Astrophysics (index)about

Spectral Density

(strength of power or energy as a function of frequency)

Spectral Density is a term used in signal processing and Time Series Analysis. (Similar terms are used to describe the distribution of Electromagnetic Radiation or other Frequency-related phenomena.)

Power Spectral Density (PSD) is the distribution of power as described by the Fourier Transform of the auto-correlation function of a signal. It shows the strength of the variations in power as a function of frequency.

Energy Spectral Density (ESD) is similar, taken over a specific interval of time.

The terms energy and power are, in a sense, "borrowed", used because one is an amount and the other a rate of the same concept over time, analogous to how the terms are used for physical energy.

The terms can be used for analysis of a continuous signal, at least in theory, but modern electronics and data collection is generally digital and records and analyzes a discrete signal formed by sampling, taking periodic samples from an incoming signal (such as a voltage output from a Radio Telescope antenna over time), thus time series analysis. In the discrete case, the analysis is on a sequence of numbers, using computer algorithms, e.g., for the Fourier analysis, using the Fast Fourier Transform (calculating the Discrete Fourier Transform).


(statistics,analysis,function)
http://en.wikipedia.org/wiki/Spectral_density
http://www.fysik.lu.se/fileadmin/fysikportalen/UDIF/Bilder/Signal_analysis_in_astronomy.pdf
http://adsabs.harvard.edu/full/2002ASPC..278..123H
http://user.it.uu.se/~ps/SAS-new.pdf

Referenced by:
Antenna Temperature
Magnetic Energy Spectrum

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