Spectral analysis of unevenly spaced or discontinuous data using the “normperiod” code

“Normperiod”, a Fortran code permitting spectral analysis of non-equidistant data in various fields of engineering and natural sciences is presented. This code is based on the Lomb normalized periodogram and has two basic merits; first, it permits analysis of discontinuous or non-equidistant time series without prior interpolations or their fragmentation, as is the case with FFT, and hence noisy results or loss of information is avoided. Second, it is very simple, can be easily modified, can be used in the analysis of both very short and very long time series and permits the determination of the statistical significance of obtained results. The tolerance of this code is demonstrated on the basis of several examples, in which obtained dominant frequencies are compared with independently known values.