Wireless sensor network technology helps monitor forest fires

introduction

In order to reduce the losses caused by forest fires, countries around the world attach great importance to forest fire monitoring. Forest fire monitoring measures can usually be divided into four spatial levels, namely ground patrol, fixed-point observation by lookout towers, aerial aircraft patrol and space satellite monitoring. The function of the forest fire monitoring system is to detect fires in a timely manner, accurately detect the starting point of the fire, determine the size and direction of the fire, and monitor the entire process of the occurrence and development of forest fires. However, in the vast forest, it is not enough to rely solely on patrol officers to detect fires. The observation of the lookout tower is also subject to many conditions. Under normal circumstances, when a small fire is small, the smoke is small and it is not easy to detect. When it is discovered, it is often a disaster. When a large fire spreads, the smoke is diffuse, and it is difficult to determine the location and development trend of the large fire; the data measured by observing the smoke often has large errors; and it is difficult to observe at night. Observation by aircraft patrol is not only costly, but also not the fastest, and the image resolution is low. Generally, a fire can only be discovered after burning for several kilometers. Due to the above shortcomings, the forest fire prevention headquarters may cause unnecessary losses due to inaccurate fire locations when formulating fire fighting plans and mobilizing fire fighting forces.

With the development of science and technology, high technology has been continuously applied to forest fire monitoring, and forest fire prevention work is increasingly moving towards high technology, intelligence, systematization and integration. Environmental monitoring is a typical application of sensor networks. Compared with traditional environmental monitoring methods, the use of sensor networks for environmental monitoring has three significant advantages: First, the size of sensor nodes is very small and the entire network only needs to be deployed once, so the deployment of sensor networks has little human impact on the monitored environment. This is especially important in environments that are very sensitive to the activities of foreign organisms. Second, the number of sensor network nodes is large and the distribution density is high. Each node can detect detailed information about the local environment and summarize it to the base station. Therefore, the sensor network has the characteristics of large data collection volume and high accuracy. Third, the wireless sensor nodes themselves have certain computing power and storage capacity, and can perform more complex monitoring according to changes in the physical environment. The sensor nodes also have wireless communication capabilities and can perform collaborative monitoring between nodes. By increasing the battery capacity and improving the battery efficiency, as well as using low-power wireless communication modules and wireless protocols, the life of the sensor network can be extended for a long time, which ensures the practicality of the sensor network. The computing power and wireless communication capabilities of the nodes enable the sensor network to be reprogrammed and redeployed, and to respond promptly to environmental changes, changes in the sensor network itself, and network control instructions. Therefore, the sensor network is suitable for a variety of environmental monitoring applications.

1 Wireless Sensor Networks

1.1 Introduction to Wireless Sensor Networks

A wireless network is a wireless communication network formed by many independent wireless nodes through radio waves and light waves in the air. It is a wireless network composed of a large number of miniature, intelligent, low-power sensors using a certain network protocol. Its purpose is to collaboratively sense, collect and process information about perceived objects in the geographical area covered by the network and publish it to observers. It integrates sensor technology, embedded computing technology, distributed information processing technology and wireless communication technology, and is becoming an emerging technology field, and is considered one of the most important technologies in the 21st century.

Wireless sensor network nodes have functions such as wireless communication, data collection and processing, and collaborative cooperation. They can be randomly or specifically arranged in the target environment, can obtain information about the surrounding environment, and work together to complete specific tasks. Sensor nodes are mainly composed of functional modules such as power management modules, sensors, microprocessors, memory, and radio frequency modules. The typical sensor node structure is shown in Figure 1.

The power management module provides the energy necessary for the normal operation of other functional units. The sensor is used to sense and obtain information from the outside world and convert it into digital signals through the signal processing circuit. The microprocessor component is responsible for coordinating the work of various parts of the node, such as necessary processing and storage of the information obtained by the sensor, and controlling the working mode of the sensor and power supply. The radio frequency module is responsible for communication with other sensors or observers.

1.2 Routing Protocol

The routing protocol is responsible for forwarding data packets from the source node to the destination node through the network. It mainly includes two functions: finding the optimal path between the source node and the destination node, and correctly forwarding the data packet along the optimized path. In wireless sensor networks, the node energy is limited and generally there is no energy replenishment, so the routing protocol needs to use energy efficiently. At the same time, the number of sensor network nodes is often large. Nodes can only obtain local topological structure information, and the routing protocol must be able to select the appropriate path based on the local network information. Sensor networks have a strong application relevance, and the routing protocols in different applications may vary greatly. There is no universal routing protocol. In addition, the routing mechanism of sensor networks is often associated with data fusion technology to save energy by reducing the amount of communication. Therefore, the routing protocol of traditional wireless networks is not suitable for wireless sensor networks. Compared with traditional wireless communication networks, the focus of traditional wireless communication network research is on the quality of service (QoS) of wireless communication, while wireless sensor nodes are randomly distributed and battery-powered. Therefore, the current research focus of wireless sensor network routing protocols is on how to improve energy efficiency. The currently popular routing protocols for wireless sensor networks are: Flooding protocol, Gossiping protocol, SPIN protocol, Directed Diffusion protocol, LEACH protocol, etc.

