The PI requests MRI funding to develop and evaluate the performance of a novel profiling buoy system for the calibration of satellite ocean color observations and the validation of their data products. This measurement capability is essential for creating long-term satellite climate data records of the ocean biosphere The Near Surface Profiling Buoy (NSPB), will autonomously collect 100's of high-quality, near-surface irradiance / radiance profiles during each multi-day deployment as part of a standard oceanographic research cruise. The NSPB is built upon recent advances in optical profiling instrumentation designed for turbid water environments that is adapted to the calibration and validation of ocean color satellite data. The NSPB system is aimed at making day-long to week-long deployments improving the likelihood of high quality match-ups with satellite data than is possible with conventional profiling techniques.
Broader Impacts
Increased provision of sea-truth radiometry for vicarious calibration of ocean colour sensors, particularly in geographical regions not covered by existing installations, is urgently required by the remote sensing community. In principle, the buoy-plus-profiler device offers a novel and exciting technique for satisfying this need. The improved satellite validation and calibration made possible by the proposed instrumentation will likely benefit a wide group of scientists and other users. The proposed solution combines the benefits of a moored system with a boat based deployment. The buoy will be left so that it can collect large amounts of data, but not so long that bio-fouling starts to become a significant issue. In addition, the smaller overall size will reduce the infrastructure required for deployment. The proposal highlights the positive impact this development will have on a commercial company (Biospherical Instruments, Inc.).
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 program also validated the cable design and the control software. We conducted dockside trim tests for the hotel buoy before conducting an all-up one day test with the system deployed and in automatic mode (Figure 2). All aspects of the system were tested at sea in automatic mode except for the two-way Iridium communication link. Broader Impacts The concept of the NSPB solves a number of problems in optical oceanography, primarily the shadowing issue and the problem of wire time. The NSPB would allow researchers on a time-series site program to deploy the system on the way out to the time series site, spend a few days on the site, and recover the system on the way back, without having to do hand-held deployments from the ship. The suite of instruments on the NSPB are also useful for studying processes like penetrating radiation flux (physical and photobiological / photochemical oceanography) as well as for direct ocean color applications. The thruster equipped profiler design and other aspects of the NSPB development have led to new product offerings from Biospherical Instruments.
