The trawl function is parametrised by the two parameters \(\delta
\geq 0\) and \(\gamma \geq 0\) as follows: $$g(x) =
(1-2x\gamma^{-2})^{-1/2}\exp(\delta \gamma(1-(1-2x\gamma^{-2})^{1/2})),
\mbox{ for } x \le 0.$$ It is assumed that \(\delta\) and \(\gamma\) are
not simultaneously equal to zero. Its autocorrelation function is given by:
$$r(x) = \exp(\delta\gamma (1-\sqrt{1+2 x/\gamma^2})), \mbox{ for } x
\ge 0.$$