傅里叶变换光谱仪干涉信号高阶非线性畸变的在轨校正算法研究

The Geostationary Interferometric Infrared Sounder (GIIRS) on board FY-4A satellite is an infrared Fourier transform spectrometer. Mercury Cadmium Telluride (MCT) infrared detectors are used in GIIRS, which have a nonlinear response. Detector nolinearity does no only add a bias but also affects the shape of the spectra significantly. This nonlinearity must be characterized and corrected to provide accurate infrared radiance observations. A correction scheme based solely on the out-of-band signal does not produce satisfactory results. Best results will be obtained if a combined second- and third-order correction is applied. Based on the relationship that the maximum value in the interferogram is related to the average value in a manner that depends on the modulation efficiency of the interferometer, the dc-level model will be built. Following the algorithm baseline released by GSICS and using the high spectral resolution sounder as a reference, the cubic nonlinearity coefficient will be obtained based on the in-band information of calibrated spectra computed from GIIRS. Second- and third-order corrections to the measured interferogram will be tested by analyzing the measured signal both within and outside the spectral response region of the detector. Then, a combined correction scheme will be proposed that best represents the real nonlinear response of the detector. The proposed framework model of the nonlinearity correction applied to FY-4A GIIRS will be suitable for improving the calibration accuracy of the infrared Fourier transform spectrometer, which can meet the requirement in quantitative applications.

风云四号A星干涉式大气垂直探测仪（GIIRS）的核心是一台傅里叶变换光谱仪。GIIRS有两个红外探测波段，均采用碲镉汞（MCT）探测器。对于干涉测量系统，干涉图中心受到MCT探测器非线性响应的影响最大，由此得到的光谱图，不仅会产生辐射测量误差，还会造成谱线形状畸变。傅里叶变换光谱仪干涉信号高阶非线性畸变在轨校正的难点是如何得到干涉图直流分量和高阶非线性校正系数。本项目研究利用干涉图峰值、干涉图平均值和干涉仪调制效率三者之间的关系，建立干涉图直流分量模型；参考全球天基交叉定标系统推荐的方法，研究利用高辐射精度的对地观测数据，实现傅里叶变换光谱仪干涉信号高阶非线性畸变的校正；在此基础上，建立风云四号A星GIIRS干涉信号高阶非线性畸变的在轨宽动态范围校正模型，并定量评估其在轨校正效果。该项目的实施不仅能够有效提高风云四号A星GIIRS数据精度，而且提出的模型对傅里叶变换光谱仪具有通用性。

探测器非线性响应是傅里叶变换光谱仪辐射测量误差主要来源之一，直接影响卫星资料定量化应用水平。本项目基于傅里叶变换光谱仪非线性响应原理和辐射定标方法推导出针对风云四号卫星大气垂直探测仪GIIRS的非线性校正算法，并且，通过分析GIIRS连续5个月的在轨观测数据发现，仪器工作环境温度变化后，利用参考辐射基准，修正响应率常数项，可以得到宽动态范围内的非线性校正系数。经仪器热真空定标试验数据验证，在各环境温度工况下，180K~320K观测范围内的辐射定标精度均有明显提高。以850cm-1和950cm-1为例，观测数据经过非线性校正，辐射定标精度有明显提升，平均偏差从2K@250K减小至0.2K@250K。该项目的实施有助于提高风云四号GIIRS观测数据精度，促进探测数据的遥感应用。在研究基础上，项目共发表论文2篇，获得1项国家发明专利授权，开发了一套非线性校正软件。