Coastal nations, through their dedicated Hydrographic Offices (HOs), have the obligation to provide nautical charts for the waters of national jurisdiction in support of safe maritime navigation. Accurate and reliable charts are essential to seafarers whether for commerce, defense, fishing, or recreation. Since navigation can be an international activity, mariners often use charts published from different national HOs. Standardization of data collection and processing, chart feature generalization methods, text, symbology, and output validation becomes essential in providing mariners with consistent and uniform products regardless of the region or the producing nation. Besides navigation, nautical charts contain information about the seabed and the coastal environment useful in other domains such as dredging, oceanography, geology, coastal modelling, defense, and coastal zone management. The standardization of hydrographic and nautical charting activities is achieved through various publications issued by the International Hydrographic Organization (IHO). This chapter discusses the purpose and importance of nautical charts, the establishment and role of the IHO in coordinating HOs globally, the existing hydrographic geospatial data standards, as well as those under development based on the new S-100 Universal Hydrographic Data Model.
Acoustic remote sensing is used to collect information about the shape and material properties of the seabed and subsurface. Sensors, traditionally deployed from ships and boats, are increasingly being installed on remotely operated or autonomous vehicles. These active remote sensing techniques transmit sonar (sound/acoustic) pulses and measure the two-way travel time for the pulse to be reflected, scattered, or refracted from the seafloor or subsurface and returned to the sensor. Knowing the speed of sound in water, sediment and rock, the relative position of the target on or below the seafloor can be determined. Absolute positioning of the target is determined by the integration of the sensor platform with ancillary Global Navigation Satellite Systems (GNSS) and motion referencing units (MRU). Reflected energy is used to determine the shape (or morphology) of the target, and scattered energy is used as a proxy for material properties. Applications of these methods have expanded significantly in recent years as coastal and marine landscapes are being transformed due to climate change impacts and anthropogenic forcing, with cables, pipelines, offshore renewables, and a broad range of complex engineering structures now ubiquitous on the seafloor.