Shadow Height Research Articles

SMARTPHONE-BASED TRAFFIC NOISE MAPPING SYSTEM

Abstract. Noise pollution is one of the most serious environmental threats to human health. Noise is becoming more prevalent in urban areas, and it is having a negative impact on human health. The increase in noise is due to the increase in the number of vehicles that creates chaos over the road due to honking. Smart monitoring using is smartphones is required to reduce human dependency and monitor data efficiently to reduce logistical obstacles. A smartphone-based noise monitoring solution can handle the problem of monitoring noise at various traffic crossings in a metropolis. The topographical data, noise data, and noise prediction models are required for forecasting noise levels and showing them as maps. In the Indian city of Lucknow, the entire procedure is being performed by providing a map of 2D and 3D forms. The smartphone-based software tracks noise levels at three road crossings at three different times each day. The collected noise levels were calibrated against a standard noise metre to achieve correct noise levels for these sites. Following that, three noise environment types are chosen and mapped using open-source satellite images and conventional noise models through the web on the GIS platform. The anticipated noise levels on the maps were compared to recorded noise data from identical locations using a conventional noise metre for these three crossings and were found to be within 5.5 dB of accuracy. For 3D mapping, shadow height provides the Z value for point cloud DEM generation for 3D model for noise data of city of Lucknow.

Shading and Masking of PV Collectors on Horizontal and Sloped Planes Facing South and North—A Comparative Study

With the increase in PV system installations, the available free land and rooftops for these systems may become scarcer, and therefore sloped fields facing the north may be utilized for that purpose. In deployments of PV collectors in multiple rows, either on horizontal or sloped planes, the second and subsequent rows are subject to two effects: shading and masking. Both effects reduce the electric energy generated by the PV systems. Multiple rows of collectors are deployed on horizontal planes and on sloped planes facing south, and literature on the topic has been published. No literature deals analytically with deployments of PV fields on north-facing slopes in the northern hemisphere, to the best of our knowledge. The present study develops explicit analytical expressions for the shadow height and length cast on a collector row by a row in front in multiple-row PV systems installed on slopes facing north. In addition, analytical expressions are developed for row spacing and sky view factors, altogether leading consequently to the determination of shading and masking losses. Having the developed expressions, a comparison was made between PV deployments on north-facing sloped planes to PV deployments on horizontal and south-facing slopes regarding shading and masking losses. The main finding is that the percentage of masking losses (diffuse radiation) may exceed the percentage of shading losses (beam radiation) in PV fields. At the local site 32∘ N, collector inclination angle β=25∘ and sloped-plane ε=10∘, for example, the percentage of masking losses for a horizontal plane is 6.90%; for a sloped plane facing south, the losses are 5.39%, and for a sloped plane facing north, the losses are 6.86%. In comparison to the masking losses, the percentage of shading losses for the horizontal plane is 0.83%; for the sloped plane facing south, the losses are 0.42%, and for the sloped plane facing north, the losses are 1.37%.

Statistical Study of Auroral/Resonant‐Scattering 427.8‐nm Emission Observed at Subauroral Latitudes Over 14 Years

AbstractAuroral emission at 427.8‐nm from N2+ ions is caused by precipitation of energetic electrons, or by resonant scattering of sunlight by auroral N2+ ions. The latter often causes impressive purple aurora at high altitudes. However, statistical characteristics of auroral 427.8‐nm emission have not been well studied. In this paper we report occurrence characteristics of high 427.8‐nm emission intensities (more than 100 R) at subauroral latitudes, based on measurements by a filter‐tilting photometer over 14 years (2005–2018) at Athabasca, Canada (magnetic latitude: ~62°). We divided the data set into solar elevation angles (θs) more than and less than −24° (shadow height of sunlight: 600 km) to separate the 427.8‐nm emissions caused by resonant scattering of sunlight and those excited by auroral electrons, respectively. The occurrence rate of 427.8‐nm emissions of more than 100 R is 10.6% and 7.65% for θs more than and less than −24°, respectively, confirming that resonant scattering of sunlight by N2+ ions is a cause of the strong 427.8‐nm emissions of more than 100 R in the sunlit ionosphere. The occurrence rate is high in the postmidnight sector and increases with increasing geomagnetic activity, solar wind speed, and density. The occurrence rate is lowest in winter. A high occurrence rate was observed in 2015–2018, during the declining phase of the 11‐year solar activity. Superposed epoch analysis indicates that the 427.8‐nm emission exceeds 100 R when solar wind speed increases and solar wind density concurrently decreases, though the standard deviation of the data is rather large.

