Journal articles: 'Angular emissivity'

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Zhang, Yaqi, and Gerald Diebold. "Photothermal determination of the angular dependence of emissivity." Applied Optics 57, no. 22 (July 30, 2018): 6561. http://dx.doi.org/10.1364/ao.57.006561.

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Dimenna, R. A., and R. O. Buckius. "Electromagnetic Theory Predictions of the Directional Scattering From Triangular Surfaces." Journal of Heat Transfer 116, no. 3 (August 1, 1994): 639–45. http://dx.doi.org/10.1115/1.2910917.

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Angular predictions of directional scattering distributions for metal and dielectric surfaces with length scales of the order of the wavelength are made from rigorous electromagnetic scattering theory. The theoretical and numerical formulation of the electromagnetic scattering solution based on the extinction theorem is presented. One-dimensional triangular surface profiles are generated using a Fourier series representation for various correlation lengths, deviations, and surface peak positions. Bidirectional reflection functions and directional emissivities are calculated for the surface geometry parameters above and various optical properties. Angular enhancements in bidirectional reflection and emissivity are quantified. Angular scattering and emissivity predictions have been extended beyond those previously reported to include surfaces with equivalent correlation length and deviation.

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Chao, Jinlong, Chengyu Liu, Yingjun Xu, Wei Gu, Ying Li, and Feng Xie. "Multi-angular thermal infrared emission characteristics of Bohai Sea ice based on in situ measurements." Journal of Glaciology 61, no. 229 (2015): 864–74. http://dx.doi.org/10.3189/2015jog14j143.

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AbstractWe report on the radiative transfer process and optical properties of sea ice in the thermal infrared (TIR) band, presenting two new linear kernel driver models (Relative Emissivity Distribution Function, REDF) that describe TIR emission characteristics of smooth and rough ice. In order to test the models and determine the necessary coefficients, in situ measurements from the Bohai Sea were carried out during the 2011/12 and 2012/13 boreal winters. The results show that the relative emissivity of smooth sea ice decreases along with increasing viewing zenith angle, and the shape of the relative emissivity curve is similar to that of an ideal plane. Affected by parameters such as roughness and surface temperature distribution, the anisotropy of relative emissivity of sea ice with a high degree of roughness is stronger relative to the cosine emitter. The model coefficients were also obtained using a robust regression method based on the measured data. The presented models are more practical than the numerical radiative transfer model and can be used for multi-angular TIR remote sensing.

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Xu, Jin, Jyotirmoy Mandal, and Aaswath P. Raman. "Broadband directional control of thermal emission." Science 372, no. 6540 (April 22, 2021): 393–97. http://dx.doi.org/10.1126/science.abc5381.

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Controlling the directionality of emitted far-field thermal radiation is a fundamental challenge. Photonic strategies enable angular selectivity of thermal emission over narrow bandwidths, but thermal radiation is a broadband phenomenon. The ability to constrain emitted thermal radiation to fixed narrow angular ranges over broad bandwidths is an important, but lacking, capability. We introduce gradient epsilon-near-zero (ENZ) materials that enable broad-spectrum directional control of thermal emission. We demonstrate two emitters consisting of multiple oxides that exhibit high (>0.7, >0.6) directional emissivity (60° to 75°, 70° to 85°) in the p-polarization for a range of wavelengths (10.0 to 14.3 micrometers, 7.7 to 11.5 micrometers). This broadband directional emission enables meaningful radiative heat transfer primarily in the high emissivity directions. Decoupling the conventional limitations on angular and spectral response improves performance for applications such as thermal camouflaging, solar heating, radiative cooling, and waste heat recovery.

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Warren, T. J., N. E. Bowles, K. Donaldson Hanna, and J. L. Bandfield. "Modeling the Angular Dependence of Emissivity of Randomly Rough Surfaces." Journal of Geophysical Research: Planets 124, no. 2 (February 2019): 585–601. http://dx.doi.org/10.1029/2018je005840.

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REES, W. G., and S. P. JAMES. "Angular variation of the infrared emissivity of ice and water surfaces." International Journal of Remote Sensing 13, no. 15 (October 1992): 2873–86. http://dx.doi.org/10.1080/01431169208904088.

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García-Santos, Vicente, Enric Valor, Vicente Caselles, M. Ángeles Burgos, and César Coll. "On the angular variation of thermal infrared emissivity of inorganic soils." Journal of Geophysical Research: Atmospheres 117, no. D19 (October 10, 2012): n/a. http://dx.doi.org/10.1029/2012jd017931.

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Vidal, Matias, Clive Dickinson, S. E. Harper, Simon Casassus, and A. N. Witt. "Modelling the spinning dust emission from LDN 1780." Monthly Notices of the Royal Astronomical Society 495, no. 1 (April 30, 2020): 1122–35. http://dx.doi.org/10.1093/mnras/staa1186.

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ABSTRACT We study the anomalous microwave emission (AME) in the Lynds Dark Nebula (LDN) 1780 on two angular scales. With publicly available data at an angular resolution of 1°, we studied the spectral energy distribution of the cloud in the 0.408–2997 GHz frequency range. The cloud presents a significant (>20σ) amount of AME, making it one of the clearest examples of AME on 1 ° scales, and its spectrum can be well fitted with a spinning dust (SD) model. We also find at these angular scales that the location of the peak of the emission at lower frequencies (23–70 GHz) differs from the location at the higher frequencies (90–3000 GHz) maps. In addition to the analysis on 1° angular scales, we present data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at 31 GHz with an angular resolution of 2 arcmin, in order to study the origin of the AME in LDN 1780. We studied morphological correlations between the CARMA map and different infrared tracers of dust emission. We found that the best correlation is with the 70- μm template, which traces warm dust (T ∼ 50 K). Finally, we study the difference in radio emissivity between two locations within the cloud. We measured a factor of ≈6 difference in 31-GHz emissivity. We show that this variation can be explained, using the SD model, by a variation on the dust grain size distribution across the cloud, particularly changing the fraction of polycyclic aromatic hydrocarbon for a fixed total amount of carbon.

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Ermida, Sofia L., Isabel F. Trigo, Glynn Hulley, and Carlos C. DaCamara. "A multi-sensor approach to retrieve emissivity angular dependence over desert regions." Remote Sensing of Environment 237 (February 2020): 111559. http://dx.doi.org/10.1016/j.rse.2019.111559.

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Cuenca, Juan, and José A. Sobrino. "Experimental measurements for studying angular and spectral variation of thermal infrared emissivity." Applied Optics 43, no. 23 (August 10, 2004): 4598. http://dx.doi.org/10.1364/ao.43.004598.

