Reflection Of Sunlight Research Articles

Solar Geoengineering: History, Methods, Governance, Prospects

Solar geoengineering, also called sunlight reflection or solar radiation modification (SRM), is a potential climate response that would cool the Earth's surface and reduce many other climate changes by scattering on order 1% of incoming sunlight back to space. SRM can only imperfectly correct for elevated greenhouse gases, but it might complement other climate responses to reduce risks, while also bringing new risks and new challenges to global governance. As climate alarm and calls for effective near-term action mount, SRM is attracting sharply increased attention and controversy, with many calls for expanded research and governance consultations along with ongoing concerns about risks, misuse, or overreliance. We review SRM's history, methods, potential uses and impacts, and governance needs, prioritizing the approach that is most prominent and promising, stratospheric aerosol injection. We identify several policy-relevant characteristics of SRM interventions and identify four narratives that capture current arguments over how SRM might be developed or used in sociopolitical context to either beneficial or destructive effect, with implications for near-term research, assessment, and governance activity.

AEA-RDCP: An Optimized Real-Time Algorithm for Sea Fog Intensity and Visibility Estimation

Sea fog reduces visibility to less than 1 km and is a major cause of maritime accidents, particularly affecting the navigation of small fishing vessels as it forms when warm, moist air moves over cold water, making it difficult to predict. Traditional visibility measurement tools are costly and limited in their real-time monitoring capabilities, which has led to the development of video-based algorithms using cameras. This study introduces the Approximating and Eliminating the Airlight–Reduced DCP (AEA-RDCP) algorithm, designed to address the issue where sunlight reflections are mistakenly recognized as fog in existing video-based sea fog intensity measurement algorithms, thereby improving performance. The dataset used in the experiment is categorized into two types: one consisting of images unaffected by sunlight and another consisting of maritime images heavily influenced by sunlight. The AEA-RDCP algorithm enhances the previously researched RDCP algorithm by effectively eliminating the influence of atmospheric light, utilizing the initial stages of the Dark Channel Prior (DCP) process to generate the Dark Channel image. While the DCP algorithm is typically used for dehazing, this study employs it only to the point of generating the Dark Channel, reducing computational complexity. The generated image is then used to estimate visibility based on a threshold for fog density estimation, maintaining accuracy while reducing computational demands, thereby allowing for the real-time monitoring of sea conditions, enhancing maritime safety, and preventing accidents.

Cellulose acetate hierarchical porous coated textile with passive daytime radiative cooling, flexibility and durability

Passive daytime radiative cooling technology is a highly efficient cooling technology with zero energy consumption. When utilized for personal thermal management, radiative cooling textiles are capable of finely regulating the temperature of the human skin microenvironment. This study presents a cellulose acetate (CA) hierarchical porous coated textile that accomplishes high reflectance of sunlight over the full wavelength range, with a low cost and scalability, and a simple preparation procedure. With a high reflectance of 0.91 in the solar wavelength band and a high emissivity of 0.95 in the atmospheric window wavelength band, the CA hierarchical porous coated textile offers exceptional spectrally selective performances. It manifests a subambient cooling temperature of up to 19.0 °C and a skin overheating prevention effect of up to 4.2 °C. Furthermore, the coated textile possesses promising abrasion resistance, acid-alkali corrosion resistance, and mechanical properties. The present work provides a facile path for the development of green-based radiative cooling coated textiles.

Optimising surface morphology for enhanced radiative properties in thermal energy-efficient materials

Environmental concerns related to heat-absorbing materials in the construction industry can be effectively addressed by optimising the reflectivity of incoming sunlight and thermal emissivity of materials. These radiative properties are closely tied to the surface morphology characteristics of building materials, making superficial topography a critical factor in determining their thermal and energy performance. In our research, we performed reflectance analysis in the UV-Vis-NIR-MIR region and conducted FT-IR analysis to assess the colour and reflectance behaviour of the samples, along with surface morphology and topography investigations. The data collected were utilised in a statistical study to analyse the relationship between superficial topography and thermo-optical characteristics. Our findings underscore the significant impact of surface morphology as a secondary factor influencing radiative properties. Specifically, our results indicate that large-scale components influence mid-infrared absorbance, while surface roughness is crucial in determining solar reflectance properties. Notably, an increase in roughness consistently leads to a reduction in near-infrared and visible reflectance properties by up to 17% and 8%, respectively, with no noticeable effect in the UV region. In conclusion, our research demonstrates the potential for customising and optimising surface properties to reduce energy consumption for cooling purposes and alleviate the urban heat island effect.

