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We measured the degree of linear polarization of Comet C/2020 S3 (Erasmus) on 2020 November 13, 20, 22, and 23, while the comet was observed at large phase angles, α = 62.6°–66.6°. On the first two epochs, the polarization closely matched what was previously observed in Comet C/1989 X1 (Austin). On the third epoch, the polarization was found to rise slightly, and on the latest epoch, it rose significantly, exceeding that of Comet Austin. On the last observation, the polarization of Comet Erasmus appears to be more consistent with what was previously seen in Comet C/1996 B2 (Hyakutake) at a similar phase angle. While such short-term transient behaviour has been seen previously, Comets Austin and Hyakutake belong to two different classes in classifications based on the amplitude of their positive polarization Pmax and, hence, Comet Erasmus revealed a transition from the class of low-Pmax comets to that of high-Pmax comets within only a few days. Polarization images and modelling suggest that the transition occurred due to a decrease in the relative abundance of Mg-rich silicate particles in the inner coma by 1/3, revealing a qualitative change in emanations of dust particles from the Erasmus nucleus.

We applied a time-resolved, optical trapping-Raman spectroscopy (OT-RS) technique to characterize single, trapped bioaerosol particles under well-controlled reactive conditions that mimic the native state of particles in the atmosphere.

The lack of knowledge of the relation between a lidar backscatter signal and particle size makes it challenging to retrieve ice-cloud particle size from spaceborne lidar observations. This study employs a synergistic combination of the state-of-the-art invariant imbedding T-matrix method and the physical geometric-optics method (PGOM) to investigate the relation between the ice-crystal scattering phase function at 180° (P11(180°)) and particle size (L) for typical ice-crystal shapes. In particular, the P11(180°) −L relation is quantitatively analyzed. The dependence of the P11(180°) −L relation on particle shape can be used with spaceborne lidar observations to detect ice-cloud particle shapes.

We measure the degree of linear polarization of comet 46P/Wirtanen during two months, embracing the perihelion passage in 2018 December with phase angles ranging from {\alpha}=18.1 to 46.4 deg. The polarimetric response PQ obtained resembles what was previously found in comet C/1975 V1 (West). This suggests 46P/Wirtanen belongs to a group of comets with high maximum positive polarization. We conducted BVRI photometry of 46P and found either neutral or blue colour of its dust which is in good accordance with measurements of C/1975 V1 (West). While aperture-average polarimetry of 46P/Wirtanen reveals a nearly zero polarization PQ at the lowest phase angle {\alpha} = 18.1 deg, simultaneous imaging polarimetry suggests that the negative polarization (PQ, Comment: 12 pages, 5 figures

We observe Comet C/2019 Y4 (ATLAS) before and after its disintegration while making polarimetric measurements over a wide range of phase angles. The disintegration event was marked with a dramatic growth of the positive polarization branch that is consistent with a large relative abundance of absorbing material of up to (96.5 ± 3.4) per cent. This polarization spike relaxed as the carbonaceous particles are preferentially swept from the coma due to solar-radiation pressure. The observations suggest that the primordial material stored within comets is extremely rich in carbonaceous material. The pristine cometary material is processed by subsequent solar interactions, forming a refractory crust on the nucleus surface. Polarimetry provides a means of measuring the volume ratio of carbonaceous material, and hence the weathering that has occurred on the comet due to these interactions. The polarimetric response of Comet C/2019 Y4 (ATLAS) appears similar to that of Comet C/1995 O1 (Hale-Bopp), except on few epochs that are similar to that of Comet C/1996 B2 (Hyakutake).

We measured Raman spectra of single particles of six different bioaerosol samples using optical trapping-Raman spectroscopy (OT-RS). Results show that the OT-RS technique can be potentially used for identification and detection of single bioaerosol particles.

We measured the Raman spectra of trapped single fungal aerosol particles under controlled environments using optical trapping-Raman spectroscopy. Results reveal the loss, formation, and chemical reaction of a single particle in simulated atmospheric conditions.

