Spectral Diffractive Lenses for Measuring a Modified Red Edge Simple Ratio Index and a Water Band Index

We propose a novel type of spectral diffractive lenses that operate in the ±1-st diffraction orders. Such spectral lenses generate a sharp image of the wavelengths of interest in the +1-st and –1-st diffraction orders. The spectral lenses are convenient to use for obtaining remotely sensed vegetation index images instead of full-fledged hyperspectral images. We discuss the design and fabrication of spectral diffractive lenses for measuring vegetation indices, which include a Modified Red Edge Simple Ratio Index and a Water Band Index. We report synthesizing diffractive lenses with a microrelief thickness of 4 µm using the direct laser writing in a photoresist. The use of the fabricated spectral lenses in a prototype scheme of an imaging sensor for index measurements is discussed. Distributions of the aforesaid spectral indices are obtained by the linear scanning of vegetation specimens. Using a linear scanning of vegetation samples, distributions of the above-said water band index were experimentally measured.

Evaluation of hydrogel use in the development of Rapanea ferruginea with water restriction by vibrational Fourier Transform Infrared Spectroscopy (FTIR-UATR)

This study evaluated the use of hydrogel on the development of Rapanea ferruginea under water restriction through Vibrational Fourier Transform Infrared Spectroscopy (FTIR-UATR). Seedlings of approximately 30 cm height were transferred in pots with 3 L of soil. The group of seedlings was separated into 5 different triplicate treatments according to the amount of hydrogel, as follows: H1 (25%), H2 (20%), H3 (15%), H4 (10%) and S (control without hydrogel). The applied hydrogel was mixed homogeneously with the soil. All treatments were irrigated with 40 mL of water. FTIR spectra were obtained from fresh leaves collected during 13 months of monitoring. The correlation of the hydroxyl (water) band with the main biomolecules between treatments with the control was evaluated using the Mann-Whitney test (p<0.05). The biomolecule bands were subjected to principal component analysis (PCA) and hierarchical clustering analysis (HCA). The results indicate a significant correlation of the water band with the lipid, hemicellulose, cell wall and starch components in the species. The use of hydrogel resulted in a significant difference in the water absorption band in relation to the control group through the Mann-Whitney test and in biomolecules as the HCA and PCA analysis suggested. The best development was observed in groups H4 (10%), H2 (20%) and H3 (15%). The use of hydrogel positively influences the biomolecular development of the Rapanea ferruginea and monitoring is viable by FTIR. Keywords: FTIR infrared spectroscopy, plant water management, superabsorbent polymer.

Colour–magnitude diagrams of transiting exoplanets – III. A public code, nine strange planets, and the role of phosphine

ABSTRACT Colour–magnitude diagrams provide a convenient way of comparing populations of similar objects. When well populated with precise measurements, they allow quick inferences to be made about the bulk properties of an astronomic object simply from its proximity on a diagram to other objects. We present here a python toolkit that allows a user to produce colour–magnitude diagrams of transiting exoplanets, comparing planets to populations of ultra-cool dwarfs, of directly imaged exoplanets, to theoretical models of planetary atmospheres, and to other transiting exoplanets. Using a selection of near- and mid-infrared colour–magnitude diagrams, we show how outliers can be identified for further investigation, and how emerging subpopulations can be identified. Additionally, we present evidence that observed differences in the Spitzer’s 4.5 μm flux, between irradiated Jupiters and field brown dwarfs, might be attributed to phosphine, which is susceptible to photolysis. The presence of phosphine in low-irradiation environments may negate the need for thermal inversions to explain eclipse measurements. We speculate that the anomalously low 4.5 μm flux of the nightside of HD 189733b and the daysides of GJ 436b and GJ 3470b might be caused by phosphine absorption. Finally, we use our toolkit to include Hubble Wide Field Camera 3 spectra, creating a new photometric band called the ‘Water band’ (WJH band) in the process. We show that the colour index [WJH − H] can be used to constrain the C/O ratio of exoplanets, showing that future observations with James Webb Space Telescope and Ariel will be able to distinguish these populations if they exist, and select members for future follow-up.

