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The Chlorophyll-a (Chl-a) concentration in the surface layer of the Bohai Sea from 2003 to 2022 was obtained after processing the MODIS data with the improved shortwave infrared (SWIR) atmospheric correction algorithm and the Clack three-channel method. Its spatial and temporal variation were analyzed. The results show that it has obvious interannual spatial distribution characteristics, showing a trend of being high in nearshore waters and low in offshore waters, high in the estuarine bays and low in other sea areas. The interannual Chl-a variation shows an inverted U-shape. The year-by-year seasonal average spatial characteristics are basically consistent, with high in nearshore waters and low in other waters. The Chl-a in spring and summer was higher than that in autumn and winter. The temporal trend of the four seasons was similar to the interannual trend, showing an inverted U-shaped trend of first increasing, then stabilizing and then decreasing.

Seals, sea lions, and other aquatic animals rely on their whiskers to identify and track underwater targets, offering valuable inspiration for the development of low-power, portable, and environmentally friendly sensors. Here, we design a single seal-whisker-like cylinder and conduct experiments to measure the forces acting on it with nine different upstream targets. Using sample sets constructed from these force signals, a convolutional neural network (CNN) is trained and tested. The results demonstrate that combining the seal-whisker-style sensor with a CNN enables the identification of objects in the water in most cases, although there may be some confusion for certain targets. Increasing the length of the signal samples can enhance the results but may not eliminate these confusions. Our study reveals that high frequencies (greater than 5 Hz) are irrelevant in our model. Lift signals present more distinct and distinguishable features than drag signals, serving as the primary basis for the model to differentiate between various targets. Fourier analysis indicates that the model's efficacy in recognizing different targets relies heavily on the discrepancies in the spectral features of the lift signals. [ABSTRACT FROM AUTHOR]

A harbor seal's whisker is able to sense the trailing vortices of marine organisms due to its unique three-dimensional wavy shape, which suppresses the vibrations caused by its own vortex-shedding, while exciting large-amplitude and synchronized vibrations in a wake flow. This provides insight into the development of whisker-inspired sensors, which have broad applications in the fields of ocean exploration and marine surveys. However, the harbor seal's whisker may lose its vibration suppression ability when the angle of attack (AoA) of the incoming flow is large. In order to explore the flow-induced vibration (FIV) features of a harbor seal's whisker at various angles of attack ( θ = 0 – 90 ∘ ), this study experimentally investigates the effect of AoA on the vibration response of a whisker model in a wide range of reduced velocities ( U r = 3–32.2) and the Reynolds number, Re = 400–7000, in a circulating water flume. Meanwhile, for the sake of comparison, the FIV response of an elliptical cylinder with the same equivalent diameters is also presented. The results indicate that an increase in AoA enhances the vibration amplitude and expands the lock-in range for both the whisker model and the elliptical cylinder. The whisker model effectively suppresses vibration responses at θ = 0 ∘ due to its unique three-dimensional wavy shape. However, when θ ≥ 30 ∘ , the wavy surface structure gradually loses its suppression ability, resulting in large-amplitude vibration responses similar to those of the elliptical cylinder. For θ = 30 ∘ and 45 ∘ , the vibration responses of the whisker model and the elliptical cylinder undergo three vibration regimes, i.e., vortex-induced vibration, transition response, and turbulent-induced vibration, with the increasing U r . However, at θ = 60 ∘ and 90 ∘ , the vortex-shedding gradually controls the FIV response, and only the vortex-induced vibration is observed. [ABSTRACT FROM AUTHOR]