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Extinction of laser rangefinder (LRF) pulses by the atmosphere depends on the LRF wavelength, weather conditions and theaerosol concentration along the optical path. The total atmospheric extinction a(?) is the sum of the molecular and aerosolcontributions, am and aa. We present simple expressions for am(X) and aaO) for the LRF sources; Er:glass, Ho:YAG andCo2 which operate near 1.54, 2.1 and 10.6 jtm respectively. Also included are results for Nd:YAG which may be made to laseat the eyesafe wavelength of 1.444 pm. The expressions give an estimate of a() as a function of standard meteorologicalparameters, assuming honzontal beam propagation. The effect of forward scattering on the received LRF signal is alsodiscussed. 1. INTRODUCTION Eyesafe LRFs operating at 10.6 j.tm have a good performance record but are bulky, relatively expensive and require cooleddetectors. Recently, solid state laser sources have become available that are good candidates to replace CO2 lasers for most LRFapplications. One of the most promising is the Ecglass laser which operates at 1.54 j.tm, but other candidates include NCLYAGoperating at 1.444 jim and Ho:YAG operating near 2.1 j.tm. All of these wavelengths are eyesafe for use in LRF applications.As extinction of a LRF laser pulse by the atmosphere is one of the most important factors that limit performance, it is useful tobe able to estimate the atmospheric extinction coefficient. We present simple expressions for the molecular and aerosol extinc-tion components, am() and aa(X) based on standard meteorological parameters; tempemture, humidity and visibility. Byassuming ahorizontalpath and a homogeneous extinction profile, the expressions can be used to estimate the signal-to-noiseratio of LRF returns, given system and target characteristics. The results can be used to estimate the maximum range of a LRFsystem and are useful for estimating the relative performance of systems in cost/benefit analysis. |
