Hawaii Ocean Time-series (HOT)
in the School of Ocean and Earth Science and Technology at the University of Hawai'i at Manoa

Inherent Optical Properties (IOPs): Absorption and Beam Attenuation


Optics Cage Deployment
To assist in the interpretation of the data, it can be displayed using the Hawaii Ocean Time-series Data Organization & Graphical System (HOT-DOGS©).

Sampling Procedure

Profiles of absorption (a(λ)) and beam attenuation (c(λ)) were made using a WET Labs AC-9 & a WET Labs AC-S. The AC-9 simultaneously determined the spectral attenuation and spectral absorption of water at 412, 440, 488, 510, 532, 555, 650, 676 and 715 nm. Each of these wavebands have bandpasses of approximately 10 nm. The sampling frequency is approximately 6 Hz. The AC-S is similar to the AC-9, except it provided 80+ wavelengths from 400-730nm with 4nm increments.

The AC-9 & AC-S were part of an instrument package that also included a Sea-Bird CTD, WET Labs ECO-BBF2 Triplet (measuring Chlorophyll, CDOM & Phycoerythrin), a Chelsea Fast Repitition Rate Fluorometer (FRRf) and a Sequoia Laser In-Situ Scattering and Transmissometry (LISST-100X) instrument. The AC-9 & AC-S were oriented horizontally and lowered at a more-or-less constant speed of 10 m/min to a bottom depth of approximately 200 m. At least 2 back-to-back profiles were normally taken, one using a 0.2 µm cartridge filter and one without. This allowed the spectral absorption and attenuation coefficient of both the total and dissolved matter to be determined. The particulate absorption and attenuation components were derived by subtracting the dissolved from the total component. The scattering of particles was estimated by subtracting the absorption from the attenuation particle spectrum.

This study is a collaborative effort between the College of Oceanic and Atmospheric Sciences of Oregon State University and the Laboratory for Microbial Oceanography of the University of Hawai'i at Manoa.