Modulation techniques for an airborne laser scanner

Methods of modulating the laser output power of an airborne scanner which can measure slant range and reflectance are analyzed. The performance factors used in the range measurement are the range ambiguity interval, the range resolution, and the variance of the range estimate. Variance of the estimate is used to compare reflectance measurements. Three modulation techniques-the sinusoid, the FM chirp of a subcarrier, and a pseudonoise (PN) coded pulse train-are shown to have promise. If range ambiguity can be tolerated, the simplicity of the sinusoidal modulation technique makes it a prime contender, while the PNcoded technique shows most promise as detector and laser modulation bandwidth increase.