Serio Carmine, Masiello Guido, Mastro Pietro, Tobin David C
School of Engineering, University of Basilicata, 85100 Potenza, Italy.
CIMSS/SSEC, University of Wisconsin, Madison, WI 53706, USA.
Sensors (Basel). 2020 Mar 9;20(5):1492. doi: 10.3390/s20051492.
The observational covariance matrix, whose diagonal square root is currently named radiometric noise, is one of the most important elements to characterize a given instrument. It determines the precision of measurements and their possible spectral inter-correlation. The characterization of this matrix is currently performed with blackbody targets of known temperature and is, therefore, an output of the calibration unit of the instrument system. We developed a methodology that can estimate the observational covariance matrix directly from calibrated Earth-scene observations. The technique can complement the usual analysis based on onboard blackbody calibration and is, therefore, a useful back up to check the overall quality of the calibration unit. The methodology was exemplified by application to three satellite Fourier transform spectrometers: IASI (Infrared Atmospheric Sounder Interferometer), CrIS (Cross-Track Infrared Sounder), and HIRAS (Hyperspectral Infrared Atmospheric Sounder). It was shown that these three instruments are working as expected based on the pre-flight and in-flight characterization of the radiometric noise. However, for all instruments, the analysis of the covariance matrix reveals extra correlation among channels, especially in the short wave spectral regions.
观测协方差矩阵，其对角平方根目前被称为辐射噪声，是表征给定仪器的最重要元素之一。它决定了测量的精度及其可能的光谱相互相关性。目前，该矩阵的表征是使用已知温度的黑体目标来进行的，因此，它是仪器系统校准单元的一个输出结果。我们开发了一种方法，可以直接从校准后的地球场景观测数据中估计观测协方差矩阵。该技术可以补充基于机载黑体校准的常规分析，因此，它是检查校准单元整体质量的有用备用方法。该方法通过应用于三台卫星傅里叶变换光谱仪进行了示例说明：IASI（红外大气探测干涉仪）、CrIS（交叉轨道红外探测仪）和HIRAS（高光谱红外大气探测仪）。结果表明，基于辐射噪声的飞行前和飞行中表征，这三台仪器的运行符合预期。然而，对于所有仪器，协方差矩阵的分析揭示了通道之间存在额外的相关性，特别是在短波光谱区域。
