Instrument: Deep Autonomous Profiler

The Deep Autonomous Profiler (DAP) is described in detail in the following publication:
Muir, L., Roman, C., Casagrande, D., and D'Hondt, S. (2021) The Deep Autonomous Profiler (DAP), a Platform for Hadal Profiling and Water Sample Collection. Journal of Atmospheric and Oceanic Technology, vol. 38, no. 10, pp. 1833–1845, 2021. doi:10.1175/JTECH-D-20-0139.1. URL: https://journals.ametsoc.org/view/journals/atot/38/10/JTECH-D-20-0139.1.xml

To summarize:
DAP is a full-ocean-depth profiler rated to 11 kilometers. It was designed to expand the capabilities of a CTD system to the full ocean depth (11 km) by removing the constraints associated with wire-based operations. Removing the tether allows the vehicle to autonomously profile and sample seawater into the hadal region. Because it only requires the ship for deployment and retrieval, the ship can perform other tasks while the DAP is underway. The only source of communication to the DAP while deployed are the acoustic releases.

The DAP is built around a 24-bottle Sea-Bird SBE 32 rosette for 10- or 12-Liter Niskin bottles. The large aluminum bottle-support rings from the standard rosette were modified to reduce weight and are held by the vehicle's custom frame. Syntactic foam provides buoyancy and drop weights are used for descent.

The DAP stands 3.2 meters tall and has a mass of approximately 1400 kilograms (kg) in air empty and 1700 kg when full of water. The titanium electronics bottle, tested to 960 decibars (dBar) in a pressure facility, was designed to house the embedded Raspberry Pi computer and power circuitry. This computer logs data from the SBE 9plus CTD and SBE 43 oxygen sensor, sends commands to the SBE 32 sampler carousel to trigger the sample bottles, and controls the burnwire release. Power for a nominal 24-hour operating time is provided by a 24-volt, 40-amp-hour oil-filled DeepSea Power and Light SeaBattery.

Using drop weights, the profiler descends at a nominal speed of 60 meters per minute through the water column, collecting CTD data. Upon reaching the bottom, a timer is activated and an onboard algorithm processes the descent profile to set the trigger depths for any sample bottles set with an adaptive criteria. Bottom water samples can also be collected according to any preset delays. The bottom time can vary anywhere from 5 minutes to 18 hours. During the ascent, at a nominal speed of 60 meters per minute, the Niskin bottles are triggered at any preset depths specified in the mission file or at adaptively calculated depths based on downcast data. When the DAP surfaces, a radio beacon, Iridium beacon, strobe, radar reflector, and flag are used for recovery by the ship.

The vehicle can currently hold up to 24 Niskin bottles, and up to four pressure-maintaining sample bottles provided by the Scripps Institution of Oceanography.