Autonomous Sensing of Layered Structures in Hawaiian Waters

Our long-term goals are (1) to determine the spatial and temporal scales of thin layers, (2) to identify the processes responsible for the formation, maintenance and dissipation of vertically thin layers, and (3) to develop the capability to predict thin layer formation and presence in the sea. The central focus of our research is to investigate: the spatial and temporal scales of thin layers, the relationship between physical processes (from the mesoscale to the microscale) and thin layers. In March of 2007 we were awarded $112,842 for the fabrication of an autonomous profiler (the SeaHorse) for the detection of thin layers of phytoplankton in the coastal ocean. The SeaHorse makes use of wave energy to power extended, high-resolution profiling of water properties. The instrument is moored to the seafloor and is left to collect samples autonomously. High-resolution (< 2 cm) vertical profiles will be collected roughly once each hour between the bottom and the surface at an average ascent rate of 8 cm per second. Between profiles, the sensor package remains stationary at the bottom until the next sampling interval. A SeaBird SBE-19 plus CTD on the profiler will measure temperature, salinity, and pressure. A SeaBird SBE-43 O2 sensor will measure dissolved oxygen. A WET Labs Inc. WET Star Chlorophyll fluorometer on the profiler will measure chlorophyll fluorescence (an estimate of chlorophyll concentration). Finally, a WET Labs Inc. cs-25-66-p(red) CStar transmissometer will measure beam transmittance. The unique aspect of this profiler is that it is equipped with 2-way telemetry. We will receive profiles of temperature, salinity, oxygen, chlorophyll concentration and beam transmittance throughout the water column (from the surface to the bottom) autonomously once each hour.