detectfn: Detection Functions
Description
A detection function relates the probability of detection to the distance
of a detector from a point. The reference point is usually thought of as
an animal's home-range centre. In secr only simple 2- or
3-parameter functions are used. Each type of function is identified by a
numeric code (see below).
Some functions are defined only for simulation: these either cannot be
fitted by maximum likelihood (uniform) or have yet to be implemented
(compound halfnormal).
llll{
Code Name Parameters Function
0 halfnormal g0, sigma $g(d) = g_0 \exp \left(\frac{-d^2} {2\sigma^2} \right)$
1 hazard-rate g0, sigma, z $g(d) = g_0 [1 - \exp{ {-(^d/_\sigma)^{-z}} }]$
2 exponential g0, sigma $g(d) = g_0 \exp { -(^d/_\sigma) }$
3 compound halfnormal g0, sigma, z $g(d) = 1 - (1 - g_0 \exp \left(\frac{-d^2} {2\sigma^2} \right) ^ z)$
4 uniform g0, sigma $g(d) = g_0, d References
Efford, M. G. and Dawson, D. K. (2009) Effect of distance-related
heterogeneity on population size estimates from point counts. Auk
126, 100--111.
Efford, M. G., Dawson, D. K. and Borchers, D. L. (2009) Population
density estimated from locations of individuals on a passive detector
array. Ecology 90, 2676--2682.
Hayes, R. J. and Buckland, S. T. (1983) Radial-distance models for the
line-transect method. Biometrics 39, 29--42.