Tidal influences on optical variability in shallow water

Alan D. Weidemann; W. Scott Pegau; Laurie A. Jugan; Todd E. Bowers

doi:10.1117/12.266463

6 February 1997 Tidal influences on optical variability in shallow water

Alan D. Weidemann, W. Scott Pegau, Laurie A. Jugan, Todd E. Bowers

Proceedings Volume 2963, Ocean Optics XIII; (1997) https://doi.org/10.1117/12.266463
Event: Ocean Optics XIII, 1996, Halifax, Nova Scotia, Canada

Abstract

Over the past few years, several extensive exercises supported by NRL Optics Programs have taken place in US coastal waters. Analysis of optical data collected has progressed from simply observing high spatial and temporal variability, to linking this variability with physical forcing factors. Data from the most recent exercises off the Oceanside, CA and Le Jeune, NC areas are presented. Optical and oceanographic casts were taken at Oceanside in October 1995 using an ac-9 and an associated CTD. Optical properties were observed to correlate very well with the temperature and density structure of the water column. In turn, the temperature/density structure varied in conjunction with the main component of the local tidal cycle. Optical casts over a 15 hour period when other physical forcing factors are believed to be minimal are presented. During the two-week Oceanside exercise, an optical mooring recorded absorption, total attenuation, irradiance, and backscattering. Cyclic changes in the optical properties of a factor between two and four were observed, with a base of 0.5 to 1.0 m^-1. Phase shifts in the optical data indicate that tidal influences were also modulated and at times overshadowed by large scale meteorological events, local long shore currents, and other physical forces. At Le Jeune, absorption, attenuation, temperature, and density fields were observed to fluctuate with the tidal cycle at distances of up to 12 mi from New River Inlet. The mean tidal height and density are shown to correlate with a factor of three change in both the absorption ad attenuation over a tidal cycle. Warm, high density water with low optical properties advected through the area during the measurement period and overshadowed the variability attributable to tides.

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Alan D. Weidemann, W. Scott Pegau, Laurie A. Jugan, and Todd E. Bowers "Tidal influences on optical variability in shallow water", Proc. SPIE 2963, Ocean Optics XIII, (6 February 1997); https://doi.org/10.1117/12.266463

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