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Langsdale, Mary F., Martin Wooster, Jeremy J. Harrison, Michael Koehl, Christoph Hecker, Simon J. Hook, Elsa Abbott, et al. "Spectral Emissivity (SE) Measurement Uncertainties across 2.5–14 μm Derived from a Round-Robin Study Made across International Laboratories." Remote Sensing 13, no. 1 (December 30, 2020): 102. http://dx.doi.org/10.3390/rs13010102.

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Information on spectral emissivity (SE) is vital when retrieving and evaluating land surface temperature (LST) estimates from remotely sensed observations. SE measurements often come from spectral libraries based upon laboratory spectroscopic measurements, with uncertainties typically derived from repeated measurements. To go further, we organised a “round-robin” inter-comparison exercise involving SE measurements of three samples collected at seven different international laboratories. The samples were distilled water, which has a uniformly high spectral emissivity, and two artificial samples (aluminium and gold sheets laminated in polyethylene), with variable emissivities and largely specular and Lambertian characteristics. Large differences were observed between some measurements, with standard deviations over 2.5–14 μm of 0.092, 0.054 and 0.028 emissivity units (15.98%, 7.56% and 2.92%) for the laminated aluminium sheet, laminated gold sheet and distilled water respectively. Wavelength shifts of up to 0.09 μm were evident between spectra from different laboratories for the specular sample, attributed to system design interacting with the angular behaviour of emissivity. We quantified the impact of these SE differences on satellite LST estimation and found that emissivity differences resulted in LSTs differing by at least 3.5 K for each artificial sample and by more than 2.5 K for the distilled water. Our findings suggest that variations between SE measurements derived via laboratory setups may be larger than previously assumed and provide a greater contribution to LST uncertainty than thought. The study highlights the need for the infrared spectroscopy community to work towards standardized and interlaboratory comparable results.

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Niclòs, Raquel, Enric Valor, Vicente Caselles, César Coll, and Juan Manuel Sánchez. "In situ angular measurements of thermal infrared sea surface emissivity—Validation of models." Remote Sensing of Environment 94, no. 1 (January 2005): 83–93. http://dx.doi.org/10.1016/j.rse.2004.09.002.

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Sobrino, José A., and Juan Cuenca. "Angular variation of thermal infrared emissivity for some natural surfaces from experimental measurements." Applied Optics 38, no. 18 (June 20, 1999): 3931. http://dx.doi.org/10.1364/ao.38.003931.

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Zhang, Bufa, John Redgrove, and Jamie Clark. "New apparatus for measurement of the spectral, angular, and total emissivity of solids." High Temperatures-High Pressures 35/36, no. 3 (2003): 289–302. http://dx.doi.org/10.1068/htjr124.

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15

Arce-Tord, Carla, Matias Vidal, Simon Casassus, Miguel Cárcamo, Clive Dickinson, Brandon S. Hensley, Ricardo Génova-Santos, et al. "Resolved observations at 31 GHz of spinning dust emissivity variations in ρ Oph." Monthly Notices of the Royal Astronomical Society 495, no. 3 (January 2020): 3482–93. http://dx.doi.org/10.1093/mnras/staa1422.

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ABSTRACT The ρ Oph molecular cloud is one of the best examples of spinning dust emission, first detected by the cosmic background imager (CBI). Here, we present 4.5 arcmin observations with CBI 2 that confirm 31 GHz emission from ρ Oph W, the PDR exposed to B-type star HD 147889, and highlight the absence of signal from S1, the brightest IR nebula in the complex. In order to quantify an association with dust-related emission mechanisms, we calculated correlations at different angular resolutions between the 31 GHz map and proxies for the column density of IR emitters, dust radiance, and optical depth templates. We found that the 31 GHz emission correlates best with the PAH column density tracers, while the correlation with the dust radiance improves when considering emission that is more extended (from the shorter baselines), suggesting that the angular resolution of the observations affects the correlation results. A proxy for the spinning dust emissivity reveals large variations within the complex, with a dynamic range of 25 at 3σ and a variation by a factor of at least 23, at 3σ, between the peak in ρ Oph W and the location of S1, which means that environmental factors are responsible for boosting spinning dust emissivities locally.

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Chen, Jinnan, Liang-Yao Chen, and Junpeng Guo. "Equilibrium temperature of a spectral selective solar light absorber with angular dependent thermal emissivity." Journal of the Optical Society of America B 37, no. 10 (September 8, 2020): 2873. http://dx.doi.org/10.1364/josab.399171.

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Ren, Huazhong, Guangjian Yan, Ling Chen, and Zhaoliang Li. "Angular effect of MODIS emissivity products and its application to the split-window algorithm." ISPRS Journal of Photogrammetry and Remote Sensing 66, no. 4 (July 2011): 498–507. http://dx.doi.org/10.1016/j.isprsjprs.2011.02.008.

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Dauser, T., J. Wilms, C. S. Reynolds, and L. W. Brenneman. "Broad emission lines for a negatively spinning black hole." Proceedings of the International Astronomical Union 6, S275 (September 2010): 100–101. http://dx.doi.org/10.1017/s1743921310015735.

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AbstractWe present an extended scheme for the calculation of the profiles of emission lines from accretion disks around rotating black holes. The scheme includes disks with angular momenta which are parallel and antiparallel with respect to the black hole's angular momentum, as both configurations are assumed to be stable (King et al. 2005). Based on a Green's function approach, an arbitrary radius dependence of the disk emissivity and arbitrary limb darkening laws can be easily taken into account, while the amount of precomputed data is significantly reduced with respect to other available models. We discuss line shapes for such disks and present a code for modelling observational data with this scheme in X-ray data analysis programs. A detailed discussion will soon be presented in a forthcoming paper (Dauser et al. 2010).

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Garcia-Santos, Vicente, Enric Valor, Vicente Caselles, Cesar Coll, and Ma Angeles Burgos. "Effect of Soil Moisture on the Angular Variation of Thermal Infrared Emissivity of Inorganic Soils." IEEE Geoscience and Remote Sensing Letters 11, no. 6 (June 2014): 1091–95. http://dx.doi.org/10.1109/lgrs.2013.2286747.

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Hori, Masahiro, Teruo Aoki, Tomonori Tanikawa, Akihiro Hachikubo, Konosuke Sugiura, Katsuyuki Kuchiki, and Masashi Niwano. "Modeling angular-dependent spectral emissivity of snow and ice in the thermal infrared atmospheric window." Applied Optics 52, no. 30 (October 15, 2013): 7243. http://dx.doi.org/10.1364/ao.52.007243.

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Huazhong Ren, Rongyuan Liu, Guangjian Yan, Xihan Mu, Zhao-Liang Li, Francoise Nerry, and Qiang Liu. "Angular Normalization of Land Surface Temperature and Emissivity Using Multiangular Middle and Thermal Infrared Data." IEEE Transactions on Geoscience and Remote Sensing 52, no. 8 (August 2014): 4913–31. http://dx.doi.org/10.1109/tgrs.2013.2285924.

