Development of an automatic autonomous sensor carrier for sound profile measurement in deep sea

Abstract: This Master Thesis main purpose was to answer the question "Can you measure or calculate the velocity sound profile while performing a bathrymetric survey in an offshore environment like the North Sea, without any interaction nor modification of the existing equipment?".This, since today underwater surveys are a complex and expensive operation to perform where you either are mapping the sea floor or on a searching mission for a sunken wrecks. To achieve this successfully, one has to ensure that the accuracy of the position for every discovery or created map over the sea floor is entirely correct. This is an identified problem since the bathrymetric device sends its position by sonar, which relies in the sound propagation velocity, which in return varies with the water density. In order to increase the accuracy one need to determine the water density for all depths, i.e measure the salinity and temperature between the towing ship and the device that travels close to the sea bed. This because of layers consisting of fresh water and saltwater that never entirely mixes with each other in the ocean.The outcome of this project is a manufactured conceptual design of an autonomous sensor carrier that has the ability to measure temperature to a theoretical maximum depth down to 150m. It ascends and descends autonomously with an propagation speed of 0.54m/s in a static condition along an existing tether line, connected to a bathrymetric device that follows the sea floor. The sensor carrier ascend and descends its motion with help of two connected drive wheels powered by an electric motor, combined with two hall sensors to to reverse its movement when reaching desired depth. It has the ability to store sampled data onto a removable SD card, with a theoretical maximum endurance of 6,2km and it can be handled by one single person.Unfortunately, the concept as a whole is not entirely successful, and must therefore be supplemented within some areas. The major occurrence is that the drive mechanism tender to slip along the tether when climbing in vertical direction with a risk of damaging the tether coating. Furthermore one needs to increase the operational depth rating. This to be able to utilize the sensor carrier at all depths in the North Sea and also the Baltic Sea. However, the project as whole has achieved a solid framework and platform ready to be developed further in a future second version.