Importance sampling is a technique which can significantly reduce the numbe
r of Monte Carlos necessary to accurately estimate the probability of low-p
robability of occurrence events (e.g., the probability of false alarm P-F a
ssociated with a given detection scheme). A new technique called the Cherno
ff Importance Sampling Method is introduced. It is shown that the number of
required Monte Carlos can be reduced by a factor of a Chernoff-like bound
on P-F. In addition, techniques for choosing the multiplying factor of the
distorted variance method (the most common method used in importance sampli
ng) are presented.