Detection of impact-produced dust clouds near the lunar terminator

Analysis of observations of unique impact-produced flash near the lunar terminator was performed. Maximal brightness of detected thermal flash is 5.2–5.9m in R band, mass of impacted meteoroid is about 0.18–28 kg. Height of shadow in the place of meteoroid’s impact was only about 1 km, making it possible observations of impact-produced dust particles ejected to the lunar exosphere through their sunlight-scattering response. We detected two (fast and slow) clouds that were expanding with 3 km/s and 0.1 km/s, respectively. The maximal brightness reached by these fast and slow clouds in R band was 6.7m and 10m, respectively. Apparent mass of visible ejecta in fast and slow clouds is constrained to 80–8300 and 6–180 kg, respectively. Fast cloud consists of melt droplets and condensed grains while slow cloud consists of ejected lunar regolith dust particles.

Carbon sink calculation model of urban construction land based on building capacity.

The exploitation and utilization of mineral materials during urban construction causes a large amount of carbon emission, but could also contribute to carbon sequestration. In the related literature, carbon sequestration process of building mineral materials has received limited attention and scientific quantification. On the basis of extracting building capacity and identifying building types, we used the technology of remote sensing image shadow height inversion to quantify mineral material consumption and carbon content parameters. Carbonization rate was measured by thermogravimetric analysis (TGA). Finally, a calculation method for carbon sink in urban buildings was constructed. We investigated the uncertainty of this method with Puhe New Town in Shenyang as an example. The results showed that the order of carbon sink density of different types of buildings followed the order of residential buildings > public service buildings > other types of buildings > commercial and financial buildings > industrial buildings; the ratio of carbon sink volumetric in diffe-rent types of construction land followed the order of commercial and financial buildings > residential buildings > public service buildings > other types of buildings > industrial buildings. The carbon sink calculation method based on the urban scale of building capacity in this study could quickly and accurately estimate the magnitude of carbon sinks from the inorganic materials in various types of urban construction lands. Under the background of limited urban natural carbon sequestration, using building carbon sequestration to enhance the urban carbon sequestration could provide new ideas for the low-carbon development of cities in China.

Shadow identification and height estimation of defects by direct processing of grayscale images

This paper presents a visual inspection system designed to identify and indirectly measure defect heights on aluminum castings. In the proposed approach, a metallic surface is illuminated at three different positions and grayscale images are captured. Unlike other methods that employ a threshold value from one image, the method shown in this article processes information from the three grayscale images to identify shadows. The data from these images is stored in matrices, and four data sets are obtained from element by element operations among the sets. The data sets exhibit a specific pattern at the position of a shadow, and it is possible to identify the pixels where it starts and ends. The method allows discriminating between actual shadows and dark spots. Height estimation was made based on the shadow’s size and they were compared to the actual height with an average error of 5.9%. The system uses a camera connected to a Jetson TX1 board, and the data is processed in parallel on a GPU to obtain results in real time.

Erratum: Zielewska-Büttner, K.; Adler, P.; Ehmann, M.; Braunisch, V. Automated Detection of Forest Gaps in Spruce Dominated Stands Using Canopy Height Models Derived from Stereo Aerial Imagery. Remote Sens. 2016, 8, 175

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A NEW ALGORITHM FOR VOID FILLING IN A DSM FROM STEREO SATELLITE IMAGES IN URBAN AREAS