1.3 Wireless Sensor Network Management Technology

In sensor networks, sensor nodes are tiny embedded devices powered by batteries with limited energy. Their computing and communication capabilities are very limited. Therefore, in addition to designing energy-efficient MAC protocols, routing protocols, and application layer protocols, it is also necessary to design an optimized network topology control mechanism. For self-organizing wireless sensor networks, network topology control has a great impact on network performance. A good topology can improve the efficiency of routing protocols and MAC protocols, provide a basis for many aspects such as data fusion, time synchronization, and target positioning, and help extend the lifetime of the entire network. Therefore, topology control is a basic issue in sensor networks.

The main research problem of sensor network topology control is: under the premise of meeting the network coverage and connectivity, through power control and backbone network node selection, unnecessary communication links between nodes are eliminated to form an optimized network structure for data forwarding. Specifically, the topology control in sensor networks can be divided into two categories according to the research direction: node power control and hierarchical topology organization. The power control mechanism adjusts the transmission power of each node in the network, and balances the number of single-hop reachable neighbors of the node under the premise of meeting the network connectivity. Hierarchical topology control uses the clustering mechanism to make some nodes as cluster head nodes, and the cluster head nodes form a backbone network for processing and forwarding data. Other non-backbone network nodes can temporarily shut down the communication module and enter a dormant state to save energy. The current development trend of topology control research is to use a variety of mechanisms in combination with practical applications, emphasizing the adaptability and robustness of network topology control, and improving the efficiency of network communication under the premise of ensuring network connectivity and coverage, and maximizing energy saving to extend the survival time of the entire network. Considering that different application backgrounds have their own characteristics and network survival time, topology control is generally used in combination.

2 System Design

The whole system consists of several wireless sensor nodes, base stations and users, as shown in Figure 2.

In addition to sensor nodes, a sensor network suitable for fire monitoring also has base stations and the Internet. The bottom layer of sensor nodes is connected to the transmission layer, base station, and finally to the Internet. In order to obtain accurate data, the sensor node transmits the sensed data to a gateway node. The gateway node is responsible for sending the data from the sensor node to the base station via a transmission network. The transmission network is a local network responsible for coordinating the gateway nodes of each sensor network and integrating the information of the gateway nodes. The base station is a computer that can be connected to the Internet. It sends the sensor data to the data processing center through the Internet. It also has a local database copy to cache the latest sensor data. Monitoring personnel can access the data center through any terminal connected to the Internet, or issue commands to the base station. Considering that the forest farm may be in a very remote area, the base station needs to be connected to the Internet wirelessly. For remote areas, using satellites is a more reliable method. Satellite communication stations near the monitoring area can be used as base stations for sensor networks.

The number of sensor nodes in a wireless sensor network is usually large. They are not only small in size and low in cost, but also require very low power consumption to maintain a long working state with batteries. Therefore, these characteristics determine that the design of sensor nodes needs to be as simple as possible to meet application requirements.

Wireless sensor nodes are composed of hardware and software layers working together to complete tasks.

2.1 Hardware Layer

Generally, it includes the following four units: power supply unit, data acquisition unit (including sensor and A/D analog-to-digital converter), data processing unit (including memory and microcontroller), and wireless communication unit. The microcontroller is the "heart" of the sensor node, running embedded system software on it to control the work of the other three units. In the selection of hardware, low-power devices should be used as much as possible. It is also possible to consider commanding the microcontroller to enter the "sleep" state and cut off part of the power supply of the wireless communication unit when there is no data acquisition and no data communication, thereby reducing power consumption.

The software layer is used to control the hardware layer and is the "brain" of the entire sensor. In addition to the most basic data collection and transmission, it is also necessary to implement a series of algorithms and designs for network topology, self-organization, routing selection, energy saving, error handling, reliability assurance, etc., depending on the application scenario. For some simple applications, a single loop logic software can be used to complete it. For some more complex application scenarios, it is necessary to use an embedded operating system tailored to the characteristics of wireless sensor networks. In addition to meeting the requirements for limited resources, portability, real-time performance, etc., this type of operating system must also focus on energy saving requirements. In addition, the use of event-driven methods can also adapt to the data flow-centric characteristics of wireless sensor networks.

2.2 Software Layer

It includes three levels: hardware abstraction layer, system service layer and application layer. The hardware abstraction layer realizes the abstraction of the hardware platform (power management, data acquisition, data processing and wireless communication unit), shields the underlying hardware details for the upper layer, and simplifies the system platform transplantation. The system service layer includes four parts: communication service, sensor service, energy consumption management service and real-time kernel. In this layer, in addition to realizing the kernel services of the operating system such as task scheduling and semaphore, it will also complete the implementation of various routing and security algorithms and support various communication transmission protocols. The application layer is defined by the user according to the needs of the specific application. Using the interface provided by the system service layer, the upper layer software can be easily designed.

3 Conclusion

Forest fire monitoring is an interdisciplinary subject. Sensor networks provide a new means to achieve more accurate, larger data volume, and less environmental impact forest fire monitoring. The design of the wireless sensor hardware platform is crucial to the development and application of the entire wireless sensor network. As the underlying support of the entire system, it will inevitably develop in the direction of miniaturization, high integration, networking, energy saving, and intelligence. In recent years, with the decline in computer costs and the reduction in the size of microprocessors, the development and construction of wireless sensors will have broader application prospects. In particular, the application in environmental monitoring has received everyone's attention. All countries are exploring this aspect and strive to develop an environmental monitoring system that is more in line with wireless sensor networks.

However, we should also be aware that wireless sensor networks have just begun to develop, and their technology and applications are far from mature. We look forward to the early application of practical wireless sensor network systems in forest fire monitoring.