In-flight radiometric and polarimetric calibration of the Directional Polarimetric Camera onboard the GaoFen-5 satellite over the ocean
In-flight radiometric and polarimetric calibration of the Directional Polarimetric Camera onboard the GaoFen-5 satellite over the ocean
复制标题
高分五号卫星海洋上空定向偏振相机的飞行中辐射和偏振校准
DOI：
10.1364/ao.422980
复制
发表时间：
2021-08-20
期刊：
影响因子：
1.9
通讯作者：
Tu, Bihai
中科院分区：
文献类型：
--
作者：
Qie, Lili;Li, Zhengqiang;Tu, Bihai
定向偏振相机（DPC）是中国第一个多角度偏振地球观测卫星传感器，于2018年5月9日成功发射，搭载在中国高分辨率地球观测计划的高分五号卫星上。DPC的观测是现阶段全球地气系统最重要的星载多光谱、多角度偏振测量之一。虽然DPC在发射前已经进行了严格的辐射定标，但其飞行性能可能会因为发射过程、恶劣的空间环境以及传感器老化而发生变化。由于没有机载校准系统，DPC的飞行性能监测和校准需要替代校准方法。本文采用瑞利绝对定标法、太阳闪烁带间定标法和太阳闪烁偏振定标法对DPC传感器进行定标。首先，这三种方法的校准误差由辅助数据不确定性（例如，气溶胶、叶绿素浓度、吸收气体量和风速）进行了详细分析。误差预算表明，气溶胶参数（光学厚度和气溶胶模型）是影响瑞利和太阳闪烁方法的辐射和偏振校准精度的一些关键因素。然后在其调试阶段进行DPC辐射和偏振飞行校准。短光谱带（443，490，565和670 nm）的绝对系数进行了校准的良好特征的瑞利散射信号在海洋。使用565 nm波段作为参考波段，然后通过使用海洋上太阳的镜面反射的波段间校准将瑞利绝对校准转移到其他波段（443、490、670和865 nm）。利用海洋上空太阳闪烁的偏振反射对DPC在偏振波段（490、670和865 nm）的偏振测量进行了校准。初步结果表明，DPC的辐射灵敏度在发射后的四个可见波段变化很小。在443和670 nm波段，与飞行前校准的绝对校准系数差异小于0.5%，而在490和565 nm波段，它们在+/- 2%以内。然而，在865 nm波段的约9%的飞行前校准的太阳闪烁带间校准表明，大的偏差。验证了DPC的线偏振度测量在865 nm波段具有约0.02的高精度，而在490和670 nm波段的偏差相对较大，达到0.04。DPC/高分五号卫星在飞行中表现出良好的辐射测量性能，发射后的偏振测量总体上是可靠的。(C)2021美国光学学会
The Directional Polarimetric Camera (DPC) is the first Chinese multi-angle polarized Earth observation satellite sensor, which was successfully launched on 9 May 2018, onboard the GaoFen-5 satellite in the Chinese High-Resolution Earth Observation Program. The DPC's observation is one of the most important space-borne multi-spectral, multi-angular polarimetric measurements of the global Earth-atmosphere system at the present stage. Although rigorous radiometric calibration had been performed for the DPC before launch, its in-flight performance may change because of the process of launch, harsh environment of space, and aging of the sensor. Due to the absence of the onboard calibration system, vicarious calibration methods are necessary for the DPC's in-flight performance monitoring and calibration. In this paper, we adapted the Rayleigh absolute calibration method, the sun glint inter-band calibration method, and the sun glint polarization calibration method to the DPC sensor. First, the calibration errors of these three methods caused by ancillary data uncertainties (e.g., aerosol, chlorophyll concentration, absorption gases amount, and wind speed) were analyzed in detail. The error budgets show that the aerosol parameters (optical thickness and aerosol model) are some of the critical factors affecting both the radiometric and polarimetric calibration accuracies for the Rayleigh and sun glint methods. The DPC radiometric and polarimetric in-flight calibration during its commissioning phase was then implemented. The absolute coefficients of short spectral bands (443, 490, 565, and 670 nm) were calibrated by the well-characterized Rayleigh scattering signal over the ocean. Using the 565 nm band as a reference band, the Rayleigh absolute calibration was then transferred to other bands (443, 490, 670, and 865 nm) through inter-band calibration using the specular reflection of the sun over the ocean. The polarization measurements of the DPC at polarized bands (490, 670, and 865 nm) were calibrated with the polarized reflection of the sun glint over ocean. The preliminary results show that the radiometric sensitivity of the DPC changed very little after launch at the four visible bands. The absolute calibration coefficient differences from pre-flight calibration are smaller than 0.5% at the 443 and 670 nm bands, while they are within +/- 2% at the 490 and 565 nm bands. However, a large deviation at 865 nm band of about 9% from pre-flight calibration was indicated by the sun glint inter-band calibration. The degree of linear polarization measurement of the DPC is validated with high accuracy of about 0.02 at the 865 nm band, while the deviation at 490 and 670 nm bands are relatively larger, reaching 0.04. The DPC/GaoFen-5 shows a good in-flight performance of radiometric measurement and generally reliable polarimetric measurement after launch. (C) 2021 Optical Society of America