Operational BRDF Effects Correction for Wide-Field-of-View Optical Scanners (BREFCOR)

The radiometric correction of airborne imagery aims at providing unbiased spectral information about the Earth´s surface. Correction steps include system calibration, geometric correction, and the compensation for atmospheric effects. Such preprocessed data are affected by the bidirectional reflectance distribution function (BRDF), which requires an additional compensation step. We present a novel method for a surface-cover-dependent BRDF effects correction (BREFCOR). It uses a continuous index based on bottom-of-atmosphere reflectances to tune the Ross-Thick Li-Sparse BRDF model. This calibrated model is then used to correct for observation-angle-dependent anisotropy. The method shows its benefits specifically for wide-field-of-view airborne systems where BRDF effects strongly affect image quality. Evaluation results are shown for sample data from a multispectral photogrammetric Leica ADS camera system and for HYSPEX imaging spectroscopy data. The scalability of the procedure for various kinds of sensor configurations allows for its operational use as part of standard processing systems.