# Data Access Based on a Guide Map of the Underwater Wireless Sensor Network  
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1 College of Computer Science and Technology, Harbin Engineering University, Harbin 150001, China; [EMAIL_ADDRESS] (Z.W. ); [EMAIL_ADDRESS] (G.Y. ); [EMAIL_ADDRESS] (H.W.) [PERSON]  
3 Information Technology Centre, Beijing Foreign Studies University, Beijing 100089, China; [EMAIL_ADDRESS] ([PERSON]  
7 Department of Electrical, Computer, Software, and Systems Engineering, Embry-Riddle Aeronautical University, Dayton Beach, FL 32114, USA; [EMAIL_ADDRESS] ([PERSON]  
7 Department of Computer Science, University of Houston, Houston, Houston, TX 77204 development of sensor and wireless network technologies, underwater wireless sensor networks (UWSNs) have gradually become the focus of new research interest because of their low cost, high reliability, and potential for a wide range of applications. When compared to wireless sensor networks based on radio communication, UWSNs are very different in terms of network composition, deployment and networking patterns. This is because of differences in utilization objectives, the environment, the scope of work and the patterns of communication. Among them, UWSNs used for deep ocean marine exploration and monitoring are composed of floating or submerged floating sensor nodes, mobile nodes (Unmanned Underwater Vehicles or UUVs and Autonomous Underwater Vehicles or AUVs) and observation nodes (ships), to form a network system. The sensor nodes carry out real-time monitoring and collect a variety of data distributed in the monitoring region. By way of underwater acoustic communication [3] or up-water radio communication, they send the specific application data (such as target detection information and ocean environmental information) to the mobile node or observation node. The mobile nodes (UUVs, AUVs) can carry sensor nodes, which have the function of redeploying the sensor node and reconfiguring the network, as well as monitoring, communication, data collection, and processing. The observation node is responsible for deployment of sensor nodes, configuring the network, and collecting and processing the application data distributed in the network effectively as well. For UWSNs, in the process of monitoring ocean environment and detecting underwater targets, first of all sensor nodes are distributed in a wide range for underwater monitoring and collection of the environmental information and target information. Then, this is stored by an appropriate mechanism. For the collection and processing of the distributed data, it can be divided into two types: non-real-time data (such as environmental information and data) and real-time data (such as military target and rescue target information). At the same time, in a specific scenario such as search and detection of underwater targets for rescue, the observation node should reduce the times and distances of active communication as far as possible on collecting the distributed data in the network. This is in order to lower the background noise in the UWSN. Underwater acoustic communication is mainly used in UWSNs, and is characterized by low bandwidth, high delay and higher bit error rate, showing great differences on comparison with sensor networks based on radio communication from the perspective of transmission reliability, transmission delay, energy consumption on storage, and query data. The above has brought about new challenges for UWSN data storage, discovery and query [4; 5; 6]. The main challenges are as follows:  
1. Efficient UWSN data access includes storage, discovery and query. Networks of different types generate different types of data, and the data on the sensor node needs to be collected and stored efficiently. At the same time, the query sentences from the users need to be dealt with as far as possible in order to return different granularity data (especially in military application and emergency rescue) to the users with the smallest delay possible. 2.