Abstract Many derived Earth Observation products share surface reflectance as a common step in their processing chains. This makes the maintenance and improvement of surface reflectance product quality of fundamental importance to ensure information derived from these downstream products can be trusted. Despite this, the literature is relatively light on the implementation of validation methodologies designed for surface reflectance. In response to the need to improve general EO validation methodologies, the concept of fiducial reference measurements (FRM) was created that would produce validation data that is fully characterised and independent, with associated uncertainties, and traceable to SI. This paper describes a field campaign designed to produce surface reflectance validation data, in line with the FRM ideology, for validating the Sentinel-2 L2A (S2) and Proba-V S1-TOC (Proba) surface reflectance products. The key methodological procedures are outlined in detail to facilitate uptake of FRM methods in future validation studies. These include the calibration and characterisation of field instruments, the field measurement protocol, and uncertainty propagation. Comparison of S2 with field measurements showed agreement within the stated uncertainties present for all bands and locations at the pixel and area scales. The Proba comparison results demonstrated a general disagreement within the stated uncertainties. However, there is a lack of uncertainty information provided by the product as well as publicly available product uncertainty requirements which mean that it is difficult to assess this fully. The aim of this practical demonstration of FRM-based surface reflectance validation, that utilises metrological practices for uncertainty characterisation, is to encourage the adoption of these procedures in future land surface reflectance validation studies and operational activities.

中文翻译：

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用于验证 Sentinel-2 和 Proba-V 表面反射产品的基准参考测量

摘要 许多衍生的地球观测产品共享表面反射作为其处理链中的一个常见步骤。这使得表面反射产品质量的维护和改进变得至关重要，以确保从这些下游产品中获得的信息是可信的。尽管如此，有关为表面反射设计的验证方法的实施的文献相对较少。为了响应改进通用 EO 验证方法的需要，创建了基准参考测量 (FRM) 的概念，该概念将生成具有完整特征和独立性、具有相关不确定性并可追溯到 SI 的验证数据。本文描述了一个现场活动，旨在产生符合 FRM 意识形态的表面反射验证数据，用于验证 Sentinel-2 L2A (S2) 和 Proba-V S1-TOC (Proba) 表面反射产品。详细概述了关键的方法学程序，以促进在未来的验证研究中采用 FRM 方法。其中包括现场仪器的校准和表征、现场测量协议和不确定性传播。S2 与现场测量的比较表明，在像素和面积尺度上所有波段和位置存在的所述不确定性内是一致的。Proba 的比较结果表明在规定的不确定性范围内普遍存在分歧。然而，缺乏产品提供的不确定性信息以及公开可用的产品不确定性要求，这意味着很难对其进行全面评估。