The Measurement Influence of Reflectivity Factor Caused by Scanning Mode from Phased Array Radar

The beam design of active phased array weather radar is flexible, and this variable beam width and multi-beam mode can satisfy the requirement of various tasks and get much higher temporal resolution than general weather radar. However, the performance of active phased array weather radar can be hardly kept consistent due to the massive digital T/R components, and any variations of antenna parameters between the beam direction and axis normal would be a huge challenge for radar calibration. The X-band phased-array weather radar (X-PAR) developed by State Key Laboratory of Severe Weather of Chinese Academy of Meteorological Sciences and Anhui Sun-create Electronic Co Ltd is tested for the first time from April to June in 2013. The X-PAR and C-band polarization weather radar (C-POL) are installed at the same site, so their observations provide reflectivity measure deviation information and correction scheme for radar debugging and calibration of antenna parameters.During the operation of X-PAR, 3 kinds of observing modes with different beam width are applied, each using different parameters in their radar equations of calibration algorithm. Observations from C-POL and X-PAR (fine mode) with single scanning beam, X-PAR (quick mode) with multi scanning beams and X-PAR (fine Mode) are contrasted in detail. In order to reduce the comparison bias, severe convection and attenuation should be avoided. Results from statistical analysis indicate that observations from each elevation of X-PAR (fine mode) is 3 dB higher than C-POL, the measurement deviation between quick mode and fine mode changes along 4° regularly, and is inconsistent in higher elevation. The deviation source of X-PAR (fine mode) and C-POL comes from differences between the antenna parameter and the effective cross section, and the fast mode is also influenced by beam pattern, gaining in different elevation. A correction scheme based on data statistics and fitting is proposed to decrease the bias within 1 dB. By the comparison through vertical structures, the dependability of the above method is testified, and the resolution of X-PAR is also higher than C-POL, which is significant for convective precipitation research.The actual performance of phased array antenna could not keep strictly consistent with theoretical value because of its complicated structure. The result suggests that antenna measurement and digital T/R test during the factory inspection and acceptance are very indispensable. In the future field experiments, a well-calibrated radar should be installed at the same position to correct the X-PAR observation bias.