Normalization of Lidar Intensity Data Based on Range and Surface Incidence Angle

The analysis of airborne laser scanner data to extract surface features is of great interest in photogrammetric research. Especially for applications based on airborne measurements, where the intensity is crucial (e.g. for segmentation, classification or visualization purposes), a normalization considering the beam divergence, the incidence angle and the atmospheric attenuation is required. Our investigations show that the same material of a surface (e.g. gabled roof) yields to different measured values for the intensity. These values are strongly correlated to the incidence angle of the laser beam on the surface. Therefore the intensity value is improved with the incidence angle derived by the sensor and object position as well as its surface orientation. The surface orientation is estimated by the eigenvectors of the covariance matrix including all object points inside a close environment. Further the atmospheric attenuation is estimated. The adaptation of vegetation areas is disregarded in this study. After these improvements the intensity does no longer depend on the incidence angle but may be influenced by the material of the object surface only. For surface modelling the Phong model is introduced, considering diffuse and specular backscattering characteristics of the surface. A measurement campaign was carried out to investigate the influences of the incidence angle on the measured intensity. By considering the incidence angle and the distance between sensor and object the laser data captured from different flight paths (data stripes) can be successfully fused. In our experiments it could be shown that the radiometric normalization of the intensity for the investigated areas are improved.