Diffuse Solar Radiation Research Articles

TRUST-DART: Land Surfaces Temperature and Emissivity Nonlinear Mapping from Nonisothermal Mixed Pixels of Satellite Images with the DART 3D Radiative Transfer Model

Abstract. Coarse spatial resolution of Thermal Infrared (TIR) satellites hampers measuring the temperature and emissivity of scene elements from space that improves our understanding of land surfaces' thermal behavior. The stringent conditions of current TIR unmixing methods hinder the production of extensive component temperature and emissivity products. To address this, we designed a gradient-based multi-pixel physical model, TRUST-DART, to derive the temperature and emissivity of urban features from non-isothermal mixed pixels of satellite images using the DART 3D radiative transfer model. Unlike traditional TIR unmixing methods, TRUSTDART is not constrained by issues related to spatial, spectral, temporal resolution, angular, scene, field measurement requirements, or manual operations. Its inputs include an at-surface radiance image, downwelling sky irradiance, a 3D urban mock-up with feature information, and DART input parameters such as spatial resolution. It generates maps of emissivity and temperature per urban feature. Its accuracy is validated for two vegetation and urban scenes and two types of images (DART simulated pseudo satellite and ASTER observed images). The accuracy of the TRUST-DART depends heavily on the fraction of components. TRUST-DART proves robust for high-fraction components. However, its accuracy decreases with decreasing fractions. TRUST-DART is distributed with DART and is available for education and research via Toulouse III University (https://dart.omp.eu).

Thermal performance of a double-layer pipe-embedded phase change wall system in wood structures coupled with solar energy

In this study, we propose a dual-layer, pipe-embedded phase change wall system for wooden structures that integrates sky radiation cooling and solar heat collection for cross-seasonal operation. This system harnesses renewable energy and reduces the operational energy consumption of buildings. The primary focus of this study is the performance improving of the system during winter conditions. In winter, the system captures solar energy for daytime indoor heating and load reduction and stores excess heat in phase-change material (PCM) embedded within the wooden wallboard. The stored heat is then released at night to further reduce building loads. To assess the thermal performance of the proposed wall system under winter conditions, experiments were conducted across four different scenarios and a reference system was established for comparative analysis. The results indicate that the proposed wall system significantly improves the indoor thermal environment. Specifically, this integration increased the average indoor air temperature by 6.0 °C compared to the reference system and substantially increased the temperature of the wallboard. The inclusion of PCM notably enhanced the thermal performance by reducing nighttime heat loss. Consequently, the average indoor temperature in systems equipped with PCM-enhanced wallboards was 3.0 °C higher than that in the reference system.

A minute-resolution downscaling algorithm for high-resolution global irradiance time series

Numerous studies have demonstrated the significant impact of the resolution of solar irradiation data on the outcomes of hourly production models. Accurate integration of photovoltaic (PV) systems sometimes demands a high-resolution global horizontal irradiance (GHI) time series to capture the rapid fluctuations in PV power output induced by swift irradiance changes. Most of the available databases provide data at hourly resolution, leading to a lack of accuracy in PV simulations. Those existing hourly averages of global horizontal irradiance in open sources fail to represent this volatility adequately, especially when PV systems are coupled with fast ramp rate technologies. In the present work, an easy-to-use algorithm is implemented to synthesize high-resolution GHI time series from hourly averaged and clear sky irradiance datasets. By employing Linear interpolation, a technique that helps to achieve the desired time resolution and afterward computing critical factors, the algorithm identifies periods characterized by short-term weather phenomena, thus creating a high-resolution time series that accurately represents these dynamics. Avoiding the probabilistic components and machine learning techniques conserves computational power and reduces calculation time, but this comes at the cost of reduced fidelity in reproducing the results. Improving accuracy in PV simulations is not always directly related to reproducing real phenomena, but enhancing the amount of information contained in the data is sufficient. This study’s approach enhances user-friendliness and facilitates seamless integration into existing energy modeling frameworks, aiming for representation with sub-hourly time steps. The algorithm’s effectiveness is demonstrated by applying the model to hourly averaged data to revert them to a one-minute time step, and finally comparing the synthetically produced one-minute GHI data to the original measured data. The comparative analysis between synthesized and measured data demonstrated a strong agreement, with normalized mean bias error (MBE) values ranging between 1.8% and 9.6% and normalized root mean square error (NRMSE) values between 2.7% and 16.1%, depending on weather conditions. Additionally, the coefficient of determination (R2) consistently remained above 0.64. Successful algorithm validation makes our algorithm suitable for use in meteorological datasets and locations, with similar climatic characteristics.

