Overview

This chapter introduces the basic concepts of single-input/single-output (SISO) frequency-response identification theory. An understanding of these concepts is an important prerequisite to the success of the system-identification process. The reader is referred to many excellent textbooks on Laplace transform analysis of dynamic systems (for example, see Franklin et al.104). A clear and succinct primer that presents a physical interpretation of the frequency-domain, time-series analyses, and the fast Fourier transform (FFT) is that of Ramirez.105 The details of spectral analysis and frequency-response identification principles are covered in books by Bendat and Piersol106 ^,107 and Otnes and Enochson.108 The method of tapered overlapped windows or periodograms is key to achieving spectral estimates with low random error from real test data. Analytical and computational results can be found in the very useful reports by Nuttall109 ^,110 and Carter et al.111

The analysis of a signal or input-to-output process as a function of frequency (rather than time) is referred to as spectral analysis. Spectral analysis is often considered "more art than science" because of the many aspects of sampling, filtering, windowing, and FFT calculations that require user selection of processing parameters. CIFER incorporates into its graphical user interface many practical guidelines for aircraft, rotorcraft, and subsystem identification, based on extensive practical experience. With much of the nuts and bolts of the analysis machinery taken care of, the analyst can focus more on the correct interpretation of the frequency-domain results.

To put this chapter into the proper context, refer...