In 2009, major advances were made in sampling intensity and screening of biodiversity from water samples obtained with MBARI’s autonomous underwater vehicle (AUV) gulper water-sampling system. The upper-water-column vehicle with “gulper samplers”, a payload developed at MBARI, is designed to rapidly acquire multiple large-volume water samples aboard the AUV.
This AUV is unique in that it can collect up to ten 1.8-liter water samples while traveling through the water or through a plume.
Gulper sampler description
The gulper sampling system is an array of 10 syringe-like water samplers mounted in the mid-body of the upper-water-column vehicle. Each sampler takes two-liter water samples when commanded by mission software. These additions were installed when all the other oceanographic instruments were moved forward into the new blunt-shaped nose. Each gulper sampler has a one-way valve opening which extends through the fairing. An electromagnetic pin-puller releases a dual spring array under tension which causes a plunger to suck in the water sample in about two seconds.
Each gulper contains two liters of volume. When ballasting operations are conducted, the gulpers are full of seawater. Therefore, the AUV will not be able to dive if the gulpers are full of air. They need to be in the “cocked” position before launch, so the upper chambers can fill with seawater when the AUV is launched.
After the mission, these water samples are analyzed either onboard the mother ship or back at the laboratory. An ongoing software effort is developing the capability to trigger the gulpers based on the measurements of other on-board instruments.
CTD (conductivity, temperature, depth) instrument description
The upper-water-column vehicle can use a conductivity, temperature, and depth (CTD) instrument, which is a series of sensors that continuously measure conductivity (salinity), temperature, and depth.
This vehicle is 54 centimeters (21 inches) in diameter, 366 centimeters (12 feet) long, weighs 476 kilograms (1050 pounds) in air, and weighs about 907 kilograms (2000 lbs) when the interior is flooded with seawater.
Main power is provided by three pressure tolerant Lithium Polymer rechargeable batteries (Bluefin), which have a combined capacity of about 6 kilowatt hours. There is also a 12 volt alkaline battery pack which runs the Radio Direction Finder and strobe after the main power pack has been exhausted.
Propulsion and control is accomplished with the same ducted tailcone assembly that the Mapping AUV uses. Vehicle Range and mission time is approximately 80 kilometers, about 20 hours.
On board upper-water-column vehicle sensors include:
- A CTD Pair: Conductivity and Temperature: SBE3F and SBE4 with temperature sensor accuracy 0.001 degree C, and conductivity sensor accuracy 0.0003 S/meter (Seabird Electronics).
- Oxygen: SBE43 Oxygen sensor with a 2% accuracy of saturation (Seabird Electronics).
- An MBARI In Situ Ultraviolet Spectrophotometer (ISUS). Ultraviolet light source and spectrometer measures nitrate concentration. Accuracy: 2 micrometers. (Satlantic).
- A Laser In Situ Spectrometer and Transmissometer (LISST): Laser diffraction measurement of particle sizes (1.25 to 250 microns) using a multi-ring detector. (Sequoia Scientific, Inc.).
- A Laser Optical Plankton Counter (LOPC): Measures cross-sectional profiles from one millimeter to 40 millimeters. (Brooke Ocean Technology).
- A Bathyphotometer: measures bioluminescence. Photomultiplier tube and pump, agitates water sample and counts light flashes. (UCSB Jim Case Life Science Lab). A HydroScat-2 Backscattering Sensor and fluorometer measures turbidity at 420 and 700 nanometers (nm) and chlorophyll fluorescence. Hobi Labs. OCR-507, a seven channel irradiance sensor which measures from 400 to 865 nm (Satlantic).