Geoscience Reference
In-Depth Information
4.8 Point Transect Sampling
Point transects are like line transects for which the lines have zero length.
What happens is that a number of points are chosen within the study area,
and each point is visited. The objects detected from each point are then
recorded, with their distances from the points, as shown in Figure 4.7. This
sampling method is called variable circular plot sampling by ornithologists,
who seem to be the main users of such methods. Information about the anal-
ysis of data from such studies was provided by Buckland et al. (2001).
4.9 Software for Line and Point Transect
Sampling and Estimation
Distance, the standard program for line and point transect sampling
and estimation, is available free on the Internet from the University of St.
Andrews in Scotland (Thomas et al
.
, 2009), and an updated description of
the history and procedures currently implemented in this program has been
published by the original authors and contributors (Thomas et al
.,
2010). The
most recent version of Distance includes three analysis engines: the conven-
tional or classic distance sampling (line transect and point transect), multiple
covariate distance sampling, and mark-recapture distance sampling (MRDS;
Borchers et al
.,
1988). This last method is useful when sampling involves
double observers (Manly et al
.,
1996; Buckland et al
.,
2010), but it can only
run in Distance in conjunction with routines written in the R language. To
FIGURE 4.7
An illustration of point transect sampling, with six sample points (◼) and from none to three
objects (⚪) detected.