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Prigent, Catherine, Frédéric Chevallier, Fatima Karbou, Peter Bauer, and Graeme Kelly. "AMSU-A Land Surface Emissivity Estimation for Numerical Weather Prediction Assimilation Schemes." Journal of Applied Meteorology 44, no. 4 (April 1, 2005): 416–26. http://dx.doi.org/10.1175/jam2218.1.

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Abstract This study describes the work performed at the European Centre for Medium-Range Weather Forecasts (ECMWF) to estimate the microwave land surface emissivities at Advanced Microwave Sounding Unit (AMSU)-A frequencies within the specific context and constraint of operational assimilation. The emissivities are directly calculated from the satellite observations in clear-sky conditions using the surface skin temperature derived from ECMWF and the Radiative Transfer for the Television and Infrared Observation Satellite Operational Vertical Sounder (RTTOVS) model, along with the forecast model variables to estimate the atmospheric contributions. The results are analyzed, with special emphasis on the evaluation of the frequency and angular dependencies of the emissivities with respect to the surface characteristics. Possible extrapolation of the Special Sensor Microwave Imager (SSM/I) emissivities to those of the AMSU is considered. Direct calculation results are also compared with emissivity model outputs.

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Garcia-Santos, Vicente, Enric Valor, Claudia Di Biagio, and Vicente Caselles. "Predictive Power of the Emissivity Angular Variation of Soils in the Thermal Infrared (8–14 $\mu$ m) Region by Two Mie-Based Emissivity Theoretical Models." IEEE Geoscience and Remote Sensing Letters 15, no. 7 (July 2018): 1115–19. http://dx.doi.org/10.1109/lgrs.2018.2826446.

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LABED, J., and M. P. STOLL. "Angular variation of land surface spectral emissivity in the thermal infrared: laboratory investigations on bare soils." International Journal of Remote Sensing 12, no. 11 (November 1991): 2299–310. http://dx.doi.org/10.1080/01431169108955259.

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François, C., and C. Ottlé. "Estimation of the angular variation of the sea surface emissivity with the ATSR/ERS-1 data." Remote Sensing of Environment 48, no. 3 (June 1994): 302–8. http://dx.doi.org/10.1016/0034-4257(94)90004-3.

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Hu, Tian, Hua Li, Biao Cao, Albert I. J. M. van Dijk, Luigi J. Renzullo, Zhihong Xu, Jun Zhou, Yongming Du, and Qinhuo Liu. "Influence of emissivity angular variation on land surface temperature retrieved using the generalized split-window algorithm." International Journal of Applied Earth Observation and Geoinformation 82 (October 2019): 101917. http://dx.doi.org/10.1016/j.jag.2019.101917.

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Marquier, F., M. Laroche, R. Carminati, and J. J. Greffet. "Anisotropic Polarized Emission of a Doped Silicon Lamellar Grating." Journal of Heat Transfer 129, no. 1 (June 21, 2006): 11–16. http://dx.doi.org/10.1115/1.2360594.

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Thermal emission of a doped silicon grating has been studied in the plane perpendicular to the grooves. We show how the excitation of surface plasmons produce a resonant emission weakly depending on the polarization and azimuthal angle. We analyze in detail the polarization and angular dependence of the emission out of the plane perpendicular to the grooves. Two kinds of thermal sources, directional and quasi-isotropic, are studied. They have been designed in a previous paper. We also compute the total hemispherical emissivity of these gratings. In addition we show that in applications such as radiative cooling, these sources are less efficient than other structures.

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Pérez-Planells, Lluís, Raquel Niclòs, Jesús Puchades, César Coll, Frank-M. Göttsche, José A. Valiente, Enric Valor, and Joan M. Galve. "Validation of Sentinel-3 SLSTR Land Surface Temperature Retrieved by the Operational Product and Comparison with Explicitly Emissivity-Dependent Algorithms." Remote Sensing 13, no. 11 (June 7, 2021): 2228. http://dx.doi.org/10.3390/rs13112228.

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Land surface temperature (LST) is an essential climate variable (ECV) for monitoring the Earth climate system. To ensure accurate retrieval from satellite data, it is important to validate satellite derived LSTs and ensure that they are within the required accuracy and precision thresholds. An emissivity-dependent split-window algorithm with viewing angle dependence and two dual-angle algorithms are proposed for the Sentinel-3 SLSTR sensor. Furthermore, these algorithms are validated together with the Sentinel-3 SLSTR operational LST product as well as several emissivity-dependent split-window algorithms with in-situ data from a rice paddy site. The LST retrieval algorithms were validated over three different land covers: flooded soil, bare soil, and full vegetation cover. Ground measurements were performed with a wide band thermal infrared radiometer at a permanent station. The coefficients of the proposed split-window algorithm were estimated using the Cloudless Land Atmosphere Radiosounding (CLAR) database: for the three surface types an overall systematic uncertainty (median) of −0.4 K and a precision (robust standard deviation) 1.1 K were obtained. For the Sentinel-3A SLSTR operational LST product, a systematic uncertainty of 1.3 K and a precision of 1.3 K were obtained. A first evaluation of the Sentinel-3B SLSTR operational LST product was also performed: systematic uncertainty was 1.5 K and precision 1.2 K. The results obtained over the three land covers found at the rice paddy site show that the emissivity-dependent split-window algorithms, i.e., the ones proposed here as well as previously proposed algorithms without angular dependence, provide more accurate and precise LSTs than the current version of the operational SLSTR product.

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Niclòs, Raquel, Vicente Caselles, César Coll, and Enric Valor. "Determination of sea surface temperature at large observation angles using an angular and emissivity-dependent split-window equation." Remote Sensing of Environment 111, no. 1 (November 2007): 107–21. http://dx.doi.org/10.1016/j.rse.2007.03.014.

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Béthune, William, and Henrik Latter. "Electric heating and angular momentum transport in laminar models of protoplanetary discs." Monthly Notices of the Royal Astronomical Society 494, no. 4 (May 5, 2020): 6103–19. http://dx.doi.org/10.1093/mnras/staa908.

