Emission Of Thermal Radiation Research Articles

Weather‐Induced Satellite Orbit Perturbations

AbstractSatellites in Earth's orbit are exposed to Earth radiation, consisting of reflected solar and emitted thermal radiation, thereby exerting a non‐conservative force that causes acceleration and affects the orbits. Gravity Recovery and Climate Experiment Follow‐On (GRACE‐FO) mission aiming to retrieve the Earth's gravity potential is critically dependent on accounting for this force and all other non‐gravitational forces. There are both diurnal and seasonal variations in the Earth's radiation pressure, of which the seasonal variability can be represented by climatology. Nevertheless, the daily variations in the Earth's radiation pressure, due to the transient changes in the weather; for example, clouds and their properties, are not accounted for in the orbit perturbations studies. We show here that the top‐of‐atmosphere radiation fluxes computed with a numerical weather prediction (NWP) model explain most of the measured short‐term variations in the radial acceleration of the GRACE‐FO satellite. Our physics‐based modeling corrects a hitherto unexplained lack of power spectral density in the measured accelerations. For example, we can accurately model the accelerations associated with a tropical storm in the Indian Ocean in December 2020, which would not be possible when using climatological data. Our results demonstrate that using a global numerical weather prediction model significantly improves the simulation of non‐gravitational effects in the satellites' orbits. In the 7‐day data set, OpenIFS‐simulated acceleration exhibited higher accuracy than climatological‐data‐simulated acceleration (2.5 compared to 2.6 nms−2) and an improved precision (2.6 compared to 3.0 nms−2). This advancement contributes to a more precise orbit determination across various applications in Earth sciences.

Observed Energetic Adjustment of the Arctic and Antarctic in a Warming World

Abstract Satellite observations reveal that decreasing surface albedo in both polar regions is increasing the absorption of solar radiation, but the disposition of this absorbed energy is fundamentally different. Fluxes of absorbed solar radiation, emitted thermal radiation, and net energy imbalances are assessed for both polar regions for the last 21 years in the Clouds and Earth’s Radiant Energy System record. Arctic absorbed solar radiation is increasing at 0.98 ± 0.69 W m−2 decade−1, consistent with the anticipated response to sea ice loss. However, Arctic thermal emission is responding at a similar rate of 0.94 ± 0.55 W m−2 decade−1. This is surprising since the radiative impact of ice loss would be expected to favor increasing solar absorption. We find however, that clouds substantially mask trends in Arctic solar absorption relative to clear sky while having only a modest impact on thermal emission trends. As a result, the Arctic net radiation imbalance has not changed over the period. Furthermore, variability of absorbed solar radiation explains two-thirds of the variability in annual thermal emission suggesting that Arctic thermal fluxes rapidly adjust to offset changes in solar absorption and re-establish equilibrium. Conversely, Antarctic thermal emission is not responding to the increasing (although not yet statistically significant) solar absorption of 0.59 ± 0.64 W m−2 decade−1 with less than a third of the annual thermal variability explained by accumulated solar absorption. The Arctic is undergoing rapid adjustment to increasing solar absorption resulting in no change to the net energy deficit, while increasing Antarctic solar absorption represents additional energy input into the Earth system. Significance Statement The polar regions of Earth are undergoing ice loss through ongoing global warming, reducing the ice cover and decreasing solar reflectivity, which would be expected to warm these regions. We use satellite observations to measure the trends in solar absorption and emitted thermal radiation over the Arctic and Antarctic for the last two decades. Arctic thermal emission is increasing at a compensating rate to solar absorption with a close relationship between these processes. Conversely, Antarctic thermal emission is not responding to solar absorption demonstrating that Antarctic surface temperatures are not significantly influenced by the region’s reflectivity. The Arctic is undergoing rapid adjustment to increasing solar absorption through warming, while increasing Antarctic solar absorption represents additional energy input into the Earth system.

