Optimization study of metallic hole arrays as the multi-channel spectral filters in long-infrared wavelengths.

The development of miniaturized multi-channel infrared filters based on plasmonic metasurfaces is attracting growing attention, driven by its potential applications in infrared imaging, photodetectors, and spectroscopy. However, the advance of such filters in long-infrared wavelengths has rarely been reported. This paper reports our recent progress on developing multi-channel spectral filters based on micrometer metallic hole arrays in the long-infrared band of 10-15 µm. The effects of structural parameters and the shapes of metallic hole arrays on filtering performance are investigated by numerical simulations with the finite-difference time-domain method and then experimentally verified by optical characterizations of fabricated filters using electron beam lithography. The transmission peaks of the filter on a zinc selenide substrate were optimized with a maximum transmittance of 63%. A comparison of the hole shapes shows that elliptical holes give rise to sharper transmission peak quality than round ones by 28%. The progress achieved in this work should be a promising step in the development of metallic hole-based spectral filters with miniaturized dimensions.

Optimization study of metallic sub-wavelength gratings as the polarizer in infrared wavelengths.

Despite the polarimetric detection in the infrared wavelengths of 8-10 µm being of great importance and broad applications, there has been limited addressing of the grating-based polarizers in this band. One of the main issues lies in the process incompatibility between the conventional nanofabrication technique and the II-VI materials such as HgCdTe, so that the direct integration of polarizers with sensors still remains a big challenge. This paper reports our recent work on optimizing the grating structures, materials, and nanofabrication processes for enhancing both the transmittance and the extinction ratio of polarizers on Si and/or ZnSe wafers, using numerical simulations for the grating design and electron beam lithography for the nanoscale pattern generation. By utilizing the finite-difference time-domain method, both the transmittance and the extinction ratio are maximized by optimizing the grating geometric dimensions and the duty cycle for two different grating materials of Al and Au for comparison. Based on the designed structures, nanofabrications of sub-wavelength gratings in both Al and Au are carried out, and the processes are compared for achieving high polarization performance. Optical characterizations of the fabricated polarizers demonstrate that both high transmittance and extinction ratio can be achieved in feasible parameters and the nano-process developed in this work.

UAV remote sensing applications in marine monitoring: Knowledge visualization and review.

With the booming development of information technology and the growing demand for remote sensing data, unmanned aerial vehicle (UAV) remote sensing technology has emerged. In recent years, UAV remote sensing technology has developed rapidly and has been widely used in the fields of military defense, agricultural monitoring, surveying and mapping management, and disaster and emergency response and management. Currently, increasingly serious marine biological and environmental problems are raising the need for effective and timely monitoring. Compared with traditional marine monitoring technologies, UAV remote sensing is becoming an important means for marine monitoring thanks to its flexibility, efficiency and low cost, while still producing systematic data with high spatial and temporal resolutions. This study visualizes the knowledge domain of the application and research advances of UAV remote sensing in marine monitoring by analyzing 1130 articles (from 1993 to early 2022) using a bibliometric approach and provides a review of the application of UAVs in marine management mapping, marine disaster and environmental monitoring, and marine wildlife monitoring. It aims to promote the extensive application of UAV remote sensing in the field of marine research.

Can we quantify the aquatic environmental plastic load from aquaculture?

Aquaculture provides livelihoods for hundreds of millions of people, but it also forms a significant source of plastic litter that poses a serious hazard to aquatic ecosystems. How to assess and subsequently manage plastic loads from aquaculture is a pending and pressing issue for aquaculture sustainability, and an important concern for water environment monitoring and management. In this study, we developed the first framework for estimating plastic litter from aquaculture by combining data from satellite remote sensing, drones, questionnaires, and in situ measurements. By acquiring multidimensional (human and nature) and multiscale (centimeter to basin scale) data, this framework helped us understand the aquaculture farming patterns and its spatial and temporal evolution, and thus estimate the plastic load it generates and suggest effective management approaches. Applying this framework, we assessed the marine plastic load from oyster floating raft farming in the Maowei Sea, a typical mariculture bay in China, with an increasing farming area. Approximately 3840 tons of plastic waste is expected to be discharged into the sea in the next four years (the average service life of a floating raft) without improvements in aquaculture waste management. Strengthening governance, timely plastic removal, innovative replacement, and transforming farmers' behavior patterns are recommended as the subsequent measures for plastic management. This framework can be extended to other regions and other aquaculture patterns, and is applicable to local, regional, and global aquaculture plastic litter assessments. It is a source-based method for evaluating plastic pollution that is more conducive to subsequent plastic management than traditional post-contamination environmental monitoring. In the context of the global expansion of mariculture and the global commitment to action to combat plastic pollution, this approach could play a critical role in the investigation and management of plastic waste in aquatic environments.

Microcontinent subduction and S-type volcanism prior to India-Asia collision.

Continental crust has long been considered too buoyant to be subducted beneath another continent, although geophysical evidence in collision zones predict continental crust subduction. This is particularly significant where upper continental crust is detached allowing the lower continental crust to subduct, albeit the mechanism of such subduction and recycling of the upper continental crust remain poorly understood. Here, we investigate Paleocene S-type magmatic and volcanic rocks from the Linzizong volcanic succession in the southern Lhasa block of Tibet. These rocks exhibit highly enriched 87Sr/86Sr, 207Pb/206Pb and 208Pb/206Pb together with depleted 143Nd/144Nd isotope ratios. The geochemical and isotopic features of these rocks are consistent with those of modern upper continental crust. We conclude that these Paleocene S-type volcanic and magmatic rocks originated from the melting of the upper continental crust from microcontinent subduction during the late stage of India-Asia convergence.

Cetaceans and microplastics: First report of microplastic ingestion by a coastal delphinid, Sousa chinensis.

In the Anthropocene, marine microplastic debris has been rapidly increasing and interacting with wildlife. As apex predators, cetaceans have been proven to be ideal sentinel species to indicate ecosystem changes and umbrella and flagship species to help develop environmental management strategies. Here, we report the presence of microplastics in the intestines of Sousa chinensis for the first time, which highlights the potential impacts of microplastic pollution in coastal environments. Microplastics were detected in the intestinal contents of both adult and calf individuals, indicating that consumption of prey and unintentional ingestion are the potential pathways for microplastic accumulation in Sousa chinensis. The properties of the microplastics indicated that fibers, white and blue items, 1-5 mm items, and polyester were the predominant shapes, colors, sizes and plastic materials, respectively. More microplastics were detected in the foreguts and midguts than in the hindguts, which may be correlated with the specific intestinal structure of Sousa. This study indicates that coastal delphinids might suffer from microplastic pollution, even young calves. The sample size in this study is limited, whereas it's a starting point for assessing microplastics in the endangered coastal delphinid, Sousa. We suggest that assessments of the risks of microplastic consumption by cetaceans and the presence of microplastics in their habitats should be conducted at a global scale. Moreover, further works should be done to look for evidence of adverse effects of microplastics pollution on cetaceans.