Emeralds from the Most Important Occurrences: Chemical and Spectroscopic Data

The present study applied LA–ICP-MS on gem-quality emeralds from the most important sources (Afghanistan, Brazil, Colombia, Ethiopia, Madagascar, Russia, Zambia and Zimbabwe). It revealed that emeralds from Afghanistan, Brazil, Colombia and Madagascar have a relatively lower lithium content (7Li < 200 ppmw) compared to emeralds from other places (7Li > 250 ppmw). Alkali element contents as well as scandium, manganese, cobalt, nickel, zinc and gallium can further help us in obtaining accurate origin information for these emeralds. UV-Vis spectroscopy can aid in the separation of emeralds from Colombia and Afghanistan from these obtained from the other sources as the latter present pronounced iron-related bands. Intense Type-II water vibrations are observed in the infrared spectra of emeralds from Madagascar, Zambia and Zimbabwe, as well as in some samples from Afghanistan and Ethiopia, which contain higher alkali contents. A band at 2818 cm−1, supposedly attributed to chlorine, was observed only in emeralds from Colombia and Afghanistan. Samples with medium to high alkalis from Ethiopia, Madagascar, Zambia and Zimbabwe can also be separated from the others by Raman spectroscopy based on the lower or equal relative intensity of the Type I water band at around 3608 cm−1 compared to the Type II water band at around 3598 cm−1 band (with some samples from Afghanistan, Brazil and Russia presenting equal relative intensities).

From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context

Context. A new class of exoplanets has emerged: the ultra hot Jupiters, the hottest close-in gas giants. The majority of them have weaker-than-expected spectral features in the 1.1−1.7 μm bandpass probed by HST/WFC3 but stronger spectral features at longer wavelengths probed by Spitzer. This led previous authors to puzzling conclusions about the thermal structures and chemical abundances of these planets. Aims. We investigate how thermal dissociation, ionization, H− opacity, and clouds shape the thermal structures and spectral properties of ultra hot Jupiters. Methods. We use the SPARC/MITgcm to model the atmospheres of four ultra hot Jupiters and discuss more thoroughly the case of WASP-121b. We expand our findings to the whole population of ultra hot Jupiters through analytical quantification of the thermal dissociation and its influence on the strength of spectral features. Results. We predict that most molecules are thermally dissociated and alkalies are ionized in the dayside photospheres of ultra hot Jupiters. This includes H2O, TiO, VO, and H2 but not CO, which has a stronger molecular bond. The vertical molecular gradient created by the dissociation significantly weakens the spectral features from H2O while the 4.5 μm CO feature remains unchanged. The water band in the HST/WFC3 bandpass is further weakened by the continuous opacity of the H− ions. Molecules are expected to recombine before reaching the limb, leading to order of magnitude variations of the chemical composition and cloud coverage between the limb and the dayside. Conclusions. Molecular dissociation provides a qualitative understanding of the lack of strong spectral features of water in the 1−2 μm bandpass observed in most ultra hot Jupiters. Quantitatively, our model does not provide a satisfactory match to the WASP-121b emission spectrum. Together with WASP-33b and Kepler-33Ab, they seem the outliers among the population of ultra hot Jupiters, in need of a more thorough understanding.

Mapping Irrigated Area Fragments for Crop Water Use Assessment Using Handheld Spectroradiometer

As climatic change and land use are altering the hydrographic regime, most catchments are progressively becoming drier and farmers are shifting from rainfed agriculture to irrigation practices to enable them to carry out income-generating activities throughout the year. The Ghanaian government has recently been promoting irrigation agricultural practices as the population keeps increasing and the demand for food keeps soaring. In order to keep pace with high demand for food coupled with increasing aridity of the subregion, some farmers resort to informal irrigation practices. In this study, hyperspectral reflectance data of the irrigated crops under informal practices were collected to assess their efficiency of water use. Photochemical reflectance index (PRI), soil-specific nitrogen index (SSN), and water band index (WBI) were computed. ThePRIandWBIwere significantly correlated, while there was no significant correlation betweenPRIandSSN. The map showing the probability of water stress indicated that informal irrigation practices are not an efficient water management approaches.

Sapphire Fiber Evanescent Wave Absorption in Turbid Media

The influence of particulates on sapphire fiber evanescent wave absorption by water has been studied. Suspensions containing microsized graphite flakes and glassy carbon powder were used. Conventional free-space transmittance measurements of these samples showed strong absorption and scattering, which severely screened the absorption by water. However, the absorption on the water band determined from the evanescent wave interaction was unaffected by the presence of the graphite flakes. These results indicate that fiber-optic evanescent wave chemical sensors may be suitable for process control applications involving turbid reactor streams.