Improvement of Atmospheric Correction of Satellite Sentinel-3/OLCI Data for Oceanic Waters in Presence of Sargassum

The invasive species of brown algae Sargassum gathers in large aggregations in the Caribbean Sea, and has done so especially over the last decade. These aggregations wash up on shores and decompose, leading to many socio-economic issues for the population and the coastal ecosystem. Satellite ocean color data sensors such as Sentinel-3/OLCI can be used to detect the presence of Sargassum and estimate its fractional coverage and biomass. The derivation of Sargassum presence and abundance from satellite ocean color data first requires atmospheric correction; however, the atmospheric correction procedure that is commonly used for oceanic waters needs to be adapted when dealing with the occurrence of Sargassum because the non-zero water reflectance in the near infrared band induced by Sargassum optical signature could lead to Sargassum being wrongly identified as aerosols. In this study, this difficulty is overcome by interpolating aerosol and sunglint reflectance between nearby Sargassum-free pixels. The proposed method relies on the local homogeneity of the aerosol reflectance between Sargassum and Sargassum-free areas. The performance of the adapted atmospheric correction algorithm over Sargassum areas is evaluated. The proposed method is demonstrated to result in more plausible aerosol and sunglint reflectances. A reduction of between 75% and 88% of pixels showing a negative water reflectance above 600 nm were noticed after the correction of the several images.

The specific features of the thermal radiation of lake Kenon during freeze-up in the infrared band

This work is the study of the infrared images of Lake Kenon located in the city of Chita. The images were obtained from a satellite Lansat-8. The images revealed the thermal anomalies of the said internal water body. The anomalies consisted in the fact that areas of open water having negative temperature are formed in the lake in the winter period. The phenomenon may be caused both by surface supercooling of the lake water and by formation of water aerosol at the temperature below 0°C. The emergence of areas with supercooled water may be, paradoxical as it may sound, due to the impact of the thermal power plant located near the lake. Its functioning prevents formation of the ice cover, especially at the locations of warm water discharge. Analysis of the satellite images in the IR-band obtained over the recent five years has shown the area of the higher water temperature on the lake surface not to exceed 10% of the total area of the lake. The time before the freeze-up in the absence of wind, October – November, is the best time for revealing the maximum temperature difference.

Percepción remota y procesamiento de imágenes para la gestión de cultivos de caña de azúcar

This research work shows that with the use of remote sensing technology it is possible to more effectively fulfill two of the purposes pursued by farmers in the field; manage crops more efficiently and include environmental care in decision-making. Specifically, remote sensing is applied in the context of precision agriculture through geographic information systems (GIS), unmanned aerial vehicles (UAV), multispectral sensors that capture the reflectance of the infrared band of the light spectrum (for interpretation of the biochemical state of the crop), global geopositioning systems (GPS), among others. This study limits the use of this technology to the processing of multispectral images obtained by aerial photogrammetry, and its subsequent treatment for the generation of orthoimages, the calculation of the NDVI vegetation index and the classification of land cover by clustering. Finally, the effect of classification with RGB and multispectral images is analyzed.

Gold Enhanced Graphene-Based Photodetector on Optical Fiber with Ultrasensitivity over Near-Infrared Bands

Graphene has been widely used in photodetectors; however its photoresponsivity is limited due to the intrinsic low absorption of graphene. To enhance the graphene absorption, a waveguide structure with an extended interaction length and plasmonic resonance with light field enhancement are often employed. However, the operation bandwidth is narrowed when this happens. Here, a novel graphene-based all-fiber photodetector (AFPD) was demonstrated with ultrahigh responsivity over a full near-infrared band. The AFPD benefits from the gold-enhanced absorption when an interdigitated Au electrode is fabricated onto a Graphene-PMMA film covered over a side-polished fiber (SFP). Interestingly, the AFPD shows a photoresponsivity of >1 × 104 A/W and an external quantum efficiency of >4.6 × 106% over a broadband region of 980–1620 nm. The proposed device provides a simple, low-cost, efficient, and robust way to detect optical fiber signals with intriguing capabilities in terms of distributed photodetection and on-line power monitoring, which is highly desirable for a fiber-optic communication system.

