The TETHYS mass spectrometer is intended for long-term in situ observation of dissolved gases and volatile organic compounds in aquatic environments. Its design maintains excellent low mass range sensitivity and stability during long-term operations, enabling characterization of low-frequency variability in many trace dissolved gases. Results are presented from laboratory trials and a 300-h in situ trial in a shallow marine embayment in Massachusetts, U.S.A. This time series consists of over 15000 sample measurements and represents the longest continuous record made by an in situ mass spectrometer in an aquatic environment. These measurements possess sufficient sampling density and duration to apply frequency analysis techniques for study of temporal variability in dissolved gases. Results reveal correlations with specific environmental periodicities. Numerical methods are presented for converting mass spectrometer ion peak ratios to absolute-scale dissolved gas concentrations across wide temperature regimes irrespective of ambient pressure, during vertical water column profiles in a hypoxic deep marine basin off the coast of California, U.S.A. Dissolved oxygen concentration values obtained with the TETHYS instrument indicate close correlation with polarographic oxygen sensor data across the entire depth range. These methods and technology enable observation of aquatic environmental chemical distributions and dynamics at appropriate scales of resolution.

Identification and tracking of hydrocarbons in the marine environment is challenging. State of the art systems typically rely on surface slicks to identify hydrocarbon contamination such as oil spills. Subsurface detection remains challenging. This paper describes the TETHYS in-situ mass spectrometer and results of real-world deployments. TETHYS is a small, self contained mass spectrometer capable of operation to 5000 meters depth. The TETHYS instrument can quantitatively identify a wide range of hydrocarbons at trace concentrations (minimum limits of detection typically 500 parts-per-trillion) in the subsurface environment. TETHYS has been successfully deployed on AUVs, ROVs, towfish, manned submersibles, and with divers for a variety of purposes, including deep ocean scientific exploration and mapping missions as well as commercial offshore oil and gas leak detection and cleanup.

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A B S T R A C TThis technical paper describes existing capabilities and new research results for autonomous underwater vehicles (AUVs) for use in locating, characterizing, and monitoring underwater munitions. The authors introduce advances in sensor technologies and search methods pertinent to AUV-based underwater munition mitigation operations. Results are presented from a series of trials using in situ chemical sensors to detect both conventional and nonconventional underwater munitions in real time. These technologies are considered within the context of chemical plume tracing and biomimetic search algorithms. This paper concludes with a look toward future AUV sensor payloads with more extensive real-time situation awareness. Advancement of these technologies and methods will be critical for realizing the potential of AUV platforms to manage the risks posed by underwater munitions sites.