Ranging performance of satellite laser altimeters

Topographic mapping of the Earth, Moon, and planets can be accomplished with high resolution and accuracy using satellite laser altimeters. These systems employ nanosecond laser pulses and microradian beam divergences to achieve submetre vertical range resolution from orbital altitudes of several hundred kilometres. In this paper the authors develop detailed expressions for the range and pulsewidth measurement accuracies and use the results to evaluate the ranging performances of several satellite laser altimeters currently under development by NASA for launch during the next decade. The analysis includes the effects of the target surface characteristics, spacecraft pointing jitter, and waveform digitizer characteristics. The results show that ranging accuracy is critically dependent on the pointing accuracy and stability of the altimeter, especially over high-relief terrain where surface slopes are large. At typical orbital altitudes of several hundred kilometres, single-shot accuracies of a few centimetres can be achieved only when the pointing jitter is on the order of 10 μrad or less