Uko, E. D., I. Tamunobereton-ari, and V. B. Omubo-Pepple. “Comparison of Compressional-Wave Velocity-Depth Profiles from Surface and Downhole Detectors in the Near Surface in the Southeast Niger Delta, Nigeria”. International Journal of Asian Social Science, vol. 2, no. 6, June 2012, pp. 869-80, https://archive.aessweb.com/index.php/5007/article/view/2265.