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ABSTRACT The vertical temperature structure of a protoplanetary disc bears on several processes relevant to planet formation, such as gas and dust grain chemistry, ice lines, and convection. The temperature profile is controlled by irradiation from the central star and by any internal source of heat such as might arise from gas accretion. We investigate the heat and angular momentum transport generated by the resistive dissipation of magnetic fields in laminar discs. We use local 1D simulations to obtain vertical temperature profiles for typical conditions in the inner disc (0.5–4 au). Using simple assumptions for the gas ionization and opacity, the heating and cooling rates are computed self-consistently in the framework of radiative non-ideal magnetohydrodynamics. We characterize steady solutions that are symmetric about the mid-plane and which may be associated with saturated Hall-shear unstable modes. We also examine the dissipation of electric currents driven by global accretion-ejection structures. In both cases we obtain significant heating for a sufficiently high opacity. Strong magnetic fields can induce an order-unity temperature increase in the disc mid-plane, a convectively unstable entropy profile, and a surface emissivity equivalent to a viscous heating of α ∼ 10−2. These results show how magnetic fields may drive efficient accretion and heating in weakly ionized discs where turbulence might be inefficient, at least for a range of radii and ages of the disc.

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Dziarski, Krzysztof, Arkadiusz Hulewicz, and Grzegorz Dombek. "Thermographic Measurement of the Temperature of Reactive Power Compensation Capacitors." Energies 14, no. 18 (September 12, 2021): 5736. http://dx.doi.org/10.3390/en14185736.

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An excessive increase in reactive power consumption is unfavorable from the point of view of a power system. For this reason, devices compensating reactive power consumption are used. The capacitor is one such device. Capacitors must be tested regularly during their exploitation. One of the activities that should be performed is testing the degree of heating of the cells of a capacitor bank. Thermography can be used to perform such tests. This non-contact method has its limitations. Due to the angular emissivity and the change in the distance between the lens and the object under observation, the temperature measured with a thermographic camera may differ from the actual temperature. This phenomenon is visible on cylindrical capacitor cases. Consequently, depending on the location of the observation point on the capacitor case, the result of the thermographic temperature measurement may be different. To investigate this phenomenon, experimental work has been undertaken.

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Heygster, G., V. Alexandrov, G. Dybkjær, F. Girard-Ardhuin, W. von Hoyningen-Huene, I. L. Katsev, A. Kokhanovsky, et al. "Remote sensing of sea ice: advances during the DAMOCLES project." Cryosphere Discussions 6, no. 1 (January 3, 2012): 37–88. http://dx.doi.org/10.5194/tcd-6-37-2012.

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Abstract. In the Arctic, global warming is particularly pronounced so that we need to monitor its development continuously. On the other hand, the vast and hostile conditions make in situ observation difficult, so that available satellite observations should be exploited in the best possible way to extract geophysical information. Here, we give a résumé of the sea ice remote sensing efforts of the EU project DAMOCLES (Developing Arctic Modeling and Observing Capabilities for Long-term Environmental Studies). The monthly variation of the microwave emissivity of first-year and multiyear sea ice has been derived for the frequencies of the microwave imagers like AMSR-E and sounding frequencies of AMSU, and has been used to develop an optimal estimation method to retrieve sea ice and atmospheric parameters simultaneously. A sea ice microwave emissivity model has been used together with a thermodynamic model to establish relations between the emisivities at 6 GHz and 50 GHz. At the latter frequency, the emissivity is needed for assimilation into atmospheric circulation models, but more difficult to observe directly. A method to determine the effective size of the snow grains from observations in the visible range (MODIS) is developed and applied. The bidirectional reflectivity distribution function (BRDF) of snow, which is an essential input parameter to the retrieval, has been measured in situ on Svalbard during the DAMOCLES campaign, and a BRDF model assuming aspherical particles is developed. Sea ice drift and deformation is derived from satellite observations with the scatterometer ASCAT (62.5 km grid spacing), with visible AVHRR observations (20 km), with the synthetic aperture radar sensor ASAR (10 km), and a multi-sensor product (62.5 km) with improved angular resolution (Continuous Maximum Cross Correlation, CMCC method) is presented. CMCC is also used to derive the sea ice deformation, important for formation of sea ice leads (diverging deformation) and pressure ridges (converging). The indirect determination of sea ice thickness from altimeter freeboard data requires knowledge of the ice density and snow load on sea ice. The relation between freeboard and ice thickness is investigated based on the airborne Sever expeditions conducted between 1928 and 1993.

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Zhong, Zhimeng, Jianyao Zhao, and Chao Li. "Outdoor-to-Indoor Channel Measurement and Coverage Analysis for 5G Typical Spectrums." International Journal of Antennas and Propagation 2019 (September 16, 2019): 1–10. http://dx.doi.org/10.1155/2019/3981678.

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The fifth-generation (5G) mobile communications system will adopt the millimeter wave (mmWave) band for outdoor-to-indoor (O2I) coverage to achieve ultrahigh data rate. However, it is a challenging task because of the large path loss and almost total blocking by building walls. In this work, we performed extensive measurements on the O2I propagation at 3.5, 4.9, and 28 GHz simultaneously by using a multiband channel sounder. We captured the path loss distribution and angular power arrival profiles. We also measured the penetration loss at 28 GHz through different kinds of glass windows. The widely adopted ordinary glass windows introduce the penetration loss of 3 to 12 dB that is acceptable and makes mmWave O2I coverage feasible. But the low-emissivity (low-E) windows that will be more popular in the future introduce 10 dB higher loss. The measurement results in this work can help analyse and anticipate the O2I coverage by mmWave, which is important for the design and deployment of the 5G network.

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Paradis, D., C. Mény, M. Juvela, A. Noriega-Crespo, and I. Ristorcelli. "Revisiting the dust properties in the molecular clouds of the Large Magellanic Cloud." Astronomy & Astrophysics 627 (June 25, 2019): A15. http://dx.doi.org/10.1051/0004-6361/201935158.

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Context. Some Galactic molecular clouds show signs of dust evolution as compared to the diffuse interstellar medium, most of the time through indirect evidence such as color ratios, increased dust emissivity, or scattering (coreshine). These signs are not a feature of all Galactic clouds. Moreover, molecular clouds in the Large Magellanic Cloud (LMC) have been analyzed in a previous study based on Spitzer and IRIS data, at 4′ angular resolution, with the use of one single dust model, and did not show any signs of dust evolution. Aims. In this present analysis we investigate the dust properties associated with the different gas phases (including the ionized phase this time) of the LMC molecular clouds at 1′ angular resolution (four times greater than the previous analysis) and with a larger spectral coverage range thanks to Herschel data. We also ensure the robustness of our results in the framework of various dust models. Methods. We performed a decomposition of the dust emission in the infrared (from 3.6 to 500 μm) associated with the atomic, molecular, and ionized gas phases in the molecular clouds of the LMC. The resulting spectral energy distributions were fitted with four distinct dust models. We then analyzed the model parameters such as the intensity of the radiation field and the relative dust abundances, as well as the slope of the emission spectra at long wavelengths. Results. This work allows dust models to be compared with infrared data in various environments for the first time, which reveals important differences between the models at short wavelengths in terms of data fitting (mainly in the polycyclic aromatic hydrocarbon bands). In addition, this analysis points out distinct results according to the gas phases, such as dust composition directly affecting the dust temperature and the dust emissivity in the submillimeter and different dust emission in the near-infrared (NIR). Conclusions. We observe direct evidence of dust property evolution from the diffuse to the dense medium in a large sample of molecular clouds in the LMC. In addition, the differences in the dust component abundances between the gas phases could indicate different origins of grain formation. We also point out the presence of a NIR-continuum in all gas phases, with an enhancement in the ionized gas. We favor the hypothesis of an additional dust component as the carrier of this continuum.

