Influence of aerosols on off-axis laser detection capabilities

摘要

The radiation coming from a laser which operates in the coastal zone can be detected not only when a detector is placed in front of the laser beam but also when it is located outside the main beam direction. The reason is that in a real detection scheme the power collected by a detector not only comes from direct radiation but also from other radiation sources, like port scattering, aerosol scattering and background radiation. Their relative contributions depend on many factors, i.e. laser features, collecting optics features, meteorological conditions, etc. An important contributor is aerosol scattering and its intensity depends on the aerosol composition and particle density. It was found that more humid conditions cause a decrease in the direct radiation and an increase in the diffuse component. This effect depends on the contribution of hygroscopic and non-hygroscopic aerosols. In the marine-continental atmosphere, represented by a mixture of sea-salts (SSA), anthropogenic salts (WS) and organic carbon (OC), a change in relative humidity from 80% to 95% can change the result for the predicted irradiance level on the sensor by more than a factor of three. Dust-like (DL) particles produce much stronger scatter irradiance than other aerosol types, independently of the off-axis distance.