Prince William Sound Field Experiment

autonomous underwater vehicles

REMUS-100 (see figure three)
Slocum glider (see figure one)

Participants

  • Cal Poly
  • JPL/UCLA
  • Rutgers University
  • AOOS


Autonomous Underwater Vehicle surveys

Principal Investigator:
Mark Moline, CAL POLY

Nearly continuous measurements of temperature and salinity are to be collected using two autonomous underwater vehicles (AUV).   The first is a Slocum glider (Figure 1)and the second a REMUS-100 (Figure 3).  The Slocum glider is a 1.8 m long torpedo-shaped winged vehicle built by Webb Research Corporation (WRC) of East Falmouth, MA. It maneuvers through the ocean at a forward speed of 30-40 cm/s in a saw tooth gliding trajectory. The vehicle carries a range of high-quality scientific payloads including a Sea-Bird CTD and a WetLabs ECO puck for chlorophyll and optical backscatter. The primary vehicle navigation system uses an on-board GPS receiver, with backup positioning and communications provided by an Argos transmitter. Two-way communication with the vehicle is maintained by RF modem or global satellite phone service via Iridium.  The operating range using batteries is about 500 km with a maximum depth of 200 m.  The vehicle provides data when it surfaces (approximately every 3 hours), which will then be provided to the modeling groups. 

glider deploymentGlider operations are expected to continue throughout the experiment, being deployed on or around the 19 July, 2009.  The glider is proposed to be deployed in the center section of Prince William Sound and be programmed to fly along a line starting south of Naked Island and ending north of the midpoint of Hawkins Island.  The glider will continue back and forth along this line for the duration of the experiment until 3 August, 2009.  The estimated distance of the line is ~ 65 km, so the glider will be able to transit the line at least 4 times during the experiment.  These activities will be in coordination with Rutgers University while in the field during the field campaigns to provide a regional scale view of water column structure (i.e. pycnoclines, mixed layer depths) from 0-200 m to help evaluate and improve the large scale performance of the ocean model in collaboration with Yi Chao (JPL/UCLA).  Cal Poly and Rutgers University have employed this 24-hour operations strategy over three field efforts with success and is proposed here as well. Cal Poly will coordinate with Rutgers University and JPL/UCLA on optimal data formats, QA/QC of data and metadata.

auv transet lines

The REMUS-100 AUV proposed for this study is a propeller driven platform with a standard length of 160 cm, 19 cm in diameter, with a weight of 37 kg (Figure 2).  Background information on the vehicle and vehicle performance is detailed in Moline et al. (2005).  Four 26 V/10 Ah Lithium-ion batteries power the vehicle for maximum mission distances of greater than 80 km at ~3 knots.  In addition to the batteries, the mid-section of REMUS houses the compass, heading sensors, yaw rate sensor and the PC-104 control computer. Forward of the mid-section is a 1200-kHz RD Instruments REMUS Workhorse Navigator ADCP. This ADCP consists of four upward and four downward looking transponder beams. Upward and downward looking beam arrays are used to measure current velocity and direction in a range of user-specified depth bins above and below the vehicle. The vehicle incorporates the ADCP data to adjust for currents and calculate its position in real time while navigating. The downward looking array is also used as an altimeter, allowing for bottom tracking/mapping and fixed altitude flight. Protruding out of the pressure bulkhead against the ADCP is a Neal Brown CT sensor.  Data are collected at 2 Hz with a nominal vehicle speed of 1.7 m s-1, yielding a horizontal data resolution of 0.85 m for the optical measurements.  Although the REMUS has many ways of navigation (Moline et al. 2005), the primary mode of navigation will be using the onboard compass with repeated surface GPS fixes approximately every 3 km.  With this surfacing interval, the mean horizontal positional error is ~ 1%. 

auv REMUS deploymentTwo periods of the field effort will be focused on the REMUS AUV operations; 21-25 July and 29 July – 2 August.  During these periods, Cal Poly will be responsible for deployment and recovery of the REMUS-100 AUV systems.  Observations from Prince William Sound will include CTD, currents, and chl fluorescence from 0-100 m. The AUV will be deployed to provide a regional scale view of water column structure (i.e. pycnoclines, mixed layer depths) to help evaluate and improve the large scale performance of the model in collaboration with Yi Chao (JPL/UCLA).  These missions will typically consist of long transects that cover significant cross sections of the Sound, but can also be deployed to systematically map particular areas of interest (i.e. fronts, salinity wedges).  Figure 4 shows a potential mission path in yellow, which could be covered in a single deployment lasting ~10 hours.  Alternate missions ideas are shown as dotted yellow lines. After retrieval of the vehicle each mission, the data will be sent to the server at Cal Poly via cell phone modem for access and retrieval for the ocean model in collaboration with Yi Chao (JPL/UCLA).