Sky Component Research Articles

Enhancing daylighting predictions in urban planning: A workflow for setting bespoke Vertical Sky Component (VSC) targets

In Sweden, urban planners are legally obligated to design neighbourhoods that allow future buildings to meet daylight requirements. However, this is challenging because planners can only define the building masses, without control over future building details such as glazing ratios, room layouts, and orientation.The Vertical Sky Component (VSC) is a well-established indicator for early daylight assessments of buildings, and it is often used by Swedish urban planners to verify daylight access for their massing designs, even though it has its limitations. A VSC target value VSC ≥ 27 % has been widely applied in the urban planning practice. However, a single universal VSC target does not necessarily guarantee compliance with daylight requirements indoors. This article proposes a workflow for setting bespoke VSC targets. The goal is to provide urban planners with more reliable tools for early daylighting predictions. The workflow uses parametric simulations to establish VSC thresholds that assure compliance with current daylight regulations, such as the Swedish building code (BBR) and the European standard (EN 17037). While this article focuses on Sweden, the workflow could be readily applied to any location with prevalence of overcast sky conditions. Some potential practical urban planning applications of the workflow are suggested.

Disentangling the anisotropic radio sky: Fisher forecasts for 21 cm arrays

ABSTRACT The existence of a radio synchrotron background (RSB) excess is implied by a number of measurements, including excess emission seen by the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) and Long Wavelength Array (LWA) experiments. Highly sensitive wideband radio arrays, of the kind used to measure the cosmic 21 cm signal, provide a promising way to further constrain the RSB excess through its anisotropy, providing additional insight into its origin. We present a framework for evaluating the potential of 21 cm arrays to disentangle different components of the diffuse radio sky based on the combination of their frequency spectrum and angular power spectrum. The formalism is designed to calculate uncertainties due to the intrinsic cosmic variance alone or together with instrumental noise. In particular, we predict the potential for measuring the anisotropy of a broad generalized class of excess radio background models using the low-frequency Hydrogen Epoch of Reionization Array (HERA) as an example. We find that a HERA-like array can distinguish an RSB excess from other sky components based on its angular clustering and spectral dependence, even if these are quite similar to one or more of the other components – but only in the case that the RSB excess is relatively bright.

Sub-kpc scale gas density histogram of the galactic molecular gas: a new statistical method to characterise galactic-scale gas structures

Abstract To understand physical properties of the interstellar medium (ISM) on various scales, we investigate it at parsec resolution on the kiloparsec scale. Here, we report on the sub-kpc scale Gas Density Histogram (GDH) of the Milky Way. The GDH is a density probability distribution function (PDF) of the gas volume density. Using this method, we are free from an identification of individual molecular clouds and their spatial structures. We use survey data of 12CO and 13CO (J=1–0) emission in the Galactic plane (l = 10○–50○) obtained as a part of the FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45m telescope (FUGIN). We make a GDH for every channel map of 2○ × 2○ area including the blank sky component, and without setting cloud boundaries. This is a different approach from previous works for molecular clouds. The GDH fits well to a single or double log-normal distribution, which we name the low-density log-normal (L-LN) and high-density log-normal (H-LN) components, respectively. The multi-log-normal components suggest that the L-LN and H-LN components originate from two different stages of structure formation in the ISM. Moreover, we find that both the volume ratios of H-LN components to total (fH) and the width of the L-LN along the gas density axis (σL) show coherent structure in the Galactic-plane longitude-velocity diagram. It is possible that these GDH parameters are related to strong galactic shocks and other weak shocks in the Milky Way.

