The recent launch of Landsat-9 satellite enriches the opportunities to work with dense time series of multispectral medium-resolution images. The integration of Landsat-9 in a multi-constellation series with Landsat-8 and Sentinel-2 requires a harmonization of the surface reflectance values that can be obtained from the official Level-2 products. This paper proposes the coefficients of the optimal linear transformations for the European continent, which allow to integrate Landsat-9 with the similar operating missions. These coefficients are based on a regression over 30 independent random extractions of 240,000 samples from images of the same areas but acquired by different sensors within two days. The coefficients were validated on an independent dataset. Furthermore, the effects of the proposed harmonization were tested on four popular vegetation indices, by evaluating the distributions of the differences in values obtained from each sensor pair. Finally, a test on a local scale was carried out with a spectroradiometer survey on 16 locations to collect some reference spectra to be compared with the reflectance values provided by the images. The results demonstrate the interoperability of Landsat and Sentinel-2 missions, since reflectance differences are in most cases within the accuracy specifications of the sensors. However, some discrepancies are observed in the blue and SWIR bands, probably due to inconsistencies in the atmospheric correction processes.

中文翻译：

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Landsat-9 与 Sentinel-2 和 Landsat-8 在欧洲的互操作性评估以及与现场调查的本地比较

最近发射的 Landsat-9 卫星丰富了处理多光谱中分辨率图像的密集时间序列的机会。将 Landsat-9 与 Landsat-8 和 Sentinel-2 集成到多星座系列中需要协调可以从官方 Level-2 产品获得的表面反射率值。本文提出了欧洲大陆的最佳线性变换系数，允许将 Landsat-9 与类似的操作任务结合起来。这些系数基于对 240,000 个相同区域图像的 240,000 个样本进行 30 多次独立随机提取的回归，这些样本是在两天内由不同传感器获取的。这些系数在独立数据集上进行了验证。此外，通过评估从每个传感器对获得的值的差异的分布，对四种流行的植被指数测试了所提出的协调的效果。最后，利用光谱辐射计对 16 个地点进行了局部测试，收集了一些参考光谱，与图像提供的反射率值进行比较。结果证明了 Landsat 和 Sentinel-2 任务的互操作性，因为反射率差异在大多数情况下都在传感器的精度规格范围内。然而，在蓝色和短波红外波段中观察到一些差异，这可能是由于大气校正过程的不一致造成的。