HydroC underwater CO2 (Contros Systems and Solutions GmbH)

Field of research: Experimentation

Institution: GEOMAR Helmholtz-Center for Ocean Research, KIMOCC, GEOMAR-Benthic Ecology
Contact: Dr. Claas Hiebenthal
Location: Düsternbrooker Weg 17 / Geomar-Pier


The instrument measures the CO2 mole fraction in a headspace behind a membrane equilibrator with a two-wavelength non-dispersive infra-red detector (NDIR). The equilibrator is composed of a flat silicone composite membrane, the NDIR unit and additional sensors for pressure, temperature and relative humidity used to correct the NDIR signal and calculate the partial pressure. A small internal pump insures the continuous circulation of air in the equilibrator. To correct the drifting of the instrument with time, regular zeroings are automatically performed by scrubbing the CO2 from the internal gas stream. The zeroings are accounted during post processing of the data. The instrument is calibrated by the manufacturer. In order to achieve a constant and sufficiently short response time of the instrument, the HydroCTM is equipped with a water pump (Sea-Bird Electronics, USA) that provides a continuous water flow of approx. 35 ml sec21 to the membrane, leading to a response time T63% of 3 min and a T99% of approximately 15 min. However, good accuracy has been demonstrated without the use of the pump. The need for deconvolution of the signal is therefore important.

Technical Data

See manufacturer data www.contros.eu


Accuracy in test tanks at varying salinity, temperature and pCO2 (bubbling in the tank of CO2 modified air): using as base Baltic Sea water.

Large discrepancy is visible between pCO2 calculated from discrete samples (pCO2=f(TA, DIC) at high pCO2. This appears to be a problem coming from the discrete samples analysis and / or calculations and not from the sensor.


Long and short term measurement of pCO2 in aqueous environments. Autonomous deployment requires a battery pack.