Pixelwise high-temperature calibration for in-situ temperature measuring in powder bed fusion of metal with laser beam

High-temperature calibration methods in additive manufacturing involve the use of advanced techniques to accurately measure and control the temperature of the build material during the additive manufacturing process. Infrared cameras, blackbody radiation sources and non-linear optimization algorithms are used to correlate the temperature of the material with its emitted thermal radiation. This is essential for ensuring the quality and repeatability of the final product. This paper presents the calibration procedure of an imaging system for in-situ measurement of absolute temperatures and temperature gradients during powder bed fusion of metal with laser beam (PBF-LB/M) in the temperature range of 500 K–1500 K. It describes the design of the optical setup to meet specific requirements in this application area as well as the procedure for accounting the various factors influencing the temperature measurement. These include camera-specific effects such as varying spectral sensitivities of the individual pixels of the sensor as well as influences of the exposure time and the exposed sensor area. Furthermore, influences caused by the complex optical path, such as inhomogeneous transmission properties of the galvanometer scanner as well as angle-dependent transmission properties of the f-theta lens were considered. A two-step fitting algorithm based on Planck's law of radiation was applied to best represent the correlation. With the presented procedure the calibrated thermography system provides the ability to measure absolute temperatures under real process conditions with high accuracy.

Cofiring of renewable biodiesel fuels inside natural gas flame for enhancement of thermal properties of flame and NOx reduction

AbstractThis study investigates the co‐combustion of palm oil biodiesel fuel, as a renewable alternative for diesel fuel, inside natural gas flame to enhance the flame thermal specifications and NOx reduction. A power natural gas burner with a maximum heat capacity of 418,400 kJ/h was installed at the inlet of a laboratory furnace and biodiesel fuel was injected inside natural gas burner with a 100 μm in diameter solid cone nozzle. Flame temperature, thermal radiation, Infrared radiation, and CO, CO2 and NOx emission were measured. The results revealed that biodiesel injection increases the flame size and turns the non‐luminous blue flame into yellow‐colored flame. Furthermore, higher flash point and Sauter Mean Diameter of biodiesel promote the thermal decomposition of fuel droplets and increase the concentrations of Intermediate Soot Particles in the flame which in turn increases the flame emissivity coefficient and consequently flame thermal radiation. Also, the oxygen content of biodiesel fuel has an important role in the complete combustion of Intermediate Soot Particles to CO2 which increases the heat release of biodiesel combustion and raises the flame temperature. The average enhancement in thermal radiation and flame temperature were 5.6% and 43.38%, respectively. Finally, although biodiesel injection increases the flame temperature, it also increases the flame surface reaction and eliminates the hot spot region in the flame. Therefore, the rate of heat generation per unit volume of flame decreases and this decreases the rate of NOx emission as much as 10.84%.

Harnessing the characteristic of compound parabolic concentrators for directional concentration of emitted thermal radiation and solar shielding in building-integrated radiative cooling

Radiative sky cooling (RC) is a promising solution for meeting the growing cooling demands by passively dissipating waste heat into frigid outer space. However, current RC systems suffer from low cooling power density and limited installation flexibility, impeding their effective application as building cooling strategies. To overcome these challenges, a novel concentrated RC system coupled with a compound parabolic concentrator (CPC) is proposed and experimentally studied. The objective is to investigate the effectiveness of the CPC in enhancing the cooling capability of the RC system and the feasibility of achieving all-day RC in unfavorable working conditions when integrated with building roofs. During nighttime experiments in the humid Nottingham region, the CPC-RC system exhibited an average emitter temperature that was 5.83 °C lower than the ambient temperature, representing a 30 % and 13.6 % improvement in RC performance compared to the flat-RC system and trapezoidal-concentrated RC system, respectively. The Photopia optical software simulation indicates that when the modules are tilted to the north, the CPC functions as a solar shield, effectively limiting solar radiation reaching the emitter surface, which is advantageous for conducting daytime RC experiments. In the daytime experiment, the emitter temperature of the CPC-RC module in anti-sunward group was still 1.59 °C lower than the ambient temperature and 5.49 °C lower than that of flat-RC module. At night, the CPC-RC module of the three placement groups all showed the highest RC effect in the same group. The average emitter temperature of the CPC-RC module in the horizontal placement group is 0.6 °C lower than that of the flat RC module. This novel CPC-RC scheme presents a new energy-saving strategy for buildings and showcases its potential for achieving 24-hour RC when integrated into anti-sunward roofs.

