Landsat-8 OLI与Sentinel-2 MSI山区遥感影像辐射一致性研究

Radiometric Consistency between Landsat 8 OLI and Sentinel-2 MSI Imagery in Mountainous Terrain

受影像获取时间、大气条件、观测角度、传感器波段设置以及山地地形等因素的影响,山区多源、多时相光学遥感卫星影像间的辐射不一致问题较为突出。以Landsat-8 OLI与Sentinel-2 MSI为例探究山地多源遥感影像间的辐射一致性,旨在为多源影像在山区的协同应用提供理论支持。选取同期OLI和MSI影像,进行大气校正、BRDF校正、光谱通道校正以及影像间的辐射一致性分析,并研究地形对辐射一致性的影响。结果表明:(1)未经校正的Landsat-8 OLI-L1T与Sentinel-2 MSI-L1C反射率影像间的辐射一致性较高(各波段R2均大于0.9);(2)经过6S大气校正、C因子法BRDF校正,影像间辐射一致性进一步提高(如蓝波段反射率RMSD依次减小22%、10%),但光谱通道校正后一致性并未显著增强;(3)地形效应导致了影像阴坡、阳坡辐射一致性水平的较大差异(如BRDF校正后SWIR波段阳坡的反射率平均绝对差为0.010、RMSD为0.006 6,阴坡平均绝对差为0.005、RMSD为0.004 3),且阳坡辐射差异随坡度增大而增大,阴坡则相反。因此,在进行多源遥感影像协同之前,需要进行有效的大气校正、BRDF校正以及光谱通道校正。另外,针对山地遥感影像还应开展地形辐射校正以进一步提高影像间的辐射一致性。

The combined use of multi-sensor/multi-temporal images provides more opportunities for long-term land surface monitoring with high resolution and frequency requirements.However，as sensors differ in their orbital，spatial，or spectral configuration，uncertainty was introduced in the radiometric consistency of multi-sourse images，and that becomes more outstanding in mountainous terrain with the sharp topographic relief.Therefore，a series of radiometric corrections need to be carry out before further application.The objective of this study was to indicate the radiometric consistency of Landsat-8 OLI and Sentinel-2 MSI images.Thus the radiometric differences between the corresponding bands of these two images acquired almost simultaneously by OLI and MSI over 2 areas at different latitude was calculated for the TOA reflectance images first.Then several radiometric corrections（atmospheric correction，BRDF correction and bandpass adjustment） were carried out successively and after each of them the radiometric differences were researched again to assess the performance of each correction method.The results first indicate that there is high radiometric consistency between OLI-L1T and MSI-L1C images with the R2greater than 0.9 for each band involved.Then higher consistency was found after the 6S atmospheric correction and C-factor BRDF correction，while no remarkable improve was found after the fixed-parameter bandpass adjustment.Furthermore，in area with great topographic relief，the radiometric consistency were higher for hillside facing the sun than hillside in shadow （the MAD of SWIR2 band was 0.010 and RMSD was 0.007 in sun-light area，while the MAD was 0.005 and RMSD was 0.004 in shadowed area）.The results point out that proper atmospheric correction，BRDF correction and bandpass adjustment could be used to improve the radiometric consistency，and topographic correction might also be carried out to balance the radiometric consistency differences between different hillsides.