4.9 The levels of salt concentration known to have occurred over rows, corresponding to the average temperature levels for the soil science data considered in Figures 1.15 and 1.16, are shown in Figure 4.32. The data are in the file salt.dat, which consists of one column of 128 observations;

the first 64 observations correspond to the temperature series. Identify the dominant frequencies by performing separate spectral analyses on the two series. Include confidence intervals for the dominant frequencies and interpret your findings.