Digital Surface Models (DSM) derived from stereo-pair satellite images are the main sources for many Geo-Informatics applications like 3D change detection, object classification and recognition. However since occlusion especially in urban scenes result in some deficiencies in the stereo matching phase, these DSMs contain some voids. In order to fill the voids a range of algorithms have been proposed, mainly including interpolation alone or along with auxiliary DSM. In this paper an algorithm for void filling in DSM from stereo satellite images has been developed. Unlike common previous approaches we didn’t use any external DSM to fill the voids. Our proposed algorithm uses only the original images and the unfilled DSM itself. First a neighborhood around every void in the unfilled DSM and its corresponding area in multispectral image is defined. Then it is analysed to extract both spectral and geometric texture and accordingly to assign labels to each cell in the voids. This step contains three phases comprising shadow detection, height thresholding and image segmentation. Thus every cell in void has a label and is filled by the median value of its co-labelled neighbors. The results for datasets from WorldView-2 and IKONOS are shown and discussed.

Ionospheric superstorms: Polarization terminator effects in the Atlantic sector

A combination of the effects of stormtime penetration electric fields, the reduced magnetic field strength in the South Atlantic magnetic anomaly (SAA), and the geographic distortion of the magnetic field in the Atlantic sector influence the characteristics of polarization electric fields which form in the E region conductivity-gradient region at the sunset terminator. These effects lead to a strong localized enhancement of total electron content (TEC) at dusk at low-mid latitudes in the American sector during ionospheric superstorms. The E region electric fields map along field lines to the F region and into the opposite hemisphere. We define the polarization terminator (PT) to be the ensemble of points at a given altitude above the E region for which the shadow height at either end of the magnetic field line equals 100km. Electric fields associated with polarization charge build-up in the conductivity-gradient region along the PT are directed perpendicular to the magnetic field and increase in magnitude as the PT is approached from the dayside. The configuration of the magnetic field in the Atlantic sector due to the offset of the poles and declination effects near the SAA creates a preferred longitude/Universal Time sector (western Atlantic/21UT) for the build-up of enhanced disturbance time TEC at lower mid latitudes. During strong storms, DMSP observations reveal that the plasma in the equatorial ionization anomaly (EIA) crests moves westward in lockstep with the PT. Electric fields at the PT sweep up the plasmas of the EIA crests and redistribute it into magnetically-conjugate regions at mid latitudes. This effect is strongest in the western Atlantic sector for northern hemisphere summer conditions.

Cassini UVIS observations of Titan nightglow spectra

In this paper we present the first nightside EUV and FUV airglow limb spectra of Titan showing molecular emissions. The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed photon emissions of Titan's day and night limb‐airglow and disk‐airglow on multiple occasions, including during an eclipse observation. The 71 airglow observations analyzed in this paper show EUV (600–1150 Å) and FUV (1150–1900 Å) atomic multiplet lines and band emissions arising from either photoelectron induced fluorescence and solar photo‐fragmentation of molecular nitrogen (N2) or excitation by magnetosphere plasma. The altitude of the peak UV emissions on the limb during daylight occurred inside the thermosphere at the altitude of the topside ionosphere (near 1000 km altitude). However, at night on the limb, a subset of emission features, much weaker in intensity, arise in the atmosphere with two different geometries. First, there is a twilight photoelectron‐excited glow that persists with solar depression angle up to 25–30 degrees past the terminator, until the solar XUV shadow height passes the altitude of the topside ionosphere (1000–1200 km). The UV twilight glow spectrum is similar to the dayglow but weaker in intensity. Second, beyond 120° solar zenith angle, when the upper atmosphere of Titan is in total XUV darkness, there is indication of weak and sporadic nightside UV airglow emissions excited by magnetosphere plasma collisions with ambient thermosphere gas, with similar N2 excited features as above in the daylight or twilight glow over an extended altitude range.

