Calibration and Comparison of a LISST-100 and an OBS-3 Using Quartz Sand and Silicon Carbide
Abstract
Recent technological advances have provided new methods for the in-situ measurement of suspended sediment concentration. The Laser In-situ Scatterer and Transmissometer (LISST-100) uses laser diffraction to measure suspended sediment concentration and particle size distribution of particles ranging in size from 2.5 to 500 microns. The LISST-100 reports the concentration of sediment suspension in 32 logarithmically spaced size classes. The OBS-3 is an optical backscatter sensor that measures turbidity by detecting infrared radiation scattered by particles in the water column. A series of experiments was conducted in a 200-liter volume mixing tank at Davidson Laboratory. The goals of the experiments were to verify the ability of the LISST-100 to measure concentration and determine sediment diameter over a size range of non-cohesive quartz sand and silicon carbide. In addition, the resultant data from the LISST-100 and the OBS-3 were inter-compared to evaluate their respective particle sensitivities and output correlations. The test matrix included uni-modal distributions from one standard sieve/mesh size, with sediments ranging in diameter from 3 to 500 microns. Normal and bimodal distributions of sediment were also tested across the same size range. Analysis of the data showed that the LISST-100 determined the correct median sediment diameter for uni-modal size distributions. However, for a normal grain size distribution, the LISST-100 consistently underestimated the mean diameter by approximately 40 percent. For a bimodal distribution, the LISST correctly determined the grain size for smaller sediments and produced either a weak or no peak for larger sediments. Sediment concentrations were underestimated by the LISST-100 for uni-modal tests; the error increased with larger sediment diameters. Similar trends were observed for the normal and bimodal distributions. New volumetric constants were determined to correct for errors in sediment concentration. Grab samples of total suspended sediments were obtained from the field to compare with concurrent measurements of the LISST-100.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFMOS22B0270P
- Keywords:
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- 4200 OCEANOGRAPHY: GENERAL;
- 4235 Estuarine processes;
- 4294 Instruments and techniques;
- 4299 General or miscellaneous