What are the typical data processing steps recommended for each instrument?
Section 3: Typical Data Processing Sequences in the SBE Data Processing manual provides typical data processing sequences for our profiling CTDs, moored CTDs, and thermosalinographs. Typical values for aligning, filtering, etc. are provided in the sections detailing each module of the software. This information is also documented in the software's Help file. To download the software and/or manual, go to SBE Data Processing.
How should I pick the pressure sensor range for my CTD? Would the highest range give me the most flexibility in using the CTD?
While the highest range does give you the most flexibility in using the CTD, it is at the expense of accuracy and resolution. It is advantageous to use the lowest range pressure sensor compatible with your intended maximum operating depth, because accuracy and resolution are proportional to the pressure sensor's full scale range. For example, the SBE 9plus pressure sensor has initial accuracy of 0.015% of full scale, and resolution of 0.001% of full scale. Comparing a 2000 psia (1400 meter) and 6000 psia (4200 meter) pressure sensor:
- 1400 meter pressure sensor ‑ initial accuracy is 0.21 meters and resolution is 0.014 meters
- 4200 meter pressure sensor ‑ initial accuracy is 0.63 meters and resolution is 0.042 meters
How often do I need to have my instrument and/or auxiliary sensors recalibrated? Can I recalibrate them myself?
- Profiling CTD — recalibrate once/year, but possibly less often if used only occasionally. We recommend that you return the CTD to Sea-Bird for recalibration. (In principle, it is possible for calibration to be performed elsewhere, if the calibration facility has the appropriate equipment andtraining. However, the necessary equipment is quite expensive to buy and maintain.) In between laboratory calibrations, take field salinity samples to document conductivity cell drift.
- Thermosalinograph — recalibrate at least once/year, but possibly more often depending on the degree of bio-fouling in the water.
- DO sensor —
— SBE 43 — recalibrate once/year, but possibly less often if used only occasionally and stored correctly (see Application Note 64), and also depending on the amount of fouling and your ability to do some simple validations (see Application Note 64-2)
— SBE 63 — recalibrate once/year, but possibly less often if used only occasionally and stored correctly and also depending on the amount of fouling and your ability to do some simple validations (see SBE 63 manual)
- pH sensor —
— SBE 18 pH sensor or SBE 27 pH/ORP sensor — recalibrate at the start of every cruise, and then at least once/month, depending on use and storage
— Satlantic SeaFET pH sensor — recalibrate at least once/year. See FAQ tab on Satlantic's SeaFET page for details (How often does the SeaFET need to be calibrated?).
- Transmissometer — usually do not require recalibration for several years. Recalibration at the manufacturer’s factory is the most practical method.
We often have requests from customers to have some way to know if the CTD is out of calibration. The general character of sensor drift in Sea-Bird conductivity, temperature, and pressure measurements is well known and predictable. However, it is very difficult to know precisely how far a CTD calibration has drifted over time unless you have access to a very sophisticated calibration lab. In our experience, an annual calibration schedule will usually maintain the CTD accuracy to within 0.01 psu in Salinity.
Conductivity drifts as a change in slope as a result of accumulated fouling that coats the inside of the conductivity cell, reducing the area of the cell and causing an under-reporting of conductivity. Fouling consists of both biological growth and accumulated oils and inorganic material (sediment). Approximately 95% of fouling occurs as the cell passes through oil and other contaminants floating on the sea surface. Most conductivity fouling is episodic, as opposed to gradual and steady drift. Most fouling events are small and mostly transitory, but they have a cumulative affect over time. A severe fouling event, such as deployment through an oil spill, could have a dramatic but only partially recoverable effect, causing an immediate jump shift toward lower salinity. As fouling becomes more severe, the fit becomes increasingly non-linear and offsets and slopes no longer produce adequate correction, and return to Sea-Bird for factory calibration is required. Frequently checking conductivity drift is likely to be the most productive data assurance measure you can take. Comparing conductivity from profile to profile (as a routine check) will allow you to detect sudden changes that may indicate a fouling event and the need for cleaning and/or re-calibration.
Temperature generally drifts slowly, at a steady rate and predictably as a simple offset at the rate of about 1-2 millidegrees per year. This is approximately equal to 1-2 parts per million in Salinity error (very small).
