Many natural land surfaces, such as sand or snow, consist of densely packed grains, often covered by dust, water droplets, contaminated with other materials such as possible oil leaks, hoar frost, ...and can also be internally cracked, porous, and heterogeneous. Most scattering models ignore these complications, but here a more detailed approach is taken to test all these effects. The current model is composed of three techniques: 1) Monte Carlo-based electromagnetic volume integral equation technique for non-spherical wavelength scale dust particles, 2) Monte Carlo ray tracing for stochastic-shaped grains much larger than the wavelength, with optional point scattering from dust cover, internal inclusions, and liquid surface layer, in a layer of an optical depths of few units, and 3) adding-doubling to combine smaller layers into an arbitrary, thick and vertically inhomogeneous medium. The model allows the medium to be built in a modular way, and after initialisation, rather complicated layered structures can be computed quickly and flexibly. The computed results are compared against experimental measurements of snow and sand. The model agrees with measurements usually within the measurement accuracy (∼ 0:05). The scattering is observed to depend significantly on grain size, shape, orientation, composition, fine structures, dust, and some other properties that need to be defined. Both, measurement and modelling, require much deeper attention to these properties.
The Earth’s spherical albedo describes the ratio of light reflected from the Earth to that incident from the Sun, an important variable for the Earth’s radiation balance. The spherical albedo has ...been previously estimated from satellites in low-Earth orbits, and from light reflected from the Moon. We developed a method to derive the Earth’s spherical shortwave albedo using the images from the Earth Polychromatic Imaging Camera (EPIC) on board National Oceanic and Atmospheric Administration’s (NOAA) Deep Space Climate Observatory (DSCOVR). The satellite is located in the Lagrange 1 point between the Earth and the Sun and observes the complete illuminated part of the Earth at once. The method allows us to provide continuously updated spherical albedo time series data starting from 2015. This time series shows a systematic seasonal variation with the mean annual albedo estimated as 0.295±0.008 and an exceptional albedo maximum in 2020, attributed to unusually abundant cloudiness over the Southern Oceans.
A great volume of data has been accumulated thus far related to the photoregistration of the paths of meteor bodies in the terrestrial atmosphere. Most images have been obtained by four bolide ...networks, which operate in the USA, Canada, Europe, and Spain in different time periods. The approximation of the actual data using theoretical models makes it possible to achieve additional estimates, which do not directly follow from the observations. In the present study, we suggest an algorithm to find such parameters of the theoretical relationship between the height and the velocity of the bolide motion that help to fit observations along the luminous part of the trajectories in the best way. The main difference from previous studies is that the given observations are approximated using the analytical solution of the equations of meteor physics. The model presented in this study was applied to a number of bright meteors observed by the Canadian camera network and by the US Prairie network and to the Benesov bolide, which is one of the largest fireballs registered by the European network. The correct mathematical modeling of meteor events in the atmosphere is necessary for further estimates of the key parameters, including the extra-atmospheric mass, the ablation coefficient, and the effective enthalpy of evaporation of entering bodies. In turn, this information is needed by some applications, namely, those aimed at studying the problems of asteroid and comet security, to develop measures of planetary defense, and to determine the bodies that can reach Earth's surface.
The extra-atmospheric masses of meteoric bodies have previously been determined using the so-called photometric formula, by integrating the luminosity along the visible portion of the trajectory. On ...the other hand, the mass of a meteoroid characterizes the braking height and intensity of the meteoroid in the atmosphere. Some studies note a substantial disagreement between the masses obtained in these two ways, using bolides of the European Bolide Network and of the US Prairie Network as examples. In nearly all cases, the photometric mass exceeds the mass determined from the braking intensity by an order of magnitude or more. Two explanations were suggested for this fact. According to one of them, a swarm of fragments, similar in size, rather than a single body is moving. This swarm brakes as an individual fragment, while it glows as a collection of fragments; i.e., it is much brighter than an individual fragment. The extra-atmospheric mass is determined here by properly fitting the parameters describing the braking of the meteor along the entire visible section of the trajectory. The results obtained for the bolides of the Canadian Network confirm again that the photometric approach is not tenable.
We explored how justifiable the use of a model with a constant mass loss parameter as applied is to real meteor events. The model with variable mass loss parameter used in this work is based on the ...calculation of the luminosity parameter and of the radiative heat exchange coefficient at separate points of trajectory. Agreement between models with constant and variable mass loss parameters is demonstrated by the example of observations of two big meteor bodies (MORP 219 and MORP 872).
