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Small-scale fluctuations of different tracers of the interstellar the mediumcan be used to study the nature of turbulence in astrophysical scales. Ofthese, the `continuum' emission traces the fluctuations integrated along theline of sight whereas, the spectral line tracers give the information alongdifferent velocity channels as well. Recently, Miville-Desch\^enes et al.(2016) have measured the intensity fluctuation power spectrum of the continuumdust emission, and found a power law behaviour with a power law index of $-2.9\pm 0.1$ for a region of our Galaxy. Here, we study the same region usinghigh-velocity resolution 21-cm emission from the diffuse neutral medium, andestimate the power spectrum at different spectral channels. The measured 21-cmpower spectrum also follows a power law, however, we see a significantvariation in the power law index with velocity. The value of the power-lawindex estimated from the integrated map for different components are quitedifferent which is indicative of the different nature of turbulence dependingon temperature, density and ionization fraction. We also measure the powerspectra after smoothing the 21 cm emission to velocity resolution ranging from$1.03$ to $13.39~{\rm km~s^{-1}}$, but the power spectrum remains unchangedwithin the error bar. This indicates that the observed fluctuations aredominantly due to density fluctuations, and we can only constrain the power-lawindex of velocity structure function of $0.0 \pm 1.1$ which is consistent withthe predicted Kolmogorov turbulence $(\gamma=2/3)$ and also with ashock-dominated medium $(\gamma=1.0)$.

Turbulent power spectrum in warm and cold neutral medium using the Galactic HI 21 cm emission