Pressure sensor drift is also an offset, and annual comparisons to an accurate barometer to determine offset will generally keep the sensor within specification for several years, particularly as the sensors age over time.
Do I need to remove batteries before shipping my instrument for a deployment or to Sea-Bird?
Alkaline batteries can be shipped installed in the instrument. See Shipping Batteries for information on shipping instruments with Lithium or Nickel-Metal Hydride (NiMH) batteries.
What are the major steps involved in deploying a moored instrument?
Application Note 83: Deployment of Moored Instruments contains a checklist, which is intended as a guideline to assist you in developing a checklist specific to your operation and instrument setup.
What are the recommended practices for connectors - mating and unmating, cleaning corrosion, and replacing?
Mating and Unmating Connectors:
It is important to prepare and mate connectors correctly, both in terms of the costs to repair them and to preserve data quality. Leaking connectors cause noisy data and even potential system shutdowns. Application Note 57: Connector Care and Cable Installation describes the proper care and installation of connectors for Sea-Bird instruments. The Application Note covers connector cleaning and cable or dummy plug installation, locking sleeve installation, and cold weather tips.
Checking for Leakage and Cleaning Corrosion on Connectors:
If there has been leakage, it will show up as green-colored corrosion product. Performing the following steps can usually reverse the effect of the leak:
- Thoroughly clean the connector with water, followed by alcohol.
- Give the connector surfaces a light coating of silicon grease.
Re-mate the connectors properly — see Application Note 57: Connector Care and Cable Installation and 9-minute video covering O-ring, connector, and cable maintenance.
- The main concern when replacing a bulkhead connector is that the o-rings on the connector and end cap must be prepared and installed correctly; if they are not, the instrument will flood. See the question below for general procedure on handling o-rings.
- Use a thread-locking compound on the connector threads to prevent the new connector from loosening, which could also lead to flooding.
- If the cell guard must be removed to open the instrument, take extra care not to break the glass conductivity cell.
What are the recommended practices for storing sensors at low temperatures, and deploying at low temperatures or in frazil or pancake ice?
Large numbers of Sea-Bird conductivity instruments have been used in Arctic and Antarctic programs.
Special accommodation to keep temperature, conductivity, oxygen, and optical sensors at or above 0 C is advised. Often, the CTD is brought inside protective doors between casts to achieve this.
When freezing is possible, we recommend that the conductivity sensor be stored dry. Remove larger droplets of water by blowing through the cell. Do not use compressed air, which typically contains oil vapor. Attach a length of Tygon tubing to each end of the conductivity cell to close the cell ends. See Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells for details.
There are several considerations to weigh when contemplating deployments at low temperatures in general, and in frazil or pancake ice:
- Ensure that the instrument is at or above water temperature before it is deployed. If the cell gets colder than 0 to -2 ºC while on deck, when it enters the water a layer of ice forms inside the cell as the cell warms to ocean temperature. If ice forms inside the conductivity cell, measurements will be low of correct until the ice layer melts and disappears. Thin layers of ice will not hurt the conductivity cell, but repeated ice formation on the electrodes will degrade the conductivity calibration (at levels of 0.001 to 0.020 psu) and thicker layers of ice can lead to glass fracture and permanent damage of the cell.
- For accurate measurements, keep ice out of the sensing region of the conductivity cell. The conductivity measurement involves determining the electrical resistance of the water inside the sensor. Ice is essentially a non-conductor. To the extent that ice displaces the water, the conductivity will register (very) misleadingly low. Some type of screening is necessary to keep ice out of the cell. This is relatively easy to arrange for the Sea-Bird conductivity cell, which is an electrode-type cell, because its sensing region is totally inside a long tube; plastic mesh could be positioned at each end and would have zero effect on accuracy and stability.
The above considerations apply to all known conductivity sensor types, whether electrode or inductive types.
If deploying at low temperatures but no surface frazil or pancake ice is present, rinse the conductivity cell in one of the following salty solutions (salty water depresses the freezing point) to prevent freezing during deployment. But this does not mean you can store the cell in one of these solutions outside . . . it will freeze.
- Solution of 1% Triton in sterile seawater (use 0.5-micron filtered seawater or boiled seawater), or
- Brine solution (distilled seawater or homemade salt solution that is higher than 35 psu in salinity).
