Page 20: of Marine Technology Magazine (March 2013)

Instrumentation: Measurement, Processing & Analysis

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infrared detector (NDIR-detector) and the principle of absorption spectrometry (1). To overcome the temperature de- pendency of the NDIR sensors, the de- tector is temperature stabilized and the gas is lead through a heater before en-tering the NDIR unit both during initial instrument calibration as well as during operation in the Þ eld. To compensate for the long term drift of the sensor, a Òzero pointÓ reference is routinely taken by the NDIR-detector within the instru-ment after the air within the gas stream has been chemically freed from CO2 or CH4. This zero reference data can be used to track the temporal signal drift of the NDIR-detector and allows for the derivation of the sensorÕs actual re- sponse time (2). The HydroCO2 and HydroCH4 physi-cal packaging allows for a wider range of deployment possibilities than previous- ly available with existing dissolved CO2 and CH4 measurement systems. When conÞ gured as a ß ow through system in- side of a vessel or within a laboratory, these instruments have a signiÞ cantly reduced maintenance effort and smaller size than prevailing underway systems that use large equilibration chambers and bottles of reference gasses. Use of the HydroCO2 and HydroCH4 systems enable deployment from smaller ves- sels, adding a valuable measurement parameter while reducing the energy and space requirements (e.g., less room occupied in a vesselÕs wet lab). When conÞ gured as a self-contained submers- ible system, the systems will operate from water surface to 6000m of depth. The 9 cm diameter pressure housing on the system allows for easy deployment on buoys, moorings, AUVÕs, gliders and Argo ß oats (2 and 3). Example of a bottom lander deployment combining an ADCP and the HydroCH4 sensor is shown here. Instrumentation Left: A bottom lander deployment combining an ADCP and the HydroCH4 sensor. March 2013 20 MTRMTR #2 (18-33).indd 20MTR #2 (18-33).indd 203/5/2013 4:02:38 PM3/5/2013 4:02:38 PM

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