 acoust signal detect turbul airflow acoust signal detect turbul airflow improv detect signal-to-nois ratio period signal mask addit nois turbul nois background comparison autocorrel crosscorrel combin frequenc filter crosscorrel method provid greatest improv crosscorrel techniqu success singl method turn maximum improv obtain limit dynam rang correl comput error finit averag time scan delai improv signal mask turbul nois 5 db addit nois 