Optical Properties of C−rich (12C, SiC and FeC) Dust Layered Structure of Massive Stars

The composition and structure of interstellar dust are important and complex for the study of the evolution of stars and the interstellar medium (ISM). However, there is a lack of corresponding experimental data and model theories. By theoretical calculations based on ab-initio method, we have predicted and geometry optimized the structures of Carbon-rich (C-rich) dusts, carbon (12C), iron carbide (FeC), silicon carbide (SiC), even silicon (28Si), iron (56Fe), and investigated the optical absorption coefficients and emission coefficients of these materials in 0D (zero−dimensional), 1D, and 2D nanostructures. Comparing the nebular spectra of the supernovae (SN) with the coefficient of dust, we find that the optical absorption coefficient of the 2D 12C, 28Si, 56Fe, SiC and FeC structure corresponds to the absorption peak displayed in the infrared band (5−8) µm of the spectrum at 7554 days after the SN1987A explosion. And it also corresponds to the spectrum of 535 days after the explosion of SN2018bsz, when the wavelength in the range of (0.2−0.8) and (3−10) µm. Nevertheless, 2D SiC and FeC corresponds to the spectrum of 844 days after the explosion of SN2010jl, when the wavelength is within (0.08−10) µm. Therefore, FeC and SiC may be the second type of dust in SN1987A corresponding to infrared band (5−8) µm of dust and may be in the ejecta of SN2010jl and SN2018bsz. The nano−scale C−rich dust size is ∼ 0.1 nm in SN2018bsz, which is 3 orders of magnitude lower than the value of 0.1 µm. In addition, due to the ionization reaction in the supernova remnant (SNR), we also calculated the Infrared Radiation (IR) spectrum of dust cations. We find that the cation of the 2D layered (SiC)2+ has a higher IR spectrum than those of the cation (SiC)1+ and neutral (SiC)0+.

Sensitivity characterization of polarization operating by embedded reflective grating

In this paper, a novel embedded reflective grating (ERG) is presented to realize bi-function polarization operating at infrared band by finite element analysis (FEM). For transverse electric (TE) polarization, a two-port output (0th and −2nd orders) with an efficiency of more than 47% and excellent uniformity can be obtained. For transverse magnetic (TM) polarization, a high efficiency output of 94.72% can be achieved at the −2th order. The results of the analysis of the electric field intensity distribution, angular and wavelength bandwidths further demonstrate the advantages of the proposed grating. In addition, the tolerance analysis of period and duty cycle prove the feasibility of the grating in practical production.

A Comparison of UAV RGB and Multispectral Imaging in Phenotyping for Stay Green of Wheat Population

High throughput phenotyping (HTP) for wheat (Triticum aestivum L.) stay green (SG) is expected in field breeding as SG is a beneficial phenotype for wheat high yield and environment adaptability. The RGB and multispectral imaging based on the unmanned aerial vehicle (UAV) are widely popular multi-purpose HTP platforms for crops in the field. The purpose of this study was to compare the potential of UAV RGB and multispectral images (MSI) in SG phenotyping of diversified wheat germplasm. The multi-temporal images of 450 samples (406 wheat genotypes) were obtained and the color indices (CIs) from RGB and MSI and spectral indices (SIs) from MSI were extracted, respectively. The four indices (CIs in RGB, CIs in MSI, SIs in MSI, and CIs + SIs in MSI) were used to detect four SG stages, respectively, by machine learning classifiers. Then, all indices’ dynamics were analyzed and the indices that varied monotonously and significantly were chosen to calculate wheat temporal stay green rates (SGR) to quantify the SG in diverse genotypes. The correlations between indices’ SGR and wheat yield were assessed and the dynamics of some indices’ SGR with different yield correlations were tracked in three visual observed SG grades samples. In SG stage detection, classifiers best average accuracy reached 93.20–98.60% and 93.80–98.80% in train and test set, respectively, and the SIs containing red edge or near-infrared band were more effective than the CIs calculated only by visible bands. Indices’ temporal SGR could quantify SG changes on a population level, but showed some differences in the correlation with yield and in tracking visual SG grades samples. In SIs, the SGR of Normalized Difference Red-edge Index (NDRE), Red-edge Chlorophyll Index (CIRE), and Normalized Difference Vegetation Index (NDVI) in MSI showed high correlations with yield and could track visual SG grades at an earlier stage of grain filling. In CIs, the SGR of Normalized Green Red Difference Index (NGRDI), the Green Leaf Index (GLI) in RGB and MSI showed low correlations with yield and could only track visual SG grades at late grain filling stage and that of Norm Red (NormR) in RGB images failed to track visual SG grades. This study preliminarily confirms the MSI is more available and reliable than RGB in phenotyping for wheat SG. The index-based SGR in this study could act as HTP reference solutions for SG in diversified wheat genotypes.