Multifrequency range imaging of atmospheric structures using VHF-band atmosphere radars

Radars at very-high-frequency (VHF) band have been applied to the atmospheric sounding for several decades, with the aid of many advanced radar techniques. In 2008, the range imaging (RIM) based on frequency-domain interferometric method was implemented in the Chung-Li VHF atmosphere radar, and since then plenty of experiments with different radar parameters such as pulse length,pulse shape, receiver bandwidth, transmitter frequency set, and so on, have been conducted to testify the performance of RIM. With the multifrequency-received data, the small-scale atmospheric refractivity structures in the range direction can be retrieved by using optimization methods such as the Capon method. Double-layer structures as well as their temporal and spatial variations have been resolved for the first time of the Chung-Li VHF radar. These findings are achieved after effective calibrations of the range/time delay as well as the range-weighting function effect on the radar echoes. According to the calibration results of the RIM data collected between 2008 and 2013, it is suspected that aging of cable lines and/or some key components of the radar system led to an increase of the range/time delay of the radar echoes. Moreover, the values of range/time delay were slightly different for the radar echoes with and without significant precipitation. In view of this, a procedure of point-by-point correction of range/time delay has been employed to improve the performance of RIM in the clear-air and precipitation conditions. It is expected that the high-resolution imaging for the atmospheric structures can be of help for an inspection of small-scale dynamic atmosphere.