Heating of nanoparticles and their environment by laser radiation and applications

This review considers the fundamental dynamic processes involved in the laser heating of metal nanoparticles and their subsequent cooling. Of particular interest are the absorption of laser energy by nanoparticles, the heating of a single nanoparticle or an ensemble thereof, and the dissipation of the energy of nanoparticles due to heat exchange with the environment. The goal is to consider the dependences and values of the temperatures of the nanoparticles and the environment, their time scales, and other parameters that describe these processes. Experimental results and analytical studies on the heating of single metal nanoparticles by laser pulses are discussed, including the laser thresholds for initiating subsequent photothermal processes, how temperature influences the optical properties, and the heating of gold nanoparticles by laser pulses. Experimental studies of the heating of an ensemble of nanoparticles and the results of an analytical study of the heating of an ensemble of nanoparticles and the environment by laser radiation are considered. Nanothermometry methods for nanoparticles under laser heating are considered, including changes in the refractive indices of metals and spectral thermometry of optical scattering of nanoparticles, Raman spectroscopy, the thermal distortion of the refractive index of an environment heated by a nanoparticle, and thermochemical phase transitions in lipid bilayers surrounding a heated nanoparticle. Understanding the sequence of events after radiation absorption and their time scales underlies many applications of nanoparticles. The application fields for the laser heating of nanoparticles are reviewed, including thermochemical reactions and selective nanophotothermolysis initiated in the environment by laser-heated nanoparticles, thermal radiation emission by nanoparticles and laser-induced incandescence, electron and ion emission of heated nanoparticles, and optothermal chemical catalysis. Applications of the laser heating of nanoparticles in laser nanomedicine are of particular interest. Significant emphasis is given to the proposed analytical approaches to modeling and calculating the heating processes under the action of a laser pulse on metal nanoparticles, taking into account the temperature dependences of the parameters. The proposed models can be used to estimate the parameters of lasers and nanoparticles in the various application fields for the laser heating of nanoparticles.

Controlling Thermal Radiation in Photonic Quasicrystals Containing Epsilon-Negative Metamaterials

The transfer matrix approach is used to study the optical characteristics of thermal radiation in a one-dimensional photonic crystal (1DPC) with metamaterial. In this method, every layer within the multilayer structure is associated with its specific transfer matrix. Subsequently, it links the incident beam to the next layer from the previous layer. The proposed structure is composed of three types of materials, namely InSb, ZrO2, and Teflon, and one type of epsilon-negative (ENG) metamaterial and is organized in accordance with the laws of sequencing. The semiconductor InSb has the capability to adjust bandgaps by utilizing its thermally responsive permittivity, allowing for tunability with temperature changes, while the metamaterial modifies the bandgaps according to its negative permittivity. Using quasi-periodic shows that, in contrast to employing absolute periodic arrangements, it produces more diverse results in modifying the structure’s band-gaps. Using a new sequence arrangement mixed-quasi-periodic (MQP) structure, which is a combination of two quasi periodic structures, provides more freedom of action for modifying the properties of the medium than periodic arrangements do. The ability to control thermal radiation is crucial in a range of optical applications since it is frequently unpolarized and incoherent in both space and time. These configurations allow for the suppression and emission of thermal radiation in a certain frequency range due to their fundamental nature as photonic band-gaps (PBGs). So, we are able to control the thermal radiation by changing the structure arrangement. Here, the We use an indirect method based on the second Kirchoff law for thermal radiation to investigate the emittance of black bodies based on a well-known transfer matrix technique. We can measure the transmission and reflection coefficients with associated transmittance and reflectance, T and R, respectively. Here, the effects of several parameters, including the input beam’s angle, polarization, and period on tailoring the thermal radiation spectrum of the proposed structure, are studied. The results show that in some frequency bands, thermal radiation exceeded the black body limit. There were also good results in terms of complete stop bands for both TE and TM polarization at different incident angles and frequencies. This study produces encouraging results for the creation of Terahertz (THz) filters and selective thermal emitters. The tunability of our media is a crucial factor that influences the efficiency and function of our desired photonic outcome. Therefore, exploiting MQP sequences or arrangements is a promising strategy, as it allows us to rearrange our media more flexibly than quasi-periodic sequences and thus achieve our optimal result.