Automation and optimization in daylight analysis and life cycle assessment for automated daylight monitoring device for a metro rail station box in Ahmedabad, India

Daylight analysis and optimization are pre-requisites for energy-efficient and sustainable infrastructure. Conventional practices of designing and providing artificial lighting often ignore the consideration of the availability of natural daylight for the infrastructure. This paper aims to analyze the availability and potential of natural daylight reviewing the sky component type at a designated location, real-time sensor-based illuminance measurement on-site and BIM-based daylight simulation. Consequently, a sensor prototype was deployed to the metro rail station for automated optimization. Firstly, the sky component type of Ahmedabad was determined based on the literature review. Subsequently, sensors were integrated at the strategic grid point location covering the entire metro rail station to collect real-time Illuminance for daylight factor calculation. Furthermore, BIM-based sun path and shadow analysis and daylight simulation were carried out to suggest the possibility and potential of daylight savings. Finally, based on all the analysis and results, a newly designed sensor-based prototype was developed and equipped to enhance automated optimization for daylight savings, which resulted in 29% energy savings monthly. This approach significantly helps the project stakeholders to enhance building energy performance and lead a step closer towards sustainable infrastructure.

Analysing the Daylighting Performance of the Main Prayer-hall in the Great Mosque of Hama, Syria

Daylighting and solar availability at urban scale has come to play a crucial role in the perception of discomfort conditions for people, both in outdoor and indoor spaces, and on the energy consumption of buildings. Daylighting and solar analyses are typically done separately. The paper presents a novel method, called the ‘sunlight-daylight signature’ (SDS), which allows the qualitative analysis of urban settings with respect to sunlight and daylight. The method can be used to classify different urban settings in terms of daylight/sunlight access or to test new development proposals by referring to existing locations and confirm whether a certain daylight quality is met. The SDS relies on a new analysis tool, called ‘sunlight-daylight wedge’ (SDW), which combines obstruction (through the vertical sky component VSC) and sunlight access (through the annual probable sunlight hours PASH and the winter probable sunlight hours PWSH). The orientation of the façade at each point is also included as it will affect the times of the day when the sun-hours from PASH and PWSH occur, thus affecting the character of the corresponding sunlight. The SDS approach is based on a clustering technique to subdivide large datasets (in this case, daylight data points across entire cities or major urban areas) into smaller groups, using machine learning by way of the k-medoids clustering technique. This is used to derive typical daylight and sunlight scenarios representing groups of data points with similar conditions. Additional data is included to account for urban density and daylight availability in public areas. Final output of the clustering process consists of a map showing areas with the same daylight signature (SDS), which means areas with the same sunlight and daylight conditions. The SDS can be useful for urban planners and building practitioners to predict the access to both daylight and sunlight of large urban settings to optimize comfort for people and energy usage.

Vertical Sky Component (VSC) and daylight regulation compliance by the EN 17037 and BFS 2011:6 standards

This paper explores the relationship between the Vertical Sky Component (VSC) metric and the European and Swedish daylighting regulations. VSC, a static geometrical metric, is considered a useful early indicator of indoor daylighting, as it is insensitive to late-stage design details such as material properties and internal layout. However, its relationship with modern building daylighting legislation has not been established. To address this gap, the paper investigates the relationship of VSC and daylight compliance by static and dynamic methods through simulations of a ‘shoebox’ room with varying Window-to-Floor Ratios (WFRs) and external obstruction dimensions. The results demonstrate that VSC has a large effect on daylighting compliance and can be a useful early planning tool. The study concludes that using VSC as a daylighting indicator in the urban planning process can lead to improved early design routines for better daylight compliance in the late design stages. Future work should aim to establish VSC performance thresholds.

Sky subtraction of LAMOST at bright night

ABSTRACT Sky subtraction is a crucial step in the data reduction process for LAMOST, including dark, bright, and grey nights. During the pilot survey, on bright nights, atmospheric scattering of moonlight can introduce gradients in the sky background. In observations during bright moonlit nights, the sky component is significant, and sometimes, variations in colour can be observed in the sky spectra. This phenomenon is not universally present during observations on bright moonlit nights. Taking this into consideration, this paper proposes a weighted trend-surface method to reconstruct the sky component within the science target fibre, aiming to achieve the subtraction of the sky component. We constructed a sky model using a trend surface, utilizing data from all sky fibre spectra on the same spectrograph to predict the sky component for each fibre spectrum. Subsequently, the reconstructed sky spectrum data were compared with the actually observed sky spectrum data and the ‘super sky’ from LAMOST’s pipeline. The results indicate that our method is closer to the observed real sky spectrum than the ‘super sky’, showing smaller residuals and variance, with an average closer to zero. This method serves as a viable solution, particularly when dealing with colour variations observed during bright moonlit nights.

