D'Odorico Petra, Guanter Luis, Schaepman Michael E, Schläpfer Daniel
Remote Sensing Laboratories, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Appl Opt. 2011 Aug 20;50(24):4755-64. doi: 10.1364/AO.50.004755.
Accurate spectral calibration of airborne and spaceborne imaging spectrometers is essential for proper preprocessing and scientific exploitation of high spectral resolution measurements of the land and atmosphere. A systematic performance assessment of onboard and scene-based methods for in-flight monitoring of instrument spectral calibration is presented for the first time in this paper. Onboard and ground imaging data were collected at several flight altitudes using the Airborne Prism Experiment (APEX) imaging spectrometer. APEX is equipped with an in-flight characterization (IFC) facility allowing the evaluation of radiometric, spectral, and geometric system properties, both in-flight and on-ground for the full field of view. Atmospheric and onboard filter spectral features present in at-sensor radiances are compared with the same features in reference transmittances convolved to varying instrument spectral configurations. A spectrum-matching algorithm, taking advantage of the high sensitivity of measurements around sharp spectral features toward spectrometer spectral performance, is used to retrieve channel center wavelength and bandwidth parameters. Results showed good agreement between spectral parameters estimated using onboard IFC and ground imaging data. The average difference between estimates obtained using the O(2) and H(2)O features and those obtained using the corresponding filter features amounted to about 0.3 nm (0.05 of a spectral pixel). A deviation from the nominal laboratory instrument spectral calibration and an altitude-dependent performance was additionally identified. The relatively good agreement between estimates obtained by the two approaches in similar spectral windows suggests they can be used in a complementary fashion: while the method relying on atmospheric features can be applied without the need for dedicated calibration acquisitions, the IFC allows assessment at user-selectable wavelength positions by custom filters as well as for the system on-ground.
对机载和星载成像光谱仪进行精确的光谱校准，对于对陆地和大气的高光谱分辨率测量进行适当的预处理和科学利用至关重要。本文首次对用于仪器光谱校准飞行中监测的机载和基于场景的方法进行了系统的性能评估。使用机载棱镜实验（APEX）成像光谱仪在几个飞行高度收集了机载和地面成像数据。APEX配备了飞行中特性表征（IFC）设施，可在飞行中和地面上对全视场的辐射、光谱和几何系统特性进行评估。将传感器处辐亮度中存在的大气和机载滤光片光谱特征与卷积到不同仪器光谱配置的参考透过率中的相同特征进行比较。利用在尖锐光谱特征周围的测量对光谱仪光谱性能的高灵敏度的光谱匹配算法，用于检索通道中心波长和带宽参数。结果表明，使用机载IFC和地面成像数据估计的光谱参数之间具有良好的一致性。使用O(2)和H(2)O特征获得的估计值与使用相应滤光片特征获得的估计值之间的平均差异约为0.3 nm（一个光谱像素的0.05）。此外，还识别出了与标称实验室仪器光谱校准的偏差以及与高度相关的性能。在相似光谱窗口中通过两种方法获得的估计值之间相对较好的一致性表明，它们可以以互补的方式使用：虽然依赖大气特征的方法无需专门的校准采集即可应用，但IFC允许通过定制滤光片在用户可选择的波长位置进行评估，也可用于地面系统。
