DLOC Principles of Meteorological Doppler Radar:
WSR-88D Fundamentals

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Previous Page: Section #6: WSR-88D Data Collection

Clear Air Mode Operations

The WSR-88D is sensitive enough to detect non-precipitation targets or even clouds as long as they are good reflectors. This is possible if the diameter of small point targets or conglomerates of small targets fall into the Rayleigh scattering range. Also, gradients or abrupt changes in the refractive index detectable at the wavelength of the WSR-88D (e.g., changes in temperature or moisture along the radar beam's path) can cause some energy to reflect back toward the radar. VCP 31 is the only VCP that uses long pulse with a pulse length three times that of all the other VCPs.

VCP 31 and VCP 32 are the Clear Air Mode VCPs. VCP 31 is about 3 dB more sensitive compared to VCP 32. This means that weaker targets at longer ranges will be detectable with VCP 31. Though VCP 32 employs short pulse (along with all the Precipitation Mode VCPs), the slow antenna rotation rate results in a larger number of pulses per radial, compared with the other short pulse VCPs. This improves the quality of the base data. Both VCPs 31 and 32 can be good choices for light precipitation events, especially winter weather events.

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