Correction of Incidence Angle and Distance Effects on TLS Intensity Data Based on Reference Targets

Abstract

Abstract:The original intensity value recorded by terrestrial laser scanners is influenced by multiple variables, among which incidence angle and distance play a crucial and dominant role. Further studies on incidence angle and distance effects are required to improve the accuracy of currently available methods and to implement these methods in practical applications. In this study, the effects of incidence angle and distance on intensity data of the Faro Focus 3D 120 terrestrial laser scanner are investigated. A new method is proposed to eliminate the incidence angle and distance effects. The proposed method is based on the linear interpolation of the intensity values of reference targets previously scanned at various incidence angles and distances. Compared with existing methods, a significant advantage of the proposed method is that estimating the specific function forms of incidence angle versus intensity and distance versus intensity is no longer necessary; these are canceled out when the scanned and reference targets are measured at the same incidence angle and distance. Results imply that the proposed method has high accuracy and simplicity in eliminating incidence angle and distance effects and can significantly reduce the intensity variations caused by these effects on homogeneous surfaces.

Specular Reflection Effects Elimination in Terrestrial Laser Scanning Intensity Data Using Phong Model

“…Empirically, the distance and incidence angle effects were satisfactorily corrected by polynomials in [21] or by using reference targets in [19].…”

“…The range-dependent inverse square model from the radar range equation is insufficient to estimate the accurate intensity at the entire range scale. Considering the fact that the incidence angle and distance effects are theoretically independent of each other and can be solved individually [24], the intensity is written as [19,21]:…”

“…The irregular TLS distance effect is strongly dominated by instrumental factors (e.g., aperture size, automatic gain control, amplifier for low-reflective surfaces, and a brightness reducer for near distances [1]) and differs significantly among different systems. The distance effect does not completely follow the inverse square range function from the radar range equation [18][19][20]. Empirically, the distance effect was satisfactorily corrected by a polynomial in [21] or based on reference targets in [19].…”

“…During one campaign period, instrumental configurations are kept constant and atmospheric attenuation can be ignored. As such, the intensity data recorded by the same TLS system are predominantly influenced by the target reflectance, distance, and incidence angle [19]. In order to utilize the intensity for further applications, all influences not related to the material composing the scanned surface should be corrected [5].…”

“…The distance effect does not completely follow the inverse square range function from the radar range equation [18][19][20]. Empirically, the distance effect was satisfactorily corrected by a polynomial in [21] or based on reference targets in [19]. In this study, the polynomial method was adopted to eliminate the distance effect to obtain the distance-independent intensity value.…”