The importance of sensor linearity is often overlooked. It is naively assumed that one can simply employ
a lookup table to provide calibration corrections. This assumption can result in serious misinterpreta-
tions of spectral data, especially in a multimode system. A classic example of artifacts (nonreal signals)
that result from a nonlinear sensor is to be found in the ear. The phenomenon, known as aural
harmonics, is well known to musicians and ﬁgures in the use of “fortissimo” and “pianissimo” in
orchestral music. In this chapter we describe how the artifacts mentioned in Chapter 2 are generated.
Figure 3.1 illustrates differences according to the nature of the nonlinearity.