Distance sampling

Abstract

With distance sampling we can estimate abundance from a single survey because the method involves a strong (but often reasonable) assumption about detection probability. Distance sampling comprises several related methods which involve measuring or estimating distances of detected animals from a line or point. The two main methods are line transect sampling and point transect sampling (sometimes called variable circular plots). Both are extensions of plot sampling, in which only incomplete counts of animals within the covered region are made. The key assumption about detection probability is that all animals that are located on the line or at the point are certain to be detected. Detection probability p(x) is assumed to fall off in a smooth way out to some distance x = w from the line or point.