  The Hilbert Huang Transform is a new technique for the analysis of
non--stationary signals. It comprises two distinct parts: Empirical Mode
Decomposition (EMD) and the Hilbert Transform of each of the modes found from
the first step to produce a Hilbert Spectrum. The EMD is an adaptive
decomposition of the data, which results in the extraction of Intrinsic Mode
Functions (IMFs). We discuss the application of the EMD to the calibration of
two optical scintillometers that have been used to measure C_n^2 over
horizontal paths on a building rooftop, and discuss the advantage of using the
Marginal Hilbert Spectrum over the traditional Fourier Power Spectrum.