Highly Stable Polyimide Composite Nanofiber Membranes with Spectrally Selective for Passive Daytime Radiative Cooling.

Passive radiative cooling technology without electric consumption is an emerging sustainability technology that plays a key role in advancing sustainable development. However, most radiative cooling materials are vulnerable to outdoor contamination and thermal/UV exposure, which leads to decreased performance. Herein, we report a hierarchically structured polyimide/zinc oxide (PINF/ZnO) composite membrane that integrates sunlight reflectance of 91.4% in the main thermal effect of the solar spectrum (0.78-1.1 μm), the mid-infrared emissivity of 90.0% (8-13 μm), UV shielding performance, thermal resistance, and ideal hydrophobicity. The comprehensive performance enables the composite membrane to yield a temperature drop of ∼9.3 °C, compared to the air temperature, under the peak solar irradiance of ∼800 W m-2. In addition, the temperature drop of as-obtained composite membranes after heating at 200 °C for 6 h in a nitrogen/air atmosphere can be well maintained at ∼9.0 °C, demonstrating their ideal radiative cooling effect in a high-temperature environment. Additionally, the PINF/ZnO composite membrane shows excellent chemical durability after exposure to the outdoor environment. This work provides a new strategy to integrate chemical durability and thermal resistance with radiative cooling, presenting great potential for passive radiative cooling materials toward practical applications in harsh environments.

Dynamic Spectral Metafabric with Unidirectional Moisture Transport Property for Personal Thermal Management.

Personal thermal management technology, which adjusts the heat exchange between the human body and the environment, can passively heat or cool the body to maintain a comfortable core temperature, thereby enhancing comfort and reducing energy consumption. However, most existing personal thermal management materials have static properties, such as fixed solar reflectance and infrared emissivity, which do not support real-time dynamic temperature regulation. Moreover, sweat accumulation on the skin surface, while contributing to temperature regulation, can significantly reduce comfort. This study constructs a unidirectional moisture-permeable intelligent thermal management fabric system to achieve superior thermal and moisture comfort in complex environments. The fabric incorporates thermochromic microcapsules into PAN nanofibers by using electrospinning technology for intelligent thermal management. Subsequent hydrophobic treatment of the fiber film surface imparts the fabric with unidirectional wetting properties. The nanofibrous structure provides intrinsic elasticity and breathability. In heating mode, the fabric's average sunlight reflectance is 42.1%, which increases to 82.2% in cooling mode, resulting in a reflectance difference of approximately 40%. The hydrophobic treatment endows the fabric with excellent moisture absorption and perspiration properties, demonstrated by a unidirectional moisture transport index of 696.63 and a perspiration evaporation rate of 5.88 mg/min. When the fabric temperature matches the ambient temperature, the photothermal conversion power difference of the Janus metafabric in two modes reaches 248.37 W m-2. Additionally, Janus metafabrics show the potential for temperature-responsive design and repeated writing applications. The outstanding wearability and dynamic spectral properties of these metafabrics open new pathways for sustainable energy, smart textiles, and thermal-moisture comfort applications.

Superhydrophobic stereocomplex-type polylactide/ultra-fine glass fibers aerogel for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) technology offers a green and sustainable strategy for cooling, eliminating the need for external energy sources through its exceptional efficiency in heat radiation and sunlight reflection. Despite its benefits, the widespread usage of non-biodegradable PDRC materials has unfortunately caused environmental pollution and resource wastage. Furthermore, the effectiveness of outdoor PDRC materials can be significantly diminished by rainfall. In this work, a superhydrophobic composite aerogel composed of stereocomplex-type polylactide and ultra-fine glass fiber has been successfully developed through simple physical blending and freeze-drying, which exhibits low thermal conductivity (36.26 mW m−1 K−1) and superhydrophobicity (water contact angle up to 150°). Additionally, its high solar reflectance (91.68 %) and strong infrared emissivity (93.95 %) enable it to effectively lower surface temperatures during daytime, resulting in a cooling effect of approximately 3.8 °C below the ambient temperature during the midday heat of summer, with a cooling power of 68 W/m2. This aerogel offers an environmentally friendly and sustainable approach for the utilization of radiative refrigeration materials, paving the way for environmental protection and sustainable development.

