Calibration and Validation
Surface reflectance is the fundamental quantity required in the majority of optical earth observation analyses, and as an essential input to biophysical variable retrieval algorithms, it forms the basis of many higher level products. These products, which include essential climate variables (ECVs) such as leaf area index (LAI) and the fraction of absorbed photo synthetically active radiation (FAPAR), in addition to parameters such as the fraction of vegetation cover (FCOVER), provide insight into the evolution of the terrestrial environment. In turn, they are crucial in understanding vegetation productivity/yield, biogeochemical cycles, and the weather and climate systems. In the context of an increasing global population, the need to ensure food security, and environmental change, accurate estimates of these parameters are required to enable sustainable management of natural resources. To ensure their accuracy, validation of decametric surface reflectance and vegetation products is required, using independent ground reference measurements to verify product performance. However, the collection of ground reference measurements is time-consuming and resource intensive, limiting the extent of validation efforts in both space and time. Recently, the potential of unmanned aerial vehicles (UAVs) to reduce required resources and increase spatial and temporal coverage has been recognised. The aim of this project is to evaluate the capability of UAVs as a source of reference data for validating decametric surface reflectance and vegetation products, with a specific focus on the European Sentinel-2 and Chinese Gaofen-6 missions. The project will provide an opportunity to transfer knowledge gained from existing ESA-funded projects on fiducial reference measurements (FRM), which focus on traceability and uncertainty evaluation in earth observation validation efforts. The aim of the project will be achieved by the collection, processing, and analysis of ground measurements over a number of European and Chinese sites, coinciding with UAV acquisitions. The project will investigate the feasibility of using UAV data as an alternative to traditional ground measurements for validating Sentinel-2 and Gaofen-6 products.
