EFFECTS OF AEROSOL FORWARD SCATTER ON THE LONG-EXPOSURE AND SHORT-EXPOSURE ATMOSPHERIC COHERENCE DIAMETER

An experimental investigation of the atmospheric coherence diameter is presented in order to examine the relative effects of turbulence and aerosol forward scattering. The investigation includes measurements th rough the open atmosphere for path lengths of several kilometres. In a ddition to turbulence degradation of the atmospheric coherence diamete r, it is shown here that aerosol forward scattering also causes severe limitations, particularly for short exposures. Two methods, direct (s patial domain) and indirect (spatial frequency domain), for measuring the atmospheric coherence diameter are presented. The methods are theo retically and experimentally independent. The results of both methods are in very good agreement, emphasizing measurement reliability. It is shown that, in contradiction to turbulence, aerosols affect light coh erence identically for both short and long exposures. Experimental res ults during rather extreme atmospheric conditions such as fog are pres ented too. The results here are applicable to cost-effective imaging s ystem design involving aperture size, and to predicting imaging system performance through the atmosphere.