Spatial Filtering Design Considerations for a Laser Line Scanning Sensor.

摘要

The performance of an airborne laser terrain mapper, which collects slant range and reflectance data simultaneously, is determined in part by the spatial filtering effects of the finite laser beam spot size. An analysis of the spatial filtering effects and the resulting distortion of the terrain profile slant range to the aircraft is made to interpret the interaction between the terrain characteristics and the resulting laser line scan information. Emphasis is placed on the range interactions. In particular, the terrain height profile is modeled as a single sinusoid in one spatial dimension with constant reflectivity. The laser transmitter is sinusoidally intensity modulated, so that the received signal is subcarrier phase modulated by the terrain height profile. This phase modulated signal is low pass filtered to represent the effects of the spatial filter. Numerical analysis is utilized to evaluate this nonlinear filtering problem and to examine the range error in terms of the maximum range height variations. The resulting mean-squared range distortion error is added to the range squared distortion error originating from the receiver noise in the Phase Locked Loop phase tracking circuit. The distortion due to spatial filtering is shown to increase with the laser modulation frequency while the errors due to detection noise decrease with frequency.