Sunlight-Daylight Signature: a Novel Concept to Assess Sunlight and Daylight Availability at Urban Scale

Daylighting and solar availability at urban scale has come to play a crucial role in the perception of discomfort conditions for people, both in outdoor and indoor spaces, and on the energy consumption of buildings. Daylighting and solar analyses are typically done separately. The paper presents a novel method, called the ‘sunlight-daylight signature’ (SDS), which allows the qualitative analysis of urban settings with respect to sunlight and daylight. The method can be used to classify different urban settings in terms of daylight/sunlight access or to test new development proposals by referring to existing locations and confirm whether a certain daylight quality is met. The SDS relies on a new analysis tool, called ‘sunlight-daylight wedge’ (SDW), which combines obstruction (through the vertical sky component VSC) and sunlight access (through the annual probable sunlight hours PASH and the winter probable sunlight hours PWSH). The orientation of the façade at each point is also included as it will affect the times of the day when the sun-hours from PASH and PWSH occur, thus affecting the character of the corresponding sunlight. The SDS approach is based on a clustering technique to subdivide large datasets (in this case, daylight data points across entire cities or major urban areas) into smaller groups, using machine learning by way of the k-medoids clustering technique. This is used to derive typical daylight and sunlight scenarios representing groups of data points with similar conditions. Additional data is included to account for urban density and daylight availability in public areas. Final output of the clustering process consists of a map showing areas with the same daylight signature (SDS), which means areas with the same sunlight and daylight conditions. The SDS can be useful for urban planners and building practitioners to predict the access to both daylight and sunlight of large urban settings to optimize comfort for people and energy usage.

SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-sky Surface-brightness Measurements. I. Survey Overview and Methods

We give an overview and describe the rationale, methods, and testing of the Hubble Space Telescope (HST) Archival Legacy project “SKYSURF.” SKYSURF uses HST’s unique capability as an absolute photometer to measure the ∼0.2–1.7 μm sky-surface brightness (sky-SB) from 249,861 WFPC2, ACS, and WFC3 exposures in ∼1400 independent HST fields. SKYSURF’s panchromatic data set is designed to constrain the discrete and diffuse UV to near-IR sky components: Zodiacal Light (ZL), Kuiper Belt Objects (KBOs), Diffuse Galactic Light (DGL), and the discrete plus diffuse Extragalactic Background Light (EBL). We outline SKYSURF’s methods to: (1) measure sky-SB levels between detected objects; (2) measure the discrete EBL, most of which comes from AB≃17–22 mag galaxies; and (3) estimate how much truly diffuse light may exist. Simulations of HST WFC3/IR images with known sky values and gradients, realistic cosmic ray (CR) distributions, and star plus galaxy counts were processed with nine different algorithms to measure the “Lowest Estimated Sky-SB” (LES) in each image between the discrete objects. The best algorithms recover the LES values within 0.2% when there are no image gradients, and within 0.2%–0.4% when there are 5%–10% gradients. We provide a proof of concept of our methods from the WFC3/IR F125W images, where any residual diffuse light that HST sees in excess of zodiacal model predictions does not depend on the total object flux that each image contains. This enables us to present our first SKYSURF results on diffuse light in Carleton et al.

Resolving Radiant: Combining Spatially Resolved Longwave and Shortwave Measurements to Improve the Understanding of Radiant Heat Flux Reflections and Heterogeneity

