## 3 Methods
### Intercomparison  
The mean bias between the two radars was calculated to evaluate the homogeneity of the radar network. Figure 5 indicates that the radar bins in geometrical overlapping areas between two radars (overlapping volume) was selected by calculating the height of the radar beam at the center of equidistant from the two radars (thick vertical solid line in Figure 5b). The shadow area in Figure 5a represents the overlapping volume at the equidistance from two radars and the dashed line in Figure 5a represents the range of the azimuth angle for equidistance including overlapping volume. Figure 5b shows an example on how an elevation angle is selected. The solid line represents the height at the center of the beam, while the dotted line represents the height at the top and bottom of the beam. The conditions for matching the overlapping volume are as follows:  
1. The difference between the heights at the center of beam is less than 500 m.
2. The center of beam is within volume of beam of each radar.
3. The height at the center of the beam was limited to 0.5 to 3.0 km to select the \(Z_{\text{H}}\) in the rain region.
4. The range of volume of beam from the radar was limited to 200 km.  
Figure 4: Scatter plot of the calculated and measured differential phase from GSN radar for the rainfall event on 3 July 2020. The red solid line represents the calibration bias (\(\varepsilon_{\text{SC}}\)), while the red dashed lines represent the \(\varepsilon_{\text{SC}}\pm 1\) dB.  
The blue solid line and dotted line represents the volume of beam for the first elevation angle of the GSN radar. The volume of beam for elevation angles of the JNI radar, which satisfy the predefined conditions, are shown in red solid and dotted lines. The black solid and dotted lines represent the volume of beam for elevation angles of the JNI radar which do not satisfy the predefined conditions. The two radars with the largest number of overlapping volumes were matched for comparison. The maximum number of overlapping volumes was determined as the maximum number of pairs of \(Z_{\text{H}}\) between two radars at one time (the rain echoes pass all overlapping volume). The distance and number of overlapping volumes for matched radar pairs are shown in Table 3. Observational errors, such as calibration bias, beam blockage (\(\Delta Z_{\text{H}}=-10\text{log}(1-\text{BBF})\)), and rain attenuation, were corrected before inter-comparison. The data with a \(\rho_{\text{HV}}\) of more than 0.97 were used to extract \(Z_{\text{H}}\) for rain echoes. The mean bias was calculated by averaging the difference in \(Z_{\text{H}}\) in the overlapping volume after excluding the beam where the BBF was greater than 10% to avoid the effect of beam blockage.  
Figure 5: Example of selection of overlapping volume of the two radars. (**a**) Overlapping volume at equidistance between adjacent radars. The black dashed line indicates the range of azimuth angles including equidistance line. (**b**) Example for the selection of overlapping volumes between adjacent radars (GSN and JNI radar). The solid vertical line indicates the range at the center of equidistance. The solid (dotted) lines indicate the height at center (top and bottom) of the radar beams. The top and bottom of the radar beams are defined by considering the beam width. The red lines represent the matched elevation angles relative to blue line.