Modification of receiver operating characteristic curves for ocean variability

Abstract

In this study, acoustic signal fluctuation in a continental shelf break is analyzed to examine the effects of detection probability and false alarm probability due to internal waves frequently observed on the east coast of Korea. Internal waves induce ocean temperature changes with time and space, and thus cause acoustic signal fluctuation. Internal waves are analyzed by measuring vertical ocean temperature changes with time using three thermister chains placed at three different positions. An acoustic signal is also measured during internal wave events. The observed internal waves have the following characteristics: a typical period of 25 min, a wavelength of 1,200 m, and an average amplitute of 5 m. The acoustic fluctuation parameters are estimated to be 3.7, 3.9, and 4.8 at frequencies of 300, 500, and 700 Hz, respectively. As a result, using a modified receiver operating characteristic curve, it is concluded that the detection probability decreases from 95 to 64% at a false alarm probability of 1% and increases from 23 to 44% at a false alarm probability of 10−4% at a frequency of 300 Hz.