Ultra-efficient machine learning design of nonreciprocal thermal absorber for arbitrary directional and spectral radiation

Development of nanophotonics has made it possible to control the wavelength and direction of thermal radiation emission, but it is still limited by Kirchhoff's law. Magneto-optical materials or Weyl semimetals have been used in recent studies to break the time-reversal symmetry, resulting in a violation of Kirchhoff's law. Currently, most of the work relies on the traditional optical design basis and can only realize the nonreciprocal thermal radiation at a specific angle or wavelength. In this work, on the basis of material informatics, a design framework of a multilayer nonreciprocal thermal absorber with high absorptivity and low emissivity at any arbitrary wavelength and angle is proposed. Through a comprehensive investigation of the underlying mechanism, it has been discovered that the nonreciprocal thermal radiation effect is primarily attributed to excitation of the cavity mode at the interface between the metal and the multilayer structure. Moreover, the impact of factors, such as layer count, incidence angle, extinction coefficient, and applied magnetic field on nonreciprocal thermal radiation, is thoroughly explored, offering valuable insights to instruct the design process. Additionally, by expanding the optimization objective, it becomes feasible to design fixed dual-band or even multi-band nonreciprocal thermal absorbers. Consequently, this study offers essential guidelines for advancing the control of nonreciprocal thermal radiation.

Climate extremes likely to drive land mammal extinction during next supercontinent assembly

Mammals have dominated Earth for approximately 55 Myr thanks to their adaptations and resilience to warming and cooling during the Cenozoic. All life will eventually perish in a runaway greenhouse once absorbed solar radiation exceeds the emission of thermal radiation in several billions of years. However, conditions rendering the Earth naturally inhospitable to mammals may develop sooner because of long-term processes linked to plate tectonics (short-term perturbations are not considered here). In ~250 Myr, all continents will converge to form Earth’s next supercontinent, Pangea Ultima. A natural consequence of the creation and decay of Pangea Ultima will be extremes in p_{mathrm{CO}_2} due to changes in volcanic rifting and outgassing. Here we show that increased p_{mathrm{CO}_2}, solar energy (F⨀; approximately +2.5% W m−2 greater than today) and continentality (larger range in temperatures away from the ocean) lead to increasing warming hostile to mammalian life. We assess their impact on mammalian physiological limits (dry bulb, wet bulb and Humidex heat stress indicators) as well as a planetary habitability index. Given mammals’ continued survival, predicted background p_{mathrm{CO}_2} levels of 410–816 ppm combined with increased F⨀ will probably lead to a climate tipping point and their mass extinction. The results also highlight how global landmass configuration, p_{mathrm{CO}_2} and F⨀ play a critical role in planetary habitability.

