Department of Interior -- U.S. Geological Survey -- Woods Hole Field Center -- Plot Index Page

caption: Mass Bay attenuation data graphs

Light attenuation data

Transmissometers measured the transmission of light (wavelength 650 nm) from a Light Emitting Diode (LED) along a 25 cm water path. The voltage output by a photovoltaic detector was converted to light beam attenuation (units of 1/m) as -4(ln(V/C) where V is voltage and C is 95% of the voltage recorded when the light was transmitted through clear air (the 95% adjusts for the light attenuation by clear water). The light attenuation coefficient is linearly proportional to the concentration of suspended material in the water if the particles are of uniform size and composition (Moody et al., 1987). However, the size of the particles in the water changes with time, especially during resuspension events, and thus the attenuation coefficients must be interpreted with care. The steady rise in attenuation during many of the early deployments results from biological fouling of the transmissometer lenses.

Significant wave height is reported by NODC based on data measured at the large navigational buoy.

PSDEV is the standard deviation of burst-sampled pressure measurements recorded by the tripod systems , and is a measure of the disturbance at the sea floor caused by surface waves.

The data are hour-averaged.


This page is <URL:http://woodshole.er.usgs.gov/~fhotchki/caption_light.html>.
Maintained by Fran Hotchkiss (fhotchkiss@usgs.gov)
Updated on 15 April 1997.