PIs: David A. Siegel and Norman B. Nelson, UCSB

UCSB Personnel: Stuart Halewood, Erik Stassinos

Vendors: Biospherical Instruments Inc, John Morrow; Mooring Systems, Inc.

Intellectual Merit

Under the auspices of this grant we designed, constructed, and tested a prototype Near Surface Profiling Buoy (NSPB) system. The NSPB is designed to make highly accurate measurements of light radiation fluxes near and just above the ocean surface, autonomously and without the problem of shadowing which is chronic when measurements are made from vessels or fixed platforms.

The NSPB consists of two main elements (Figure 1). First, a drifting spar-like hotel buoy, which contains surface sensors and batteries, computers, cabling interfaces and power supplies, and satellite (Iridium and Argos) communication facilities. The aluminum buoy hull was constructed by Mooring Systems Inc, Calumet MA, with the system integration performed by our group at UCSB. The mooring mast mounts the surface sensors, a GPS unit, the Iridium transceiver, and also a Service Argos transmitter for backup location. The mooring mast is configured as a radar reflector and we also have strobe lights and a short distance RDF transmitter for recovery. The system is designed to have a ten-day endurance in the field on battery power (Figure 2). Tethered to the hotel buoy by a custom designed cable is a profiler (Figure 3) that contains the underwater sensors and a thruster system which brings the profiler to the surface after a free fall to approximately 20 meters.

The optical sensors and profiler package were manufactured by Biospherical Instruments, San Diego. The system uses novel microradiometer units from Biospherical covering the solar spectrum from the ultraviolet to the near infrared (Figure 4). Control software located in the buoy hull computer manages data acquisition and controls the thruster that returns the profiler to the surface after each freefall descent (Figure 5).

The system sensors include downwelling irradiance sensors on the surface and profiler unit. The profiler unit also includes an upwelling radiance sensor, which is necessary for satellite ocean color data product validation, and also an upwelling irradiance sensor which is useful for tracking net energy fluxes in the water column. Each sensor package is equipped with internal temperature and tilt sensors. Finally, the surface sensor has a computer controlled shadowband accessory which allows for computation of direct and diffuse solar radiation fluxes near the surface (Figure 6), which in turn can be analyzed to gain information about the aerosol and cloud state near the buoy. Communication with the buoy computer can be accomplished over a short-range WiFi link, or via the Iridium link. Over the Iridium link the NSPB can be monitored for status (location, battery power, data collection) at any time from any location.

Construction and integration of the system proceeded largely without difficulty except for one major design change that happened in the first year of the project. The original plan for the profiler was to mount a piston-type buoyancy control system to regulate depth. Biospherical was unable to source the system as planned, so depth control was changed to a small thruster. This consumes more power than the piston buoyancy system would have, so an increase in battery size and weight mandated a major increase to the buoy hull size. Future improvements to the NSPB concept will focus on improvements in battery technology that will allow smaller and lighter systems that can be deployed from small boats.

While the hotel buoy and profilers were being designed and constructed, we carried out an extensive testing program for the system radiometers, comparing their results to existing instruments on parallel deployments and testing the calibration and data quality. This test p...

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