Reflectance reference target at Järvselja, Estonia for the calibration of optical remote sensing sensors and lessons learned

A calibration target for the support of airborne and satellite measurements was built at the Järvselja site for ecological and remote sensing studies located in southeastern Estonia. The calibration target is a 10 × 10 m concrete panel which is protected by a removable roof. Optical properties of the panel are carefully studied in order to serve as a reference in spectroscopic remote sensing measurements. In this study we report the spectral distribution of reflectance in the wavelength range of 350-2500 nm, the angular distribution of directional reflectance and the linear polarization of the reflected radiation. The reflectance spectrum of the panel is smooth in the visible and NIR wavelengths but with steep decrease at wavelengths less than 400 nm. Variations of reflectance over the panel surface are less than 1%. The radiation is partly polarized in forward scattering direction. No temporal changes of optical properties have been observed. The calibration target improves the metrological quality of airborne spectral measurements at the Järvselja test site and neighboring areas. It can also be used for ground truth to aid the validation of adjacency correction algorithms for data from high spatial resolution satellite images, as well as a reference for the registration of airborne and satellite images. It can also serve as an elevation reference for both lidar and radar altimeter measurements.