An easily constructed, very inexpensive, solar cell transmissometer (SCT)

Abstract

Suspended sediment concentration (SSC), one of the standard measures of water quality in aquatic systems, is of widespread interest because of its role in particulate flux and light attenuation. The conventional method of sampling and filtration to determine SSC is rather slow and cumbersome, and does not allow resolution of high-frequency variations. In contrast, the beam transmissometer has been used as a convenient way to obtain time-series estimates of SSC in environments ranging from the deep ocean to the continental shelf and estuaries. In situ observation of suspended particles in fluvial, estuarine, lagoonal, and inner-shelf environments has in fact revealed that most of the volume of material in suspension exists as aggregates (> 50--100 {micro}m diameter) of smaller components and that aggregate properties may change on time scales of only a few minutes and length scales of less than one meter. Here, the authors describe a very inexpensive, easily constructed solar cell transmissometer (SCT) that has been developed for use with an in situ suspended-sediment photography system. Conventional optical SSC sensors can provide excellent predictive capability when deployed during conditions of relatively uniform aggregate characteristics. However, this system may provide better results than commercially available systems because it disaggregates suspendedmore » material prior to measurement of light attenuation, thereby reducing the effects of aggregation and changes in aggregate characteristics, which can occur over very short temporal and spatial scales. This paper describes the solar cell transmissometer and gives results of laboratory calibration, design, construction, and field testing alongside an optical backscatter sensor (OBS).« less