複數連續小波轉換應用於透地雷達信號之分析

GROUND PENETRATING RADAR SIGNAL ANALYSIS USING COMPLEX CONTINUOUS WAVELET TRANSFORM

倪勝火(Sheng-Huoo Ni) ； 張裕(Yu Zheng)

《中國土木水利工程學刊》 33卷2期 (2021/04) Pp. 105-118

https://doi.org/10.6652/JoCICHE.202104_33(2).0003

摘要

工程開挖施工的進行中常會遇到地下管線、鋼筋等地下埋設物，為了得知其地下異物或空洞及其位置，以期降低破壞現場結構物的風險，使用透地雷達能夠快速且經濟地檢測出其大略的位置，並可即時顯示影像，經由相關經驗之專業人士現場判釋，即可約略描繪出該地之地層構造，然有時細微之雷達反射訊號容易被忽視或被強度高的反射訊號覆蓋，若能進一步利用其它方法進行後續雷達訊號處理，可突顯信號特徵以降低誤判。本研究利用過去檢測的試驗資料，將複數連續小波轉換應用於透地雷達原始信號分析，可觀察訊號隨著時間及頻率之間的變化，藉著改變尺度與平移，可以凸顯介電常數變化之處，進而推論異常結構物在地下的大略位置，經本文之研究所得由複數連續小波轉換重新繪出振幅圖及相角圖，對振幅圖能突顯淺層訊號，但深層訊號則會漏失訊號特性，無明顯振盪，而相角圖則以相位角形式表現，其在深層表現不如雷達波振幅易衰減，兩者呈現截然不同的特性，可與雷達影像圖同時比對，以提高判讀效率。

關鍵字

透地雷達 ； 信號處理 ； 地下空洞 ； 非破壞檢測 ； 小波轉換

並列摘要

The lack of efficient management may potentially lead to dangerous situations in which the underground pipes, rebar, etc., are destroyed during engineering excavation. It is important to know the positions of these objects to prevent the risk of destroying structures and incurring additional cost. By applying different methods to potential objects, we can quickly detect approximate locations of underground objects by using ground penetrating radar in an economical way. The images can be displayed in real time. After on-site interpreting by professionals with relevant experience, the stratigraphic picture of the area can be roughly depicted. Furthermore, other post-processing technologies may enhance the signal characteristics. In this study the test data provided by previous research are used as raw signals in applying the complex continuous wavelet transform. Both time domain and frequency domain results were analyzed by translating at different scales. The changes in dielectric constant can be highlight and then we can infer the approximate locations of the objects in the ground. The complex continuous wavelet transform can display not only the amplitude but also the phase angle changing with time and frequency. The amplitude can be enhanced in the shallow signals, however, the deep signals completely lose the oscillation characteristics. Unlike the amplitude, the phase angle doesn't attenuate rapidly. These two completely different features can be compared with the radar image at the same time, improving interpretation efficiency.

並列關鍵字

ground penetration radar ； signal processing ； underground void ； non-destructive testing ； wavelet transform