Comet C/2017 K2 (PanSTARRS) was observed at two wavelengths using two different-sized apertures in two measurement campaigns. We find that all the observations can be interpreted using a two-component mixture of dust composed of Mg-rich silicates and amorphous carbon. The modeling suggests a slight increase in the absorption of the refractory component at shorter wavelengths, which is consistent with the optical properties of Mg-rich silicates, and a change in the size distribution as a function of distance from the cometary nucleus, a result of smaller particles accelerating more rapidly from the expanding-gas and radiative-pressure forces.

We present a novel method for actively controlling circular and/or spin-rotational motion of an optically trapped airborne micro-particle. A 532-nm Gaussian laser beam is shaped into an elliptical ring by a pair of axicons and a cylindrical lens. The shaped beam is then focused into an elliptic cone that produces an optical trap. As the cylindrical lens is rotated, a torque is exerted on the trapped particle, resulting in circular or spin-rotational motion. We show examples of the circular-rotational movement as a function of laser power and the rotation rate of the cylindrical lens.

We have measured the degree of linear polarization of the Moon during its total eclipse on 2022 November 8, and found P ≈ −2% in the V filter. The plane of preferential polarization was oriented at ∼36° counting clockwise from the lunar equator. These measurements suggest global asymmetry in the spatial distribution of aerosol particles in the uppermost atmosphere of Earth, with their net linear polarization being P ≈ −6.5%.

We quantify the performance of aerosol and ocean remote sensing products from the PolCube instrument using a previously developed polarimeter retrieval algorithm based on optimal estimation. PolCube is a modified version of the PolCam lunar instrument on the Korea Pathfinder Lunar Orbiter that has been optimized for Earth-Science observations of aerosol, ocean, and thin cloud optical properties. The objective of the PolCube instrument is to retrieve detailed fine-mode (pollution and smoke) and coarse-mode (sea-salt and dust) aerosol properties over the ocean for a range of light to heavy aerosol loadings using its polarimetric-imaging capability at multiple angles and wavelengths from 410−865 nm. An additional objective is to discriminate aerosols from thin clouds. PolCube’s retrieval performance of aerosol optical and microphysical properties and ocean products is quantitatively assessed. We estimate that PolCube can retrieve total aerosol optical depth at 555 nm (AOD555) within ±0.068, fine-mode AOD555 within ±0.078, and fine-mode single-scattering albedo within ±0.036, where all uncertainties are expressed as one standard deviation (1σ). PolCube’s accurate and high-resolution aerosol-retrieval products will provide unique spatial and temporal coverage of the Earth that can be used synergistically with other instruments, such as the Geostationary Environmental Monitoring Spectrometer to improve air-quality forecasting.

We present a multi-scale light-scattering model that is capable of simulating the reflectance spectra of a regolith layer. In particular, the model can be applied to a case where the regolith grains have varying amounts of nanophase inclusions due to space weathering of the material. As different simulation tools are employed for different size scales of the target geometry (roughly, nano-, micro-, and millimeter scales), the particle size effects, the surface reflections, and the volume scattering can all be properly accounted for. Our results with olivine grains and nanophase iron inclusions verify the role of the nanoinclusions in the reflectance spectra of space-weathered materials. Together with the simulation results, we give simplified explanations for the space-weathering effects based on light scattering, namely the decrease of albedo, the general increase of the red spectral slope, and the dampening of the spectral bands. We also consider the so-called ultraviolet bluing effect and show how the change in the spectral slope over the ultraviolet-visual wavelengths is due to the decrease of reflectance in the visual wavelengths rather than the increase of reflectance in the ultraviolet part.

We apply machine-learning algorithms to the calculated light-scattering patterns from particles having seven different common and naturally occurring shapes to assess the accuracy of shape classification based on light scattering. We consider different input data sets including one- and two-dimensional scattering functions of both intensity and polarization. Our scattering data set is produced from particles of volume-equivalent size parameter 5, and refractive index m = 1.5 + 0i. As expected, classification capabilities were much greater when the two-dimensional scattering data were used than when only one-dimensional data were considered. When the two-dimensional intensity patterns are considered, classification accuracies were approximately 70% for the regularly shaped particles and above 90% for the highly irregularly shaped particles. These capabilities increased slightly when linear polarization was used as input. Although all our results are specific to our particular data set, machine-learning techniques are easily generalizable. This exercise suggests that particle discrimination can be achieved in practical experiments using light-scattering patterns through deep learning.

