Doppler spectral broadening

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Doppler spectral broadening

Increase in the Doppler spread arising from different processes or phenomena. The Doppler spectrum is ordinarily regarded as a reflectivity-weighted distribution of the radial velocities of the scatterers in the pulse volume.

A spread of radial velocities exists because of turbulence and wind shear in the pulse volume and, for precipitation targets, because the particles have a range of fall velocities. The spectrum may be further broadened by processes that have little to do with the radial velocity distribution of the scattering elements. These processes include 1) the cross-beam wind velocity, which induces a broadening proportional to the beamwidth because of the radial component of the cross-beam wind vector pointing in directions away from the beam axis; 2) uncertainties in the measurement of the Doppler spectrum because of statistical fluctuations in the spectral estimates that arise from short sampling times; and 3) motion of the radar beam relative to the targets as a result of scanning in azimuth or elevation, which further reduces the sampling times.

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