# Internet of Things in Marine Environment Monitoring: A Review
## 2 Overview of IoT in Marine Environment Monitoring
### Common IoT-Based System Architectures for Marine Environment Monitoring and Protection  
The Internet of Things is usually to achieve \"knowing, thinkable, and controllable\" to the surrounding world [19], which means that the IoT is able to perceive, think, and control the world by collecting, processing, and analyzing the data of the world. It can make intelligent judgments that impact on the outside world. IoT researchers have proposed different IoT system architectures in the research literature. Among them, a five layered system architecture was proposed by [PERSON] et al. [20]. Similarly, we also believe that a typical IoT-based marine environment monitoring and protection system has five layers: Perception and execution layer, transmission layer, data pre-processing layer, application layer, and business layer, as shown in Figure 1.  
(1) Perception and Execution Layer  
The perception and execution layer is the bottom layer of the architecture. It includes sensor and actuator devices, with the objective of sensor data collection and command actuation. In IoT-based marine environment monitoring and protection systems, this layer can also include GPS sensors, energy harvesting devices, in addition to regular water condition and quality monitoring sensors. Note that most existing marine environment monitoring systems do not have any execution functions and therefore do not include actuators. (2) Data Transmission Layer  
The main function of the data transmission layer is to transmit various collected data to the data processing layer via communication networks, mostly mobile or wireless communication networks. At the same time, control measures made by users or intelligent applications (reference engines) are transferred from the application layer to the perception and execution layer, thus that corresponding devices or actuators can take required actions (such as device repositioning, increasing or decreasing temperature settings, releasing food in fish farms). (3) Data Pre-Processing Layer  
The data pre-processing layer is in the middle of the IoT system architecture, where the raw data received can be stored and pre-processed, using advanced data mining technologies. It also completesinformation aggregation or disaggregation, data cleaning and fitting or screening, sharing as needed, and sometimes it triggers alerts or warnings based on pre-defined rules. (4) Application Layer  
The application layer provides services according to different applications requested by users. For example, it provides water condition and quality data as well as the amount of fecal waste and uneaten feed for a fish farm. The main purpose of this layer is to provide smart application services to meet users' needs. In IoT-based marine environments, this later covers water quality monitoring, coral reef monitoring, marine (either offshore or deep-sea) fish farm monitoring, wave and current monitoring [21; 22; 23]. (5) Business Layer  
The business layer is the top layer and manages the overall IoT system activities and services, including creating business models, business logic flowcharts, graphic representations, according to the data received from the application layer. It also monitors and verifies outputs of the other four layers according to the business models in order to enhance services and maintain users' privacy [21; 23]. Such a layered system architecture provides a good picture of the data/information flow in IoT-based marine environment monitoring and protection systems. Figure 2 shows a common physical  
Figure 1: Common layered architecture for Internet of Things (IoT)-based marine environment monitoring and protection applications. architecture of IoT-based marine environment monitoring and protection systems. It includes sensor nodes and actuator nodes, sink nodes, a base station, a system server, and user terminals.