由于超声导波多模态、易频散的特性，导致其在检测高速公路护栏立柱时会产生复杂的回 波信号，现有方法很难从中提取出有效的特征信号。为了解决该问题，首先提出了一种改进的子空间匹配追踪算法(ISMP)。它是将回波信号的先验信息在过完备Chirp 原子库上逐次迭代，得到 强相关原子集，然后对其再次进行迭代得到待匹配信号的最佳时频原子，从而实现对护栏立柱回波信号的特征提取。利用中心频率为128kHz和64kHz的检测信号进行实验验证，结果表明，ISMP可以有效提取出超声导波回波信号的特征原子，立柱检测长度与实际长度误差小于1%，满足工程检测要求。此外，还提出了一种基于离散傅里叶变换的相位检波算法，通过设置相位检测误差减少噪声带来的干扰。实验表明，在128kHz 和64kHz 检测信号下，可以得到设定相位的有用回波信息，满足工程检测要求。

Due to the characteristics of multimoding and easy dispersion of ultrasonic guided wave, the complex echo signal is brought about in guardrail column detection on expressway. It is difficult to extract useful information from complex echo using existing methods. Two algorithms were proposed to solve this problem in the paper. Firstly, Improved Subspace Matching Pursuit(ISMP) algorithm was presented. By successive iteration of the priori information of echo signal in the overcomplete chirp atom library, the strong correlated atomic set was obtained. And then, by iterating, the best time-frequency atoms of the signal to be matched were obtained, so as to realize the characteristic extraction of guardrail column echo signal. A 128 kHz and a 64 kHz center frequency signal were used to verify the result in detection with the algorithm. The test results show that ISMP can effectively extract the features of atomic of ultrasonic guided wave echo signal, within the length error less than 1% which can meet the requirements of actual detection. Secondly, the phase detection algorithm based on the Discrete Fourier Transform (DFT) was presented too. This algorithm can reduce noise by setting the phase detection error. Through experimental verification with a 128 kHz and a 64 kHz signal, the results showed that useful information of echo signal with set phase can be obtained, which met the requirements of actual detection.