## 2 Materials and Methods
### Experiment, Instrument, and Measurements
CI has a high detection range and moderate Nyquist velocity and velocity resolution, but a larger blind range from 0.12 m to 2.01 km. The radar system operates the three modes periodically, i.e., once the radial measurement is finished in one mode, the radar immediately switches to another. Each mode requires \(\sim\)3 s for signal dwell and data processing, so the final temporal resolution of the radar is \(\sim\)9 s. The observations collected by the three modes are saved separately and a merging algorithm is used to produce the integrated spectral moments [28]. Operational parameters of the three modes are summarized in Table 2.  
To simply assess the detection capability of this radar, the probability distribution of measured reflectivity at different heights, collected from June to August 2014 and July to September 2015, was calculated. As shown in Figure 1, the realistic minimum detectable reflectivities of BL and CI at \begin{table}
\begin{tabular}{c c} \hline
**Items** & **Technical Specifications** \\ \hline Radar system & Doppler, solid-state, depolarization, multi-mode \\ \hline Frequency & 33.44 GHz \\ \hline Wavelength & 8.9 mm \\ \hline Transmitted peak power & \(\geq\)100 W \\ \hline Sensitivity & \(-\)38 dBZ at 5 km \\ \hline Antenna diameter & 2 m \\ \hline Antenna gain & \(\geq\)53 dB \\ \hline Pulse width & 0.2 us, 12 us \\ \hline Beam width & 0.3\({}^{\circ}\) \\ \hline Pulse repetition frequency & 8333 Hz \\ \hline Range gate number & 510 \\ \hline \multirow{4}{*}{Detection range} & Height: 150 m \(\sim\)15.3 km \\ \cline{2-3}  & Measurable reflectivity range: \(-\)50 \(\sim\)30 dBZ \\ \cline{2-3}  & Unambiguous velocity range: \(-\)18.54 \(\rightarrow\)+18.54 m\(\cdot\)s\({}^{-1}\) (maximum) \\ \hline \multirow{4}{*}{Resolution} & Temporal resolution: \(\sim\)9 s (adjustable) \\ \cline{2-3}  & Vertical resolution: 30 m \\ \cline{2-3}  & horizontal resolution: 26 m at 5 km \\ \hline \multirow{4}{*}{Measurements} & Original data: Doppler spectra \\ \cline{2-3}  & Spectral moments: reflectivity (Z), mean Doppler velocity (MV), spectrum width (\(\sigma_{\
u}\)), linear depolarization ratio (LDR), skewness (S\({}_{\mathrm{k}}\)), kurtosis (K\({}_{\mathrm{t}}\)), etc. \\ \hline \end{tabular}
\end{table} 
Table 1: Major technical and operational parameters of the Third Tibetan Plateau Meteorological Science Experiment (TIPEX-III) cloud radar. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters** & \multicolumn{4}{c}{**Mode**} \\ \cline{2-4}  & **BL** & **CI** & **PR** \\ \hline Detectable range (km) & 0.12–7.5 & 2.04–15.3 & 0.12–12 \\ Pulse width (\(\upmu\)s) & 0.2 & 12 & 0.2 \\ Pulse period (\(\upmu\)s) & 120 & 120 & 120 \\ Pulse repetition frequency (Hz) & 8333 & 8333 & 8333 \\ Number of coherent & 4 & 2 & 1 \\ integrations & & & \\ Number of incoherent & & & \\ integrations & 16 & 32 & 64 \\ Sensitivity & \(-\)24 dBZ at 5 km & \(-\)38 dBZ at 5 km & \(-\)18 dBZ at 5 km \\ Spectral bin number & 256 & 256 & 256 \\ Nyquist velocity (m\(\cdot\)s\({}^{-1}\)) & \(\pm\)4.635 & \(\pm\)9.27 & \(\pm\)18.54 \\ Velocity resolution (cm\(\cdot\)s\({}^{-1}\)) & 3.64 & 7.27 & 14.54 \\ \hline \end{tabular}
\end{table} 
Table 2: Operational parameters of three modes. BL = boundary mode; CI = cirrus mode; and PR = precipitation mode. different heights are coincident with the theoretical results (marked curves), indicating that they met expectations for weak cloud observation. CI has a 20 dB and a 14 dB weaker minimum detectable reflectivity than PR and BL, respectively. However, strong reflectivity, greater than 30 dBZ, was rarely observed due to signal attenuation and Mie scattering at this wavelength. [PERSON] investigated the measurement deviation of this radar by comparing it with a C-band vertically pointing radar and suggested that a 2 dB bias may exist under light precipitating conditions, with a maximum reflectivity of no more than 27 dBZ [29]. Figure 2 presents an example of 3-h time-height cross-sections of reflectivity from the three different modes made on 20 July 2015.