An OBS-3 was placed in one end of an acrylic plastic bubble generator test tank (BGTT; outer dimensions 28.5 x 35.7 x 58.5 cm) with the emitting side of the sensor facing towards the far end of the tank. Each bubble generator was tested under variable conditions, by emplacement at the bottom of the tank a variety of distances from the OBS. In cases where the water in the BGTT required stirring, the bubbler was fixed 10 cm from the OBS. In addition, eight bilge pumps with pumping capacities ranging from 8.3 to 33.3 l min-1 were used to mix the water and arranged in such a fashion that the bubbles traveled toward the OBS. Five bubble generators were used consisting of fine and coarse sintered metal tubes, PVC pipe with drilled holes, porous ceramic brick and an aquarium air stone. All bubblers were tested at several flow rates in both sand and muddy conditions of ranging concentration in fresh, salt and synthetic salt water. FIGURE 1. shows one example of the calibration curve for the fine sintered tube that occurs for both mud and sand. The lines represtnan
FIGURE 1. Calibration curves for mud and sand in 3 different water types at various flow rates (black - no bubbles, blue - low air flow rate, pink - medium air flow rate, green high air flow rate).
Because Figure 1 contains as large quantity of information, it is necessary to develop a simple means to observe the data from all 5 bubblers simultaneously rather than reproducing additional figures similar to Figure 1. we chose the calibration slope as the parameter of interest and investigate the ratio of the calibration slope, s, to the calibration slope of the background bubble free condition, sb as R= s/sb (Figure 2). The ratio determines the quantity of OBS output voltage that would need to be measured in a bubbly environment to yield a corresponding sediment concentration based on the background calibration curves. As an example, using the fine sintered tube in synthetic salt water (Figure 2 and 3 panel Bs), R is slightly larger than 0.5 suggesting that the OBS output in a bubbly environment would only have to be approximately half that measured in a bubble-free environment to infer a sediment concentration based on the bubble-free calibration curve.
FIGURE 2. The calibration slope ratio R=s/sb for the five bubblers, various flow rates, sand (left panels; subscript s) and mud (right panels; subscript m), and water types (F=fresh, S=salt, SS=Synthetic Salt). As,Am) Point4 with flow rates of <0.05 L/min and 0.1 L/min for each water type. Bs,Bm) Fine sintered tube with flow rates of 1.0 L/min, 2.0 L/min and 5.0 L/min for each water type. Cs,Cm) Coarse sintered tube with flow rates of 1.0 L/min, 2.0 L/min and 5.0 L/min for each water type. Ds,Dm) Aquarium air stone with flow rates of 1.0 L/min, 2.0 L/min and 5.0 L/min for each water type. Es,Em) PVC pipe with a flow rate of 3.3 L/min for each water type.
For more information on this topic see Puleo et al. Review of Scientific Instruments V75 (2004) or Puleo et al. Marine Geology (To Be Submitted Late 2005)
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