A method comprising: receiving first information for defining a first algebraic function that relates a time variable to a first mapped variable; using the function to convert a time variable value to a first value of the first mapped variable e. In the method, a field containing the target is illuminated, and one or more spectral emission characteristics of the light-scattering particles in the field are detected. The region of the cable having the first thickness of the dry insert provides andor increases the coupling level of the at least one optical fiber to the cable jacket.