We consider light scattering from a new type of model particle whose shape is represented in the form of a generalized ellipsoid having N foci, where N is greater than two. Such particles can be convex as well as concave. We use the geometrical optics approximation to study the light scattering from 3-foci particles. Non-zero elements of the scattering matrix are calculated for ensembles of randomly oriented independent transparent particles, m = n + i0. Several internal reflection orders are considered separately. It was found that the transmission-transmission (TT) and transmission-reflectance-transmission (TRT) components dominate in the formation of intensity of scattered light at large and small phase angles, respectively. We found a significant role of the total internal reflections of the TRT in the middle portion of the phase angle range. The main factors in the formation of positive linear polarization are the R and TRT component. The TT component is responsible for the formation of negative polarization branch at large phase angles.

Carbon nanotubes (CNTs) have become recognized as a potential environmental and health hazard as their applications are broadening and manufacturing costs are reducing. Fundamental information of CNTs in air is of significant importance to our understanding of their environmental fate as well as to further applications. Extensive efforts have been made over decades on characterizing CNTs; however, a majority of the studies are of bulk or CNTs dispersed on substrates. In the present study, we characterize single CNT particles in air using optical trapping Raman spectroscopy (OT-RS). Different types of CNT particles, as well as glassy carbon spheres, were optically trapped in air. Their physical properties were viewed by microscopic bright field images and scattering images; their chemical properties and structural information can be inferred from characteristic Raman bands. The system can also spatially resolve the morphology and chemical distribution of optically trapped CNT particles in air. The OT-RS technique combines single-particle morphological and chemical information and offers an online method to characterize the physicochemical properties of single CNT particles at their native states in air.

Significance Anthropogenic skyglow is currently a serious threat to natural environments near human settlements; however, a spread of light over wide areas is difficult to predict due to uncertainties in the city emission function (CEF) from many light sources. The CEF determines the rate at which skyglow varies with distance to a light source but remains virtually unexplored because appropriate retrieval tools have been unavailable. However, we have now obtained the CEF from ground-based night-sky radiometry and conducted a successful experiment to retrieve the CEF of an urban area. The method provides information on the CEF and allows for its systematic full-area economic monitoring while initiating a phase in light-pollution research., The city emission function (CEF), describing the angular emission from an entire city as a light source, is one of the key elements in night-sky radiance models. The CEF describes the rate at which skyglow depends on distance and is indispensable in any prediction of light-pollution propagation into nocturnal environments. Nevertheless, the CEF remains virtually unexplored because appropriate retrieval tools have been unavailable until very recently. A CEF has now been obtained from ground-based night-sky observations and establishes an experiment successfully conducted in the field to retrieve the angular emission function for an urban area. The field campaign was conducted near the city of Los Mochis, Mexico, which is well isolated from other cities and thus dominates all light emissions in its vicinity. The experiment has proven that radiometry of a night sky can provide information on the light output pattern of a distant city and allows for systematic, full-area, and cost-efficient CEF monitoring worldwide. A database of CEFs could initiate a completely new phase in light-pollution research, with significant economy and advanced accuracy of night-sky brightness predictions. The experiment and its interpretation represent unique progress in the field and contribute to our fundamental understanding of the mechanism by which direct and reflected uplight interact while forming the CEF.

We provide and test a method to obtain significant improvement of available Chandrayaan-1 M3 data. The advance is achieved using the Gaussian λ-convolution of spectra and Fourier filtration of images. The main result is imagery of the reflectance across different wavelengths as well as parameters of 1 µm and 2 µm absorption bands with unprecedented quality. This approach can be particularly useful for further investigations using M3 data, since it produces improved imagery of various lunar surface characteristics. We studied a region comprising a portion of the Aristarchus Plateau, Montes Agricola, and a small part of the mare surface in Ocean Procellarum to the north of Montes Agricola. We found that the lava flows in the area between the Aristarchus Plateau and Montes Agricola have a chemical/mineral composition different in comparison with mare areas to the northwest of the ridge Montes Agricola. We also identified distinct spectral properties of morphologically young craters located on the plateau and mare surface. A correlation diagram for positions of the minima of the 1 µm and 2 µm bands allows a cluster analysis of the region, and we map areas associated with a cluster corresponding to pyroclastic glasses. Relationships between geologic and spectral parameter maps were established.

