Evaluating Underwater Data Transmission Using Wi-Fi Considering Variable Salinity Levels

With the immerging utilization of autonomous underwater vehicles (AUV) in oceanographic research and ocean technology, it is to determine that the interface between mounted sensors and the affiliated equipment for a evaluation can become a bottleneck. Therefore, the demand for underwater data transmission suitable for large data sets is growing. Conventionally, three methods for underwater data transmission have established oneself - based on either acoustic, optic or electromagnetic signals. Each of the mentioned brings specific advantages. It can be stated that data transmission based on electromagnetic waves travelling through water brings relatively high data rates on the cost of a very low transmission range [1]. Introducing a measurement platform equipped with a winch for environmental measurements in the water column, this paper examines the applicability of Wi-Fi data transmission to the interface between externally mounted sensors and the vehicle. On the one hand, the study aims at the quantification of achievable data transmission ranges in fresh water and salt water in general. On the other hand, it aims to conceptually prove the use of Wi-Fi to integrate the mentioned sensor into a specific research vehicle. Two experimental setups are designed. In each of them the linear distance, and - if applicable - the turning angle is increased until the Wi-Fi modules lose connection. The measured parameters for the evaluation of the transmission quality are the received signal strength indicator (RSSI) and the achieved data rate for the transmission of test data packets. All tests are respectively repeated in fresh water, as well as in four levels of salt water with salinities between 15 PSU and 50 PSU. Predictably an increasing salinity level results in a strong decrease of the achievable transmission range. Starting with a range of around 250mm in fresh water it declines to below 50mm in salt water with 50PSU.