Longitudinal-optical-phonon resonant thermal emission efficiency and spectrum control of metal-GaAs surface micro-stripe structures

Phonon-based tera-Hertz or mid-infrared emission has been investigated because it can be applied to high-efficiency light sources for optical communication and material diagnostics, where thermal energy can be utilized as an energy source of emission. Particularly, nano- and micro-surface structures have been investigated for versatile emission controllability. We present the polarized longitudinal optical (LO) phonon resonant thermal emission of radiation (LORE) peaked at approximately 8.5 THz in a range of 450–650 K from simple surface Au–GaAs–Au micro-stripe structures on undoped (u-) GaAs wafers, where the metal component, which has been avoided for surface phonon polariton (SPhP) emission, is introduced. This LORE is based on electric dipoles formed by coherently oscillating polarization charges on pairs of interfaces and has a feature of structure size or emission direction-independent frequency, which is quite different from the properties of SPhPs. The dependence of emission properties on structural factors and temperature reveals the approximately evenly matched radiative and nonradiative LO-phonon annihilation rates in the local surface field and shows the controllability of emission and absorption balance based on the surface structures. Higher emission efficiency in the higher temperature region is found for structures with narrow emission windows of less than 2 μm. The decrease in the volume occupied by electric dipoles reduces the reabsorption probability of LORE, which shortens the effective radiative lifetime and, resultantly, increases the fraction of the radiative rate in the total annihilation rate. By comparing the emission from a pure graphite wafer, a short LORE mean time interval of approximately 2 ps is found. The background emission subject to Planck’s law is significantly reduced particularly in the region of 250–300 cm−1 using emission window widths narrower than 2 μm because of the sub-diffraction phenomenon.

Techno-economic analysis on prospects and implementation of employing radiative cooling technology across broader atmospheric conditions

Achieving a transition to maximize the utilization of radiative cooling as a passive cooling strategy is challenging for several regions worldwide, mainly due to unawareness, lack of government support, and extreme seasonal climatic variations. Being characterized by a variety of atmospheric conditions from tropical coastline to arid regions along with humid highland areas to regions with continental atmospheric conditions, Pakistan faces significant seasonal and daily variations in atmospheric parameters, such as solar irradiance, temperature, precipitation patterns, humidity, etc., making it a steppe country with diverse atmospheric conditions and an energy-intensive economy dominated by fossil fuels. Therefore, following United Nation's Sustainable Development Goals, here we investigate the radiative cooling potential resource map across Pakistan, providing it as a sustainable alternative to lower the cooling demand by maximizing the emitted thermal radiation to the deep space and minimizing solar irradiance absorption by utilizing the materials' inherent properties of being highly reflective within solar spectrum range and extremely emissive within the atmospheric window. A comprehensive comparison between annual, seasonal, diurnal, and nocturnal radiative cooling capability is conducted and analyzed across all provinces of Pakistan based on the variation in regional climatic conditions. The yearly average radiative cooling capacity varies from 69.39 to 96.41 W/m2 due to swift variation from humid continental to arid climatic regions, with a 24.27 % discrepancy in daytime and nighttime radiative cooling potentials owing to the significant influence of solar irradiance. An office building model incorporating radiative cooling coating at the rooftop is further implemented to illustrate the real-case scenarios of using radiative cooling coatings as a cool roof. Compared to traditional roofs, applying radiative cooling coatings on the rooftop of a single-storey office building can reduce the annual cooling load by 76.01 to 112.77 kWh/(m2.year) for various cities under diverse climatic conditions. The annual electricity savings in several cities are estimated to be 30.40 to 45.11 kWh/(m2.year) based on the refrigerator COP of 2.5. The application of radiative cooling coatings on rooftops induces the incremental cost of 24 $/m2, with a simple payback period of 5.32 to 7.89 years in response to annual electricity savings across varying meteorological conditions. Besides, the maximum carbon emissions reduction is estimated to be up to 27.77 kg/(m2.year) based on a carbon emission factor of 0.606 kgCO2/kWh. In the end, valuable insights are discussed based on policy recommendations and limitations for developing strategies to adapt the radiative cooling technology on a broader scale based on innovative solutions, spreading public awareness, and offering financial incentives.

Simultaneous Control of Spectral And Directional Emissivity with Gradient Epsilon-Near-Zero InAs Photonic Structures.

