Empirical Modelling of Public Lighting Emission Functions

Study of light at night has increased in recent decades due to the recognition of its impact on the environment, potential health concerns, as well as both the financial and carbon cost of energy waste. The advent of more extensive and improved ground-based measurements together with quantifiable satellite data has revolutionised the field, and provided data to test improved theoretical models. However, “closing the loop” and finding a detailed connection between these measurements requires knowledge of the “city emission function”, the angular distribution of upwelling radiation with zenith distance. Simplified analytical functions have been superseded by more complex models involving statistical approximation of emission sources and obstructions and inversion techniques now permit the estimation of emission functions from the observed sky brightness measurements. In this paper, we present an efficient GIS-based method to model public lighting using real-world photometric data and high-resolution digital elevation maps of obstructions such as buildings and trees at a 1 m scale. We discuss the results of this work for a sample of Irish towns as well as a city area. We also compare our results to previous emission functions as well as to observed asymmetries in emission detected by satellites such as SUOMI VIIRS.

Satellite observation of the dust trail of a major bolide event over the Bering Sea on December 18, 2018

Context. One of the most energetic bolide events in recent decades was detected by the US Government sensors (USGS) over remote areas of the Bering Sea on December 18, 2018, 23:48 UT. No ground-based optical observations exist. Aims. Using the satellite imagery of the dust trail left behind by the bolide, we tried to reconstruct the bolide trajectory. In combination with the bolide speed reported by the USGS, we computed the pre-atmospheric orbit. Observations in various spectral bands from 0.4 to 13.3 μm enabled us to study the dust properties. Methods. Images of the dust trail and its shadow obtained from various angles by the Multi-angle Imaging SpectroRadiometer (MISR) on board the Terra polar satellite and geostationary satellites Himawari-8 and Geostationary Operational Environmental Satellite 17 (GOES-17) were used. The initial position and orientation of the trail was varied, and its projections into the geoid coordinate grid were computed and compared with real data. Trail motion due to atmospheric wind was taken into account. Radiances and reflectances of selected parts of the dust trail were taken from the Moderate-resolution Imaging Spectroradiometer (MODIS) on board Terra. Reflectance spectra were compared with asteroid spectra. Results. The bolide radiant was found to be 13° ± 9° from that reported by the USGS, at azimuth 130° (from south to west) and zenith distance 14°. The bolide position was confirmed, including the height of maximum dust deposition around 25 km. The incoming asteroid had to be quite strong to maintain a high speed down to this height. The speed of 32 km s−1, reported by the USGS, was found to be plausible. The orbit had a high inclination of about 50° and a perihelion distance between 0.95–1 AU. The semimajor axis could not be restricted well but was most probably between 1–3 AU. The dust reflectance was much lower in the blue than in the red, consistent with the material of A- or L-type asteroid. The absorption at 11 μm confirms the presence of crystalline silicates in the dust.

The Sky Disk of Nebra Reveals Its Secrets

The paper presents the method and results of decoding the content on the Sky Disk of Nebra. It has been shown that the symbols found on it, suggesting the Sun, the Moon and the solar barge are only geometric figures facilitating the recording of astronomical knowledge. The paper first defines a polar system on the horizon plane. This system describes the range of the directions of sunrise and sunset in the annual period and the Moon in the 18.61-year cycle. It turned out that astronomical knowledge was recorded on the surface of the disk on two planes: horizontal and perpendicular one (the meridian plane). With the help of geometric constructions located on the meridian plane, it was possible to decode the range of changes in the altitude (zenith distance) of the Sun in the annual period, at the time of its upper culmination. Also, using two different geometric structures, the range of changes in altitude (zenith distance) of the Moon at the time of its upper culmination in the 18.61-year cycle was decoded

Small iron meteoroids

Context. A significant fraction of small meteors are produced by iron meteoroids. Their origin and the interaction with the atmosphere have not been well explained up to now. Aims. The goals of the study are to observe faint, slow, low altitude meteors, to identify candidates for iron meteoroids among them, to model their ablation and light curves, and to determine their properties. Methods. Double station video observations were used for the determination of atmospheric trajectories, heliocentric orbits, light curves, and spectra of meteors. Meteors with iron spectra or of suspected iron composition based on beginning heights and light curves were modeled. The immediate removal of liquid iron from the surface as a cloud of droplets with Nukiyama–Tanasawa size distribution and their subsequent vaporization was assumed as the main ablation process on the basis of our previous work. The numerical model has only five parameters: meteoroid initial velocity v∞, zenith distance z, initial mass m∞, mean drop size Ddr, and luminous efficiency τ. The theoretical light curves were compared with the observed ones. Results. The model is able to explain the majority of the selected light curves, and meteoroid parameters that are not directly observable – m∞, Ddr, and τ – are determined. Unlike in most meteor studies, the mass and luminous efficiency are determined independently. Luminous efficiency ranges from 0.08 to 5.8%; it weakly decreases with increasing initial meteoroid mass. No simple dependency on initial velocity was found. The mean size of iron drops depends on the meteoroid velocity. Slower meteoroids can produce drops with a wide range of mean sizes, whereas faster ones are better matched with larger drops with a smaller dispersion of sizes.

