ERAD 2010 - THE SIXTH EUROPEAN CONFERENCE ON RADAR IN METEOROLOGY AND HYDROLOGY Resonance scattering at close wavelengths in hail and “clear air”
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چکیده
Carrier frequencies of networked weather radars are allocated in a narrow band, i.e., in X-, C-, and Sbands. To reduce signal interference among adjacent radars, the carrier frequencies are offset. A calibration procedure, running on radars, brings reflectivity values to the same level assuming that the intrinsic reflectivity of the scattering media is the same. This assumption is good for rain but not for hail. Scattering by hailstones exhibits a resonance effect. This effect has been studied and used for hail detection with radars operating at X-, C-, and S-bands. Resonance scattering at close wavelengths belonging to the same frequency band is studied in this paper. It is shown that for a frequency shift of about 10% at S-band, the difference in reflectivity values vary from 2 to 6 dB. Flying birds and some insects are not small compared to the weather radar wavelengths. Resonance scattering at close S-band frequencies is demonstrated on radar data collected in “clear air”. Measured reflectivity differences can exceed 10 dB. To explain such a difference, computational results are presented. Reflectivity values and polarimetric parameter differences at Xand C-bands with small frequency deviations inside the bands are also presented. Hail detection is also discussed. A frequency shift of 10% is sufficient to measure reflectivity differences produced by hail. Such a shift can be implemented within a single radar.
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تاریخ انتشار 2010