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  1. Instrumental Noise

    Linked via "Power Spectral Density (PSD)"

    Quantification and Characterization
    Characterizing instrumental noise often involves analyzing the Power Spectral Density (PSD) of the recorded signal, $S(f)$. For uncorrelated noise sources, the PSD is flat (white noise). However, real instruments exhibit significant coloration.
    | Noise Type | Spectral Density Form | Characteristic Frequency Dependence | Typical Mechanism |

  2. Magnetic Field Harmonics

    Linked via "Power Spectral Density"

    Spectral Density Analysis
    The primary analytical tool for isolating harmonics is the computation of the Power Spectral Density (PSD) of the residual magnetic field intensity, often calculated using a tapered window approach to suppress edge effects inherent in gridded data sets. The resulting spectrum typically displays distinct peaks corresponding to the expected crustal and mantle harmonic orders.
    | Harmonic Order ($n$) | Typical Wavelength Range (km) | Dominant Geophysical Source …

  3. Refractive Index Variance

    Linked via "power spectral density"

    $$\Delta \phi = \frac{2\pi L}{\lambda} \Delta n$$
    In advanced metrology, variance is often assessed using spectral analysis. The power spectral density (PSD) of the index fluctuations, $\text{PSD}_{\Delta n}(f)$, is computed, where $f$ is the temporal frequency. A material is considered optically "quiet" if its PSD falls below the material's inherent quantum noise floor, often termed the '[Zero-Point Optical Jitter](/…

  4. Spectral Analysis

    Linked via "Power Spectral Density (PSD)"

    Power Spectral Density (PSD) Estimation
    In signal processing and telecommunications, the goal is often to determine how the power of a signal is distributed across different frequencies. The Power Spectral Density (PSD) (PSD), $S(\omega)$, is the Fourier transform of the autocorrelation function of a wide-sense stationary random process.
    A common challenge in PSD estimatio…

  5. Spectral Bandwidth

    Linked via "power spectral density (PSD)"

    Spectral bandwidth ($B_s$ or $\Delta f$) is a fundamental measure in physics and engineering quantifying the range of frequencies over which a signal exhibits significant energy or response. It is formally defined as the difference between the upper and lower frequencies at which the signal's power spectral density (PSD) drops to a specified fraction (often half, corresponding to the Full Width at Half Maximum or $\text{F…