# A High Signal-Noise Ratio UWB Radar for Buried Pipe Location Using Golay Complementary Sequences
## 5 Detection Performance  
To analyze the performance of the proposed Golay complementary sequences radar system, we give the comparison among the proposed radar, chaotic radar, and stepped frequency signal radar. Here, the vector network analyzer was regarded as the stepped frequency signal radar whose modulated frequency range is from 1.80 GHz to 5.00 GHz. The chaotic radar was based on the chaotic pulse position modulation (CPPM) signal. CPPM was used to generate a sequence of pulse distanced by time intervals generated by a chaotic map [40]. Compared with the chaotic pulse amplitude modulation signal, it had a low crest factor and thus had great robustness to external noise [41]. We have a detailed description of the CPPM signal radar in our previous work [42]. In this paper, the CPPM signal with 1.00 GHz bandwidth is up-converted to 2.40-4.40 GHz. Then we used the up-converted signal as the probe signal. Besides, other parameters in these three radar systems were the same. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Pipes** & **Material** & **Diameter (m)** & **Length (m)** & **Thickness (mm)** \\ \hline P1 & Plastic & 0. 20 & 0.52 & 3 \\ P2 & Plastic & 0.15 & 0.60 & 4 \\ M1 & Metallic & 0.10 & 0.60 & 2 \\ M2 & Metallic & 0.05 & 0.35 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of the pipes used in the experiment. Figure 5: Experimental results of underground pipes location. (**a**) P2 and P1 at position of (23, 60) cm and (72, 85) cm. (**b**) M2 and M1 at position of (20, 78) cm and (72, 57) cm. (**c**) Two different types of pipes at positions of (18, 40) m and (68, 49) cm. Figure 6 shows a comparison result of normalization curves. The plastic pipe was buried at 40 cm in three radar systems. In the normalization curves, the peak position presents the buried depth of the pipe. The higher this peak value, the easier it was to identify the target. Thus, observing Figure 6, we obtain that the peak of the curve based on Golay complementary sequences is remarkably higher than that based on the CPPM signal or stepped frequency signal when the pipe was buried at the same depth. Besides, by using chaotic radar and Golay-based radar, the reflection of the tank bottom at 120 cm can also be clearly observed. While it cannot be obtained by using stepped frequency signal radar. Figure 7 shows the SNR of the normalization curve as a function of the buried depth. The SNR is defined as follows [43]:  
\[SNR=20\log\frac{A_{\mathrm{S}}}{A_{\mathrm{N}}}, \tag{6}\]  
where \(A_{\mathrm{S}}\) refers to the amplitude of the target reflection peak and \(A_{\mathrm{N}}\) refers to the amplitude of the maximum noise peak. From Figure 7a,b, we can see that the SNR obtained from the Golay complementary sequences radar is also higher than that of CPPM signal radar or stepped frequency signal radar at the same buried depth, no matter whether the target is a plastic pipe or metallic pipe. The results mean the proposed radar system was capable of detecting deeper buried pipe. Additionally, the SNRs of stepped frequency signal radar, CPPM signal radar, and Golay-based radar at 40 cm (correspond to the results in Figure 6) are 2.65 dB, 6.61 dB, and 13.44 dB, respectively. Figure 6: Normalization curves of three different types of radar systems. Figure 7: The signal–noise ratios (SNRs) of (**a**) metallic pipe and (**b**) plastic pipe as the function of buried depth. Furthermore, to intuitive analysis of the performance of these three radar systems in the underground pipe location, 2D images are given. Figure 8a-c show the 2D images of stepped frequency signal radar, chaotic radar, and Golay complementary sequences radar, respectively, when the same plastic pipe is buried at about 60 cm. Comparing the 2D images, we obtain that although the position of pipe can be seen in these three figures, Figure 8c shows the greatest contrast between the target and the surroundings. It means the value at this position is the largest in these three figures, which is beneficial to locate the deeper buried pipe.