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Tabone, B., S. Cabrit, G. Pineau des Forêts, J. Ferreira, A. Gusdorf, L. Podio, E. Bianchi, E. Chapillon, C. Codella, and F. Gueth. "Constraining MHD disk winds with ALMA." Astronomy & Astrophysics 640 (August 2020): A82. http://dx.doi.org/10.1051/0004-6361/201834377.

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Context. Large millimeter interferometers (ALMA, NOEMA, SMA), with their high spectral resolution and sensitivity, are revealing a growing number of rotating outflows, which are suggested to trace magneto-centrifugal disk winds (MHD DWs). However, the angular momentum flux that they extract and its impact on disk accretion are not yet well quantified. Aims. We aim to identify systematic bias in the process of retrieving the true launch zone, magnetic lever arm, and associated angular momentum flux of an MHD DW from apparent rotation signatures, as measured by observers from position-velocity (PV) diagrams at ALMA-like resolution. Methods. We constructed synthetic PV cuts from self-similar MHD DW solutions over a broad range of parameters. We examine three methods for estimating the specific angular momentum jobs from PV cuts: the “double-peak separation” method (relevant for edge-on systems), and the “rotation curve” and “flow width” methods (applicable at any view angle). The launch radius and magnetic lever arm are then derived from jobs through the widely used theory of MHD flow invariants, and are compared to their true values on the outermost streamline. Predictions for the “double-peak separation” method are tested on published ALMA observations of the HH212 rotating SO wind at resolutions from ~250 au to ~18 au. Results. The double-peak separation method and the flow width method provide only a lower limit to the true outer launch radius rout. This bias is mostly independent of angular resolution, but increases with the wind radial extension and radial emissivity gradient and can reach a factor of ten. In contrast, the rotation curve method leads to a good estimate of rout when the flow is well resolved, and an upper limit at low angular resolution. The magnetic lever arm is always underestimated due to invisible angular momentum stored as magnetic field torsion. ALMA data of HH212 confirm our predictions of the bias associated with the double-peak separation method, and the large rout ≃ 40 au and small magnetic lever arm first suggested by Tabone et al. (2017, A&A, 607, L6) from PV cut modeling. We also derive an analytical expression for the fraction of disk angular momentum extraction performed by a self-similar MHD disk wind of given radial extent, magnetic lever arm, and mass ejection-to-accretion ratio. The MHD DW candidate in HH212 extracts enough angular momentum to sustain steady accretion through the whole disk at the current observed rate. Conclusions. The launch radius estimated from observed rotation signatures in an MHD DW can markedly differ from the true outermost launch radius rout. Similar results would apply in a wider range of flow geometries. While in principle it is possible to bracket rout by combining two observational methods with opposite bias, only comparison with synthetic predictions can properly take into account all observational effects, and also constrain the true magnetic lever arm. The present comparison with ALMA observations of HH212 represents the most stringent observational test of MHD DW models to date, and shows that MHD DWs are serious candidates for the angular momentum extraction process in protoplanetary disks.

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Rigby, A. J., N. Peretto, R. Adam, P. Ade, P. André, H. Aussel, A. Beelen, et al. "A NIKA view of two star-forming infrared dark clouds: Dust emissivity variations and mass concentration." Astronomy & Astrophysics 615 (July 2018): A18. http://dx.doi.org/10.1051/0004-6361/201732258.

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Context. The thermal emission of dust grains is a powerful tool for probing cold, dense regions of molecular gas in the interstellar medium, and so constraining dust properties is key to obtaining accurate measurements of dust mass and temperature. Aims. By placing constraints on the dust emissivity spectral index, β, towards two star-forming infrared dark clouds – SDC18.888–0.476 and SDC24.489–0.689 – we aim to evaluate the role of mass concentration in the associated star-formation activity. Methods. We exploited the simultaneous 1.2 and 2.0 mm imaging capability of the NIKA camera on the IRAM 30 m telescope to construct maps of β for both clouds, and by incorporating Herschel observations, we created H2 column density maps with 13′′ angular resolution. Results. While we find no significant systematic radial variations around the most massive clumps in either cloud on ≳0.1 pc scales, their mean β values are significantly different, with β̅ = 2.07 ± 0.09 (random) ± 0.25 (systematic) for SDC18.888–0.476 and β̅ = 1.71 ± 0.09 (random) ± 0.25 (systematic) for SDC24.489–0.689. These differences could be a consequence of the very different environments in which both clouds lie, and we suggest that the proximity of SDC18.888–0.476 to the W39 H II region may raise β on scales of ~1 pc. We also find that the mass in SDC24.489–0.689 is more centrally concentrated and circularly symmetric than in SDC18.888–0.476, and is consistent with a scenario in which spherical globally-collapsing clouds concentrate a higher fraction of their mass into a single core than elongated clouds that will more easily fragment, distributing their mass into many cores. Conclusions. We demonstrate that β variations towards interstellar clouds can be robustly constrained with high signal-to-noise ratio (S/N) NIKA observations, providing more accurate estimates of their masses. The methods presented here will be applied to the Galactic Star Formation with NIKA2 (GASTON) guaranteed time large programme, extending our analysis to a statistically significant sample of star-forming clouds.

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Heygster, G., V. Alexandrov, G. Dybkjær, W. von Hoyningen-Huene, F. Girard-Ardhuin, I. L. Katsev, A. Kokhanovsky, et al. "Remote sensing of sea ice: advances during the DAMOCLES project." Cryosphere 6, no. 6 (December 3, 2012): 1411–34. http://dx.doi.org/10.5194/tc-6-1411-2012.

