Abstract

We have conducted experiments involving the use of a multi-aperture dual-balanced heterodyne laboratory tunable Differential-Absorption Lidar (DIAL) system which used an eye-safe 1.55 micron laser source. The system was used to detect the absorption spectrum of a gas in a remote multi-pass absorption cell by smoothly tuning the laser wavelength across the absorption line of the gas. The system measured the influence of target surface roughness, orientation, velocity, and vibration on the DIAL returns, under controlled conditions. Different signal recombination techniques were studied including (1) direct detection, (2) single detector heterodyne, (3) non-coherent summation of dual-detector heterodyne, (4) coherent summation of heterodyne dual-detector signals, and (5) dual-balanced, dual-detector improvements. We also studied the influence of refractive and wind driven turbulence on the lidar returns from various targets. It was found that the S/N of the DIAL signal was often distorted by several noise like processes (laser linewidth fluctuations, atmospheric turbulence, lidar target vibrations) and that the use of the coherent summation of the multi-detector heterodyne signals could help improve the S/N value under certain experimental conditions.

© 2006 Optical Society of America