Compressive Sensing Imaging Spectrometer for UV-Vis Stellar Spectroscopy: Instrumental Concept and Performance Analysis.

Compressive sensing (CS) has been proposed as a disruptive approach to developing a novel class of optical instrumentation used in diverse application domains. Thanks to sparsity as an inherent feature of many natural signals, CS allows for the acquisition of the signal in a very compact way, merging acquisition and compression in a single step and, furthermore, offering the capability of using a limited number of detector elements to obtain a reconstructed image with a larger number of pixels. Although the CS paradigm has already been applied in several application domains, from medical diagnostics to microscopy, studies related to space applications are very limited. In this paper, we present and discuss the instrumental concept, optical design, and performances of a CS imaging spectrometer for ultraviolet-visible (UV-Vis) stellar spectroscopy. The instrument-which is pixel-limited in the entire 300 nm-650 nm spectral range-features spectral sampling that ranges from 2.2 nm@300 nm to 22 nm@650 nm, with a total of 50 samples for each spectrum. For data reconstruction quality, the results showed good performance, measured by several quality metrics chosen from those recommended by CCSDS. The designed instrument can achieve compression ratios of 20 or higher without a significant loss of information. A pros and cons analysis of the CS approach is finally carried out, highlighting main differences with respect to a traditional system.

A Compact LIF Spectrometer for in-Field Operation in Polar Environments.

We present a compact laser-induced fluorescence (LIF) spectrometer prototype (SFIDA-405) designed for in-field operation in polar environments. It uses 405 nm excitation to acquire LIF spectra in the 450-930 nm spectral range on a solid surface via an optical-fiber coupled measurement head. The prototype (battery powered; module + measurement head weight: <1.6 kg) is controlled via a military-grade smartphone and has a limit of detection for chlorophyll better than 5 ng/cm2. The instrument was successfully tested during two summer field campaigns in the Arctic (Svalbard Islands) and Antarctic (Southern Victoria Land) regions for studying biological soil crusts. To the best of the authors' knowledge, this represents the first LIF spectrometer used in situ in Antarctica to acquire LIF spectra directly on biological soil crusts. Finally, the paper also suggests the use of the SFIDA-405 prototype for different application fields.

A fluorescence LIDAR sensor for hyper-spectral time-resolved remote sensing and mapping.

In this work we present a LIDAR sensor devised for the acquisition of time resolved laser induced fluorescence spectra. The gating time for the acquisition of the fluorescence spectra can be sequentially delayed in order to achieve fluorescence data that are resolved both in the spectral and temporal domains. The sensor can provide sub-nanometric spectral resolution and nanosecond time resolution. The sensor has also imaging capabilities by means of a computer-controlled motorized steering mirror featuring a biaxial angular scanning with 200 µradiant angular resolution. The measurement can be repeated for each point of a geometric grid in order to collect a hyper-spectral time-resolved map of an extended target.

A retrieval algorithm to evaluate the Photosystem I and Photosystem II spectral contributions to leaf chlorophyll fluorescence at physiological temperatures.

A new computational procedure to resolve the contribution of Photosystem I (PSI) and Photosystem II (PSII) to the leaf chlorophyll fluorescence emission spectra at room temperature has been developed. It is based on the Principal Component Analysis (PCA) of the leaf fluorescence emission spectra measured during the OI photochemical phase of fluorescence induction kinetics. During this phase, we can assume that only two spectral components are present, one of which is constant (PSI) and the other variable in intensity (PSII). Application of the PCA method to the measured fluorescence emission spectra of Ficus benjamina L. evidences that the temporal variation in the spectra can be ascribed to a single spectral component (the first principal component extracted by PCA), which can be considered to be a good approximation of the PSII fluorescence emission spectrum. The PSI fluorescence emission spectrum was deduced by difference between measured spectra and the first principal component. A single-band spectrum for the PSI fluorescence emission, peaked at about 735 nm, and a 2-band spectrum with maxima at 685 and 740 nm for the PSII were obtained. A linear combination of only these two spectral shapes produced a good fit for any measured emission spectrum of the leaf under investigation and can be used to obtain the fluorescence emission contributions of photosystems under different conditions. With the use of our approach, the dynamics of energy distribution between the two photosystems, such as state transition, can be monitored in vivo, directly at physiological temperatures. Separation of the PSI and PSII emission components can improve the understanding of the fluorescence signal changes induced by environmental factors or stress conditions on plants.

Arx is a direct target of Dlx2 and thereby contributes to the tangential migration of GABAergic interneurons.

The Arx transcription factor is expressed in the developing ventral telencephalon and subsets of its derivatives. Mutation of human ARX ortholog causes neurological disorders including epilepsy, lissencephaly, and mental retardation. We have isolated the mouse Arx endogenous enhancer modules that control its tightly compartmentalized forebrain expression. Interestingly, they are scattered downstream of its coding region and partially included within the introns of the downstream PolA1 gene. These enhancers are ultraconserved noncoding sequences that are highly conserved throughout the vertebrate phylum. Functional characterization of the Arx GABAergic enhancer element revealed its strict dependence on the activity of Dlx transcription factors. Dlx overexpression induces ectopic expression of endogenous Arx and its isolated enhancer, whereas loss of Dlx expression results in reduced Arx expression, suggesting that Arx is a key mediator of Dlx function. To further elucidate the mechanisms involved, a combination of gain-of-function studies in mutant Arx or Dlx tissues was pursued. This analysis provided evidence that, although Arx is necessary for the Dlx-dependent promotion of interneuron migration, it is not required for the GABAergic cell fate commitment mediated by Dlx factors. Although Arx has additional functions independent of the Dlx pathway, we have established a direct genetic relationship that controls critical steps in the development of telencephalic GABAergic neurons. These findings contribute elucidating the genetic hierarchy that likely underlies the etiology of a variety of human neurodevelopmental disorders.