The University of Maine Maine In-situ Sound & Color Lab
School of Marine Sciences
Intercomparison of Field Measurements of b and c by LISST-100 and AC-9

Two instruments that measure similar optical properties of water were deployed from a common profiling device at the LEO-15 site during the 2001 HyCODE experiment. The AC-9 measures beam attenuation, c, using incandescent light sources, a colored filter wheel, and a receiver. It measures absorption, a, by including light that is scattered by particles over angles covering from about 0.75 to 41 degrees. The difference, c-a, can be computed to estimate the total scattering coefficient, b, over this angular range. The LISST-100 instrument measures beam attenuation using a laser. It measures scattering over 32 small angular ranges represented by ring detectors in the receiver optics. In contrast to the AC-9, the LISST-100 differs in two ways: first, its receiver aperture is much smaller at 0.05 degree thus rejecting scattered light more completely and producing a higher beam-c value. Second, the LISST-100 covers scattering measurements over the range 0.1-20 degrees, whereby it captures more of the forward scattering, but excludes the 20-41 degree range. The data obtained by these two instruments at the LEO-15 field site will be compared along with a discussion of the error sources. Variability in time and space of the attenuation and scattering coefficients will be related to the underlying particle composition, size distribution, and environmental forcing.

Bergmann, T., Boss, E., and Agrawal, Y., 2004. Intercomparison of Field Measurements of b and c by LISST-100 and AC-9. AGU Ocean Sciences Meeting, Portland, OR, Jan.

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