We introduce and demonstrate new measurement and modeling techniques to fully resolve the spatial variation in shortwave and longwave radiant heat transfer in the outdoor environment. We demonstrate for the first time a way to directly resolve the shortwave radiant heat transfer from terrestrial reflected and diffuse sky components along with the standard direct solar radiation using an adapted thermopile array and ray-tracing modeling techniques validated by 6-direction net radiometer. Radiant heat transfer is a major component of heat experienced in cities. It has significant spatial variability that is most easily noticed as one moves between shade and direct solar exposure. But even on a cloudy and warm day the invisible longwave infrared thermal radiation from warm surfaces makes up a larger fraction of heat experienced than that caused by convection with surrounding air. Under warm or hot climate conditions in cities, radiant heat transfer generally accounts for the majority of heat transfer to people. Both the shortwave (visible/solar) and the longwave (infrared/thermal) have significant spatial variation. We demonstrate sensor methods and data analysis techniques to resolve how these radiant fluxes can change the heat experienced by >1 kWm−2 across small distances. The intense solar shortwave radiation is easily recognized outdoors, but longwave is often considered negligible. Longwave radiation from heat stored in urban surfaces is more insidious as it can cause changes invisible to the eye. We show how it changes heat experienced by >200 Wm−2. These variations are very common and also occur at the scale of a few meters.

Optimization of Daylighting Outdoor Availability in Urban Kampung

Liveability interprets as making residents comfortable in their built environment. As daylighting becomes a necessity for human beings, daylight availability can improve the liveability of dwelling habitats, especially in high-density urban areas. Relayouting the building block without reducing the usable floor area can improve daylight availability. Kampung Braga is an example of how a heavy slum area has a low liveability quality and classifies into impoverished slum settlements at the stake of being resettled. The spatial arrangement becomes necessary to enhance the community’s quality of life. This article aims to examine how the intervention through urban layout can affect daylight availability to improve the liveability for kampung Braga. This research uses simulation methods with climate-based daylight modelling (CBDM) software to simulate daylighting with a dynamic approach. Rhinoceros for modelling, Honeybee for vertical sky component (VSC) simulation, and DIVA for daylight availability simulation. Based on the simulation on three alternative urban layouts in line with spatial plan context, it is shown that intervention through urban layout and typology of kampung Braga has shown better VSC and daylight availability values than the existing conditions. It is necessary to pay attention to the context of the building around the site when designing a specific building typology. Modifying configuration, floor height, model, and orientation show a better VSC reception and vertical facade illumination. City stakeholders need to be aware of the low liveability of the urban kampung. Planning the right urban plan design can improve daylighting availability and increase the liveability of the urban kampung.

LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N): subtraction of geocoronal Hα emission

We introduce a method of subtracting geocoronal Hα emissions from the spectra of LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N). The flux ratios of the Hα sky line to the adjacent OH λ6554 single line do not show a pattern or gradient distribution in a plate. More interestingly, the ratio is well correlated to solar altitude, which is the angle of the Sun relative to the Earthʼs horizon. It is found that the ratio decreases from 0.8 to 0.2 with the decreasing solar altitude from –17 to –73 degree. Based on this relation, which is described by a linear function, we can construct the Hα sky component and subtract it from the science spectrum. This method has been applied to the LAMOST-MRS-N data, and the contamination level of the Hα sky to nebula is reduced from 40% to less than 10%. The new generated spectra will significantly improve the accuracy of the classifications and the measurements of physical parameters of Galactic nebulae.

SKAO H i intensity mapping: blind foreground subtraction challenge

ABSTRACT Neutral Hydrogen Intensity Mapping (H i IM) surveys will be a powerful new probe of cosmology. However, strong astrophysical foregrounds contaminate the signal and their coupling with instrumental systematics further increases the data cleaning complexity. In this work, we simulate a realistic single-dish H i IM survey of a 5000 deg2 patch in the 950–1400 MHz range, with both the MID telescope of the SKA Observatory (SKAO) and MeerKAT, its precursor. We include a state-of-the-art H i simulation and explore different foreground models and instrumental effects such as non-homogeneous thermal noise and beam side lobes. We perform the first Blind Foreground Subtraction Challenge for H i IM on these synthetic data cubes, aiming to characterize the performance of available foreground cleaning methods with no prior knowledge of the sky components and noise level. Nine foreground cleaning pipelines joined the challenge, based on statistical source separation algorithms, blind polynomial fitting, and an astrophysical-informed parametric fit to foregrounds. We devise metrics to compare the pipeline performances quantitatively. In general, they can recover the input maps’ two-point statistics within 20 per cent in the range of scales least affected by the telescope beam. However, spurious artefacts appear in the cleaned maps due to interactions between the foreground structure and the beam side lobes. We conclude that it is fundamental to develop accurate beam deconvolution algorithms and test data post-processing steps carefully before cleaning. This study was performed as part of SKAO preparatory work by the H i IM Focus Group of the SKA Cosmology Science Working Group.

