The objective identification of duplicate sightings in aerial survey for porpoise

This paper describes simulation trials of;lll estimator for effective strip width, based on duplicate sightings from a single aircraft. The aircraft c ircles back after each sighting to overfly the location of the sighting a s econd time. Pods seen during these repeat flights are called "trailing" sig htings and those seen before the aircraft circled back "leading" sightings, because die data collected is similar to that collected from two aircraft in tandem formation. Because it is not known which (if any) of the trailing sightings are re-sightings of the leading ones, the likelihood of the sigh ting locations is summed over all possible pairings. The resulting estimate s of effective strip width are robust to failure of many of the assumptions used in derivation of the likelihood.