Solar 27-day signatures in standard phase height measurements above central Europe

We report on the effect of solar variability at the 27-day and the 11-year timescales on standard phase height measurements in the ionospheric D region carried out in central Europe. Standard phase height corresponds to the reflection height of radio waves (for constant solar zenith distance) in the ionosphere near 80 km altitude, where NO is ionized by solar Lyman-α radiation. Using the superposed epoch analysis (SEA) method, we extract statistically highly significant solar 27-day signatures in standard phase heights. The 27-day signatures are roughly inversely correlated to solar proxies, such as the F10.7 cm radio flux or the Lyman-α flux. The sensitivity of standard phase height change to solar forcing at the 27-day timescale is found to be in good agreement with the sensitivity for the 11-year solar cycle, suggesting similar underlying mechanisms. The amplitude of the 27-day signature in standard phase height is larger during solar minimum than during solar maximum, indicating that the signature is not only driven by photoionization of NO. We identified statistical evidence for an influence of ultra-long planetary waves on the quasi 27-day signature of standard phase height in winters of solar minimum periods.

Re-processing and new interpretation of spectroscopic data on C/1999 S4 (LINEAR) and C/2001 Q4 (NEAT) obtained in Shamakhy Observatory

We re-processed spectroscopic echelle data on 1999 S4 (LINIER), a catastrophically disintegrated comet, and 2001 Q4 (NEAT) obtained at not quite favorable circumstances. Photometric conditions at the observations were good but measurements of the spectra for the first one were performed at a large zenith distance and the second - with a relatively low spectral resolution. Nevertheless, we succeeded in detection and identification of fluorescent emission lines of 9 polycyclic aromatic hydrocarbons and simpler molecules in the spectra of both comets. Our results are in accordance with those of other authors and substantiate present notions about origin of the comets.

The Influence of the Time Equation on Remote Sensing Data Interpretation

The interpretation of optical Earth observation data (remote sensing data from satellites) requires knowledge of the exact geographic position of each pixel as well as the exact local acquisition time. But these parameters are not available in each case. If a satellite has a sun-synchronous orbit, equator crossing time (ECT) can be used to determine the local crossing time (LCT) and its corresponding solar zenith distance. Relation between local equator crossing time (LECT) and LCT is given by orbit geometry. The calculation is based on ECT of satellite. The method of actual ECT determination for different satellites on basis of the two-line-elements (TLE), available for their full lifetime period and with help of orbit prediction package is well known. For land surface temperature (LST) studies mean solar conditions are commonly used in the relation between ECT given in Coordinated Universal Time (UTC) and LECT given in hours, thus neglecting the difference between mean and real Sun time (MST, RST). Its difference is described by the equation of time (ET). Of particular importance is the variation of LECT during the year within about ±15 minutes. This is in each case the variation of LECT of a satellite, including satellites with stable orbit as LANDSAT (L8 around 10:05 a.m.) or ENVISAT (around 10:00 a.m.). In case of NOAA satellites the variation of LECT is overlaid by a long-term orbital drift. Ignatov et al. (2004) developed a method to describe the drift-based variation of LECT that can be viewed as a formal mathematical approximation of a periodic function with one or two Fourier terms. But, nevertheless, ET is not included in actual studies of LST. Our paper aims to demonstrate the possible influence of equation of time on simple examples of data interpretation, e.g. NDVI.

Stress Distribution Characteristics in Rock Surrounding Heading Face and its Relationship with Temporary Supporting

To solve the problem of underground tunneling face from the empty top, using FLAC3D analysis software, surrounding rock stability for coal roadway 2-1121 of Ganhe Coal Mine are analyzed in numerical calculation. (1) During the tunneling, distance drivage face head-on 0.5-1m at the roof of roadway deformation and destruction features are more obvious, the two sides of roadway are even more significant. (2) Ganhe Coal Mine roof deformation has been established with different empty the experience formula of the zenith distance, obtained Ganhe underground tunneling face reasonable empty zenith distance is 3.5m. (3) Temporary support can obviously reduce roof deformation, reduce thickness of plastic zone of the top, to improve the stability of surrounding rock tunneling faces.