Experiment and result analysis of atmospheric refractivity retrieval with Doppler weather radar

In the region of microwave spectrum, atmospheric refractivity is empirically dominated by temperature, pressure and water vapor pressure. With the change of atmospheric refractivity, the propagation speed of a Doppler weather radar radio will change, and so does the echo phase angle from a fixed target (ground clutter) . The reference echo phase angle of a ground target can be attained by measuring it under a cool and almost homogenous weather, and the reference atmosphere refractivity can be calculated from the temperature, pressure and vapor pressure. The atmospheric refractivity can be calculated from the echo phase difference refer to the reference phase angle and refractivity. To carry out atmospheric refractivity experiment, an I-Q data recorder was designed to match the CINRAD-SA Doppler weather radar sited at Nanjing for collecting I and Q raw data. A 15-days' refractivity was retrieved and it was consistent with the calculated refractivity. In a case of locally thunderstorm event, the retrieved refractivity was slightly different to the calculated one because the water vapor was inhomegenous during the small-scale thunderstorm. The experiments showed that the retrieved atmospheric refractivity from Doppler weather radar was reliable and reasonable. Due to the strong relationship of water vapor to atmospheric refractivity, the retrieved refractivity can be used as an index of water vapor. The experiment results indicate that Doppler weather radar can provide not only 3 base data (Reflectivity, radial velocity and spectrum width) and also water vapor information if an I-Q data recorder was embedded.