For the past decade, the Marine Optical Buoy (MOBY), a radiometric buoy stationed in the waters off Lanai, Hawaii,
has been the primary in-water oceanic observatory for the vicarious calibration of U. S. satellite ocean color sensors,
including the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectrometers
(MODIS) instruments on the National Aeronautics and Space Administration's (NASA's) Terra and Aqua satellites.
The MOBY vicarious calibration of these sensors supports international effort to develop a global, multi-year time series
of consistently calibrated ocean color data products. A critical component of the MOBY program is establishing
radiometric traceability to the International System of Units (SI) through standards provided by the U. S. National
Institute of Standards and Technology (NIST). A detailed uncertainty budget is a core component of traceable
metrology. We present the MOBY uncertainty budget for up-welling radiance and discuss additional considerations
related to the water-leaving radiance uncertainty budget. Finally, we discuss approaches in new instrumentation to
reduce the uncertainties in in situ water-leaving radiance measurements.
The water-leaving spectral radiance is a basic ocean color remote sensing parameters required for the vicarious
calibration. Determination of water-leaving spectral radiance using in-water radiometry requires measurements of the
upwelling spectral radiance at several depths. The Marine Optical System (MOS) Remotely Operated Vehicle (ROV) is
a portable, fiber-coupled, high-resolution spectroradiometer system with spectral coverage from 340 nm to 960 nm.
MOS was developed at the same time as the Marine Optical Buoy (MOBY) spectrometer system and is optically
identical except that it is configured as a profiling instrument. Concerns with instrument self-shadowing because of the
large exterior dimensions of the MOS underwater housing led to adapting MOS and ROV technology. This system
provides for measurement of the near-surface upwelled spectral radiance while minimizing the effects of shadowing. A
major advantage of this configuration is that the ROV provides the capability to acquire measurements 5 cm to 10 cm
below the water surface and is capable of very accurate depth control (1 cm) allowing for high vertical resolution
observations within the very near-surface. We describe the integrated system and its characterization and calibration.
Initial measurements and results from observations of coral reefs in Kaneohe Bay, Oahu, extremely turbid waters in the
Chesapeake Bay, Maryland, and in Case 1 waters off Southern Oahu, Hawaii are presented.
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