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Abstract. In the Arctic, global warming is particularly pronounced so that we need to monitor its development continuously. On the other hand, the vast and hostile conditions make in situ observation difficult, so that available satellite observations should be exploited in the best possible way to extract geophysical information. Here, we give a résumé of the sea ice remote sensing efforts of the European Union's (EU) project DAMOCLES (Developing Arctic Modeling and Observing Capabilities for Long-term Environmental Studies). In order to better understand the seasonal variation of the microwave emission of sea ice observed from space, the monthly variations of the microwave emissivity of first-year and multi-year sea ice have been derived for the frequencies of the microwave imagers like AMSR-E (Advanced Microwave Scanning Radiometer on EOS) and sounding frequencies of AMSU (Advanced Microwave Sounding Unit), and have been used to develop an optimal estimation method to retrieve sea ice and atmospheric parameters simultaneously. In addition, a sea ice microwave emissivity model has been used together with a thermodynamic model to establish relations between the emissivities from 6 GHz to 50 GHz. At the latter frequency, the emissivity is needed for assimilation into atmospheric circulation models, but is more difficult to observe directly. The size of the snow grains on top of the sea ice influences both its albedo and the microwave emission. A method to determine the effective size of the snow grains from observations in the visible range (MODIS) is developed and demonstrated in an application on the Ross ice shelf. The bidirectional reflectivity distribution function (BRDF) of snow, which is an essential input parameter to the retrieval, has been measured in situ on Svalbard during the DAMOCLES campaign, and a BRDF model assuming aspherical particles is developed. Sea ice drift and deformation is derived from satellite observations with the scatterometer ASCAT (62.5 km grid spacing), with visible AVHRR observations (20 km), with the synthetic aperture radar sensor ASAR (10 km), and a multi-sensor product (62.5 km) with improved angular resolution (Continuous Maximum Cross Correlation, CMCC method) is presented. CMCC is also used to derive the sea ice deformation, important for formation of sea ice leads (diverging deformation) and pressure ridges (converging). The indirect determination of sea ice thickness from altimeter freeboard data requires knowledge of the ice density and snow load on sea ice. The relation between freeboard and ice thickness is investigated based on the airborne Sever expeditions conducted between 1928 and 1993.

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Gill, Ramandeep, and Jonathan Granot. "Temporal evolution of prompt GRB polarization." Monthly Notices of the Royal Astronomical Society 504, no. 2 (April 12, 2021): 1939–58. http://dx.doi.org/10.1093/mnras/stab1013.

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ABSTRACT The dominant radiation mechanism that produces the prompt emission in gamma-ray bursts (GRBs) remains a major open question. Spectral information alone has proven insufficient in elucidating its nature. Time-resolved linear polarization has the potential to distinguish between popular emission mechanisms, e.g. synchrotron radiation from electrons with a power-law energy distribution or inverse Compton scattering of soft seed thermal photons, which can yield the typical GRB spectrum but produce different levels of polarization. Furthermore, it can be used to learn about the outflow’s composition (i.e. whether it is kinetic-energy-dominated or Poynting-flux-dominated) and angular structure. For synchrotron emission, it is a powerful probe of the magnetic field geometry. Here, we consider synchrotron emission from a thin ultrarelativistic outflow, with bulk Lorentz factor Γ(R) = Γ0(R/R0)−m/2 ≫ 1, that radiates a Band-function spectrum in a single (multiple) pulse(s) over a range of radii, R0 ≤ R ≤ R0 + ΔR. Pulse profiles and polarization evolution at a given energy are presented for a coasting (m = 0) and accelerating (m = −2/3) thin spherical shell and for different viewing angles for a top-hat jet with sharp as well as smooth edges in emissivity. Four different magnetic field configurations are considered, such as a locally ordered field coherent over angular scales θB ≳ 1/Γ, a tangled field (B⊥) in the plane transverse to the radial direction, an ordered field (B∥) aligned in the radial direction, and a globally ordered toroidal field (Btor). All field configurations produce distinct polarization evolution with single (for B⊥ and B∥) and double (for Btor) 90○ changes in the polarization position angle.

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Su, W., J. Corbett, Z. Eitzen, and L. Liang. "Next-generation angular distribution models for top-of-atmosphere radiative flux calculation from CERES instruments: methodology." Atmospheric Measurement Techniques 8, no. 2 (February 5, 2015): 611–32. http://dx.doi.org/10.5194/amt-8-611-2015.

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Abstract. The top-of-atmosphere (TOA) radiative fluxes are critical components to advancing our understanding of the Earth's radiative energy balance, radiative effects of clouds and aerosols, and climate feedback. The Clouds and the Earth's Radiant Energy System (CERES) instruments provide broadband shortwave and longwave radiance measurements. These radiances are converted to fluxes by using scene-type-dependent angular distribution models (ADMs). This paper describes the next-generation ADMs that are developed for Terra and Aqua using all available CERES rotating azimuth plane radiance measurements. Coincident cloud and aerosol retrievals, and radiance measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from Goddard Earth Observing System (GEOS) data assimilation version 5.4.1 are used to define scene type. CERES radiance measurements are stratified by scene type and by other parameters that are important for determining the anisotropy of the given scene type. Anisotropic factors are then defined either for discrete intervals of relevant parameters or as a continuous functions of combined parameters, depending on the scene type. Significant differences between the ADMs described in this paper and the existing ADMs are over clear-sky scene types and polar scene types. Over clear ocean, we developed a set of shortwave (SW) ADMs that explicitly account for aerosols. Over clear land, the SW ADMs are developed for every 1° latitude × 1° longitude region for every calendar month using a kernel-based bidirectional reflectance model. Over clear Antarctic scenes, SW ADMs are developed by accounting the effects of sastrugi on anisotropy. Over sea ice, a sea-ice brightness index is used to classify the scene type. Under cloudy conditions over all surface types, the longwave (LW) and window (WN) ADMs are developed by combining surface and cloud-top temperature, surface and cloud emissivity, cloud fraction, and precipitable water. Compared to the existing ADMs, the new ADMs change the monthly mean instantaneous fluxes by up to 5 W m−2 on a regional scale of 1° latitude × 1° longitude, but the flux changes are less than 0.5 W m−2 on a global scale.

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Kylafis, Nikolaos D., Pablo Reig, and Iossif Papadakis. "A quantitative explanation of the type-B QPOs in GX 339–4." Astronomy & Astrophysics 640 (August 2020): L16. http://dx.doi.org/10.1051/0004-6361/202038468.

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Context. Type-B quasi periodic oscillations (QPOs) in black-hole X-ray binaries are a class of low-frequency QPOs that are observed in the soft intermediate state in the rising and the declining phases of an outburst. They are suspected to result from the precession of the jet that is ejected from the source. Aims. The objective of the present work is to investigate in detail the emissivity of the jet in hard X-rays and to see whether the type-B QPOs from GX 339−4, which is the best studied black-hole transient, can be explained quantitatively with a precessing jet. Methods. We used our simple jet model, which invokes Comptonization in the jet, and examined the angular dependence of the upscattered photons that emerge from the jet and their energy distribution, which is a power law. Results. Due to the elongation of the jet, assisted by the bulk motion of the electrons, the angular distribution of the emerging hard X-ray photons from the jet is not isotropic. More importantly, the photon-number spectral index, Γ, is an increasing function of the polar angle, θ, with respect to the axis of the jet. If the jet is fixed, then an observer at infinity sees the photon index, Γ, which corresponds to this specific observational direction. However, if the jet is precessing, then the observer sees a periodic variation of Γ with the precession period. Such a periodic variation of Γ has been observed in GX 339−4 and in this work, we reproduce it quantitatively, using our model. Conclusions. Our jet model nicely explains through quantitative means the type-B QPOs seen in GX 339−4 as originating from a precessing jet. The given model has previously explained several observed correlations thus far.

