Underwater interferometric radar sensor for distance and vibration measurement

With the growing application of autonomous underwater vehicles (AUV) and underwater construction, i.e. robotic manipulator and maintenance systems, there is an increasing demand on precise underwater distance sensors. In this paper we present a low-cost, short-range and contactless sensor which uses electromagnetical (EM) waves for measuring distances underwater. The measurement system is based on interferometric radar applying a six-port interferometer and using EM waves at a frequency of 2.4 GHz. Measurement series in fresh water have been carried out showing an precision of below 100 μm up to a distance of 35 mm with only 8 dBm of transmit power. Due to the high measurement rate the system can also be employed for vibration analysis. Additionally, by connecting a commercial 2.4 GHz data transceiver, it is imaginable for the system to be simultaneously used for high data rate communication between, e.g. AUV and unmanned underwater platforms (UUP).