Intercomparison of aerosol optical depth retrievals from GAW-PFR and SKYNET sun photometer networks and the effect of calibration

Abstract. In this study, we assess the homogeneity of aerosol optical depth (AOD) between two sun photometer networks, the Global Atmosphere Watch-Precision Filter Radiometer (GAW-PFR) and the European SKYNET radiometers network (ESR), at the common wavelengths of their main instruments (500 and 870 nm). The main focus of this work is to evaluate the effect of the improved Langley plot calibration method (ILP) used by SKYNET and to investigate the factors affecting its performance. We used data from three intercomparison campaigns that took place during 2017–2021. Each campaign was organized at two locations (mountainous rural – Davos, Switzerland; urban – Rome, Italy). Our analysis shows that differences in AOD due to post-processing and instrument differences are minor. The main factor leading to AOD differences is the calibration method. We found a systematic underestimation of AOD in ESR compared to in GAW-PFR due to underestimation of the calibration constant calculated with the ILP method compared to the calibration transfers using the PFR as a reference. The calibration and AOD differences are smaller in Davos, where the traceability criteria are satisfied at 870 nm and where the median differences are below 0.01 at 500 nm. In Rome, the AOD median differences at 500 nm were in the 0.015–0.034 range. We conducted a sensitivity study, which shows that part of the difference can potentially be explained by errors in the assumed surface albedo and instrument solid-view angle provided as inputs to the ILP code (based on Skyrad pack 4.2). Our findings suggest that the ILP method is mainly sensitive to the measured sky radiance. The underestimation in calibration is probably caused by an error in the retrieved scattering AOD (sc-AOD) through the sky radiance inversion. Using an alternative retrieval method (Skyrad MRI pack version 2) to derive sc-AOD and to recalibrate the instruments with the ILP method, we found no significant differences between the retrieved sc-AOD and no systematic increase in the ILP-derived calibration constant when using the MRI pack for sc-AOD inversion instead of the Skyrad 4.2. The potential error may be a result of the model assumptions used for the sky radiance simulations. In conclusion, the on-site calibration of sun photometers has several advantages, including the fact that instrument shipments and data gaps can be avoided. However, it has also the disadvantages of a larger uncertainty and significant systematic differences compared to the traditional Langley calibration performed under low- and constant-AOD conditions at high-altitude sites. The larger uncertainty of the ILP method can be attributed to the required modelling and input parameters.

Comparative validation of global and climate-specific decomposition models at high latitudes

Reliable modelling of the solar potential of urban surfaces (i.e. roofs, facades and ground) in the built environment can contribute to boost the exploitation of solar energy. Empirical and quasi-physical models are combined into model chains for this scope. Among these models, the decomposition models are used to separate the direct from the diffuse solar irradiance. Such variables are rarely measured, thus making necessary their computation. Studies in literature pointed out that Yang4 is the best-performing decomposition model globally. However, in geographically limited applications, quasi-universal decomposition models like Yang4 and Engerer4 can be outperformed by local models (i.e. models parametrized with climate-specific data) such as Skartveit3 and Starke3. This makes necessary to perform local validation studies to verify the findings from worldwide validation studies. In this study, the four best-performing decomposition models are implemented in Python and experimentally validated against 1-min solar irradiance data (i.e. direct and diffuse irradiance) of Trondheim (Lat. 63°26′N, Norway). More than 1-year long data are considered. The study confirms that the Yang4 model performed the best for high-latitude applications, but Starke3 can achieve a level of performance close to Yang4.