Comparative analysis of single-axis solar tracker performance with and without reflector under various weather conditions

This research explores a sun tracking system for solar panels that affects the power output of the panels. To address this, a unidirectional sun tracking system is implemented to ensure the solar panels are perpendicular to the sun, thus optimizing solar radiation. Additionally, reflectors are integrated to capture more sunlight. This research aims to design the system of unidirectional sun tracking to enhance the power output generated by solar panels and compare its performance with stationary (static) solar panels. The results demonstrate that the system of sun tracking improves the power output of solar panels. However, when reflectors are used in conjunction with the sun tracking system, no significant increase in power output is observed. Moreover, solar panels equipped with the unidirectional sun tracking system exhibit a power increase of 52.06 Watts compared to stationary solar panels. This research indicates that employing a unidirectional sun tracking system with the addition of reflectors does not enhance power output but instead reduces it due to the increased temperature effect caused by the sunlight reflection from the added reflectors.

Anti-UV Passive Radiative Cooling Chiral Nematic Liquid Crystal Films for Thermal Management.

Passive radiative cooling (PRC) can spontaneously dissipate heat to outer space through atmospheric transparent windows, providing a promising path to meet sustainable development goals. However, achieving simultaneously high transparency, color-customizable, and thermal management of PRC anti ultraviolet (anti-UV) films remains a challenge. Herein, a simple strategy is proposed to utilize liquid crystalline polymer, with high mid-infrared emissive, forming customizable structural color film by molecular self-assembly and polymerization-induced pitch gradient, which guarantees the balance of transparency in visible spectrum and sunlight reflection, rendering anti-UV colored window for thermal management. By performing tests, temperature fall of 5.4 and 7.9°C are demonstrated at noon with solar intensity of 717Wm-2 and night, respectively. Vivid red-, green-, blue-structured colors, and colorless films are designed and implemented to suppress the solar input and control the effective visible light transmissivity considering the efficiency function of human vision. In addition, temperature rise of 11.1°C is achieved by applying an alternating current field on the PRC film. This study provides a new perspective on the thermal management and aesthetic functionalities of smart windows and wearables.

Poly(vinyl alcohol) composite nanofiber membranes with hydrophobicity for daytime radiative cooling

Daytime radiative cooling materials exhibit huge potential for sustainable development, which can reflect sunlight and radiate heat to outer space in the main atmospheric window without energy consumption. Recently, polymer-based nanofiber membranes have been fabricated for radiative cooling, because of their easy processing and ideal optical performance. However, there exist big challenges in fabricating low-cost and environmentally friendly daytime radiative cooling materials for large-scale practical applications. In this work, we demonstrate a novel poly(vinyl alcohol)@silica (PVA@SiO2) composite membrane via typical electrospinning technology and a simple coating process. The resultant composite membrane exhibits spectral selectivity with high sunlight reflectance of ∼95.0 % as well as a mid-infrared emissivity of ∼90.2 %, UV protection, and hydrophobicity, endowing its excellent daytime radiative cooling effect with a temperature drop of ∼8.0 °C. The as-obtained membranes exhibit some promising future for the potential large-scale application of radiative cooling technology for energy savings.

The Evolving International Climate Change Regime: Mitigation, Adaptation, Reflection

