Effect of viewing angle difference on spaceborne optical estimation of floating Ulva prolifera biomass in the Yellow Sea.

Optical remote sensing provides optimal technical support for the detection and quantification of floating macroalgae. Although the spatial scale effect on optical estimation of floating macroalgae coverage or biomass from different images has been clarified, the directional effect on them has not been investigated until now. In this study, synchronous multi-angle imaging spectroradiometer (MISR) and MODIS images were collected to investigate the multi-angle remote sensing of green tides. A dual thresholding method, based on the difference vegetation index (DVI) and scaled algae index, was employed to determine algae pixels. In addition, piecewise empirical models were developed for MISR and MODIS images to estimate the total biomass of green tides based on laboratory measurements and DVI values. Comparative analysis of DVI histograms and total biomass shows that the sensor zenith angle has a significant impact on the quantification of green tides. Under the same solar conditions, as the sensor zenith angle increases, the optical signals received from algae pixels weaken, resulting in a decrease in the quantification of green tides. In future research, the observation geometry (including the solar/sensor zenith angle and the solar/sensor azimuth angle) needs to be considered to improve the accuracy of optical remote detection and quantification of floating macroalgae.

Sunglint reflection facilitates performance of spaceborne UV sensor in oil spill detection.

Ultraviolet Imager (UVI) onboard Haiyang-1C/D (HY-1C/D) satellites has been providing ultraviolet (UV) data to detect marine oil spills since 2018. Although the scale effect of UV remote sensing has been preliminarily interpreted, the application characteristics of spaceborne UV sensors with medium spatial resolution in oil spill detection deserve further investigation, especially the role of sunglint in the process of detection. In this study, the performance of the UVI is thoroughly assessed by the following aspects: image features of oils under sunglint, sunglint requirement for spaceborne UV detection of oils, and the stability of the UVI signal. The results indicate that in UVI images, it is sunglint reflection that determines the image features of spilled oils, and the appearance of sunglint can strengthen the contrast between oils and seawater. Besides, the required sunglint strength in spaceborne UV detection has been deduced to be 10-3 - 10-4 sr-1, which is higher than that in the VNIR wavelengths. Moreover, uncertainties in the UVI signal can meet the demand to discriminate between oils and seawater. The above results can confirm the capability of the UVI and the critical role of sunglint in spaceborne UV detection of marine oil spills, and provide new reference for spaceborne UV remote sensing.

Accelerated oxidation of VOCs via vacuum ultraviolet photolysis coupled with wet scrubbing process.

Vacuum ultraviolet (VUV) photolysis is a facile method for volatile organic compounds (VOCs) elimination, but is greatly limited by the relatively low removal efficiency and the possible secondary pollution. To overcome above drawbacks, we developed an efficient method for VOCs elimination via VUV photolysis coupled with wet scrubbing process. In this coupled process, volatile toluene, a representative of VOCs, was oxidized by the gas-phase VUV photolysis, and then scrubbed into water for further oxidation by the liquid-phase VUV photolysis. More than 96% of toluene was efficiently removed by this coupled process, which was 2 times higher than that in the gas-phase VUV photolysis. This improvement was attributed to the synergistic effect between gas-phase and liquid-phase VUV photolysis. O3 and HO• are the predomination reactive species for the toluene degradation in this coupled process, and the generation of O3 in gas-phase VUV photolysis can efficiently enhance the HO• production in liquid-phase VUV photolysis. The result from in-situ proton transfer reaction ionization with mass analyzer (PTR-MS) further suggested that most intermediates were trapped by the wet scrubbing process and efficiently oxidized by the liquid-phase VUV photolysis, showing a high performance for controlling the secondary pollution. Furthermore, the result of stability test and the reuse of solution demonstrated that this coupled process has a highly stable and sustainable performance for toluene degradation. This study presents an environmentally benign and highly efficient VUV photolysis for gaseous VOCs removal in the wet scrubbing process.

Ultraviolet remote sensing of marine oil spills: a new approach of Haiyang-1C satellite.

Haiyang-1C (HY-1C) is the first operational ocean color satellite of China, which is intended to obtain daily global ocean color data. The Ultraviolet Imager (UVI) onboard provides a potential novel detector for the detection of marine oil spills. Although airborne UV sensors have shown great efficiency for the detection of spilled oils, the capability of spaceborne UV sensor is not yet clear. In this study, we designed a ground-based experiment to interpret the UV characteristics of various weathered oils, and found that very thin oil films are quite sensitive to the UV radiation due to the surface interference light. Moreover, by comparing spaceborne and airborne UV images of spilled oils collected from HY-1C UVI and AVIRIS, the scale effect of ultraviolet remote sensing has been interpreted clearly. The interference light and sunglint reflection play different roles in the imaging process of spilled oils, leading them to appear radical different features (brighter or darker than the background oil-free seawater) in ground, airborne and spaceborne observation, which deserves further research. Ultraviolet remote sensing, therefore, can work as a new approach and improve the detection and monitoring of marine oil spills.

Tunable Interfacial Electronic Pd-Si Interaction Boosts Catalysis via Accelerating O2 and H2O Activation.

Engineering the interfacial structure between noble metals and oxides, particularly on the surface of non-reducible oxides, is a challenging yet promising approach to enhancing the performance of heterogeneous catalysts. The interface site can alter the electronic and d-band structure of the metal sites, facilitating the transition of energy levels between the reacting molecules and promoting the reaction to proceed in a favorable direction. Herein, we created an active Pd-Si interface with tunable electronic metal-support interaction (EMSI) by growing a thin permeable silica layer on a non-reducible oxide ZSM-5 surface (termed Pd@SiO2/ZSM-5). Our experimental results, combined with density functional theory calculations, revealed that the Pd-Si active interface enhanced the charge transfer from deposited Si to Pd, generating an electron-enriched Pd surface, which significantly lowered the activation barriers for O2 and H2O. The resulting reactive oxygen species, including O2 -, O2 2-, and -OH, synergistically facilitated formaldehyde oxidation. Additionally, moderate electronic metal-support interaction can promote the catalytic cycle of Pd0 ⇆ Pd2+, which is favorable for the adsorption and activation of reactants. This study provides a promising strategy for the design of high-performance noble metal catalysts for practical applications.

HY-1C ultraviolet imager captures algae blooms floating on water surface.

Some species of algae such as cyanobacteria can vertically migrate through water during a day, which is a notable floating feature of harmful algae blooms. To date, this process has been observed and quantified using visible and near-infrared (VNIR) bands from spaceborne sensors with high temporal resolution (i.e., Geostationary Ocean Color Imager; GOCI). In this study, we conducted an in-situ measurement at Taihu Lake in China to investigate the ultraviolet (UV) reflection spectra of floating cyanobacteria blooms, and identified that they have significant UV reflection features (higher than that of background water) associated with their floating status. This has been demonstrated using spaceborne UV images at both 355 and 385 nm from the Ultraviolet Imager (UVI) onboard Haiyang-1C (HY-1C) of China. Compared with synchronous optical images from the Chinese Ocean Color and Temperature Scanner (COCTS), we found that UVI has a special ability to distinguish cyanobacteria floating on water surface. Additionally, the intensity of the UV signals obtained is positively correlated with the cyanobacterial equivalent density. Ultraviolet remote sensing, therefore, can work as a new approach for the detection of harmful algae blooms and help determine the floating status of them, which deserves further research.