Introduction
An introduction to distance sampling surveys
Distance-sampling is a form of ecological survey designed to estimate density and abundance of survey targets (e.g., animals) when detection probability declines with distance. Distance-sampling is popular in ecology, especially when survey targets are observed from aerial platforms (e.g., airplane or drone), surface vessels (e.g., boat or truck), or along walking transects. Distance-sampling surveys can include many target detection techniques (e.g., cameras, acoustic recorders, etc.), but for purposes of an introduction, we consider all such these techniques to be implemented on either line-transects or point-transects. Line-transects measure observation distances from the closest approach of a sample route (transect) to a target (i.e., perpendicular off-transect distance). Point-transects are sequences or one or more sample points at which observation distances are measured from the point’s location to the target (i.e., radial distance). Distance-sampling is one of two primary methods in Ecology for estimating ecological abundance, the other being capture-recapture.
This online primer is an introduction to the motivation, assumptions, and methods used to estimate density and abundance when detection probability declines with distance. In many instances, analysts refer to these topics as “distance analysis”, but a better term might be “analysis of distance-sampling surveys” because more than distance is analyzed and the surveys do, in fact, sample distance (but, this author agrees that the latter term is long).
Additional Resources
Many books and paper have been written about distance-sampling surveys. For more details than provided in this primer, refer to one of the following textbooks.
Buckland et al. (1993)
Buckland et al. (2001)
This author’s recommendation for the beginner
Buckland et al. (2004)
Buckland et al. (2015)
Another excellent source of information for all things distance-sampling is the distancesampling.org website. Resources there were written by many of the primary authors in this field of ecology.