References:
Environment Agency - R &D Technical Summary E1  (download pdf)
Plymouth Marine Laboratory - Marine Biogeochemistry-Ocean Acidification (link to PML site)
Southampton Oceanography Centre (link to SOC site)

In collaboration with The UK Environment Agency and
Plymouth Marine Laboratory this system was designed
to support pollution and toxicology studies in marine estuaries.
Two versions were developed, one for permanent bulkhead
mounting in small coastal vessels, and another portable version
for up-stream use in small boats.

The systems are capable of extreme accuracy and long term stability,
giving a precision of  +/- 0.01pH unit across the salinity range
1 to 40 ppt combined with temperature precision to 0.02 deg C.

Although the project with its original remit expired some 10 years ago,
these systems have now found a new life as as surface acidity monitors
in air-sea gas exchange measurements.

They have recently been
fully restored and serviced by Ruthern Instruments.