Faculty of Center for Space and Remote Sensing Research, National Central University, Taoyuan 32001, Taiwan.
Sensors (Basel). 2018 Jun 21;18(7):1996. doi: 10.3390/s18071996.
Radiometric calibration for imaging sensors is a crucial procedure to ensure imagery quality. One of the challenges in relative radiometric calibration is to correct detector-level artifacts due to the fluctuation in discrepant responses (spatial) and electronic instability (temporal). In this paper, the integration of the empirical mode decomposition (EMD) with Hilbert⁻Huang transform (HHT) in relative radiometric calibration was explored for a new sensor, FS-5 RSI (remote sensing instrument onboard the FORMOSAT-5 satellite). The key intrinsic mode functions (IMFs) analyzed by HHT were examined with the pre-flight datasets of the FS-5 RSI in temporal and spatial variations. The results show that the EMD⁻HHT method can stabilize and improve the radiometric quality of the FS-5 imagery as well as boost its application ability to a new level. It is noticed that the IMFs of the spatial variation would be disturbed by the instability of the temporal variation. The relative response discrepancies among detector chips can be well calibrated after considering the temporal effect. Taking a test imagery dataset of gain setting G2 as an example, the standard deviation (STD) of the discrepancy in the digital number after calibration was dramatically scaled down compared to the original ones (e.g.
, PAN: 66.31 to 1.85; B1: 54.19 to 1.90; B2: 36.50 to 1.49; B3: 32.43 to 1.56; B4: 37.67 to 1.20). The good performance of pre-flight imagery indicates that the EMD⁻HHT approach could be highly practical to the on-orbit relative radiometric calibration of the FS-5 RSI sensor and is applicable to other optical sensors. To our knowledge, the proposed EMD⁻HHT approach is used for the first time to explore relative radiometric calibration for optical sensors.
成像传感器的辐射定标是确保图像质量的关键步骤。相对辐射定标中的一个挑战是校正由于不一致响应（空间）和电子不稳定性（时间）而导致的探测器级别的伪影。本文探讨了将经验模态分解（EMD）与希尔伯特-黄变换（HHT）集成用于相对辐射定标中的新型传感器 FS-5 RSI（搭载在福卫五号卫星上的遥感仪器）。通过 HHT 分析的关键固有模态函数（IMF）与 FS-5 RSI 的飞行前数据集进行了时空变化的检验。结果表明，EMD-HHT 方法可以稳定和提高 FS-5 图像的辐射质量，并将其应用能力提升到一个新的水平。需要注意的是，空间变化的 IMF 会受到时间变化不稳定性的干扰。在考虑时间效应后，可以很好地校准探测器芯片之间的相对响应差异。以增益设置 G2 的测试图像数据集为例，校准后数字号差异的标准偏差（STD）与原始值相比显著降低（例如，PAN：66.31 到 1.85；B1：54.19 到 1.90；B2：36.50 到 1.49；B3：32.43 到 1.56；B4：37.67 到 1.20）。飞行前图像的良好性能表明，EMD-HHT 方法非常适用于 FS-5 RSI 传感器的星载相对辐射定标，并且适用于其他光学传感器。据我们所知，该 EMD-HHT 方法首次用于探索光学传感器的相对辐射定标。
