Can I deploy my profiling CTD for monitoring an oil spill?
Sea-Bird CTDs can be deployed in oil; the oil will not cause long-term damage to the CTD. If the oil coats the inside of the conductivity cell and coats the dissolved oxygen sensor membrane, it can possibly affect the sensor’s calibration (and thus affect the measurement and the data). Simple measures can reduce the impact, as follows:
- To minimize the ingestion of oil into the conductivity cell and onto the DO sensor membrane:
SBE 19, 19plus, 19plus V2, 25, or 25plus CTD:
Set up the CTD so that the pump does not turn on until the CTD is in the water and below the layer of surface oil, minimizing ingestion of oil (however, some oil will still enter the system). Pump turn-on is controlled by two user-programmable parameters: the minimum conductivity frequency and the pump delay.
Set the minimum conductivity frequency for pump turn-on above the instrument’s zero conductivity raw frequency (shown on the conductivity sensor Calibration Sheet), to prevent the pump from turning on when the CTD is in air. Note that this is the same as our typical recommendation for setting the minimum conductivity frequency.
For salt water and estuarine applications - typical value = zero conductivity raw frequency + 500 Hz
For fresh/nearly fresh water - typical value = zero conductivity raw frequency + 5 Hz
If the minimum conductivity frequency is too close to the zero conductivity raw frequency, the pump may turn on when the CTD is in air as result of small drifts in the electronics. Another option is to rely only on the pump turn-on delay time to control the pump; if so, set a minimum conductivity frequency lower than the zero conductivity raw frequency.
Set the pump turn-on delay time to allow enough time for you to lower the CTD below the surface oil layer after the CTD is in the water (the CTD starts counting the pump delay time after the minimum conductivity frequency is exceeded). You may need to set the pump delay time to be longer than our typical 30-60 second recommendation.
The current minimum conductivity frequency and pump delay can be checked by sending the status command to the CTD (DS or GetCD, as applicable). Commands for modifying these parameters are:
- SBE 19: SP (SBE 19 responds with prompts for setting up these parameters)
- SBE 19plus and 19plus V2: MinCondFreq=x and PumpDelay=x (where x is the value you are programming).
- SBE 25: CC (SBE 25 responds with a series of setup prompts, including setting up these parameters)
- SBE 25plus: SetMinCondFreq=x and SetPumpDelay=x (where x is the value you are programming).
SBE 9plus CTD:
Minimum conductivity frequency and pump delay are not user-programmable for the 9plus.
If you are using your 9plus with the 11plus Deck Unit, the Deck Unit provides power to the 9plus. Without power, the pump will not turn on. At the start of the deployment, to ensure that you have cleared the surface oil layer before the pump turns on, do not turn on the Deck Unit until the 9plus is below the surface oil layer. Similarly, on the upcast, turn off the Deck Unit before the 9plus reaches the surface oil layer.
If your 9plus is equipped with the optional manual pump control, you can enable manual pump control via the Pump Control tab in Seasave V7’s Configure Inputs dialog box. Once enabled, you can turn the pump on and off from Seasave V7’s Real-Time Control menu. Do not turn the pump on until the CTD is below the surface oil layer. On the upcast, turn the pump off before the CTD reaches the surface oil layer.
- To reduce the effect of the ingestion of oil into the conductivity cell and onto the DO sensor membrane or optical window:
After each recovery, rigorously follow the cleaning and storage procedures in the following application notes ‑
- Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells
- Application Note 64: SBE 43 Dissolved Oxygen Sensor – Background Information, Deployment Recommendations, and Cleaning and Storage
- SBE 63 Optical Dissolved Oxygen Sensor manual
Quick Reference Sheets for Oil Spill Deployment: