# Sensing in Inland Waters to Promote Safe Navigation: A Case Study in the Aveiro's Lagoon
## 1 Introduction  
Maritime navigation is a combination of science and art, in which sailors must observe, understand, and analyze several factors that may affect navigation to ensure the vessel's safety. Recording data and controlling a route to move a vessel from one location to another [1, 2, 3] is heavily dependent on a human's skilled interpretation and the accuracy of the data collected by navigational instruments, including plotters, radars, and depth sounder transducers, to prevent conflicts and manage the vessels' autonomy [1, 4, 5, 6]. The importance of reliable navigational data becomes evident in different water environments [1], including ocean, coastal, and inland waters. In ocean and coastal navigation, vessels frequently face the challenge of entering inland or restricted waters [7, 8]. Navigating in such waters can be difficult, and it is crucial to approach this task with caution and precision. Therefore, nautical charts are essential to determine the position, course, and route to be taken. Modern tools, such as chart plotters, have largely replaced traditional methods, providing real-time data that enhance navigational accuracy and safety. Although these modern solutions have an improved accuracy, they often fail to address the real-time data needed for safe navigation in inland and coastal waters. Notably, during this research, which began in 2021, PredictWind's DataHub [9] emerged, offering real-time weather data for sailors. While promising, it is primarily focused on weather prediction and it requires expensive equipment and a subscription service, which can be unaffordable for many users. Despite both offshore and coastal waters presenting challenges to navigation, such as limited infrastructure for immediate aid [10], or intense currents and unexpected winds, inland waters pose even more demanding navigation conditions due to shallower depths, narrower channels, intertidal channels, and non-linear tidal propagation [11], demanding precise and anticipatory data on a vessel's position and the real water depth [10; 12] to avoid grounding. Due to these conditions, it is particularly challenging for ships and vessels with drafts higher than the available water height (observed depth) [13] to navigate through shallow navigation channels, such as bars, rivers, and harbors [12; 14]. Shallow channels pose a risk of grounding, which can lead to significant delays and potential damage to vessels. To mitigate the aforementioned risk, Figure 1 illustrates a conceptual approach to the data sharing system. This system allows Boat B to share real-time data with Boat A. These data may encompass information regarding the presence of shallow areas, strong winds, or other potential hazards that Boat B has previously encountered. By receiving this information, Boat A is thereby enabled to anticipate and adjust its maneuvers in advance, thus avoiding these dangers and ensuring a safer and more efficient passage. There are several factors that impact navigation safety, efficiency, and situational awareness within an environment that require sailors to be cautious and anticipate maneuvers in order to avoid hazardous conditions for vessels, and these include the following: (i) severe meteorological conditions, such as storms, heavy rains and strong winds, not only pose direct dangers to navigation but also make it more difficult to accurately perceive water conditions (e.g., currents and tidal heights) [15; 16]; therefore, accurate local hydrodynamic and weather forecasting is crucial to mitigate risks, such as grounding; (ii) uneven water flow propagation, which is especially problematic in inland waters, causes non-linear tidal propagation [14; 17]; (iii) high expenses from hardware, software, and network components, such as River Information Services (RIS), which are required to obtain real-time and accurate information for nautical charts; (iv) low tide and the inadequate coverage of shallow  
Figure 1: Meteoceanographic data sharing system research concept.