Measuring the absorption of a single aerosol particle is a challenging endeavor. Of the few techniques available, none are suitable for measuring the single-particle absorption of coarse-mode nonspherical aerosols. Analysis of two-dimensional angular optical scattering (TAOS) patterns provide a possible pathway to perform this measurement. Using a Multiple-Sphere T-Matrix (MSTM) code, we simulate the captured TAOS patterns with geometries similar to a previously designed instrument. By analyzing the size of the speckle and the integrated irradiance of these simulated TAOS patterns, we are able to distinguish between high-absorbing, weak-absorbing, and non-absorbing particles over the size range of 2 µm to 10 µm. In particular, the speckle present in the scattering patterns provides a means to estimate the size of the particle. Once the size of the particle is known, the integrated irradiance provides insight into the absorption of the particle.

We report photometric observations of comet 29P/Schwassmann-Wachmann 1 made on August 12, 2016 with the broadband B, V, R and I filters and the SOAR 4.1-meter telescope (Chile). We find the comet active at that time. Enhanced images obtained in all filters reveal three radial features in the 29P/ Schwassmann-Wachmann 1 coma, regardless of the image-processing algorithm. Using a high-resolution spectrum of comet 29P/Schwassmann-Wachmann 1 reported by Ivanova et al. (2018) on the same date, we estimate the relative contribution of the gaseous emission and the continuum to the total response measured with our broadband B and V filters. The gaseous-emission contribution appears to be very small 2.5%. We compute the dust production Af\r{ho} in 29P/ Schwassmann-Wachmann 1 for the four filters and find its growth with the wavelength, from 3,393 cm in the B filter to 8,561 cm in the I filter. We model the color slope of dust in Comet 29P/Schwassmann-Wachmann 1 using agglomerated debris particles. Simultaneous analysis of the color slope in the B-R and R-I pairs suggests a single dominant chemical species of 29P/Schwassmann-Wachmann 1 dust particles consisting of Fe-Mg silicates and obeying a power-law size distribution with index n=2.55. This conclusion is consistent with the previous thermal-emission study of 29P/Schwassmann-Wachmann 1., Comment: 10 pages, 7 figures

A new model of asteroid shapes is proposed for simulation of asteroid lightcurves using sparse observational data. The shape model uses logarithmic 3-foci ellipsoids and has four free parameters for describing body shapes with both convex and concave elements of global topography, as well as binary systems. We demonstrate the applicability of the model for asteroids 1580 Betulia and 8567 1996 HW1. A ray-tracing method incorporating Akimov's disk function was used to calculate the flux scattered by each elementary surface element. The simulations provide good fits to observational data, revealing the possibility for wide use of the approach.

Snow surfaces can be composed of ice crystals, melt-form snow or melt-freeze snow. Solar radiation scattered by such surfaces is polarized and the amount of polarization depends on the surface composition. This can be a source of measurement errors in satellite data if a non-polarimetric radiometric sensor is sensitive to the polarization state of light. To obtain highly accurate spectral solar radiation data from the Earth-atmosphere system for the space-borne inter-calibration studies as proposed in NASA's Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission and the CLARREO Pathfinder (CPF) mission, the spectral polarization state of the reflected solar light at the top of atmosphere (TOA) must be known with sufficient accuracy. The degree of polarization (DOP) and the angle of linear polarization (AOLP) of the light at the TOA as functions of incident and viewing geometry and scene type construct the Polarization Distribution Models (PDMs) for correction of polarization-induced error of satellite data [3] . In this work, algorithms for modeling the spectral polarization state of reflected sunlight from various types of snow, including particulate snow, melt-form snow, and melt-freeze snow crusts are developed. A particulate snow surface model based on a mixture of spherical and hexagonal-column particle shapes is used. A rough-surface ice/water facet model is introduced to approximate the melt-form snow and melt-freeze snow crusts. The area fraction of facets for typical (mostly particulate) snow, and for melt-form and melt-freeze snow crusts, is estimated by comparing the model results with the PARASOL satellite data and with ground measurements conducted in Hokkaido, Japan, and in the northwest Greenland ice sheet. Our numerical results demonstrate that the model can provide a reliable approach for making the spectral PDMs for wavelengths between 320 and 2300 nm for satellite inter-calibration applications as proposed in the CLARREO and the CLARREO CPF missions for all kinds of snow surfaces.