The complex international regime for climate change has evolved over the past three decades, from the Framework Convention on Climate Change and the Kyoto Protocol through the Paris Agreement and beyond. We assess this evolution from the 1990s to the 2020s, and its potential future evolution from the 2020s to the 2050s, across three main policy strategies: mitigation, adaptation, and reflection. In its first three decades, the regime has focused predominantly on the mitigation of net emissions and on engaging all major emitting countries in that effort. More recently, as progress on mitigation has been slow and as the impacts of climate change have risen around the world, the regime has begun to address adaptation. The next three decades may see the rise of a third strategy, reflection, if actors (collectively or unilaterally) perceive an urgent need to alleviate peak climate damages through fast-acting but controversial and risky climate interventions known as sunlight reflection methods or solar radiation modification (SRM). Several major international groups have recently issued reports on SRM, yet the international climate change regime has not yet constructed a governance regime for assessment or management of SRM. We recommend and outline comprehensive risk-risk tradeoff analyses of SRM to help avoid harmful countervailing risks. We suggest the development of an adaptive governance regime, starting early and embracing iterative and inclusive learning and updating over time. We urge that among the first key steps should be the development of a transparent international monitoring system for SRM. Such a monitoring system could provide early warning and help deter any unilateral SRM, assess the intended and unintended global and regional impacts of any research or eventual deployment of SRM, foster collective deliberation and reduce the risk of international conflict over SRM, help attribute adverse side effects of SRM to assist those adversely affected, and aid learning to improve the system adaptively over time. Thus, any reflection (of sunlight) should involve ongoing reflection (analysis and revision). Such an SRM monitoring regime is needed before SRM might be deployed, and can be developed at the same time that the focus of current efforts remains on mitigation and adaptation.

Construction of a Robust Radiative Cooling Emitter for Efficient Food Storage and Transportation.

Nowadays, food safety is still facing great challenges. During storage and transportation, perishable goods have to be kept at a low temperature. However, the current logistics still lack enough preservation ability to maintain a low temperature in the whole. Hence, considering the temperature fluctuation in logistics, in this work, the passive radiative cooling (RC) technology was applied to package to enhance the temperature control capability in food storage and transportation. The RC emitter with selective infrared emission property was fabricated by a facile coating method, and Al2O3 was added to improve the wear resistance. The sunlight reflectance and infrared emittance within atmospheric conditions could reach up to 0.92 and 0.84, respectively. After abrasion, the sunlight reflection only decreased by 0.01, and the infrared emission showed a negligible change, revealing excellent wear resistance. During outdoor measurement, the box assembled by RC emitters (RC box) was proved to achieve temperature drops of ∼9 and ∼4 °C compared with the corrugated box and foam box, respectively. Besides, the fruits stored in the RC box exhibited a lower decay rate. Additionally, after printing with patterns to meet the aesthetic requirements, the RC emitter could also maintain the cooling ability. Given the superior optical properties, wear resistance, and cooling capability, the emitter has great potential for obtaining a better temperature control ability in food storage and transportation.

A 3D porous polymer film designed for efficient passive radiative cooling

Passive daytime radiative cooling (PDRC) technique can cool objects without energy consumption by reflecting sunlight and radiating heat into the cold outer space through atmospheric transparent windows (ATW). Here, 3D porous polydimethylsiloxane (P-PDMS) films with excellent radiative cooling properties were fabricated using citric acid monohydrate (CAM) templates. Integrating with high sunlight reflectance (78.6%) and great thermal emissivity (99.4%) in ATW, the test was performed in an outdoor environment with an average solar radiation of 715.09 W/m2. The maximum temperature of P-PDMS film is reduced to 15.4℃, and in the actual roof application test, P-PDMS film also show excellent passive radiant cooling performance of 8.3℃ cooling in the house. The 3D-porous structure plays an important role in improving solar reflectivity and IR emissivity. Combined with efficient DRC capabilities and mass production compatibility, this work brings a new paradigm for the preparation of cooling devices with potential commercial applications in sustainable energy-free cooling.

An Integrated Framework with ADD-LSTM and DeepLabCut for Dolphin Behavior Classification

Caring for dolphins is a delicate process that requires experienced caretakers to pay close attention to their behavioral characteristics. However, caretakers may sometimes lack experience or not be able to give their full attention, which can lead to misjudgment or oversight. To address these issues, a dolphin behavior analysis system has been designed to assist caretakers in making accurate assessments. This study utilized image preprocessing techniques to reduce sunlight reflection in the pool and enhance the outline of dolphins, making it easier to analyze their movements. The dolphins were divided into 11 key points using an open-source tool called DeepLabCut, which accurately helped mark various body parts for skeletal detection. The AquaAI Dolphin Decoder (ADD) was then used to analyze six dolphin behaviors. To improve behavior recognition accuracy, the long short-term memory (LSTM) neural network was introduced. The ADD and LSTM models were integrated to form the ADD-LSTM system. Several classification models, including unidirectional and bidirectional LSTM, GRU, and SVM, were compared. The results showed that the ADD module combined with a double-layer bidirectional LSTM method achieved high accuracy in dolphin behavior analysis. The accuracy rates for each behavior exceeded 90%.

