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Andrea Giudici, Tomas Torsvik, and Tarmo Soomere


An extensible, low-cost drifter control unit (VELELLA) design is presented, developed for use in drifters that are deployed in inland water bodies or near-coast regions. The control unit is custom built from basic components built around a small footprint microcontroller, making use of a GPS receiver for position tracking, a Global System for Mobile Communications [Groupe SpécialMobile (GSM)] radio for data transmission, and two sensor buses to handle analog and digital data generated by an arbitrary array of external sensors. A cloud-based data collection platform has been implemented to receive and store data transmitted over general packet radio service (GPRS) from the drifter. The control unit was found to perform satisfactorily in operational testing, providing data at subhertz frequency for position and temperature during extended time. However, some issues related to temporary data loss and power consumption spikes were identified, indicating that some further development of the control unit is required to achieve a production-ready platform for extensive and prolonged field operations.

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Margus Rätsep, Kevin E. Parnell, Tarmo Soomere, Maarja Kruusmaa, Asko Ristolainen, and Jeffrey A. Tuhtan


Monitoring vessel traffic in coastal regions is a key element of maritime security. For this reason, additional ways of detecting moving vessels are explored by using the unique structure of their wake waves based on pressure measurements at the seabed. The experiments are performed at a distance of about 2 km from the sailing line using novel multisensor devices called “hydromasts” that track both pressure and near-bed water flow current velocities. The main tool for the analysis is a windowed Fourier transform that produces a spectrogram of the wake structure. It is shown that time series from the pressure sensors, measured at a frequency of 100 Hz, 0.2 m above the seabed are a valid source of input data for the spectrogram technique. This technique portrays the properties of both divergent and transverse waves with an accuracy and resolution that is sufficient for the evaluation of the speed and distance of the detected vessels from the measurement device. All the detected passings are matched with vessels using automatic identification system (AIS) data. The use of several time series from synchronized multisensor systems substantially suppresses noise and improves the quality of the outcome compared to one-point measurements. Additional information about variations in the water flow in wakes provides a simple and reasonably accurate tool for rapid detection of ship passages.

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