We estimate the volume of material that could be excavated from asteroid Dimorphos and expelled into the surrounding space by the DART impact on 2022 September 26. What emerges from our computations is that the total volume of ejected material could be as high as 5710 m3. Assuming that the fraction of fine-dust particles constitutes 5% of this volume, we estimate the apparent brightness of the ejecta to be (6.5 ± 1.5) mag in the V filter. This makes ground-based astronomical observations of the DART impact on asteroid Dimorphos with small telescopes feasible.

The lack of quantitative characterization of aerosol particles and their loading in the atmosphere is one of the greatest uncertainties in climate-change science. Improved instrumentation capable of determining the size and shape of aerosol particles is needed in efforts to reduce this uncertainty. We describe a new instrument carried by an unmanned aerial vehicle (UAV) that images free-floating aerosol particles in the atmosphere. Using digital holography, the instrument obtains the images in a non-contact manner, resolving particles larger than ten micrometers in size in a sensing volume of approximately three cubic centimeters. The instrument, called the holographic aerosol particle imager (HAPI), has the unique ability to image multiple particles freely entering its sensing volume from any direction via a single measurement. The construction of HAPI consists of 3D printed polymer structures that enable a sufficiently low size and weight that it may be flown on a commercial-grade UAV. Examples from field trials of HAPI show images of freshly emitted tree pollen and mineral dust.

All LIDAR instruments are not the same, and advancement of LIDAR technology requires an ongoing interest and demand from the community to foster further development of the required components. The ...

The lack of quantitative characterization of aerosol particles and their loading in the atmosphere is one of the greatest uncertainties in climate-change science. Improved instrumentation capable of determining the size and shape of aerosol particles is needed in efforts to reduce this uncertainty. We describe a new instrument carried by an unmanned aerial vehicle (UAV) that images free-floating aerosol particles in the atmosphere. Using digital holography, the instrument obtains the images in a non-contact manner, resolving particles larger than ten micrometers in size in a sensing volume of approximately three cubic centimeters. The instrument, called the holographic aerosol particle imager (HAPI), has the unique ability to image multiple particles freely entering its sensing volume from any direction via a single measurement. The construction of HAPI consists of 3D printed polymer structures that enable a sufficiently low size and weight that it may be flown on a commercial-grade UAV. Examples from field trials of HAPI show images of freshly emitted tree pollen and mineral dust.

Earth's atmosphere contains interplanetary dust particles (IDPs), which are a key ingredient to understand planetary phenomena, yet the study of their physicochemical properties without external interferences at the single-particle level is limited. With the optical-trapping (OT) technique, a single dust particle can be stably trapped in air for subsequent characterization. We report on measurements of the single-particle extinction of trapped particles using cavity ringdown spectroscopy at ultraviolet wavelength around 308 nm. We also present Raman spectral features of chemical groups in individually trapped particles. Two simulants of extraterrestrial materials, (Martian and lunar analogs) along with carbon spheres and volcanic ashes were trapped and spectroscopically characterized. In addition to the on-trap measurements, the particles’ morphological and mineralogical information was obtained from off-trap measurements using scanning electron microscopy and energy dispersive spectroscopy. This study demonstrates that the integration of OT with cavity ringdown and Raman spectroscopy provides a new tool to gain multimodal information on the physicochemical properties of single IDPs with minimum to no external interferences. © 2020 Elsevier Ltd. All rights reserved., This works was supported by the Army Research Office (Grant Nos. W911NF-13-1-0429 and W911NF-16-1-0483 ). The contribution of co-author O. Muñoz has been funded by project LEONIDAS ( RTI2018-095330-B-100 ) and the Centro de Excelencia Severo Ochoa Program under grant SEV-2017-0709 .