SIERRA: A new approach to atmospheric and topographic corrections for hyperspectral imagery

In mountainous areas, slope and altitude variations modulate the airborne sensed hyperspectral radiance image. A new algorithm, SIERRA, has been developed for atmospheric, relief and BRDF corrections in order to extract the surface reflectance in the form of bi-hemispherical albedo that does not depend on solar incidence and observation angles. The forward modeling efforts focus on the estimation of diffuse irradiance and upwelling diffuse radiance, and on the formulation of BRDF effects. The inversion scheme consists of four steps, that go deeper and deeper into the phenomena's complexity.To validate the model, reflectance images are assessed from radiance images simulated with different radiative transfer codes or forward models: MODTRAN4 in the case of homogeneous and flat ground, AMARTIS and SIERRA forward models for heterogeneous and mountainous cases. The surface reflectance is retrieved with a 5% relative error under standard acquisition conditions.SIERRA is applied to HyMap data acquired over the hilly landscape near Calanas, Spain. The hypercube reflectances are compared with those obtained using ATCOR4 and COCHISE. The benefit of relief correction is clearly demonstrated.