Parameters: Dye Tracing
Scientists at the Space and Naval Warfare Systems Center San Diego (SSC-SD) have developed a quick technique to manually change gain ranges on the Cyclops fluorometer. The technique was developed to facilitate making the gain changes in wet field conditions during small boat operations. The Cyclops with switch was successfully used to map out fluorescein dye on recent surveys.
A three-position switch that could ground one of two gain control lines or neither line was required. As is many times the case, there was little budget or time available as the system was required shortly after it was purchased. Custom manufactured cable and underwater switches were expensive and required weeks of lead-time. The solution was to construct a three-way switch from locally available materials. The materials used were 1/2" PVC pipe, pipe tee, pipe union, two magnetic reed switches and a magnet. The switch assembly also served to join the Cyclops cable to the cable from the CTD.
All power and signal wires were routed straight through the to the CTD cable, except for the two gain control lines. These were connected to the magnetic reed switches so that when the switches were closed the line would be grounded. The switches were bonded to the inside of the lower half of the union, positioned 180 degrees apart (see figure below). The magnet was bonded in place on the inside of the upper half of the union. By rotating the upper half of the union the magnet could be placed in proximity to one of the reed switches, closing that reed switch and thereby connecting the control to ground. The gain setting of the Cyclops was controlled by rotating the union fitting so that one of the switches was closed or neither was closed. Polyurethane potting material was used to fill the interior of the PVC pipe to waterproof the wiring assembly.
Figure 1. Surface fluorescein dye distribution during a mixing zone test. The strong gradient in dye concentrations indicates rapid mixing with ambient waters.
The Cyclops with range change switch was utilized in April 2004 to look at dye released from Navy drydock pump systems to evaluate receiving water mixing zones. The Cyclops was attached to a SeaBird 19 CTD using the cable containing the ranging switch. Surface water dye concentrations were mapped by towing the CTD with attached Cyclops sensor during various tidal conditions.
One survey result is shown in Figure 2 in units of relative fluorescence. The data from these surveys suggest that the drydock discharges are rapidly mixed with the ambient water. It turned out that the range in concentrations observed was sufficiently characterized by the mid range of the Cyclops and the switch was not needed for this particular set of surveys. However, it is expected that quickly changing ranges will be important for other planned surveys and for measuring dye concentrations of the starting mixture prior to discharge.
Figure 2. Schematic of manual gain switch for Cyclops fluorometer.
Authors: Dr. Chuck Katz & Dr. Greg Anderson
Institution: Space and Naval Warfare Systems Center, San Diego, California, USA