Ultrasonic Underground Imaging Using Amplitude Correlation Synthesizing Method

An amplitude correlation synthesis processing (ACSP) method is proposed for ultrasonic underground imaging, in order to reduce the error image reconstructed with the low-frequency signal received by linear array receivers. In contrast to the previous method of special polarity correlation processing (SPCP), the amplitudes of received signals corresponding to a processing point, in every subarray group, is multiplied according to polarity condition, and all the conditional multiplication outputs are synthesized, in the ACSP method. For the experiment, an electromagnetic induction type sound source is employed as a powerful impulse incident ultrasound. A comparison of the imaging results of bodies buried 1 m underground, derived both by the ACSP and SPCP methods shows that the new method eliminates most of the error images, and hence its efficiency for imaging with a low signal-to-noise ratio (SNR) signal is verified.