Controlling both the spectral bandwidth and directionality of emitted thermal radiation is a fundamental challenge in contemporary photonics. Recent work has shown that materials with a spatial gradient in the frequency range of their epsilon-near-zero (ENZ) response can support broad spectrum directionality in their emissivity, enabling high total radiance to specific angles of incidence. However, this capability is limited spectrally and directionally by the availability of materials with phonon-polariton resonances over long-wave infrared wavelengths. Here, an approach is designed and experimentally demonstrated using doped III-V semiconductors that can simultaneously tailor spectral peak, bandwidth, and directionality of infrared emissivity. InAs-based gradient ENZ photonic structures that exhibit broadband directional emission with varying spectral bandwidths and directional ranges as a function of their doping concentration profile and thickness are epitaxially grown and characterized. Due to its easy-to-fabricate geometry, it is believed that this approach provides a versatile photonic platform to dynamically control broadband spectral and directional emissivity for a range of emerging applications in heat transfer and infrared sensing.

Colourful phase change material-incorporated flexible film for efficient passive radiative cooling.

Passive radiative cooling (PRC) involves the emission of thermal radiation into cold space and the reflection of solar radiation, which aims to cool and lower the temperature of objects. However, currently most radiative coolers have a white appearance which restricts their potential applications. We develop a coloured bilayer radiative cooling membrane using polyvinylidene fluoride/tetraethoxysilane (PVDF/TEOS) fibres, with incorporation of phase change materials (PCMs) and active dyes through a simple and large-area electrospinning process. In comparison to traditional emitters, PCM-incorporated colourful coolers provide energy storage capacity and colourful appearances. Our phase-transition-based colourful flexible film (PCFF) achieves a total solar reflectance of 0.81 and a mid-infrared (MIR) (8-13 μm) emissivity of 0.85 with superior mechanical strength and good hydrophobicity. We experimentally demonstrate that our PCFF can significantly reduce the temperature of objects exposed to direct sunlight, with a cooling effect of up to 9 ℃ compared to commercial fabrics of similar materials and colours. Our work provides a promising starting point for the design and manufacture of colourful and flexible thermal control films.

Enhancing process efficiency through improved temperature measurement: the EMPRESS projects

EMPRESS 2 is a European project to enhance the efficiency of high value manufacturing processes by improving temperature measurement and control capability. This project seeks to address four contemporary thermometry challenges in this sector, and new developments from this and its predecessor project, EMPRESS, will be described:• Below 1000°C many industrial processes require reliable surface thermometry e.g. welding, coating, forging and forming. Conventional non-contact surface thermometry techniques e.g. thermal imaging are prone to large errors (tens of degrees) due to reflected thermal radiation and unknown emissivity. Contact thermometry approaches are prone to similarly large errors. Traceable imaging phosphor thermometry is being developed to overcome these difficulties, and is being combined with quantitative thermography to determine emissivity for thermometry over wide fields of view.• Above 1300°C sensor drift is a significant unaddressed issue for casting, forging and heat treatment, causing large errors. There is a need for more stable sensors and standardisation of at least one new thermocouple type to fill the gap from 1300°C to 1800°C. This is being addressed through improved Pt-Rh thermocouples and optimisation of double-walled mineral insulated, metal sheathed thermocouples by mitigating insulation breakdown and drift effects.• Combustion temperature measurement is very challenging and traceability is almost non-existent; for example, thermocouple measurements of flame temperatures can be in error by hundreds of degrees. A ‘standard flame’ that can be transported to users’ sites has been developed, and is being deployed in several high value manufacturing and industrial applications to a) demonstrate the possibility of reducing flame temperature uncertainties by at least an order of magnitude and b) for the first time to demonstrate in-situ traceability to the International Temperature Scale of 1990 (ITS-90).• Many processes are not amenable to any conventional thermometry techniques due to inaccessibility, ionising radiation, electromagnetic interference, and contamination; here methods based on optical fibres are ideal but there are no traceable calibration techniques for such sensors currently available. A suite of different fibre-optic thermometers and calibration techniques is being developed to address this. In some cases (ionising radiation) darkening of the fibre is a problem, and this is being overcome by the development of novel thermometry approaches based on practical ‘hollow core’ fibres.

