A fibre-based 2D-slit homogenizer concept for high-precision space-based spectrometer missions

The measurement accuracy of recent and future space-based imaging spectrometers with a high spectral and spatial resolution suffer from the inhomogeneity of the radiances of the observed Earth scene. The Instrument Spectral Response Function (ISRF) is distorted due to the inhomogeneous illumination from scene heterogeneity. This gives rise to a pseudo-random error on the measured spectra. In order to assess the spectral stability of the spectrograph, stringent requirements are typically defined on the ISRF such as shape knowledge and the stability of the centroid position of the spectral sample. The high level of spectral accuracy is particularly crucial for missions quantifying small variations in the total column of well-mixed trace gases like $$\hbox {CO}_{2}$$ CO 2 . In the framework of the $$\hbox {CO}_{2}$$ CO 2 Monitoring Mission (CO2M) industrial feasibility study (Phase A/B1 study), we investigated a new slit design called 2D-Slit Homogenizer (2DSH). This new concept aims to reduce the Earth scene contrast entering the instrument. The 2DSH is based on optical fibre waveguides assembled in a bundle, which scramble the light in across-track (ACT) and along-track (ALT) direction. A single fibre core dimension in ALT defines the spectral extent of the slit and the dimension in ACT represents the spatial sample of the instrument. The full swath is given by the total size of the adjoined fibres in ACT direction. In this work, we provide experimental measurement data on the stability of representative rectangular core shaped fibre as well as a preliminary pre-development of a 2DSH fibre bundle. In our study, the slit concept has demonstrated significant performance gains in the stability of the ISRF for several extreme high-contrast Earth scenes, achieving a shape stability of $$<0.5{\%}$$ < 0.5 % and a centroid stability of $$<0.25 \ \text {pm}$$ < 0.25 pm (NIR). Given this unprecedented ISRF stabilization, we conclude that the 2DSH concept efficiently desensitizes the instrument for radiometric and spectral errors with respect to the heterogeneity of the Earth scene radiance.

Probing Early Supermassive Black Hole Growth and Quasar Evolution with Near-infrared Spectroscopy of 37 Reionization-era Quasars at 6.3 < z ≤ 7.64

We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range 6.3 < z ≤ 7.64, including 32 quasars at z > 6.5, forming the largest quasar near-infrared spectral sample at this redshift. The spectra, taken with Keck, Gemini, VLT, and Magellan, allow investigations of central black hole mass and quasar rest-frame ultraviolet spectral properties. The black hole masses derived from the Mg ii emission lines are in the range (0.3–3.6) × 109 M ⊙, which requires massive seed black holes with masses ≳103–104 M ⊙, assuming Eddington accretion since z = 30. The Eddington ratio distribution peaks at λ Edd ∼ 0.8 and has a mean of 1.08, suggesting high accretion rates for these quasars. The C iv–Mg ii emission-line velocity differences in our sample show an increase of C iv blueshift toward higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The Fe ii/Mg ii flux ratios derived for these quasars up to z = 7.6, compared with previous measurements at different redshifts, do not show any evidence of strong redshift evolution, suggesting metal-enriched environments in these quasars. Using this quasar sample, we create a quasar composite spectrum for z > 6.5 quasars and find no significant redshift evolution of quasar broad emission lines and continuum slope, except for a blueshift of the C iv line. Our sample yields a strong broad absorption line quasar fraction of ∼24%, higher than the fractions in lower-redshift quasar samples, although this could be affected by small sample statistics and selection effects.

THE COMBINATION OF THE SIGHTING CHANNEL WITH PROJECTION CHANNEL DISPLAY MORE INFORMATION

This article describes a method of combining the sighting channel and the projection channel, which can be used in optical systems for various purposes, in which there is a prism with a mirror coating, especially sights, or systems with the output of a large amount of information, for example, rangefinders. The analysis of the factors reducing the qualitative efficiency of optical sights. The technical proposal for the implementation of this method and the expected result - the creation of an optical sight with advanced functionality by reducing radiation losses in the projection channel and reducing the parallax between the images of the target and the luminous sighting mark. The practical results of the layout of the node working on this method are shown. The results of full-scale tests showed a low light transmission coefficient of the system, however, when applying the OLED display and the reflecting layer, the possibility of increasing light transmission was not taken into account, due to the combination of spectral sample layers working on reflection for the sighting and transmission for the projection channels. The results of full-scale tests proved the possibility of combining the sighting and projection channels by applying OLED microdisplay on the reflecting face of the prism.

Spectral Characteristics of Plastic Debris in the Beach: Case Study of Makassar Coastal Area

Plastic debris becomes a global problem that threatens the coastal ecosystems, and the supralittoral area (beach) turns to be a place for plastic debris to accumulate. Data from the United Nations (UN) states that Indonesia is the second plastic debris contributor in world waters. This study aimed to examine the spectral characteristics of plastic debris accumulated on the beach. The data was collected from the coast of Makassar at 3 different stations: Jenneberang River estuary, Losari Beach and Tallo River estuary. The spectral sample was measured using a 4000 A spectroradiometer that works on a wavelength spectrum of 340 - 1040 nm. The results showed that the optimum value for plastic debris identification in the coastal area at low tide (dry sand) is 450-670 nm and at high tide (wet sand) is 450-950 nm. This value will be a reference in the remote sensing method, especially multispectral classification in mapping plastic debris found in coastal areas, and will be one solution to effectively mapping plastic debris.

Linear and Nonlinear Analysis of Base Lung Sound in Extrinsic Allergic Alveolitis Patients in Comparison to Healthy Subjects

SummaryObjective: Pulmonary disorders are frequently characterized by the presence of adventitious sounds added to the breathing or base lung sound (BLS). The aim of this work was to assess the features of BLS in extrinsic allergic alveolitis (EAA) patients in comparison to healthy subjects, applying linear and nonlinear analysis techniques.Methods: We investigated the multichannel lung sounds on the posterior chest of 16 females, 8 healthy and 8 EAA patients, when breathing at 1.5 L/s. BLS linear features were obtained from the power spectral density (PSD) while nonlinear features were extracted by the concepts of irregularity and complexity, i.e., spectral, sample and multi-scale entropy.Results: The results demonstrated that spectral percentiles of BLS were lower in EAA patients than in healthy subjects but statistical significance (p<0.05) was obtained only for expiration at the left apical and both basal regions. Also, the maximum amplitude of the PSD in patients reached statistical significance ( p < 0.05) for the expiratory phase at basal regions. In the case of nonlinear techniques, significant lower values ( p < 0.05) were obtained for EAA patients during both respiratory phases at left apical and both basal regions.Conclusion: In conclusion, we found that BLS in chronic EAA patients is characterized by lower spectral percentiles, lower irregularity and lower complexity than in healthy subjects suggesting the feasibility of its clinical usefulness by screening its temporal alteration.

The SNLS-VLT Type Ia Spectrum Evolution with Redshift: a Demographic Effect?

We build composite spectra at z ≤ 0.5 and z > 0.5 from the 3 year SuperNova Legacy Survey (SNLS) VLT spectral sample and study their differences around maximum light. We use 93 spectra near maximum of confirmed SNe Ia observed at the VLT between 2003 and 2006 as part of the 3 first years of operation of the SNLS. We find differences in the absorption depth of some intermediate mass elements (Ca ii, Si ii). Average stretches of observed distributions are 0.975 ± 0.016 and 0.983 ± 0.014 for the z ≤ 0.5 and z > 0.5 sample respectively. We use the A+B model of Scannapieco & Bildsten (2005) to interpret these results in terms of a possible demographic evolution.