detectfn                package:secr                R Documentation

_D_e_t_e_c_t_i_o_n _F_u_n_c_t_i_o_n_s

_D_e_s_c_r_i_p_t_i_o_n:

     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).

_A_u_t_h_o_r(_s):

     Murray Efford murray.efford@otago.ac.nz

_R_e_f_e_r_e_n_c_e_s:

     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.

_S_e_e _A_l_s_o:

     'detectfnplot', 'secr detection models'

