The Channelized Optical System (CHANOS) II is an autonomous, in situ sensor capable of measuring seawater dissolved inorganic carbon (DIC) and pH simultaneously in high frequency (up to ~1 Hz). Built on the original CHANOS technology, CHANOS II uses similar spectrophotometric principles to make both DIC and pH measurements with fast detection response times. A modular design is used to accommodate multiple measurement channels in a single instrument and expand the sensor’s capability (e.g., adding spectrophotometric pCO2 and total alkalinity (TA) measurement channels) in the future. In situ deployments demonstrate the sensor’s capabilities in both time-series measurements and water-column profiling in highly dynamic marine environments, such as coastal systems and deep coral reefs. CHANOS II has achieved an accuracy and precision that is close to the climate-measurement quality. The sensor can also perform calibration in situ using Certified Reference Materials (CRMs) to ensure measurement quality. As a result, the system is versatile and suitable for deployment on mobile and stationary platforms, such as moorings, profilers, AUVs, and ROVs.
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