Hierarchically designed 3-D printed porous nylon fabric-based personal thermoregulatory for radiative and directional wick-evaporative cooling

Energy consumption is increasing with global warming which remains a great challenge towards sustainable growth. Radiative cooling is an emergent technology towards personalized thermoregulation that radiates heat to outer space to attain self-cooling providing thermal comfort to humans while outdoors through economical way without any energy consumption. Herein a hydrophobic-hydrophilic porous nylon fabric (PNF) composite having unique pores across the composite with hierarchical silver nanoparticles decorated zinc stannate nanorods (Ag@ZTO) synthesized directly over the PNF. We designed the composite by novel and quick three-dimensional (3D) printing technique for the first time that utilizes synergistic innovative integration of radiative and wick-evaporation cooling. The high reflectance of solar irradiance (89.5%) and high emissivity of human body thermal radiation (91.8%) permitted the textile to reduce the temperature of simulated skin by 19.3 °C under direct sunlight demonstrating its superior passive cooling capability. An excellent water vapor transmission rate, water-wicking, washability, durability, tensile strength (70.8% compared to bare PNF) is demonstrated for the composite and a high one-way transport index R (1368 %) shows its unidirectional liquid transport behavior. This approach of designing fabric through tailoring the properties by cost-effective techniques offers new routes for personal thermoregulatory and moisture management towards advanced functional textiles introducing a pioneering direction to sustainable energy.

A full-time deep learning-based alert approach for bridge–ship collision using visible spectrum and thermal infrared cameras

With the rapid development of transportation infrastructure and the growing water transportation industry, many bridges have been constructed across navigable rivers. However, collisions between ships and bridges remain a frequent occurrence, particularly under low illumination conditions. To address this issue, this paper proposes a full-time bridge–ship collision alert approach based on the combination of visible spectrum and infrared cameras. This approach includes the following steps: (1) capturing and identifying ships in the channel using a single visible spectrum camera is challenging in low illumination environments such as nighttime. To overcome this limitation, we propose the use of infrared thermal imaging technology, which can monitor ships at night due to their inherent emissivity of ship thermal radiation. By comprehensively analyzing factors such as the real-time lighting environment and comparing the advantages of visible spectrum cameras and thermal infrared cameras in object recognition under various illuminance levels, we determine the effectiveness of the decision-making method of the dual-channel camera for ships under different illumination conditions. (2) To detect and track ships in the channel, a deep learning-based automatic detection and tracking method is designed using visible spectrum and infrared thermal imaging cameras, providing early warning of dangerous trajectories of ships that threaten the piers. To address the real-time identification and positioning of ships by dual-channel cameras in different light environments, we adopt a target detection network and a displacement calculation algorithm for multi-target tracking. Analysis results demonstrate that this method can automatically assign visible spectrum and thermal imaging cameras as effective input sources in different illumination environments to detect and warn ships with dangerous trajectories, contributing to the safety of navigable ships and bridges in low illumination conditions.

NSKY-CD: A System for Cloud Detection Based on Night Sky Brightness and Sky Temperature

Cloud cover is important meteorological information that still requires expensive equipment to be monitored from the ground, especially at night. The use of artificial lights at night causes light pollution, and clouds amplify this by reflecting light downward. In addition, cloud thermal radiation emissions affect sky temperature. In this study, we describe a system (NSKY-CD) that can be used to detect clouds at night since it integrates a sky quality meter that measures night sky brightness (NSB) and an air temperature and an infrared temperature sensor that measure sky temperature. We defined a cloud detection method based on fixed threshold values determined with two different procedures that we called ‘optimal’ and ‘antimode’. We then quantitatively assessed the performance of these methods in detecting the presence or absence of clouds in the urban area of Florence during two full moon cycles. Accuracy for the ‘optimal’ method varied between 87% and 91%, while for the ‘antimode’ method, it varied between 86% and 89%. Our results suggest that the two parameters are complementary since NSB has a better performance on moonless nights, and the difference between air temperature and sky temperature has a better performance on moonlit nights. Our method can also be used to analyze historical series of NSB to estimate cloud presence backwards, thus providing important information for meteorological, environmental and astronomical studies.

