## 3 RS Applications in Ocean
### Ocean Tide (OT)  
OT refers to the regular rise and fall of the ocean water caused by the gravitational pull of the moon and sun in relationship with the geometric location of the Earth's surface [255]. The cyclical effects of the Earth's and the moon's rotations are, respectively, the primary factors of the periodic rhythm and height of OT [256], and 24 h and 50 min is the tidal period [256]. When the water wave slowly rises to its crest (highest level), covering much of the shore, high tide occurs. Once the water wave falls to its trough (the lowest part of the wave), it is known as low tide [255; 256]. Thus, the tidal range is the vertical difference between the high and low OT [256]. Ebb tide is called the flow of water from high tide to low tide [255]. During the moon's revolution around the Earth, the direction of its gravitational attraction is aligned with that of the Sun. High spring OTs are created when the moon, Earth, and sun are in alignment. This alignment occurs every 14-15 days during full and new moons [256]. On the other hand, during the first and last quarters of the moon, neap OTs happen when the moon appears half-full [255; 256]. Intertidal zones are the lands in the tidal range categorized in the splash, high-tide, mid-tide, and low-tide zones [257; 258]. While traditionally, in situ measurements and numerical models have been used for OT studies, RS has been proposed to fill OT measurement gaps over the past four decades. RS technology has expanded our understanding of global OT [259; 260; 261] and facilitated continuous OT monitoring and predictions over wide-spread scales. RS systems can be used to study several aspects of OT, including tidal flats, tidal channels, tidal currents, Ocean Tidal Load (OTL), and tidal wetlands. In the following, a brief description of each type of OT is provided. The area inundated between low- and high-tide waterlines is defined as tidal flats and is a mixture of seawater and freshwater environments [262]. Tidal flats provide essential services, such as coastal storm protection, food production, and shoreline stabilization [262]. A recent study has discovered that tidal flats occupy approximately 130,000 km\({}^{2}\) of the planet (Figure 8) [263]. [PERSON] et al. [263] also reported that about 70% of the global tidal flats occurred in three continents, namely, Asia (44% of total), North America (15.5% of total), and South America (11% of total), 49.2% of which were concentrated in eight countries, namely, Indonesia, China, Australia, the United States, Canada, India, Brazil, and Myanmar. Monitoring tidal flats using field observations is limited to estimating the ebb/flood characteristics, adequate surveys for large tidal flats, and the field access. However, RS in combination with in situ measurements facilitates monitoring tidal flats in a more cost- and time-efficient approach. In fact, RS data with a high temporal resolution are necessary for tidal flats studies because there are coastal areas that fall dry during each tidal cycle [264], and tidal flats are only exposed fully for a short period at low tides. A tidal channel is a type of stream or a waterway that occurs during the ebb tide and flood tide in the tidal flats [265]. Tidal channel networks are crucial aspects of the neighboring ocean and estuaries. In addition to the control of the tidal basin hydrodynamics, tidal channels connect intertidal flats to the salt marshes, which play an important role in tidal propagation [266]. Due to various morphological characteristics from terrestrial river networks, conventional river system algorithms cannot be implemented on tidal channels. Thus, RS techniques have been effectively utilized to obtain the spatial distribution of tidal channels [266]. The periodic movement of water created by the out-of-phase OT, the local weather patterns (radiational tides), and ocean characteristics (internal tides) is defined as tidal currents [267]. Periodic tidal currents play an important role in the strait (a narrow waterway joining two larger water bodies) [267].