Sensor Buoy for Environmental Monitoring
An essential task of the Hamburg Port Authority is to monitor water quality and the condition of underwater structures, bridge pillars, and sheet pilings. Doing this manually—e.g., by sending out divers—is time-consuming, expensive and dangerous. It is desirable to automate these tasks by autarkic, virtually maintenance-free sensor systems. Building such a system requires careful assessment and choice of components—particularly regarding energy sources—and energy-aware task scheduling. The latter demands special attention, because power consumption of sensors typically exceeds power output of the harvester, which also depends on environmental influences such as location and weather. Limited energy resources also imply the use of low-power communication devices, putting harsh limits on available bandwidth. In order to build an extensible system, a well-defined and modular software architecture is required.
Surface Robot as Testbed for Acoustic Underwater Navigation
Localization is a mandatory prerequisite for swarms of micro AUVs (autonomous underwater vehicles). The latter have recently drawn considerable research attention, as they can be used in scenarios stretching from dam inspections over localization of pollution sources to scientific experiments. In this context an acoustic underwater modem has been developed at our institute. Based on range-based distance estimation, localization algorithms are now being developed and have to be tested against a GPS ground truth. Since range estimation dramatically changes with movement of communicating parties, further research on moving objects is needed.
Testbed for Acoustic Underwater Modems
Communication under water is a mandatory requirement for small autonomous underwater robots, used for monitoring the environment or port areas. A small, low-power and low-cost acoustic modem has been developed at the our institute for this purpose. As this modem is still under development, outdoor tests for improvements or channel measurements are necessary. For these tests, multiple modems are deployed on jetties with distances of several meters. As these tests are very time-consuming, they have to be monitored extensively during the run. Furthermore, every test configuration has to be set up on every modem separately as they are not connected via radio. This whole procedure is inefficient, time-consuming, and error-prone. It also only allows tests when a researcher is present, a long-term, unattended deployment is not possible. To solve these issues, a wireless control center for our acoustic modem is desirable. It connects all the modems via WiFi to a base station, so that they can be controlled in one-single place, in the best case even from the office. As the actual experiment of underwater communication should not be affected, communication between the modems and the control center has to be absolutely reliable.
Structural Health Monitoring through Vibro Acoustic Modulation
Complete surveillance and predictive maintenance of safety critical infrastructure such as bridges is a yet unsolved technological problem. Environmental influences, heavy loads and shocks may cause micro fissure in the material. This results in loss of stability and finally to a collapse of the building. If detected early, these damages may be fixed quickly and save lives and money. Different methods exist for checking the material for damages. One of them is Vibro Acoustic Modulation (VAM). Here, an emitter induces an acoustic signal in the structural element. A receiver measures the acoustic signal at another location on the same element. Certain damages would distort the signal in a characteristic way. Manual regular checks of the structural elements are costly and error prone. As an alternative, a wireless sensor network using VAM can provide nearly continuous assessment, allowing to detect even small changes over time.