Estimation and measurement of backscattered signals from pulsed laser radar

Current pulsed laser radar systems for ranging purposes are based on time-of-flight techniques. Nowadays first pulse as well as last pulse exploitation is used for different application, e.g. urban planning, forestry surveying. Besides this technique of time measurement the complete signal form over the time might be of interest, because it includes the backscattering characteristic of the illuminated field. This characteristic can be used for estimating the aspect angle of a plane with special surface property or estimating the surface property of a plane with a special aspect angle. In this paper a monostatic bi-directional experimental system with a fast digitizing receiver is described. The spatio-temporal beam propagation, the spatial reflectance of the surface, and receiver properties are modeled. A time dependent description of the received signal power is derived and our special surface property is considered. The transversal spatial distribution of the used laser beam was measured and displayed by the beam profile. For a plane surface under various aspect angles the transversal spatial distributions of the beam were simulated and measured. For these angles the corresponding temporal beam distributions were measured and compared with their pulse widths. The pulse spread is used to estimate the aspect angle of the illuminated object. The statistics for different angles was calculated. Different approaches which detect a characteristic time value were compared and evaluated. The consideration of the signal form allows a more precise determination of the time-of-flight. A 3-d visualization of equi-irradiance surfaces allows to assess the spatio-temporal shape of the pulses.