METHODS FOR SATELLITE DERIVED BATHYMETRY FROM SENTINEL-2 IMAGES: A COMPARISON

Abstract. In recent decades, research has been developed to estimate near-shore bathymetry depth values using satellite imagery. Visible and infrared bands are used to derive elevation profile estimates, so to obtain bathymetric in rapid way without mobilisation of persons or equipment and saving the costs. For consequence, Satellite Derived Bathymetry (SDB) is seen as a valid approach for shallow waters survey: strongly supported by the activity of scholars and researchers, multiple methods are available in the literature. This article aims to investigate and compare different SDB methods for sea depth extraction from Sentinel-2 satellite multispectral images, with particular attention to the accuracy of the results. The experiments are conducted on imagery including Blue, Green, Red and Near Infrared bands, with 10 m resolution, concerning the Bay of Pozzuoli (Italy). After removing the glint, the effects caused by the reflection of sunlight through single scattering from sea surface, three methods are applied: Band Ratio method (BRM), 3rd-degree polynomial regression line method (3DPM), and principal component analysis method (PCAM). 3DPM can be seen as a variant of the BRM where the linear law that interprets the correlation between the band ratio values and the depth values is replaced by the third order function. Models are trained using depth data extracted from an Electronic Navigational Chart (ENC) at 1:7,500 scale, which is also used to verify result accuracy. The experiments demonstrate that the 3DPM is better able to obtain a more precise bathymetric model, confirming the greater adaptability of the 3rd order function to interpretate the variability of the interaction of light with water along the water column.

Porous polypropylene produced by phase separation for high solar reflectivity and passive cooling

AbstractPassive cooling techniques have gained widespread use in everyday life and various industries by utilizing sunlight reflection to cool objects without requiring additional energy input. Porous polymer materials possess the unique ability to provide both thermal insulation and solar reflection due to their inherent multiphase structure. In this study, we developed a porous polypropylene (PP) with a hierarchically structured surface layer using a simple and efficient solvent treatment method based on recrystallization. As a result, the porous structure and hierarchically structured surface significantly increase the solar reflectance from 11 to 86%. We found that by manipulating the recrystallization process and using reflective additives, solar reflectivity can be further improved. With the use of TiO2 and BaSO4 additives, a solar reflectance of 90% was achieved, while a solar reflectance of 93% was achieved with nucleating agents. In practical terms, these improvements result in significant temperature reductions in cooling performance tests compared to extruded PP sheets: 17, 19, and 22 °C for porous PP, porous PP/TiO2 or PP/BaSO4, and porous nucleated PP, respectively. The modification method introduced could help PP offer new possibilities for developing low-cost chemically resistant and thermally insulating layers in thermal management applications.

Bionic dual-scale structured films for efficient passive radiative cooling accompanied by robust durability.

Passive radiative cooling (PRC), as an energy-free cooling approach, is ingeniously harnessed for certain natural organisms to withstand extreme high-temperature climates, which has inspired numerous bionic designs. However, it is a great challenge to enhance the durability of the designed materials in practical scenarios while inheriting the natural biological principles. We demonstrate bionic dual-scale structured (BDSS) films for efficient passive radiative cooling accompanied by robust durability after discovering the excellent thermoregulatory properties of the inner surface of Hawaiian scallop shell. We found that the inner surface of the shell consists of large-scale triangular ridges scattered with small-scale terrace steps. This dual-scale structure can enhance the reflectivity of sunlight by efficient Mie scattering and increase the emissivity in the mid-infrared range by lengthening the propagation of photons, thereby decreasing the surface temperature. Underpinned by this finding, we developed a BDSS film that features a strong solar spectrum reflectivity of 0.95 and a high mid-infrared emissivity of 0.98, achieving a sub-ambient cooling of 10.8 °C under direct sunlight. Additionally, the designed films possess robust durability including excellent self-cleaning, flexibility, mechanical strength, chemical stability, and anti-ultraviolet radiation, which is promising for thermal thermoregulation in various harsh scenarios.