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Zhou, Yan, and Christopher Grassotti. "Development of a Machine Learning-Based Radiometric Bias Correction for NOAA’s Microwave Integrated Retrieval System (MiRS)." Remote Sensing 12, no. 19 (September 26, 2020): 3160. http://dx.doi.org/10.3390/rs12193160.

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We present the development of a dynamic over-ocean radiometric bias correction for the Microwave Integrated Retrieval System (MiRS) which accounts for spatial, temporal, spectral, and angular dependence of the systematic differences between observed and forward model-simulated radiances. The dynamic bias correction, which utilizes a deep neural network approach, is designed to incorporate dependence on the atmospheric and surface conditions that impact forward model biases. The approach utilizes collocations of observed Suomi National Polar-orbiting Partnership/Advanced Technology Microwave Sounder (SNPP/ATMS) radiances and European Centre for Medium-Range Weather Forecasts (ECMWF) model analyses which are used as input to the Community Radiative Transfer Model (CRTM) forward model to develop training data of radiometric biases. Analysis of the neural network performance indicates that in many channels, the dynamic bias is able to reproduce realistically both the spatial patterns of the original bias and its probability distribution function. Furthermore, retrieval impact experiments on independent data show that, compared with the baseline static bias correction, using the dynamic bias correction can improve temperature and water vapor profile retrievals, particularly in regions with higher Cloud Liquid Water (CLW) amounts. Ocean surface emissivity retrievals are also improved, for example at 23.8 GHz, showing an increase in correlation from 0.59 to 0.67 and a reduction of standard deviation from 0.035 to 0.026.

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Laszynska, Ewa, Slawomir Jednorog, Adam Ziolkowski, Michal Gierlik, and Jacek Rzadkiewicz. "Determination of the emission rate for the 14 MeV neutron generator with the use of radio-yttrium." Nukleonika 60, no. 2 (June 1, 2015): 319–22. http://dx.doi.org/10.1515/nuka-2015-0040.

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Abstract The neutron emission rate is a crucial parameter for most of the radiation sources that emit neutrons. In the case of large fusion devices the determination of this parameter is necessary for a proper assessment of the power release and the prediction for the neutron budget. The 14 MeV neutron generator will be used for calibration of neutron diagnostics at JET and ITER facilities. The stability of the neutron generator working parameters like emission and angular homogeneity affects the accuracy of calibration other neutron diagnostics. The aim of our experiment was to confirm the usefulness of yttrium activation method for monitoring of the neutron generator SODERN Model: GENIE 16. The reaction rate induced by neutrons inside the yttrium sample was indirectly measured by activation of the yttrium sample, and then by means of the γ-spectrometry method. The pre-calibrated HPGe detector was used to determine the yttrium radioactivity. The emissivity of neutron generator calculated on the basis of the measured radioactivity was compared with the value resulting from its electrical settings, and both of these values were found to be consistent. This allowed for a positive verification of the reaction cross section that was used to determine the reaction rate (6.45 × 10−21 reactions per second) and the neutron emission rate (1.04 × 108 n·s−1). Our study confirms usefulness of the yttrium activation method for monitoring of the neutron generator.

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Ermida, Sofia, Isabel Trigo, Carlos DaCamara, and Ana Pires. "A Methodology to Simulate LST Directional Effects Based on Parametric Models and Landscape Properties." Remote Sensing 10, no. 7 (July 12, 2018): 1114. http://dx.doi.org/10.3390/rs10071114.

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The correction of directional effects on satellite-retrieved land surface temperature (LST) is of high relevance for a proper interpretation of spatial and temporal features contained in LST fields. This study presents a methodology to correct such directional effects in an operational setting. This methodology relies on parametric models, which are computationally efficient and require few input information, making them particularly appropriate for operational use. The models are calibrated with LST data collocated in time and space from MODIS (Aqua and Terra) and SEVIRI (Meteosat), for an area covering the entire SEVIRI disk and encompassing the full year of 2011. Past studies showed that such models are prone to overfitting, especially when there are discrepancies between the LSTs that are not related to the viewing geometry (e.g., emissivity, atmospheric correction). To reduce such effects, pixels with similar characteristics are first grouped by means of a cluster analysis. The models’ calibration is then performed on each one of the selected clusters. The derived coefficients reflect the expected impact of vegetation and topography on the anisotropy of LST. Furthermore, when tested with independent data, the calibrated models are shown to maintain the capability of representing the angular dependency of the differences between LST derived from polar-orbiter (MODIS) and geostationary (Meteosat, GOES and Himawari) satellites. The methodology presented here is currently being used to estimate the deviation of LST products with respect to what would be obtained for a reference view angle (e.g., nadir), therefore contributing to the harmonization of LST products.

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Churazov, E. M., I. I. Khabibullin, A. M. Bykov, N. N. Chugai, R. A. Sunyaev, and I. I. Zinchenko. "SRG/eROSITA discovery of a large circular SNR candidate G116.6−26.1: SN Ia explosion probing the gas of the Milky Way halo?" Monthly Notices of the Royal Astronomical Society 507, no. 1 (August 24, 2021): 971–82. http://dx.doi.org/10.1093/mnras/stab2125.

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ABSTRACT We report a discovery of a new X-ray-selected supernova remnant (SNR) candidate SRGe J0023+3625 = G116.6−26.1 found in the SRG/eROSITA all-sky survey. The source features a large angular extent (∼4° in diameter), nearly circular shape, and X-ray spectrum dominated by emission lines of helium- and hydrogen-like oxygen. It lacks bright counterparts of similar extent at other wavelengths which could be unequivocally associated with it. Given the relatively high Galactic latitude of the source, b ≈ −26°, we interpret these observational properties as an indication of the off-disc location of this SNR candidate. Namely, we propose that this object originated from a Type Ia supernotva which exploded some 40 000 yr ago in the low density ($\sim 10^{-3}\, {\rm cm^{-3}}$) and hot ($\sim (1{-}2)\times 10^6\, {\rm K}$) gas of the Milky Way halo at a distance of ∼3 kpc from the Sun. The low density of the halo gas implies that the cooling and collisional ionization equilibrium (CEI) time-scales downstream of the forward shock are much longer than the age of the SNR. This results in a relatively soft spectrum, reflecting pre-shock ionization state of the gas, and strong boost in the plasma emissivity (compared to CEI) due to enhanced collisional excitation through the increased electron temperature. If confirmed, such a rare object would provide us with a unique ‘in situ’ probe of physical conditions (density, temperature and metallicity) near the interface between the Milky Way’s disc and the halo.