The post-terminator ionosphere of Venus

We have modeled the near and post-terminator thermosphere/ionosphere of Venus with a view toward understanding the relative importance of EUV solar fluxes and downward fluxes of atomic ions transported from the dayside in producing the mean ionosphere. We have constructed one-dimensional thermosphere/ionosphere models for high solar activity for seven solar zenith angles (SZAs) in the dusk sector: 90°, 95°, 100°, 105°, 110°, 115° and 125°. For the first 4SZAs, we determine the optical depths for solar fluxes from 3Å to 1900Å by integrating the neutral densities numerically along the slant path through the atmosphere. For SZAs of 90°, 95°, and 100°, we first model the ionospheres produced by absorption of the solar fluxes alone; for 95°, 100°, and 105°SZAs, we then model the ion density profiles that result from both the solar source and from imposing downward fluxes of atomic ions, including O+, Ar+, C+, N+, H+, and He+, at the top of the ionospheric model in the ratios determined for the upward fluxes in a previous study of the morphology of the dayside (60°SZA) Venus ionosphere. For SZAs of 110°, 115° and 125°, which are characterized by shadow heights above about 300km, the models include only downward fluxes of ions. The magnitudes of the downward ion fluxes are constrained by the requirement that the model O+ peak density be equal to the average O+ peak density for each SZA bin as measured by the Pioneer Venus Orbiter Ion Mass Spectrometer. We find that the 90° and 95°SZA model ionospheres are robust for the solar source alone, but the O+ peak density in the “solar-only” 95°SZA model is somewhat smaller than the average value indicated by the data. A small downward flux of ions is therefore required to reproduce the measured average peak density of O+. We find that, on the nightside, the major ion density peaks do not occur at the altitudes of peak production, and diffusion plays a substantial role in determining the ion density profiles. The average downward atomic ion flux for the SZA range of 90–125° is determined to be about 1.2×108cm−2s−1.

TIMED/GUVI observation of solar illumination effect on auroral energy deposition

[1] It has been established that the local nighttime aurora is more intense in winter or darkness than in summer or sunlight. Here we expand previous work to confirm empirical relationships between energy flux and average energy of aurora and solar zenith angle (SZA) and ionospheric photoconductance by analyzing ∼6 years (2002–2007) of FUV auroral images acquired from the Global Ultraviolet Imager (GUVI) on board NASA's Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite. The total number of auroral images, north and south combined, is 55,675. The B3C auroral transport code is used to extract auroral parameters, assuming pure electron precipitation. It is found that the mean energy and energy flux carried by precipitating electrons (>0.25 erg/cm2 s) increase monotonically with SZA for SZA less than ∼108° (corresponding to an EUV shadow height of ∼430 km). The rate of increase is most pronounced in the premidnight sector, where the energy flux rate is ∼0.04 erg/cm2 s/deg and the mean energy rate is ∼0.02 keV/deg. The auroral power is anticorrelated with the ionospheric Pedersen photoconductance for all local times, with the steepest drop (−0.2 gw/mho) in the midnight sector. These results are stronger than those for the simple cases of “sunlight” versus “darkness” and/or “summer” versus “winter” used in previous work for the solar illumination effect. While the present result cannot distinguish known mechanisms, we suggest that more than one mechanism is responsible for the observed sunlight effect.

Resonance scattering by auroral N<sub>2</sub><sup>+</sup>: steady state theory and observations from Svalbard

Abstract. Studies of auroral energy input at high latitudes often depend on observations of emissions from the first negative band of ionised nitrogen. However, these emissions are affected by solar resonance scattering, which makes photometric and spectrographic measurements difficult to interpret. This work is a statistical study from Longyearbyen, Svalbard, Norway, during the solar minimum between January and March 2007, providing a good coverage in shadow height position and precipitation conditions. The High Throughput Imaging Echelle Spectrograph (HiTIES) measured three bands of N2+ 1N (0,1), (1,2) and (2,3), and one N2 2P band (0,3) in the magnetic zenith. The brightness ratios of the N2+ bands are compared with a theoretical treatment with excellent results. Balance equations for all important vibrational levels of the three lowest electronic states of the N2+ molecule are solved for steady-state, and the results combined with ion chemistry modelling. Brightnesses of the (0,1), (1,2) and (2,3) bands of N2+ 1N are calculated for a range of auroral electron energies, and different values of shadow heights. It is shown that in sunlit aurora, the brightness of the (0,1) band is enhanced, with the scattered contribution increasing with decreasing energy of precipitation (10-fold enhancements for energies of 100 eV). The higher vibrational bands are enhanced even more significantly. In sunlit aurora the observed 1N (1,2)/(0,1) and (2,3)/(0,1) ratios increase as a function of decreasing precipitation energy, as predicted by theory. In non-sunlit aurora the N2+ species have a constant proportionality to neutral N2. The ratio of 2P(0,3)/1N(0,1) in the morning hours shows a pronounced decrease, indicating enhancement of N2+ 1N emission. Finally we study the relationship of all emissions and their ratios to rotational temperatures. A clear effect is observed on rotational development of the bands. It is possible that greatly enhanced rotational temperatures may be a signature of ion upflows.

