Low Light Auto-Radiometer for Deep Sea Irradiance Measurements

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The Harbor Branch Oceanographic Institution will undertake a project to develop a sensitive radiometer for in situ measurements of irradiance in the water column. Optical measurements at sea are becoming increasingly important to ocean science field investigations and adequate optical instrumentation is often lacking. The low light auto- radiometer (LoLAR) will employ a photomultiplier tube which allows greater sensitivity than silicon-photodiode based technology permits on currently used instruments. The new instrument will increase the sensitivity of light level detection and measurement by a factor of five. At-sea use of photomultiplier tube instrumentation requires development of several special design features, including autocalibration, temperature dependency corrections, light collection, and data acquisition. In situ irradiance measurements have been primarily restricted to the near surface waters of the ocean because of limited instrumentation sensitivity. Several types of ocean science research investigations would benefit from increased sensitivity by being able to make light measurements deeper in the water column. The types of research that would benefit from this new instrument include hydrologic optics that relate to physical properties affecting light penetration in the ocean as a function of depth; photophysiology of populations, concerning the distribution of organisms and their orientation as related to different light fields; and bioluminescence research. The general purpose instrument will be usable on submersibles, remotely operated vehicles, moorings, nets, and profiling systems.