Two-stage estimation of hourly diffuse solar radiation across China using end-to-end gradient boosting with sequentially boosted features

Diffuse solar radiation (DR) constitutes a vital component of solar energy reaching the surface of the Earth. The demand for extensive temporal and spatial coverage of DR data has intensified in the realms of solar energy harvesting, agriculture, and climate change. However, until now, long-term DR observations have only been available from 17 stations across mainland China. Consequently, there is a pressing need to estimate spatially continuous, high-temporal-resolution DR for large-scale regions in China. The current hindrance to DR estimations stems from the scarcity of stations equipped with DR observations. This study proposes a two-stage strategy to efficiently estimate seamless DR in 2019 at a national scale, leveraging both DR and total solar radiation (TR) observations from numerous stations. In the first stage, the approach generates virtual DR at TR stations by establishing a learned relationship between DR and TR observations. Subsequently, in the second stage, these virtual DR data, in conjunction with satellite and reanalysis datasets, are utilized to estimate national-scale DR. Additionally, a novel model, End-to-end Gradient Boosting with Shortcuts and Feature selection (EGB-SF), is introduced to estimate DR over China. One advantage of this model is its consideration of the impact of sequentially boosted features and their interactions. Embedded shortcut connections fully exploit the influence of existing features on newly introduced ones during the learning process. Beyond enhancing the accuracy of DR estimation, the EGB-SF algorithm can also elucidate the relative importance levels of input features to the model. Moreover, the two-stage strategy outperforms the method of estimating national DR using only DR observations, as evidenced by its superior spatial generalization abilities. Statistical evaluation, collaborative analysis with influencing factors, and comparisons with related products confirm the accuracy and spatial continuity of the DR estimations in this study. These results furnish reliable DR data across China for research in agriculture, climate, solar radiation, and related fields.

Design and development of a portable tuneable radiation source from UV to IR for in situ calibration of radiometers measuring atmospheric aerosol properties.

Abstract We present the results of development of a portable tuneable radiation source (TuPS II) covering the broad spectral range from 300 nm up to 1700 nm. It was developed to provide SI-traceable in-situ calibration of bandpass functions of radiometers measuring both sky radiance and sky irradiance in the surface-based remote sensing networks for column integrated atmospheric aerosol properties. The TuPS II provides quasi-monochromatic radiation with spectral bandwidth smaller than 0.2 nm and central wavelength uncertainty lower than 0.05 nm for a specified number of aerosol wavelength bands ranging from to 300 nm to 1700 nm. In its design it represents an evolution with extended spectral capabilities of the TuPS (Smid, M. et al., 2021) that was successfully used to characterize Dobson spectrophotometers in the UV spectral range.

Aerosol Components Derived from Global AERONET Measurements by GRASP: A New Value-Added Aerosol Component Global Dataset and Its Application

Abstract Aerosols affect Earth’s climate both directly and indirectly, which is the largest uncertainty in the assessment of radiative forcings affecting anthropogenic climate change. The standard Aerosol Robotic Network (AERONET) aerosol products have been widely used for more than 30 years. Currently, there is strong community interest in the possibility of determining aerosol composition directly from remote sensing observations. This work presents the results of applying such a recently developed approach by Li et al. to extended datasets of the directional sky radiances and spectral aerosol optical depth (AOD) measured by AERONET for the retrievals of aerosol components. First, the validation of aerosol optical properties retrieved by this component approach with AERONET standard products shows good agreement. Then, spatiotemporal variations of the obtained aerosol component concentration are characterized globally, especially the absorbing aerosol species (black carbon, brown carbon, and iron oxides) and scattering aerosol species (organic carbon, quartz, and inorganic salts). Finally, we compared the black carbon (BC) and dust column concentration retrievals to the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), products in several regions of interest (Amazon zone, Indo-China Peninsula, North India, southern Africa, sub-Sahel, Gobi Desert, Middle East, Sahara Desert, and Taklamakan Desert) for new insights on the quantitative assessment of MERRA-2 aerosol composition products (R = 0.60–0.85 for BC; R = 0.75–0.90 for dust). The new value-added and long-term aerosol composition product globally is available online (https://doi.org/10.6084/m9.figshare.25415239.v1), which provides important measurements for the improvement and optimization of aerosol modeling to enhance estimation of the aerosol radiative forcing.