Mitigating Illumination-, Leaf-, and View-Angle Dependencies in Hyperspectral Imaging Using Polarimetry

Automation of plant phenotyping using data from high-dimensional imaging sensors is on the forefront of agricultural research for its potential to improve seasonal yield by monitoring crop health and accelerating breeding programs. A common challenge when capturing images in the field relates to the spectral reflection of sunlight (glare) from crop leaves that, at certain solar incidences and sensor viewing angles, presents unwanted signals. The research presented here involves the convergence of 2 parallel projects to develop a facile algorithm that can use polarization data to decouple light reflected from the surface of the leaves and light scattered from the leaf’s tissue. The first project is a mast-mounted hyperspectral imaging polarimeter (HIP) that can image a maize field across multiple diurnal cycles throughout a growing season. The second project is a multistatic fiber-based Mueller matrix bidirectional reflectance distribution function (mmBRDF) instrument which measures the polarized light-scattering behavior of individual maize leaves. The mmBRDF data was fitted to an existing model, which outputs parameters that were used to run simulations. The simulated data were then used to train a shallow neural network which works by comparing unpolarized 2-band vegetation index (VI) with linearly polarized data from the low-reflectivity bands of the VI. Using GNDVI and red-edge reflection ratio we saw an improvement of an order of magnitude or more in the mean error ( ϵ ) and a reduction spanning 1.5 to 2.7 in their standard deviation ( ϵ σ ) after applying the correction network on the HIP sensor data.

Scalable and sustainable radiative cooling enabled by renewable poplar catkin-derived films

Passive radiative cooling is a vital strategy for mitigating the greenhouse effect. However, the widespread use of synthetic plastics as the primary constituent raises environmental concerns of plastic waste. Addressing these challenges necessitates the development of radiative cooling materials based on natural and renewable resources. Herein, we utilize the abundant but underutilized poplar catkins, which are currently perceived as harmful, to fabricate a poplar catkin-derived (PC) film for radiative cooling. The PC film exhibits exceptional cooling performance, with a maximum cooling power of 75.3 W m−2 under an average sunlight intensity of 819 W m−2. Remarkably, the PC film achieves a sub-ambient temperature reduction of 6.2 °C during 9:00–13:00, within a similar solar radiation intensity. Additionally, the PC film possesses outstanding properties, including UV resistance, mold resistance, and renewability. Even after multiple regeneration cycles, the film experiences only marginal decreases of 0.9 % in sunlight reflectance and 1.4 % in infrared emissivity (8–13 μm). Furthermore, the resulting film demonstrates superior resistance to mildew compared to wood, highlighting its potential for long-term usability. This work not only addresses the environmental concerns associated with synthetic plastics but also harnesses the untapped potential of readily available natural resources to develop sustainable radiative cooling materials.

Scalable and Flexible Multi-Layer Prismatic Photonic Metamaterial Film for Efficient Daytime Radiative Cooling.

To maintain a comfortable indoor living environment in low latitude or tropical regions, humans consume significant amounts of electrical energy in air conditioning, leading to substantial CO2 emissions. Passive daytime radiative cooling (PDRC) allows objects to cool down during the daytime without any energy consumption by dissipating heat through the atmospheric transparency window (8-13µm) to outer space, which has garnered significant attention. However, the practical applications of common PDRC materials are hindered by their poor optical selectivity and high-reflective silver backing. Additionally, the availability of artificial photon emitters with complex structures and excellent performance is also limited by their high cost. Herein, a novel multilayer prismatic photonic metamaterial film without any silver reflector, easily scalable and produced by a roll-to-roll method is demonstrated, which exhibits ≈96.4% sunlight reflectance (0.3-2.5µm) and ≈97.2% emissivity in mid-infrared (IR) (8-13µm). At an average solar intensity of ≈920Wm-2, it is on average 6.8°C below ambient temperature during the day and theoretically yields a radiative cooling power of 88.9Wm-2. Furthermore, the film exhibits excellent hydrophobicity, superior flexibility, and robust mechanical strength, providing an attractive and viable pathway for practical applications addressing the pressing challenges of climate and energy issues.