Radial-Distance Models for the Line-Transect Method

Line-transect estimation of wildlife populations can be based on either right-angle distances or radial distances. Estimation based on radial distances requires more restrictive assumptions about the mechanism by which observations are generated. We examine this mechanism and show that the mean sighting angle may frequently be larger than predicted by Hayne's fixed-distance model or by Eberhardt's variable-distance model. The modified and generalized Hayne's models are also investigated. An alternative approach, based on hazard-rate analysis, is suggested, but we conclude that a nonparametric right-angle-distance model will generally result in more reliable estimation than any radial-distance model.