Heading Measurement Frame Based on Atmospheric Scattering Beams for Intelligent Vehicle

Heading Measurement Frame Based on Atmospheric Scattering Beams for Intelligent Vehicle

Bioelectrochemical performance on constructed wetland-microbial fuel cells operated under diffuse and direct solar radiation using root exudates as endogenous substrate to feed an electroactive biofilm

Exploiting fossil fuels through conventional technologies focused on energy production has led to severe environmental adversities, mainly affecting global warming and climate change. Constructed wetland-microbial fuel cells (CW-MFC) have emerged as an innovative technology that could mitigate these effects. One of the main limitations of the CW-MFC system is the low power density generated. This study evaluated the impact of diffuse (CW-MFC1) and direct (CW-MFC2) solar radiation intensity to enhance bioelectrochemical performance. To do this, the CW-MFC was inoculated with the Geobacter sulfurreducens bacteria as a bioelectrocatalyst, which was fed with the root exudates of the macrophyte Juncus effusus. The change from diffuse to direct solar radiation increased the electroactivity of the system by 43% in terms of power density, cathodic potential, anodic potential, and internal resistance, resulting in a maximum performance of 128.7 mW/m2, 172 mV, −290 mV, and 204 Ω respectively. This was obtained from a concentration of 35.3 mg/L of root exudates (total organic carbon). The analysis of results determined that solar radiation is a predominant factor that directly affects the photosynthetic efficiency and coulombic efficiency of CW-MFC by controlling the rhizodeposition process of the macrophytes, where the amount of bioelectricity produced depends on the amount of exudates discharged by the root system towards the rhizosphere.

Estimation of Diffuse Solar Radiation in the City of Natal – RN Based on the KT Index

Objective: This study aimed to validate and compare three models for estimating diffuse solar radiation in the city of Natal - RN, using data from the SONDA Project, with a focus on developing and validating the Ubial model. Theoretical Framework: The research is based on solar radiation concepts, which are essential for optimizing photovoltaic systems. Accurate models for estimating diffuse radiation are necessary for the efficient performance of these systems, especially in locations like Natal - RN. Method: The methodology adopted a quantitative and comparative approach, analyzing the Erbs, Bourges, and Ubial models. Data from the SONDA Project were used, and the statistical analysis included evaluating the Mean Bias Error (MBE) and correlating the data with the clearness index (Kt). Results and Discussion: The Ubial model showed superior performance, with a negative MBE, indicating greater accuracy without overestimating the data. These results were discussed in light of the theoretical framework, highlighting the suitability of the Ubial model for the climatic conditions of Natal - RN. Research Implications: The implications of this research include the potential application of the Ubial model in other regions with similar climatic characteristics, contributing to the optimization of photovoltaic systems. Originality/Value: This study introduces an innovative model that incorporates additional variables, resulting in more accurate estimates of diffuse solar radiation, with a direct impact on the solar energy field.

Evaluation of on-site calibration procedures for SKYNET Prede POM sun–sky photometers

Abstract. To retrieve columnar intensive aerosol properties from sun–sky photometers, both irradiance and radiance calibration factors are needed. For the irradiance the solar calibration constant, V0, which denotes the instrument counts for a direct normal solar flux extrapolated to the top of the atmosphere, must be determined. The solid view angle, SVA, is a measure of the field of view of the instrument, and it is important for obtaining the radiance from sky diffuse irradiance measurements. Each of the three sun-photometer networks considered in the present study (SKYNET, AERONET, WMO GAW) adopts different protocols of calibration, and we evaluate the performance of the on-site calibration procedures, applicable to every kind of sun–sky photometer but tested in this analysis only on SKYNET Prede POM01 instruments, during intercomparison campaigns and laboratory calibrations held in the framework of the Metrology for Aerosol Optical Properties (MAPP) European Metrology Programme for Innovation and Research (EMPIR) project. The on-site calibration, performed as frequently as possible (ideally monthly) to monitor changes in the device conditions, allows operators to track and evaluate the calibration status on a continuous basis, considerably reducing the data gaps incurred by the periodic shipments for performing centralized calibrations. The performance of the on-site calibration procedures for V0 was very good at sites with low turbidity, showing agreement with a reference calibration between 0.5 % and 1.5 % depending on wavelengths. In the urban area, the agreement decreases between 1.7 % and 2.5 %. For the SVA the difference varied from a minimum of 0.03 % to a maximum of 3.46 %.

