A Geometric Location Matching Method for Validation of Satellite Products: A Case Study for Albedo

Abstract

Validation of satellite albedo products relies on reference value on the coarse pixel scale which is acquired by independent means. In previous researches, reference value was generally obtained within the nominal spatial extent of the validation pixel from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> observations or high spatial resolution airborne/spaceborne albedo references. Nevertheless, the signal of the validation pixel may correspond to different areas due to geometric errors. This geolocation mismatch will introduce large uncertainty into validation results, particularly for pixels covering heterogeneous areas. Therefore, this study first proposed a geometric location matching method on the coarse pixel level to establish the actual position of the validation pixel. The results show that geolocation error of the validation pixels of the high-order satellite products occurs widely. And they are not systematically shifted. The errors of reference values resulting from geolocation errors range from -10% to 25%, which are very likely to be greater than the accuracy requirement of satellite albedo products. Such errors caused by geometric shifts of validation pixels significantly amplify the errors in satellite albedo products. With this geometric location matching method, the reported relative RMSE of MCD43A3 V061 reduced from 9.8% to 3.2%, and the reported correlation coefficient increased from 0.204 to 0.611. This method is very helpful to reduce the uncertainty of validation results and identify the real accuracy of satellite albedo products. Moreover, it has the generalization ability for other numerical variables over other types of land surfaces.