Modelling Scattering Distortion in 3d Range Camera

A time-of-flight camera suffers from significant range distortion due to the scattering artefact caused by secondary reflections occurring between the lens and the image plane. The reflected beam from the foreground objects undergoes multiple reflections within the camera device thereby introducing parasitic signals that bias the late-arrival, backscattered signals from the background targets. These additive signals cause degradation of the depth measurement for the background objects thus limiting the use of range imaging cameras for high precision close-range photogrammetric applications. So far the modelling of scattering distortion has been based on the linear system model using an inverse filtering approach. However, an experiment conducted for measuring the edgespread function using a two planar surfaces separated at some distance shows a non-linear and shift-variant behaviour of the scattering distortion. The non-linearity and the shift-variant behaviour of the scattering errors question the use of the linear shiftinvariant system for reversing the scattering effect. Further experimentation using two planar surfaces at different distances with different surface areas of the scattering object was conducted to heuristically quantify the range and amplitude biases caused by the scattering artefact. The range and amplitude biases were analysed as a function of the distance of the scattering object from the camera, the surface area of the scattering object and the integration time. The results show that the scattering bias monotonically increases with surface area of the scattering object and monotonically decreases with distance of the scattering object from the camera. The scattering range bias is independent of the integration time while the scattering amplitude bias monotonically increases with the integration time. Additionally, an empirical modelling of the range bias due to the scattering effect using an analytical curve-fitting method is proposed in this paper.