Validation of the Sentinel 2 surface reflectance over a corn field

In this study, we present the validation of the Sentinel 2 surface reflectance produced by LaSRC (Land Surface Reflectance code) during the summer of 2018 over a corn field at the United States Deparment of Agriculture Beltsville Agricultural Research Station. Measurements of the corn field reflectances for the coincident sentinel 2 data are taken from a boom lift 80 feet above the ground using four cameras (Red, Green, Blue and Near Infrared) taking 2000x1200 pixels images in the fifteen minutes preceding and following the sentinel 2 overpass enabling to have comparable illumination conditions for ground and satellite reflectances. The area covered is nine sentinel 2 10 meters pixels. The camera system was characterized radiometrically by using a flat fielding source (solar panel) and dark current measurements as well as geometrically by using a series of measurements of tarps located in different part of the field of view (45 degrees diagonal). After radiometric correction, the data are calibrated using a 5cm circular spectralon target mounted on the camera itself. The spectralon target is present in each image enabling precise and continuous calibration. The full radiometric chain is also checked by acquiring a 2.4mx2.4m tarp of known reflectances placed at the edge of the corn field. The results of this first measurement campaign are presented as well as recommendations for future automated implementation of this system over a larger number of sites.