To investigate the correlation between underwater noise and sea level, data collected at Ieodo Ocean Research Station (from 15 May to 27 August 2013) were analyzed. Temporal variations in the overall level of underwater noise were similar to those in sea level. The average underwater noise levels at frequencies below 50 Hz were 99.0–106.6 dB during spring tides and 78.4–90.2 dB during neap tides, with a difference of 12.6–20.6 dB. When low-pass filtering at six hours was applied to the absolute value of sea level, a high correlation coefficient of 0.7 for its association with underwater noise was obtained. This strong correlation could indicate flow noise caused by currents. Underwater noise levels around the frequency of 16 Hz were relatively strongly correlated with sea level (correlation coefficient of 0.71). Wavelet analysis of the overall level of underwater noise showed strong periodicity at 0.25, 0.50, 1.0, 16.0, and 30.0 days, as well as characteristics of a tidal constituent. In wavelet coherence analysis, the overall level at a period of 0.25 days exhibited a phase difference of −90 degrees relative to sea level. This finding indicates that the noise level peaks at 1.5 h before the high tide or low tide, which was confirmed in the correlation analysis of noise level and sea height with various time lags. This study shows that the overall level of underwater noise from ebb currents is higher than that from flood currents due to differences in current velocity.

To investigate the behavioral characteristics of the water temperature inversion layer (TIL), we used data (KODC) from areas in the Northern East China Sea from 1995 to 2016. Water temperature and salinity surveys were conducted 8820 casts over 22 years. Of these, 1589 water temperature inversion layers were found, and the probability of occurrence was 18.0%. In the Gageo island, probability of TIL occurrence in winter was 25 times higher than in summer. On the other hand, in the south of Jeju Island, summer values were 3.7 times higher than winter values. A T–S diagram analysis shows the components of the water temperature inversion layers. Yellow Sea Cold Water was mainly found in the winter, while Jeju Warm Currents and Tsushima Warm Currents were found in summer. The correlation between the probability of the occurrence of a monthly water temperature inversion layer and the amount of seawater volume transported into the study area was analyzed. The correlation coefficient was higher than r = 0.8 in parts of southern Jeju Island. On the other hand, the correlation coefficient was r = −0.6 in the Gageo Island. The spatial correlation index for the seawater volume transport and the water temperature inversion layer is presented.

In maritime countries such as the United States and European countries, studies on cetacean resource distribution, vocalization characteristics, auditory characteristics, and habitat environment are actively being conducted in order to permanently preserve cetacean resources. It is necessary to establish a real-time buoy-type marine life observation system for the surrounding waters of the Korean Peninsula, and the components of the real-time buoy-type marine life observation system that can observe the underwater acoustic environment require a line-type underwater acoustic sensor, a large-capacity file real-time transmission system, and a high-capacity battery. Planning contents for the development of the whale sound detection system include realizing scientific whale tourism by combining marine science technology (MT + ICT), presenting a plan for constructing a real-time buoy-type observation system for whales based on ICT, and presenting an analysis algorithm for identifying whale ecology through observation and analysis of radioactive sound characteristics and acoustic characteristics of whales in real time. These research results can be developed as new tourism contents in the southeast sea of Korea, contribute to expanding the base of whale-watching tourism business, and provide information on migratory routes and resource distribution by identifying the sonic characteristics of cetaceans.