Impact of 3-D structures on directional effective emissivity in urban areas based on DART model

Thermal infrared (TIR) remote sensing is effective to monitor urban land surface temperature (LST) on a large scale. The accuracy of the inversion of LST depends strongly on the emissivity. The emissivity is complex in urban areas and is largely dependent on three-dimensional (3-D) urban structure and different building materials, also called effective emissivity. The urban canyons have homogeneous temperatures to avoid the difficulty of defining the emissivity of non-isothermal surfaces. In this paper, we use the 3-D discrete anisotropic radiative transfer (DART) model to simulate the emission and propagation of thermal radiation in urban scenes by a flux tracking method and generate remote sensing images. The impact of 3-D structures on the effective emissivity was analyzed and simple relations between effective emissivity and 3-D structure parameters were proposed. Results show that the increase of emissivity at nadir is well related to wall frontal area index (F) and the mean sky view factor of flat surfaces (i.e., roof and road, SVFweighted), whereas emissivity directionality is well related to road's sky view factor (SVFroad). Overall, emissivity directionality (reaches 0.069 if reflectance is 0.2 for the road and 0.1 for the other components) due to material mixture and nadir emissivity increment (increase by 0.0646 for material reflectance R of 0.1) caused by 3-D structures can be larger than other emissivity sources. This study helps to understand the impact of 3-D structures and different material emissivity on urban effective emissivity and offers insights for addressing urban emissivity directionality in multi-angular remote sensing missions.

Spectrally Selective Thermal Emission from Graphene Decorated with Metallic Nanoparticles

We showed in past work that nanopatterned monolayer graphene (NPG) enables spectrally selective thermal emission in the mid-infrared (mid-IR) from 3 to 12 μm. In that case, the spectral selection is realized by means of the localized surface plasmon (LSP) resonances inside graphene. Here, we show that graphene decorated with metallic nanoparticles, such as Ag nanocubes or nanospheres, also realizes spectrally selective thermal emission but, in this case, by means of acoustic graphene plasmons (AGPs) localized between graphene and the Ag nanoparticle inside a dielectric material. Our finite-difference time-domain (FDTD) calculations show that the spectrally selective thermal radiation emission can be tuned by means of a gate voltage into two different wavelength regimes, namely, the atmospherically opaque regime between λ = 5 and 8 μm or the atmospherically transparent regime between λ = 8 and 12 μm. This allows for electrical switching between a radiative heat trapping mode for the former regime and a radiative cooling mode for the latter regime. Our theoretical results can be used to develop graphene-based thermal management systems for smart fabrics.

A Review of Nanoparticle Material Coatings in Passive Radiative Cooling Systems Including Skylights

Daytime passive radiative cooling (DPRC) has remained a challenge over the past decades due to the necessity of precisely defined materials with a significantly high emissivity of thermal radiation within the atmospheric transparent window wavelength range (8–13 μm) as well as high reflectivity in the solar spectrum (0.2–3 μm). Fortunately, recent advances and technological improvements in nanoscience and metamaterials are making it possible to create diverse metamaterials. This enables the production of DPRC in direct solar irradiation. The development of a material that is appropriate for effective DPRC is also a noteworthy development in this field of technology. This review gives a thorough introduction and discussion of the fundamental ideas, as well as the state-of-the-art and current trends in passive radiative cooling, and describes the cutting-edge materials and various photonic radiator structures that are useful in enhancing net cooling performance. This work also addresses a novel skylight window that offers passive cooling developed at the Åbo Akademi (ÅA) University, Finland. In conclusion, nanomaterials and nanoparticle-based coatings are preferred over all other approaches for commercialization in the future because of their low cost, the ability for large-scale production, simplicity in fabrication, and great potential for further increasing cooling performance.