A plurality of pixel areas are defined on the surface of a substrate. A threshold is computed from the detection of infrasound in the vicinity of the sensor prior to the arrival of infrasound from the turbulence and an alarm is given when the infrasound from the turbulence exceeds the computed threshold. The connector couples to the inside of the CT by means of wedges that are urged against the inside wall of the CT. The underlying cushion andor base wall define a spring constant that varies along a length of the seal. The method includes measuring substrate characteristics at a plurality of well-defined points of a reference substrate, measuring spectra at plurality of measurement points of the reference substrate, there being more measurement points than well-defined points, and associating measured spectra with measured substrate characteristics.