Waveform processing of laser pulses for reconstruction of surfaces in urban areas

In this paper we describe investigations for digital recording ofreceived laser pulses and a detailed analysis of the pulse waveform.In contrast to previous works using a single photon detection technique,we now focus on multi photon detection. An experimental system was constructed using an airborne laser scanning system anda receiver unit wih an appropriate sampling rate for a fast recording of laser pulses. Capturing the temporal waveform by simultaneousscanning of the scene delivers a data volume (spacetime cube). Sucha data cube of the received signals allows exploiting different featureswithout selecting a special feature or a measuring technique in advance. For the main investigation a groundbased sensor platform is used to measure the urban scene. Surface variations within the spatial beam width result in specialwaveforms. We explored the capabilities of analyzing the shape ofthe waveform for surface features in form of distance, roughness,and reflectance for each backscattered pulse. An iterative estimation algorithm (Gauss-Newton method) is proposed to get a parametricdescription of the original waveform by a Gaussian. Single responses and more than one response (multiple pulses) areinvestigated. Additionally, the data cube opens the possibility ofconsidering neighborhood relations for space-time filtering or segmentation.Image slices extracted from the data cube were processed to estimate line segments for surface features. This hasa significant advantage: the estimated lines are not based on singlerange points received from a pulse detector which delivers more orless accurate range values, but they are based directly on the intensity distribution of the backscattered signal. Since many valuesof the intensity distribution have contributed to each line segment, the accuracy of location can be much better than the pixeldimension of the image slice.     «

In this paper we describe investigations for digital recording ofreceived laser pulses and a detailed analysis of the pulse waveform.In contrast to previous works using a single photon detection technique,we now focus on multi photon detection. An experimental system was constructed using an airborne laser scanning system anda receiver unit wih an appropriate sampling rate for a fast recording of laser pulses. Capturing the temporal waveform by simultaneousscanning of the scene delivers a data v...     »