detectfn {secr} | R Documentation

## 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, signal strength, binary signal strength).

Code | Name | Parameters | Function
0 | halfnormal | g0, sigma | g(d) = g0 * exp(–d^2 / (2 sigma^2))
1 | hazard-rate | g0, sigma, z | g(d) = g0 * (1 – exp(– (d / sigma) ^(–z) ))
2 | negative exponential | g0, sigma | g(d) = g0 * exp(– d / sigma)
3 | uniform | g0, sigma | g(d) = g0, d<=sigma; g(d) = 0, otherwise
4 | compound halfnormal | g0, sigma, z | g(d) = 1 – (1 – g0 * exp(–d^2 / (2 sigma^2)))^z
10 | signal strength | beta0, beta1, sdS | g(d) = F((c – (beta0 + beta1 * d)) / sdS)
11 | binary signal strength | beta0, beta1, sdS | g(d) = F((c – (beta0 + beta1 * d)) / sdS)

For functions (10) and (11), 'F' is the standard normal distribution function and 'c' is an arbitrary signal threshold. These models use the same detection function, but (10) also models signal strength (see Efford et al. 2009).

The hazard-rate detection function was described by Hayes and Buckland (1983). The compound halfnormal detection function follows Efford and Dawson (2009). The signal strength and binary signal strength functions are from Efford et al. (2009).

### Author(s)

Murray Efford murray.efford@otago.ac.nz

### 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.

### See Also

`detectfnplot`, `secr detection models`

[Package secr version 1.2.11 Index]