Design and modeling of PV-integrated Double Skin Facades and application to retrofit buildings

Double Skin Façade (DSF) system comprises two glazing layers with a ventilated cavity. Integrating photovoltaic (PV) modules within the outer layer of DSFs offers an efficient method for electricity generation. Current tools for modeling and analyzing DSF systems are complex and resource-intensive, lacking the capability to evaluate the performance of innovative PV-DSF systems during the early design stage. This study develops a mathematical model to evaluate the electrical and thermal performance of PV-DSF systems, considering architectural design elements such as PV color and relative orientation. Based on an energy balance approach, the model is particularly suited for designing PV-DSF systems in heritage buildings, which often have color and relative orientation constraints. The model is applied to assess the performance of PV-DSF systems with conventional clear glass PV and colored front glass PV modules under the climatic conditions of Montreal, Canada. Results indicated that conventional clear glass PV module exhibit higher PV cell temperature than colored PV modules due to greater transmissivity, with peak temperature differences at noon of 5.5 °C, 6.2 °C, and 6.5 °C for orange, blue, and gray PV modules, respectively. On the contrary, the influence of PV's color front glass on room air temperature is non-significant. Furthermore, the optimal orientation for maximum energy yield is not always south-facing; it depends on the hourly distribution of the beam, diffuse solar irradiation, and ambient air temperature. For Montreal, west-facing DSFs produce more electrical and thermal energy on a summer design day because the hourly distribution of beam radiation is skewed towards afternoon hours.

Effect of the dimensions (width and radius) of the shading ring on the measurement of diffuse solar irradiance with the MEO shading ring measurement method

Diffuse irradiance was monitored by the Melo–Escobedo–Oliveira shading ring measurement method (MEO method) and requires the application of two corrections: one geometric and one atmospheric. The latter occurs from the interaction of radiation with atmospheric constituents and is known as circumsolar radiation, which is also obstructed by the ring. Thus, the objective of this work is to verify if geometrical aspects of the shading ring, such as width and radius, interfere in the quantification of these atmospheric corrections. Two Kipp & Zonen pyranometers were used to monitor the diffuse irradiance, one with 10/40 cm (width/radius) and one with 5/20 cm (width/radius). The values measured by the rings were compared with the diffuse irradiance obtained by the difference method. Studies were carried out under all atmospheric sky cover conditions: cloudy sky, partially cloudy sky, and clear sky. The results showed the highest atmospheric corrections were obtained for the clear sky coverage. Despite the two assemblies having the same width/radius ratio of 0.250, the assembly with the largest radius showed the lowest atmospheric correction. The application of atmospheric corrections is conditioned to the geometrical aspects of the ring, mainly the radius, to guarantee the quality of measurements carried out by the shading ring method.

Room-temperature flexible phase change material with high emissivity and high enthalpy for building energy saving

