Computer session on measurement and analysis of waves and turbulence

6th COSPAR Capacity Building Workshop

Sinaia, Romania, June 4-16, 2007

Ondrej Santolik


1. Spectral analysis

Wave measurements are often represented in the frequency domain. A simple tool to characterize the data is the power spectrum. It can be obtained from a measured time series of samples of a given quantity (a waveform) using the Fourier analysis. The result is the power spectral density as a function of frequency. For example, if we measure an electric field component in V m-1, the resulting power spectral density will be given in V2m-1Hz-1. Note: Non-Fourier methods to estimate the power spectral density are also sometimes used (for example the autoregressive or maximum entropy models) but these are not discussed here.

Instructions:

  1. Download the following IDL procedures:
  2. Read the comments and try to understand the code (the above sequence of files is recommended)
  3. Run the program example_power_spectrum.pro .
  4. Modify and re-run the program using different frequency resolutions (controlled by the nfft parameter) and different waveform data sets.

Reading: The ISSI book, Chapters 1.1-1.3