Computation of Magnitude Spectra

Magnitude or power spectra can be computed from the real and imaginary parts of the spectrum according to eq. (1.37). 

Due to the quadratic form of eq. (1.37), the magnitude spectrum is phase independent, and a manipulated signal noise improvement relative to the pure u and v modes is attained (Fig. 2.14). If only magnitude information is desired, phase correction is not necessary, and P(v) can be computed immediately after Fourier transformation. 

Weak lines are sometimes more easily localized in dispersion and magnitude spectra, as illustrated in Fig. 2.14(b, c). However, the signals of dispersion and magnitude spectra suffer from tailing (Fig. 2.14 (b, c)), and a weak line closely spaced to a strong one may be lost or distorted in the tail of the strong signal. 

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