Recovering the 21-cm signal from simulated FAST intensity maps

ABSTRACT The 21-cm intensity mapping (IM) of neutral hydrogen (H i) is a promising tool to probe the large-scale structures. Sky maps of 21-cm intensities can be highly contaminated by various foregrounds, such as Galactic synchrotron radiation, free–free emission, extragalactic point sources, and atmospheric noise. Here we present a model of foreground components and a method of removal, in particular to quantify the potential of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) for measuring H i IM. We consider a 1-yr observational time with a survey area of $20\,000\, {\rm deg}^{2}$ to capture significant variations of the foregrounds across both the sky position and angular scales relative to the H i signal. We first simulate the observational sky and then employ the principal component analysis (PCA) foreground separation technique. We show that by including different foregrounds, and thermal and 1/f noises, the value of the standard deviation between the reconstructed 21-cm IM map and the input pure 21-cm signal is $\Delta T = 0.034\, {\rm mK}$, which is well under control. The eigenmode-based analysis shows that the underlying H i eigenmode is just less than the 1 per cent level of the total sky components. By subtracting the PCA-cleaned foreground + noise map from the total map, we show that PCA method can recover H i power spectra for FAST with high accuracy.

An enhanced cloud segmentation algorithm for accurate irradiance forecasting

This paper presents a novel approach to calculate cloud cover under any illumination conditions for short-term irradiance forecasting. A sky-imaging system, in parallel with an irradiance measurement, is set up to collect a database of sky images and irradiance readings. The colour space operations and various image segmentation methods are investigated to improve the visual contrast of the cloud component. Experimental results shows the effectiveness of applying the Normalized Blue-to-Red Ratio (NBRR) colour operation for high-illumination condition and the Red/Green channel for the low-illumination condition. The pre-processed sky images are then fed into Minimum Cross Entropy (MCE) adaptive thresholding segmentation, which effectively differentiates the sky and cloud components for all-sky images. The cloud fraction calculation is employed for the segmented images as an indication of cloud coverage. The proposed method demonstrates a positive linear correlation between cloud fraction and real-time irradiance data.

Predicting diffuse solar irradiance on obstructed building façades under irregular skyline patterns for various ISO/CIE standard skies

Solar irradiance data on building façades are important for BIPV system evaluations and energy-efficient building designs. In urban cities where the building façades are always obscured by surrounding buildings, the determination of sky-diffuse solar irradiance can be complex. Previously, a mathematical model was proposed to estimate the obstructed vertical sky component (OVSC) under various skies by assuming that the obstructions are infinitely long. However, more often, in actual cases, the opposite obstructions are surfaces with different heights in azimuth which can form various irregular skyline patterns. Therefore, this study proposes new methods to determine vertical sky-diffuse solar irradiance on building façades under complex irregular obstructions. Various configurations of irregular obstructions were identified by a proposed quantification method, and the OVSCs were simulated using RADIANCE package. The simulated results were used to correlate with those of infinitely-long urban canyons. Both Artificial Neural Networks (ANN) based model and simple regression model were proposed to find the correlations between various angles defining the irregular obstruction and the equivalent obstruction angles of corresponding infinitely-long cases. The R2 values of the ANN model and regression model against simulated results using the testing datasets were above 0.97 and 0.98, respectively. Field measurements were carried out for model validations and the R2 value between the proposed methods and the measured readings was 0.8. The findings are significant to PV system designs, daylighting scheme evaluations and low/zero-energy building designs under complex obstructed environments.