Analysis of high resolution MOMS cloud scenes for CLOUDMAP validation

CLOUDMAP applied stereo registration and differential spectroscopy in the A‐band of molecular oxygen as new observation methods of clouds, provided by existing or new instruments on polar orbiting satellites with 250 to 1000 m pixel size, comparable to the cloud mean size. Cloud coverage within pixel can only be estimated from spectral effects. High resolution stereoscopic cloud images with 18 m pixel size obtained by the German Modular Opto‐electronic Multi‐spectral Scanner (MOMS) on the Russian space station MIR over crossing areas with the polar orbiting satellites at small time delays were provided for CLOUDMAP as 3D reference data within the sub‐pixel scale of the CLOUDMAP sensors. The main product is an Apparent Stereoscopic Cloud Height (ASCH) with a systematic error resulting from the cloud drift component in the ground track direction of MOMS. Estimates of cloud shadow height and shadow drift were applied to correct for this effect. The cloud data evaluation was based on software of DLR for surface photogrammetry. Cloud to shadow matching was accomplished with radiometric inverted cloud shadow regions. The validation of the applied procedures was based upon the redundancy of the results of different stereo pairs and upon an independent evaluation of the along and cross track components of the cloud and shadow parallaxes.

Generation of metastable helium and the 1083 nm emission in the upper thermosphere

Models of metastable helium, He(23S), production in the upper thermosphere and lower exosphere show that creation by recombination of He+ may be nonnegligible relative to the photoelectron impact on He(11S) source. Owing to large ground state He abundance in the winter and to photoelectrons from an illuminated conjugate thermosphere, the strongest 1083 nm intensities (arising from He(23S) solar resonance) occur during the winter at Arecibo. During late spring and early fall, however, recombination of the nighttime He+ layer begins to compete as a source of metastable He, and the contribution to the early twilight 1083 nm airglow brightness from recombinant He(23S) reaches more than 10%, regardless of solar activity levels, and becomes increasingly dominant for solar zenith angles greater than 105°. A hot metastable component from recombination potentially renders ambiguous interpretation of the 1083 nm spectral profile in terms of exospheric temperature. The presence of such a population may explain reported observations of 1083 nm line widths that increase with shadow height, implying twilight temperatures much hotter than those expected of a thermalized neutral population.

Comparison of aerosol vertical profiles derived by passive and active remote sensing techniques—a case study

Abstract Simultaneous observations were carried out with twilight photometer and lidar at the National MST Radar Facility (NMRF), Gadanki (13.45°N, 79.18°E) during March 2003, in order to validate the photometer derived profiles, especially the relative heights of the observed dust layers. The aerosol vertical profiles retrieved by both the techniques were compared. The comparison was found to be qualitative. The results showed that the screening height (correction factor to the geometrical Earth's shadow height) for twilight technique was about 6 km for red light, below which no direct information on atmospheric aerosols can be obtained. The results evidenced the presence of high cirrus cloud with base height ranging from 11 to 14 km and stratospheric aerosol layer, or Junge layer (17–23 km), in the profiles derived by both the techniques.

