Vibrational amplitude oscillation tracked by spectral shape analysis.

One hour long averaged spectra are normalised prior to being cross correlated with the three discriminant functions shown in Fig 7. The outcome is used to compute an indicator of the vibrational amplitude oscillation, which is shown from midnight to 6 am as a colour coded image. The indicator is not only good at tracking the amplitude oscillations (except for Colony No. 6) which is shown with the white curve, it also suffers less drift, as clearly demonstrated on Colony No. 5, 7, and 15. The white curve's quantitative axis is displayed on the right hand side of the individual plots. The indicator is obtained by first collapsing a one hour long averaged spectrum onto a 3D point, by computing three separate cross correlations with the curves shown in Fig 7D. The distance, D1, between the 3D point and the centroid of the black cloud in Fig 7 is further calculated, as well as the distance, D2, between the 3D point and the centroid of the other clouds. The colour-coded indicator is the ratio D2/D1.