Probing frequency-dependent half-wave plate systematics for CMB experiments with full-sky beam convolution simulations

ABSTRACT We study systematic effects from half-wave plates (HWPs) for cosmic microwave background (CMB) experiments using full-sky time-domain beam convolution simulations. Using an optical model for a fiducial spaceborne two-lens refractor telescope, we investigate how different HWP configurations optimized for dichroic detectors centred at 95 and 150 GHz impact the reconstruction of primordial B-mode polarization. We pay particular attention to possible biases arising from the interaction of frequency-dependent HWP non-idealities with polarized Galactic dust emission and the interaction between the HWP and the instrumental beam. To produce these simulations, we have extended the capabilities of the publicly available beamconv code. To our knowledge, we produce the first time-domain simulations that include both HWP non-idealities and realistic full-sky beam convolution. Our analysis shows how certain achromatic HWP configurations produce significant systematic polarization angle offsets that vary for sky components with different frequency dependence. Our analysis also demonstrates that once we account for interactions with HWPs, realistic beam models with non-negligible cross-polarization and sidelobes will cause significant B-mode residuals that will have to be extensively modelled in some cases.

Daylight and energy as active drivers in the design process of a new school in Enköping, Sweden

With the introduction of new demands targeting net-zero energy and net zero-carbon buildings and neighbourhoods on a national level in Sweden and internationally, balancing the requirements of daylight and energy is becoming more important in the design process. In order to succeed, an effective strategy needs to be defined for utilising the right digital tools and metrics for the two factors at different times in the process, and in an integrated way. This paper presents the workflow used whilst developing the concept for a new school in Enköping, Sweden (59.633°N, 17.086°E). The analyses performed during the design process included vertical sky component, daylight factor and early-stage energy calculations. Implementing photovoltaic (PV) cells and energy-efficient lighting design were also included as part of a strategy for reducing primary energy consumption. It was found that daylight and energy can be effectively balanced if an integrated strategy is followed during early stages of the design process. National regulations can also be met, and the time required for running simulations can be reduced by a factor of three by having an effective process.

Daylight compliance of residential spaces: Comparison of different performance criteria and association with room geometry and urban density

Currently, policy makers in Sweden are considering updating building regulations with respect to daylight provision. Given this context, the present paper aims to provide insight on the level of compliance of residential spaces when tested against five daylight performance criteria. These included the criterion currently in force in Sweden, the two performance criteria set by European Standard EN17037, a daylight factor-based criterion (BREEAM) and a climate-based criterion founded on the UDI metric. Compliance was tested by performing Radiance simulations on a representative sample of Swedish multi-dwelling buildings, including 10888 rooms. The criteria were compared according to the compliance they yield for different buildings and room types. Compliance per criterion was also associated with room geometry to evaluate which geometric measures affect it most substantially, and with urban density to evaluate which criterion best captures the effect of surrounding obstructions. Results indicate that the implementation of different criteria deem different building types to be better or worse performing. A consistent finding is that the vast majority of evaluated spaces are deemed to be incompliant when tested against the daylight-factor-based criterion of EN17037, which is significantly harder to comply with compared to its climate-based counterpart. The highest compliance is achieved when testing against the current Swedish criterion. The results also indicate that the Vertical Sky Component and glass-to-floor ratio affect compliance most substantially compared to other geometric measures. Finally, when daylight compliance was associated with urban density, the strongest association was acquired when rooms were tested using the UDI criterion.

Optimization of Daylight Factor Distribution Using Standard Deviations Based on Shifting Window Position

Natural lighting is an important factor that affects the comfort of building users. Natural lighting in a room requires a window area of ​​at least 1/6 of the floor area. This study was conducted to obtain the distribution of Daylight Factor (DF) as a natural lighting factor during the day in the room, based on the shift in the position of the window on the wall. The distribution of lighting entering the depth of the room through window openings is a tool to compare the best window position in the spread of illumination with DF calculations based on Sky Component (SC). Shifting the window position will be analyzed by Standard Deviation (S) and Mean (μ) based on the DF distribution. Optimizations of the DF distribution on the window position shifts if it has the largest DF mean value and the smallest DF variant value. The results of the study in a simple room showed that the optimal DF distribution was at the window position in the middle and the mean value was 2.59%. The relationship of shifting window position and DF distribution can be useful for architects to determine the function of a room in architectural design.