SediMeter™ Sensor

The sensor consists of an array of near-infrared (NIR) optical backscatter (OBS) detectors inside a vertical transparent rod. They are lit one at a time, and an analog-to-digital converter measures the amount of reflected light. This data gives an estimate of the near-bed turbidity, but near the bottom the signal is dominated by the strong reflection from the bottom itself.

If a specific detector is below the bottom level, the signal becomes near 100%. If it is far above the bottom the signal is a function of turbidity. It is therefore fairly straightforward to interpolate the level of the bottom, and minute changes in reflectivity equivalent to an elevation change of 0.1 mm can be detected.

In some cases the level of the bottom might not be well defined in the data. The reason is probably that it is not well defined in reality either. The SediMeter™ allows time-series measurements to be made of the sediment-water interface during high turbidity flows, the settling of super-concentrated suspensions, and similar events

Dr. Ulf Erlingsson, the inventor of this patented sensor, is reporting results from SediMeter sediment transport studies as well as from SediMeter sedimentation studies at his website, Erlingsson Sub-Aquatic Surveys. The latest model, SediMeter Model 2, has been designed based on those research results, both as regards hardware and software.