What is spectral derivative?
Derivative spectroscopy uses first or higher derivatives of absorbance with respect to wavelength for qualitative analysis and for quantification. The concept of derivatizing spectral data was first introduced in the 1950s, when it was shown to have many advantages.
What is the derivative of frequency?
The derivative of a sine wave of frequency f is a phase-shifted sine wave, or cosine wave, of the same frequency and with an amplitude that is proportional to f, as can be demonstrated in Wolfram Alpha.