Data Collection: We simultaneously record the acceleration and corresponding sound data on typical normal airplane skin and typical patched skin, with under-skin structure supported and unsupported, respectively. The sampling rate is 48 kHz. To keep our experiments consistent with Cawley’s and the Mitsui work, we retain frequency components only up to 8 kHz in the initial data analysis. A typical complete acceleration event lasts for less than 10 ms. To safely avoid losing useful information, for each tap we collect 512 points (10.67 ms, frequency analysis granularity 94 Hz). The data file begins with a quiet lead (36 points, or 0.075 ms). The corresponding radiated sound lasts about 150 200 ms. We take 2048 sound amplitude samples ( 43 ms, frequency analysis granularity 23.4 Hz) for analysis.