Air-coupled ultrasound time-of-flight estimation for shipping container cargo verification

The falling cost of embedded sensor systems has opened up the possibility of in-transit air-coupled ultrasound interior imaging of shipping container cargo. This new technology could allow for real-time cargo integrity verification and improved shipping and transportation security. This paper takes the initial steps in developing a temperature invariant descriptor by comparing three time-of-flight (TOF) estimation methods from the literature using in situ data. The methods compared are matched filter, leading edge envelope line fit, and a simple envelope half-peak intercept. The results show that the simple half-peak intercept method provided the most consistent TOF estimate with respect to overlapping pulse data.