Advances in quantitative remote sensing product validation: Overview and current status

The roles of quantitative remote sensing products in scientific research and quantitative applications lie in their ability to record the real states of earth surface features. Therefore, it is crucial to quantify the performance of remote sensing products. However, validation is not straightforward due to the scale effects caused by surface heterogeneity and the spatial scale mismatch between satellite- and ground-based observations, but a challenging scientific issue in the field of remote sensing. Although validation works have been widely carried out in the past decades, it is difficult to reach an accordant and compelling conclusion about the performance of different satellite products due to the inconsistencies in spatial and temporal extents, the type of in situ data sources, and the validation strategies, which hinder effective applications of remote sensing products. Therefore, it is necessary to give an overview of validation, simultaneously to point out its problems and insufficiencies, and finally to put forward the suggestions for fixture researches. The in situ data acquisition, the upscaling method, the uncertainties implied in the validation process, together with future challenges, are included in this paper. It is expected to promote the validation technique development and improve the application accuracy of remote sensing products.