Challenges in autonomous coastal water sampling

Scientists looking to ground truth data collected by in situ sensors require physical water samples collected at the sensor depth. These samples which are processed in the lab are crucial in increasing the confidence of in situ sensors; especially when such sensors are of a new type. Traditionally, water samples at depth are collected manually through the use of niskin style bottles, or with the simple filling of bottles alongside a vessel. Although this process works for sparse sampling, it is not an efficient way to collect a large number of regular samples across many sites. Shallow reefs may also be inaccessible by boat at low tide. An autonomous water sampling system is needed to allow for the quick and efficient collection of water samples. The system should be relatively inexpensive, compact and lightweight so it can easily be deployed from small boats on reefs and in larger numbers. In addition, it should be easily scalable to allow for the collection of up to 1000ml of sample in either timed intervals or at preset times of day. This paper discusses the challenges of taking such autonomous water samples in coastal reef environments. The design and development of two types of autonomous sampling systems for use in shallow coastal waters is discussed in this context. Results from field trials are also presented. Finally, the paper disuses how these systems can be modified to allow for deep operation, or operation as part of an under way sampling system on a research vessel.