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.

NOTE: Newer firmware is now available here. [SeaFET Firmware v3.6.4 - November 2016]

The SeaFET™ reports pH determined potentiometrically in two different ways.  The ISFET potential is measured against a reference electrode bearing a liquid junction (internal reference) and against a solid state reference electrode without a liquid junction (external reference).  This approach provides the user with the ability to quality assess instrument performance and ultimately achieve a greater understanding of the state of acid/base equilibria in seawater.

The SeaFET™ Ocean pH sensor has been used extensively for:

  • ocean acidification research
  • coral reef research
  • coastal marine biology
  • environmental monitoring.

The SeaFET™ Ocean pH Sensor was developed by Dr. Kenneth Johnson of the Monterey Bay Aquarium Research Institute (MBARI) and Dr. Todd Martz of the Scripps Institution of Oceanography, University of California San Diego.  We collaborated with MBARI and Scripps to make the instrument commercially available to the research community. SeaFET™ sensors have now been deployed in many locations, including Canada, USA, France, UK, Australia and China.

The sensing element of the SeaFET™ is an ion sensitive field effect transistor (ISFET).  This class of device has been used for pH sensing in industrial processes, food processing, clinical analysis and environmental monitoring. The advantages of the ISFET include robustness, stability and precision that make it suitable for ocean pH measurement at low pressure.

Replacing a SeaFET™ Ocean pH Sensor Battery (Note this is an older model)

Click on the Image to Watch the Video


Measurement Range6.5 - 9.0 pH
Initial Accuracy± 0.05 pH
Typical Stability0.003 pH/month
Precision0.004 pH
Internal Memory4 GB                                                                        
Supply Voltage Range 6 - 18 VDC
CommunicationRS-232, USB
Weight (with batteries)5.4 kg in air; 0.1 kg in water
Dimensions (Housing)Diameter 508 mm (20") x 114 mm (4.8")
Maximum Depth50 m
Temperature Range0 to 50 deg C


The Satlantic SeaFET™ Ocean pH Sensor comes complete with SeaFETCom, an interactive graphic software application. Connect the SeaFET™ to your computer via the supplied USB programming cable to enjoy these SeaFETCom features:

  • Review and modify SeaFET™ operational settings
  • Schedule SeaFET™ data collection activity
  • Manage and retrieve logged SeaFET™ data
  • View SeaFET™ data in real time
  • Reprocess SeaFET™ data and graph results

SeaFETCom provides all the tools necessary to configure and operate your SeaFETpH sensor for any deployment scenario. Manage on-board data storage, processing, and collection modes. Set up real time data streaming via USB or RS-232. Capture and plot data in real time for pre-deployment checks or interactive profiling casts. Re-process logged pH data using ancillary temperature and salinity inputs for improved accuracy.

Download SeaFETCom 1.2.4 1.2.4

Released January 4, 2015

SeaFETCom 1.2.4 is compatible with V1.0 SeaFET running firmware 3.6.0 and later.

File SeaFETCom-1.2.4-b51-x86.exe for Microsoft Windows


You may access the older SeaFETCom 1.1.3: Windows | Mac

Product Brochure

Sea-Bird Scientific Ocean pH Sensors

Wednesday, October 19, 2016
PDF icon Ocean-pH-Sensors-2016.pdf
Product Data Sheet

SeaFET™ Ocean pH Sensor Datasheet

Tuesday, January 24, 2017
PDF icon datasheet-seafet-01242017.pdf
Product Manual

SeaFET 1.2.4 Manual

Thursday, January 8, 2015
PDF icon SeaFET-1.2.4-Manual_0.pdf
Product Manual

SeaFET 1.1.3 Manual

Friday, February 28, 2014
PDF icon SeaFET-1.1.3-Manual.pdf
White Paper

ONC Ocean pH Sensor Verification Report 2015

Wednesday, January 25, 2017
PDF icon ONC Ocean pH Sensor Verification Report 2015.pdf

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.

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.

  • Philip J. Bresnahan Jr., Todd R. Martz, Yuichiro Takeshita, Kenneth S. Johnson, Makaila LaShomb (2014) Best practices for autonomous measurement of seawater pH with the Honeywell Durafet Methods in Oceanography 9 44-60 Read Now
  • Price, N.N., Martz, T.R., Brainard, R.E., Smith, J.E. (2012) Diel Variability in Seawater pH Relates to Calcification and Benthic Community Structure on Coral Reefs PLoS ONE 7(8): e43843 doi:10.1371/journal.pone.0043843 Read Now
  • Hofmann, G. E., J. E. Smith, K. S. Johnson, U. Send, L. A. Levin, F. Micheli, A. Paytan, N. N. Price, B. Peterson, Y. Takeshita, P. G. Matson, E. D. Crook, K. J. Kroeker, M. C. Gambi, E. B. Rivest, C. A. Frieder, P. C. Yu, and T. R. Martz. (2011) High-Frequency Dynamics of Ocean pH: A Multi-Ecosystem Comparison PLoS ONE 6(12): e28983. doi:10.1371/journal.pone.0028983 Read Now
  • Kroeker, K. J., F. Micheli, M. C. Gambi, and T. R. Martz. (2011) Divergent ecosystem responses within a benthic marine community to ocean acidification Proceedings of the National Academy of Sciences (PNAS) 108(35), 14515-14520 doi:10.1073/pnas.1107789108 Read Now
  • Matson, P. G., T. R. Martz, and G. E. Hofmann. (2011) High-frequency observations of pH under Antarctic sea ice in the southern Ross Sea Cambridge Journals Online 23(6) 607-613 doi:10.1017/S0954102011000551 Read Now
  • Yu, P. C., P. G. Matson, T. R. Martz, and G. E. Hofmann (2011) The ocean acidification seascape and its relationship to the performance of calcifying marine invertebrates: Laboratory experiments on the development of urchin larvae framed by environmentally-relevant pCO2/pH Journal of Experimental Marine Biology and Ecology 400, 288–295 Read Now
  • Martz. T, Connery J.G., Johnson, K.S (2010) Testing the Honeywell Durafet® for seawater pH applications Limnol. Oceanogr 172-184 doi:10.4319/lom.2010.8.172 Read Now

Flow Cell

It is essential that the SeaFET™ sensing elements remain immersed in seawater at all times.  For this reason, the SeaFET™ is equipped with a resealable flow cell. The flow cell can be fitted with brass penetrating fittings and copper-nickel tubes to which one can attach flexible tubing or hoses for flow-through applications (Image shows one fitting attached and one not).



Bio-fouling Guard

The SeaFET™ bio-fouling guard is a copper based passive fouling prevention guard. The anti-fouling guard provides a reliable and affordable approach to increase deployment time, decrease operating costs, and collect high quality data for mooring applications. 



Internal Battery Pack (For earlier models)

The SeaFET™ internal battery pack contains seven Alkaline D-Cell batteries connected in series to provide nominal 10.5 V. The nominal capacity, 19.8 mAh specified by the battery manufacturer is attained under ideal operating conditions.




Alkaline Battery Pack

Satlantic's reliable and user-friendly Alkaline Battery Packs are available in 102 Ah and 51 Ah capacities. The design of the internal battery compartment allows the user to easily change the D-Cell batteries with off-the-shelf replacements. The battery packs consist of an anodized aluminum pressure case, a D-cell battery compartment and a removable end-cap.