SeaFET pH Ocean Sensor

SeaFET™ Ocean pH Sensor

The SeaFET™ Ocean pH sensor is an ion selective field effect transistor (ISFET) type sensor for accurate long-term pH measurements in salt water.

Do I need accurate salinity and temperature data to correct the SeaFET™ pH output?

The acquisition of conductivity/salinity data alongside the SeaFETTM is recommended.  The acquisition of temperature data is not necessary as the SeaFETTM performs temperature measurements. Typically, conductivity and temperature measurements are combined in standard sensor packages.  One can use an external temperature measurement calibrated to a relevant scale to confirm the accuracy of the SeaFETTM temperature measurement.  The proximity of the two sensors, as well as, the abruptness of spatial gradients in temperature are both important considerations.

Which pH scale is relevant to the SeaFET™ Ocean pH sensor?

The SeaFETTM reports pH measurements on the total scale. Values of pH reported on the total scale represent the effective hydrogen ion concentration with contributions from both free hydrogen ions and those which have reacted with sulfate.

How often does the SeaFET™ need to be calibrated?

The stability of the SeaFETTM Ocean pH sensor is expected to be 0.005 pH units on the timescale of weeks to months (Martz et al. 2010). At minimum, the SeaFETTM should be calibrated yearly.  The body of data collected by the community of SeaFETTM users generally suggests that the stability of the ISFET-based pH measurement offers an improvement by orders of magnitude when compared to glass electrode based pH sensors. 

Wherever possible the SeaFETTM should be deployed in association with a water sampling program in order to collect water for spectrophotometric pH determination or another external measurement technique.  Additionally, coincident measurement of multiple carbonate system parameters, allow the stability of the SeaFETTM to be assessed.  These approaches have been carried out by a number of researchers over the past several years.

 

What is the response time of the SeaFET™ sensor?

The SeaFET™ samples at a rate of approximately one sample every 3 seconds. When in scheduled mode the instrument wakes up from low power sleep and is ready to take the first sample in approximately 3 seconds.

Can the SeaFET™ pH sensor be deployed with a pump?

Yes, the SeaFET™ pH sensor comes with a flow through cell with fittings that can be plumbed with a pump for flow-through operations. For in situ deployments, we recommend the Sea-Bird 5P submersible pump.

Can I integrate the SeaFET™ with a CTD?

The SeaFETTM outputs serial data in real-time that can be integrated with any data logger with a free serial port. The SeaFETTM can be integrated with an SBE 16plus V2 SeaCAT CTD Recorder or an SBE 19plus V2 SeaCAT Profiler CTD (in moored mode). In situations where a free serial port is not available, the SeaFETTM logs time-stamped data internally, that can be matched with CTD data during post processing.

Will the SeaFET™ work in high latitude regions?

Yes, provided the SeaFETTM sensing elements remain ice-free, the instrument works across the broad temperature range of 0 to 50 deg C. The original SeaFETTM prototypes developed at MBARI and SCRIPPS were deployed extensively in the Antarctic for several studies. For example times series data, please see Matson et al. 2011.