Evidence for recombination as a significant source of metastable helium

A Fabry‐Perot spectrometer optimized for maximum near infrared (NIR) transmission and featuring a germanium detector with a quantum efficiency of 86% at 10,830 Å is used to measure the brightness and spectral width of the metastable helium emission in the upper thermosphere. Observations are made at the optical facility associated with the Millstone Hill Incoherent Scatter Radar site in Massachusetts and at the optical facility associated with the Arecibo Observatory in Arecibo, Puerto Rico. Using a spectral resolution of 0.117 Å, these are the first observations to isolate the metastable helium triplet 2p3P0,1,2–2s3S1 from nearby OH airglow contamination. Measured 10,830 Å brightness decays with shadow in a manner consistent with an emission that is due to resonant scattering of the solar 10,830 Å emission. Although the technique we describe was conceived as a powerful tool to measure upper thermospheric and exospheric temperatures, the data indicate a surprising increase of temperature with shadow height to values much greater than commonly ascribed to the near solar minimum thermosphere. We assert that the broad 10,830 Å spectral line widths, retrieved when the shadow heights are above ∼300 km, are due to a nonthermal metastable helium population. This source of hot, metastable helium is very likely He+ recombination in the twilight. That conclusion is contrary to an historical understanding that the dominant source of metastable helium is the impact of photoelectrons with energies in excess of 19.8 eV with ground state helium.

SR90, Strontium Shaped‐Charge Critical Ionization Velocity Experiment

In May 1986 we carried out an experiment to test Alfvén's critical ionization velocity (CIV) effect in free space, using the first high‐explosive shaped charge with a conical liner of strontium metal. The release, made at 540 km altitude at dawn twilight, was aimed at 48° to B. The background electron density was 1.5×104 cm−3. A faint field‐aligned Sr+ ion streak with tip velocity of 2.6 km s−1 was observed from two optical sites. Using two calibration methods, we calculate that between 4.5×1020 and 2×1021 ions were visible. We have calculated an ionization time constant of 1920 s for Sr from the solar UV spectrum and ionization cross section, which combined with a computer simulation of the injection predicts 1.7×1021 solar UV ions in the low‐velocity part of the ion streak. Thus all the observed ions are from solar UV ionization of the slow (less than critical) velocity portion of the neutral jet. The observed neutral Sr velocity distribution and computer simulations indicate that 2×1021 solar UV ions would have been created from the fast (greater than critical) part of the jet. They would have been more diffuse and were not observed. Using this fact, we estimate that any CIV ions created were less than 1021. We conclude that future Sr CIV free space experiments should be conducted below the UV shadow height and in much larger background plasma density.

Geocoronal structure: 3. Optically thin, Doppler‐broadened line profiles

Theoretical line profiles, applicable to the analysis of geocoronal Hα profile measurements, are presented for illustrative cases. While retaining a number of simplifications (classical exobase and diffusive equilibrium plasmasphere conditions), distinctive spectral signatures of mechanisms governing the geocorona are isolated. Examining the consequences of solar radiation pressure dynamics is the main point here. In the prototype evaporative case, radiation pressure acts to form narrow profiles via the creation of an extensive quasi‐satellite component. Comparison with a simple extension of the earlier analytic theory discloses the influence of an exopause in this regard. The main modifications to evaporative spectral shapes in the geocoronal application, for shadow heights greater than 2 RE, are predicted to be (1) a blueward “shift” or bias near line center, for look directions parallel to the antisolar axis, generated by loss mechanisms acting over the time of flight of exospheric constituents (for example, solar ionization) and (2) an enhanced red ward wing at spectral displacements exceeding that defined by the shadow height escape speed, produced by plasmaspheric charge exchange collisions. Implications of these results for recent observations of geocoronal Hα line profiles are briefly discussed.

The effect of shading on the design of a field of solar collectors

General expressions are derived for the shading and insolation of a field of solar thermal or photovoltaic collectors. The shading on a collector may be cast by its neighbour and/or by a fence, and is dependent on the spacing between collectors, and on collector height, row length, tilt angle and latitude location. The equations for the shadow height, length and area are given in dimensionless form and are therefore general relations. The derivations pertain to collectors arranged in rows in a horizontal plane, or raised in a step-like structure. The field may be oriented either towards the equator, or towards any azimuth. The equations for the collector insolation include the direct, diffuse and global insolation for the above collector fields. The variation of the shadow on the collector during the day is most important in solar system design, where the performance is highly affected by the shape of the shadow as found in photovoltaic systems. The results of this study may be used for the design and performance analysis of a field of solar collectors (thermal or photovoltaic).