Contour plots, for the low-frequency, along-scan case, of all ten parameter combinations. The panels above the diagonal refer to the merit function P(u) while the panels below the diagonal refer to the regularised merit function P(u)·R_∗·R_∗∗. The panels are centred on the optimised parameter values (intersection of the black lines) and cover a range of 100 for a, b, c, and d and 500 for e. White areas refer to parameter combinations which violate the minimum detection percentages defined in Table 1.