和监测。以晴空视场下的高精度逐线辐射传输模拟光谱作为参考基准, 利用互相关法计算光谱频率偏差, 对发射后的HIRAS在轨数据的光谱定标精度进行了全面评估和验证研究。HIRAS在长波、中波1和中波2的光谱精度达到3×10-6, 其中长波和中波1光谱偏差标准差小于2×10-6, 远优于仪器设计指标要求; 长期的光谱精度稳定性显示HIRAS中波1和中波2的光谱定标精度较稳定, 在半年时间内频率变化小于5×10-6, 长波波段在半年的时间内有往负频率偏差变化的趋势, 变化量约为7×10-6, 需要进行持续监测。HIRAS在轨光谱精度可满足后端产品反演和同化用户的使用需求。

Fengyun-3D (FY-3D) was successfully launched on November 15, 2017. For the first time, it was equipped with the High-spectral Resolution Infrared Atmospheric Sounder (HIRAS), which was developed and manufactured entirely by the Shanghai Institute of Technical Physics (SITP), China. HIRAS measurements were mainly used for numerical weather forecast and obtaining temperature, moisture, and green-house gases profiles. To meet the high accuracy of the sounding ability, the spectral resolution of HIRAS is required to reach 0.625 cm-1, the radiation accuracy is required to reach 0.5 K, and the spectral frequency accuracy is required to reach 10×10-6. An infrared (IR) interferometer is needed to accurately evaluate and monitor the spectral frequency accuracy before data application because the accuracy of the spectral frequency will directly affect the precision of radiation measurements. In this study, spectral shifts were derived using the cross-correlation method, in which the accurate line by line radiative transfer model simulation spectra under clear conditions were used as reference, and the spectral performance and frequency accuracy of HIRAS in-orbit data after launch were comprehensively evaluated and verified. The results show that the HIRAS spectral calibration accuracy is greater than 3×10-6 in long wave, middle wave1 and middle wave2 bands and the spectral bias standards of long wave (LW) and middle wave 1 (MW1) bands are higher than 2×10-6, which are better than the requirements. The spectral accuracy of HIRAS in the past six months was stable for LW and MW1 bands and the spectral frequency variations were in range of 5×10-6. For LW band, a negative bias trend was observed that reaches approximately 7×10-6, this would require consistent monitoring in the future. The results of this study indicate that the HIRAS data on-orbit spectral accuracy can satisfy the demands of back-end retrieval and assimilation users.