Low-cost ocean monitoring systems are increasingly needed to address data gaps in coastal environments, particularly in regions where traditional research infrastructure is limited. This paper presents the design, development, and field deployment of a biophysical ocean buoy (BOB)—a compact, solar-powered autonomous buoy system capable of measuring sea surface temperature, salinity (via electrical conductivity), total dissolved solids, pH, and GPS position. The system features real-time data transmission via the Iridium satellite, local data logging, and modular sensor integration. The BOB was deployed for three missions in the Seto Inland Sea, Japan, ranging from 26–56 h in duration. The system successfully recorded high-resolution environmental data, revealing coastal gradients, diurnal heating cycles, and tidal current reversals. Over 95% of the measurements were successfully recovered, and the Iridium communications exceeded 90% reliability. The temperature and salinity data captured fine-scale variations consistent with freshwater plume interactions and tidal forcing. With a total system cost under USD 2000 and minimal deployment requirements, the BOB offers a scalable solution for distributed ocean monitoring. Its performance suggests strong potential for use in aquaculture monitoring, coastal hazard detection, and climate change research, especially in data-sparse regions. This work contributes to the growing field of democratized ocean observation, combining affordability with operational reliability.

This study investigated the flow patterns and affecting factors in the North Port of Incheon, South Korea, to understand the inner-port circulation characteristics by applying an unstructured grid finite volume community ocean model (FVCOM) together with a field survey. The FVCOM considered the tide, river discharge, surface winds, and atmospheric pressure with the highest resolution of 50 m around the port. The model results were validated with current velocity and salinity observations. In the main channel, the difference in salinity between the sea surface and bottom increased during the neap tide due to weakened tidal currents, thus strengthening the stratification. However, at the inner port, strong stratification was observed during spring tide as the near-surface freshwater from upstream of the estuary moved relatively farther south of the port than that during the neap tide. Freshwater flowed into the port during the flood current and was trapped in the semi-closed geometry of the inner port. The horizontal salinity gradient between the trapped fresher water in the port and saltier water in the main channel increased during the flood current. As a result, density-driven circulations associated with near-bed currents towards the port were maintained for more than 3 h after high tide. This result implies that the baroclinic effect, mainly due to the salinity gradient in the North Port, could significantly affect residual circulation at the inner harbor in a macro-tidal environment and the mass transport mechanism, such as sediment transport. In general, such enhanced baroclinic effects due to salinity and tides are not limited to the North Port and can have greater effects on inner-port circulation in other macro-tidal harbors that suffer from severe sedimentation problems.

The great Japan earthquake on March/11/2011provoked an extreme tsunami wave toward the northeastern Japanese coast. The tsunami inundation covered a wide range of territories stretching over 500 km2 and caused devastating influences that claimed more than 15,000 lives (Mori et al. (2011)). Miyagi Prefecture, the closest mainland to the epicentre, received massive tsunami waves that reached over 40 m in run-up height. Prasetyo et al. (2019) aimed to reproduce the tsunami wave inundation in Onagawa Town of Miyagi Prefecture by building a physical model using Hybrid Tsunami Open Flume in Ujigawa Open Laboratory (HyTOFU) at Kyoto University to study the inundation process by measuring the wave height and arrival time. For that purpose, two wave types were used, the (Pump-type) hydraulic bore, and the (Piston-type) solitary wave. Also, 2D and quasi-3D (Q3D) models were tested for their robustness and applied to emulate tsunami propagation in the complex coastal city model. In this study, we adopted adaptive mesh refinement (AMR) for its efficiency in tsunami modelling with Basilisk open-source flow solver for non-linear shallow water (Saint-Venant) equations and fully non-linear Boussinesq (Green-Naghdi) equations (Popinet (2015)). The numerical experiment was conducted to validate the model by comparing the wave height with the physical model experiment, the 2D, and Q3D model results by Prasetyo et al. (2019).