We present a database of the absolute magnitudes of asteroids named the Kharkiv Asteroid Absolute Magnitude Database (KhAAMD). The database includes a homogeneous set of the absolute magnitudes for ...about 400 asteroids in the new
HG
1
G
2
magnitude system. We performed a comparative analysis of the asteroid absolute magnitudes between the Kharkiv database and other main magnitude databases (MPC, Pan-STARRS, ATLAS, PTF, and
Gaia
). We show that the Pan-STARRS absolute magnitude dataset has no systematic deviations and is the most suitable for the determination of diameters and albedos of asteroids. For the MPC dataset, there is a linear trend of overestimating the absolute magnitudes of bright objects and underestimating the magnitudes of faint asteroids. The ATLAS dataset has both a systematic overestimation of asteroid magnitudes and a linear trend. We propose equations that can be used to correct for systematic errors in the MPC and the ATLAS magnitude datasets. There are possible systematic deviations of about 0.1 mag for the
Gaia
and PTF databases but there are insufficient data overlapping with our data for a definitive analysis.
A new method is proposed to determine the dynamic parameters of fireballs on the basis of observational data. A partial result of data processing is given for the case of bright fireballs registered ...by the Canadian Network and by the US Prairie Network as well as for the case of the Benešov bolide, which is one of the largest fireballs detected by the European Network. In this new method, no restrictions are imposed on the mass-loss parameter and on the ablation coefficient; this allows one to study the motion of fireballs and to determine their parameters for the case when the mass loss is significant.
Context. Dark gamma-ray bursts (GRBs) constitute a significant fraction of the GRB population. In this paper, we present a multi-wavelength analysis (both prompt emission and afterglow) of an intense ...(3.98 × 10 −5 erg cm −2 using Fermi -Gamma-Ray Burst Monitor) two-episodic GRB 150309A observed early on until ∼114 days post burst. Despite the strong gamma-ray emission, no optical afterglow was detected for this burst. However, we discovered near-infrared (NIR) afterglow ( K S -band), ∼5.2 h post burst, with the CIRCE instrument mounted at the 10.4 m Gran Telescopio Canarias (hereafter, GTC). Aims. We aim to examine the characteristics of GRB 150309A as a dark burst and to constrain other properties using multi-wavelength observations. Methods. We used Fermi observations of GRB 150309A to understand the prompt emission mechanisms and jet composition. We performed early optical observations using the BOOTES robotic telescope and late-time afterglow observations using the GTC. A potential faint host galaxy was also detected in the optical wavelength using the GTC. We modelled the potential host galaxy of GRB 150309A in order to explore the environment of the burst. Results. The time-resolved spectral analysis of Fermi data indicates a hybrid jet composition consisting of a matter-dominated fireball and magnetic-dominated Poynting flux. The GTC observations of the afterglow revealed that the counterpart of GRB 150309A was very red, with H − K S > 2.1 mag (95% confidence). The red counterpart was not discovered in any bluer filters of Swift UVOT/BOOTES, which would be indicative of a high redshift origin. Therefore we discarded this possibility based on multiple arguments, such as spectral analysis of the X-ray afterglow constrain z < 4.15 and a moderate redshift value obtained using the spectral energy distribution (SED) modelling of the potential galaxy. The broadband (X-ray to NIR bands) afterglow SED implies a very dusty host galaxy with a deeply embedded GRB (suggesting A V ≳ 35 mag). Conclusions. The environment of GRB 150309A demands a high extinction towards the line of sight. Demanding dust obscuration is the most probable origin of optical darkness as well as the very red afterglow of GRB 150309A. This result establishes GRB 150309A as the most extinguished GRB known to date.
The measurement uncertainty and traceability of the Finnish Geodetic Institutes׳s field gonio-spectro-polarimeter FIGIFIGO have been assessed. First, the reference standard (Spectralon sample) was ...measured at the National Standard Laboratory of MIKES-Aalto. This standard was transferred to FGI׳s field reference standard (larger Spectralon sample), and from that to the unmanned aerial vehicle (UAV), reference standards (1m2 plates). The reflectance measurement uncertainty of FIGIFIGO has been estimated to be 0.01 in ideal laboratory conditions, but about 0.02–0.05 in typical field conditions, larger at larger solar or observation zenith angles. Target specific uncertainties can increase total uncertainty even to 0.1–0.2. The angular reading uncertainty is between 1° and 3°, depending on user selection, and the polarisation uncertainty is around 0.01. For UAV, the transferred reflectance uncertainty is about 0.05–0.1, depending on, how ideal the measurement conditions are.
The design concept of FIGIFIGO has been proved to have a number of advantages, such as a well-adopted user-friendly interface, a high level of automation and excellent suitability for the field measurements. It is a perfect instrument for collection of reference data on a given target in natural (and well-recorded) conditions. In addition to the strong points of FIGIFIGO, the current study reveals several issues that need further attention, such as the field of view, illumination quality, polarisation calibration, Spectralon reflectance and polarisation properties in the 1000–2400nm range.
•We assessed the uncertainty of the Finnish Geodetic Institute׳s field goniospectropolarimeter.•The calibration is traced from the National Standard Laboratory at MIKES-Aalto.•Many new research tasks to improve the accuracy are pointed out.
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