Summer heatwave events become more and more frequent, building cooling load continues to rise, and the traditional cooling method using air conditioning consumes a lot of energy. New technologies and materials with high efficiency, energy saving and low cost are urgently needed to solve the problem of high energy consumption in buildings. In this paper, by combining phase change storage technology with passive cooling technology of sky radiation, a new type of high-emission flexible composite phase change material (CPCM) was prepared using polypropylene hollow fiber (PP hollow fiber), Styrene-Ethylene-Butylene-Styrene (SEBS) and paraffin wax (PA). The prepared CPCM with excellent thermophysical properties, including a latent heat of 175.19 J/g, room temperature flexibility, the contact angle of the hydrophobic test of 129.15°, and the infrared emissivity of the atmospheric window of 0.942. The cooling experiment results show that the maximum temperature difference between CPCM and the environment is 2.6 °C lower than the ambient temperature. In addition, the simulation results show that the external surface temperature of the CPCM roof can be reduced by 23.15 K at the highest compared with a common roof, and the maximum energy saving can reach 13.24 W/m2. Compared with the high emissivity roof without CPCM, the external surface temperature is further reduced by 0.47K, the delay time is 50min, and the maximum energy saving can reach 0.76 W/m2. It's worth getting excited that CPCM can delay the opening time of air conditioning for 10 days. In addition, the application efficiency of cities in typical climate regions is simulated, and outstanding energy-saving efficiency is obtained, among which the maximum saving energy in Guangzhou is as high as 20.16 W/m2. The successful preparation of the novel CPCM material provides a new direction for the development of radiation-cooling technology.

Observational characterization and empirical modeling of global, direct and diffuse solar irradiances at the Peruvian central Andes

Observational characterization and empirical modeling of global, direct and diffuse solar irradiances at the Peruvian central Andes

Improving semantic segmentation accuracy in thin cloud interference scenarios by mixing simulated cloud-covered samples

Thin cloud interference presents a significant challenge for the semantic segmentation of optical satellite imagery, which directly degrades the model accuracy and causes difficulties in sample selection. This paper generated a dataset named Populus euphratica and Tamarix chinensis discrimination (PTD), containing both cloudless and thin cloud scenarios. Based on this PTD dataset, an enhanced Atmospheric Scattering Model with Nonlinear Optimization (ASM_NL) was proposed to simulate high-fidelity thin clouds by incorporating two vital nonlinear terms: the point spread function and the Perlin noise. Additionally, we adopt a strategy of mixing simulated thin cloud-covered images (STCI) into the training set at a certain proportion to improve the semantic segmentation accuracy in thin cloud-covered scenarios. The conclusions are as follows: 1) ASM_NL can simulate high-fidelity clouds at an average Jensen-Shannon distance of 0.0699. 2) When dealing with medium- and high-cloud density datasets, mixing STCI proved to be more effective than cloud removal in mitigating thin cloud interference, resulting in average macro F1 score improvements of 0.164 and 0.094, respectively. 3) The semantic segmentation accuracy improved significantly by mixing STCI with a minimal proportion of 1/60, demonstrating the activation of model transfer capabilities. This study provides a concise and efficient methodology for effectively mitigating thin cloud interference in deep learning-based optical satellite imagery analysis.

Compensation Atmospheric Scattering Model and Two-Branch Network for Single Image Dehazing

Compensation Atmospheric Scattering Model and Two-Branch Network for Single Image Dehazing

Modified And Multivariate Models for Estimation of Diffuse Solar Radiation in Ogoja, Cross River State, Nigeria

Modified And Multivariate Models for Estimation of Diffuse Solar Radiation in Ogoja, Cross River State, Nigeria

Diffuse radiation influence on the performance of luminescent solar concentrators

Luminescent Solar Concentrators (LSCs) are often purported to perform pretty well under both direct and diffuse solar irradiance conditions, yet the underlying rationale supporting this assumption remains scant. Furthermore, a significant portion of previous research on these photovoltaic devices relies on indoor equipment for efficiency characterization, thereby limiting insights into their performance under real operating conditions. In this study, we provide a theoretical framework elucidating the principles governing the superior performance of LSCs under diffuse irradiance. Specifically, we demonstrate that the isotropic distribution of dipoles within the LSC optical window aligns favorably with the Lambertian distribution of diffuse radiation, thereby enhancing photon absorption under diffuse conditions (25 %) respect to clear sunny skies (21 %). This theoretical foundation is bolstered by experimental investigations involving prototypes utilizing Lumogen Red dye, conducted under adverse irradiance conditions, including sunny, hazy, and partially cloudy skies. Our experimental findings reveal that light scattering, whether arising naturally from diffuse radiation or via scattering from neighboring surfaces, significantly amplifies the short-circuit current of LSC devices (37 % relative enhancement) compared to that generated under clear sky conditions (21 % relative enhancement).