Note that there is still a risk of forming ice inside the conductivity cell if deploying through frazil or pancake ice on the surface, if the freezing point of the salt water is the same as the water temperature. Therefore, we recommend that you deploy the conductivity cell in a dry state for these deployments.
Commercially available alcohol or glycol antifreezes contain trace amounts of oils that will coat the conductivity cell and the electrodes, causing a calibration shift, and consequently result in errors in the data. Do not use alcohol or glycol in the conductivity cell.
In general, neither the accuracy of the temperature measurement nor the survival of the temperature sensor will be affected by ice.
For the SBE 43 and SBE 63 Dissolved Oxygen sensor, avoid prolonged exposure to freezing temperature, including during shipment. Do not store the with water (fresh or seawater), Triton solution, alcohol, or glycol in the plenum. The best precaution is to keep the sensor indoors or in some shelter out of the cold weather.
Many cables, mount kits, and spare parts can be ordered online.
- 801413 To computer COM port (from internal Molex connector), 2.4 m, DN 32779
- 801376 To computer COM port with 9V connector (from external XSG connector), 2.4 m, DN 32604
- 801385 To computer COM port with power leads (from external XSG connector), 2.4 m, DN 32277
- 801263 To computer COM port with 9V connector (from external Wet-pluggable connector), 2.4 m, DN 32490
- 801206 To computer COM port with power leads (from external Wet-pluggable connector), 2.4 m, DN 32366
- 50377 SBE 39 Cable Clamp Kit, 1/4-inch or 6-mm diameter
- 50378 SBE 39 Cable Clamp Kit, 5/16-inch or 8-mm diameter
- 50379 SBE 39 Cable Clamp Kit, 3/8-inch or 10-mm diameter
- 50380 SBE 39 Cable Clamp Kit, 1/2-inch or 12-mm diameter
- 50381 SBE 39 Cable Clamp Kit, 5/8-inch or 16-mm diameter
- 50423 SBE 39 Cable Clamp Kit, 3/4-inch or 19-mm diameter
- 50448 SBE 39 Cable Clamp Kit, 7/16-inch or 11.3-mm diameter
- 50523 SBE 39 Cable Clamp Kit, 9/16-inch or 14-mm diameter
- 50459 SBE 39 Cable Clamp Kit, 18-mm diameter
- 50534 SBE 39 Cable Clamp Kit, 20-mm diameter
Clamp Size Note: Mooring wire is typically specified by wire size, not by outer diameter (O.D.) of the mooring wire jacket. Verify the wire jacket O.D. before selecting the clamp size. The clamp size must be less than or equal to the wire jacket O.D. but larger than the wire diameter. For example, Mooring System Inc.’s specifications for 3x19 wire rope (in 2016) are as follows:
|Wire Diameter||Jacket Diameter||Recommended Sea-Bird Clamp|
|3/16 inch (5.0 mm)||0.255 inch (6.5 mm)||1/4 inch|
|1/4 inch (6.5 mm)||0.330 inch (8.4 mm)||5/16 inch|
|5/16 inch (8.0 mm)||0.392 inch (9.9 mm)||3/8 inch|
|3/8 inch (9.5 mm)||0.453 inch (11.5 mm)||10 mm (0.394 inch)|
|7/16 inch (11.1 mm)||0.5 inch (12.7 mm)||1/2 inch|
For mounting on a rope, verify the rope outer diameter, and select a clamp smaller than the rope O.D. to account for the rope compressibility (for example, for 5/16 inch rope, select a ¼ inch clamp; a 5/16 inch clamp will be too large).
- 22074 SBE 39 lithium battery, UltraLife U9VL, 9V
- varies Cable clamp kit for SBE 39, for use with or without fairing/net fender (document 67162 & drawing 41396)
- 60042 Spares kit for SBE 39 with serial number > 3000 (document 67159)
- 60032 Spares kit for SBE 39 with serial number < 3000 (document 67028)
- 60032.1 Spares kit for SBE 39 with low pressure Paine pressure sensor (document 67085)
- 233186 High-head pressure port plug for muddy/biologically productive environments (for instrument with Druck pressure sensor) (Application Note 84)
- 31633 Storm shipping case (iM2600) — holds up to 4 SBE 39s with external connectors or 6 SBE 39s with internal connectors (does not hold SBE 39 with net fenders)
(Click here to see an example of where to find the serial number on your instrument.)