Patent US 4,956,792

A target signal detecting apparatus for discriminating and detecting a target signal from a noise signal having an amplitude characteristic which exhibits the Weibull distribution. A received signal whose amplitude intensity distribution is in accordance with the Weibull distribution with its probability density function Pc(x) given by the following ##EQU1## is subjected to logarithmic transformation so that a mean-square value <y.sup.2 > of the amplitude of the logarithmically transformed received signal (y=lnx) and a square value <y>.sup.2 of the mean are calculated and a distributed parameter C is calculated in accordance with the mean-square value <y.sup.2 > and the square value <y>.sup.2 of the mean as follows ##EQU2## Then, the calculated distributed parameter C is compared with a predetermined threshold so that if the distributed parameter C is greater than the threshold value, it is delivered as the distributed parameter corresponding to a target signal. Also, there are cases where the calculated distributed parameter C is amplified non linearly and then compared with the threshold.