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.

Introduction of measurement techniques in ultrasonic electronics: Basic principles and recent trends

“…When ultrasound reaches the seabed, scattering and absorption occur, whose profile depends on the roughness and type of material. Hence, the measurement of ultrasound propagation is useful for predicting underwater profiles, such as temperatures, currents, tidal effects, [449][450][451][452][453][454][455][456][457][458][459][460][461][462][463][464][465][466][467][468] and underwater structures. [469][470][471][472] Such measurement has been conducted over large regions of the ocean (e.g., on the order of 100 km).…”

“…Propagation [449][450][451][452][453][454][455][456][457][458][459][460][461][462][463][464][465][466][467][468] Noise [473][474][475][476][477][478][479] Seafloor=sediment [469][470][471][472] Transducers [529][530][531][532] Positioning=ranging 501,[523][524][525][526][527][528] Acoustic imaging Imaging systems [483][484][485][486] Lenses [487][488][489][490][491]...…”

Measurement of bottom-reflected sound in bottom-limited propagation environment

“…Underwater acoustic propagation is strongly affected by the vertical sound speed profile and ocean boundary characteristics, especially bottom properties owing to frequent interactions in a bottom-limited propagation environment. [1][2][3] Major factors affecting bottom limited propagation include water depth, angle of incidence, frequency, and bottom composition. The effect of bottom reflection is to return to the depth of the propagation sound that has been carried downward by the depression angle of the transmitted acoustic sound.…”