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Rain falling on the ocean creates acoustic signals. Ma and Nystuen [(2005). J. Atmos. Oceanic Technol. 22, 1225–1248] described an algorithm that compares three narrowband "discriminant" frequencies to detect rain. In 2022, Trucco, Bozzano, Fava, Pensieri, Verri, and Barla [(2022). IEEE J. Oceanic Eng. 47(1), 213–225] investigated rain detection algorithms that use broadband spectral data averaged over 1 h. This paper implements a rainfall detector that uses broadband acoustic data at 3-min time resolution. Principal Component Analysis (PCA) reduces the dimensionality of the broadband data. Rainfall is then detected via a Linear Discriminant Analysis (LDA) on the data's principal component projections. This PCA/LDA algorithm was trained and tested on 5 months of data recorded by hydrophones in a shallow noisy cove, where it was not feasible to average spectral data over 1 h. The PCA/LDA algorithm successfully detected 78 ± 5% of all rain events over 1 mm/h, and 73 ± 5% of all rain events over 0.1 mm/h, for a false alarm rate of ≈ 1% in both cases. By contrast, the Ma and Nystuen algorithm detected 32 ± 5% of the rain events over 1.0 mm/h when run on the same data, for a comparable false alarm rate. [ABSTRACT FROM AUTHOR]

Thiols were determined in coastal waters of the western North Sea and English Channel. Detection was carried out on-board ship on-line by flow-analysis with detection by cathodic stripping voltammetry and calibration with thiourea. The thiol concentrations ranged from 0.70 to 3.60 nM (thiourea equivalents) and were found to vary over a relatively short distance perpendicular to the coast. Low concentrations in the area of greatest estuarine input (the Humber-Wash area) indicated that the thiols did not originate from low-salinity waters. Instead, variations in the thiol concentration were found to parallel those of chlorophyll. This correlation was confirmed by depth profiles which showed a trend for the thiols similar to that of chlorophyll. The data demonstrates that thiols are more widespread than anticipated, and that marine phytoplankton is an important source of the thiols. In view of their known ability to bind with metals, these data indicate that the thiols could be an important candidate to act as such ligands in the marine system. The measurements gave no evidence for the presence of sulfide in these waters which means that it must be present at less than 20% of the detected thiol levels.