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Stubenrauch, C. J., F. Eddounia, J. M. Edwards, and A. Macke. "Evaluation of Cirrus Parameterizations for Radiative Flux Computations in Climate Models Using TOVS–ScaRaB Satellite Observations." Journal of Climate 20, no. 17 (September 1, 2007): 4459–75. http://dx.doi.org/10.1175/jcli4251.1.

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Abstract Combined simultaneous satellite observations are used to evaluate the performance of parameterizations of the microphysical and optical properties of cirrus clouds used for radiative flux computations in climate models. Atmospheric and cirrus properties retrieved from Television and Infrared Observation Satellite (TIROS-N) Operational Vertical Sounder (TOVS) observations are given as input to the radiative transfer model developed for the Met Office climate model to simulate radiative fluxes at the top of the atmosphere (TOA). Simulated cirrus shortwave (SW) albedos are then compared to those retrieved from collocated Scanner for Radiation Budget (ScaRaB) observations. For the retrieval, special care has been given to angular direction models. Three parameterizations of cirrus ice crystal optical properties are represented in the Met Office radiative transfer model. These parameterizations are based on different physical approximations and different hypotheses on crystal habit. One parameterization assumes pristine ice crystals and two ice crystal aggregates. By relating the cirrus ice water path (IWP) retrieved from the effective infrared emissivity to the cirrus SW albedo, differences between the parameterizations are amplified. This study shows that pristine crystals seem to be plausible only for cirrus with IWP less than 30 g m−2. For larger IWP, ice crystal aggregates lead to cirrus SW albedos in better agreement with the observations. The data also indicate that climate models should allow the cirrus effective ice crystal diameter (De) to increase with IWP, especially in the range up to 30 g m−2. For cirrus with IWP less than 20 g m−2, this would lead to SW albedos that are about 0.02 higher than the ones of a constant De of 55 μm.

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Schubnell, M. "Sunshape and Its Influence on the Flux Distribution in Imaging Solar Concentrators." Journal of Solar Energy Engineering 114, no. 4 (November 1, 1992): 260–66. http://dx.doi.org/10.1115/1.2930015.

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Imaging solar concentrators, such as a parabolic dish, image the sun to their focal plane. Thus, the flux distribution is basically an image of the angular distribution of the direct incident solar radiation. This distribution, referred to as sunshape, is determined by solar limb darkening and by small angle scattering in the atmosphere. In this paper we present measurements of the sunshape and investigate its influence on the flux distribution in the solar furnace at Paul Scherrer Institute (PSI) and in parabolic concentrators, both experimentally and by a ray tracing procedure. Analyzing the influence of the spectral dependence of the sunshape we find that the characteristic width of the focal spot increases with longer wavelengths. In contrary, the mean concentration ratio is higher at shorter wavelengths. Although these effects are rather small, they can be important in radiometric measurement techniques to determine the emissivity and the temperature distribution of an irradiated sample as well as in designing solar pumped lasers. Comparing various sunshapes with the corresponding flux distributions in the two-stage solar furnace at PSI, we show that the influence of the circumsolar radiation on the flux distribution is usually negligible as compared to the distortion due to astigmatism. However, in more accurate optical systems, such as highly concentrating parabolic dishes, the flux distribution is a fairly accurate image of the sunshape. We find, that due to sunshape, the mean concentration ratio in a parabolic dish is decreased by about ten percent. As an example we subsequently estimate the mean annual conversion efficiency of an ideal solar converter operated in the Swiss mountains.

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Sandell, Göran. "Submillimetre Mapping and Photometry of Bipolar Flows - Evidence for Compact Disks." International Astronomical Union Colloquium 120 (1989): 244–49. http://dx.doi.org/10.1017/s0252921100023800.

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ABSTRACT:The mm/sub-mm dust emission from bipolar outflow sources is discussed. In nearby outflows the stars driving the flows appear point like and unresolved, i.e. apparent angular sizes < 7” (i.e. 700AU at lOOpc). The spectra are surprisingly flat, suggesting that the dust emission is affected by temperature and density gradients or that the dust surrounding these stars differs from that of the general interstellar medium. If the spectra are characterized with a conventional dust emissivity index, our sample gives an average value of 1.1, rather than the figure of 2, which is usually claimed at these wavelengths for dust in molecular clouds. The total dust and gas masses associated with these stars are a few tenths of a solar mass for nearby low luminosity sources and the gas densities are >107 cm−3, if the gas is in a shell, and the densities could be much higher if the gas densities fall off as a function of radius, or if the mass is distributed in a disk. These masses correspond to extremely high extinctions, which are not observed, and we therefore argue that the mass distribution must be anisotropic, most likely as an inclined disk surrounding the star. Hence, stars driving outflows are surrounded by a dense disk, possibly an accretion disks and/or collimating disk. If these stars are compared to the more evolved T Tauri stars, we find that the difference in disk mass could account for the mass loss observed in these stars. Because of the high gas densities in the disk, most commonly used molecular lines will be optically thick, and molecular observations should be done in rare isotopes and high density tracers in order to yield reliable results of gas densities and gas dynamics.

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IONICA, Ioana, Mircea MODREANU, Alexandru-Mihail MOREGA, and Cristian BOBOC. "STUDII DE TRANSFER DE CĂLDURĂ ÎN MAȘINI ELECTRICE UTILIZATE ÎN CONDIȚII DE FUNCȚIONARE SPECIALE." "ACTUALITĂŢI ŞI PERSPECTIVE ÎN DOMENIUL MAŞINILOR ELECTRICE (ELECTRIC MACHINES, MATERIALS AND DRIVES - PRESENT AND TRENDS)" 2020, no. 1 (February 10, 2021): 1–8. http://dx.doi.org/10.36801/apme.2020.1.11.

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"This paper aims to analyze the heat transfer of a DC limited angle torque motor, in special conditions, of space. Three-dimensional models will be used and two current values will be considered. As a working hypothesis, several variants will be numerically analyzed in which the boundary conditions will take into account different values of the emissivity of the motor surfaces varying in the range 0.2 ÷ 1. Inside the motor subassemblies the heat transfer will be done by conduction and between the motor and the environment by radiation. Using thermal modeling, it will be possible to determine the time in which the winding temperature reaches the maximum value allowed for the DC limited angle torque motor, in space conditions. The approached motor presents specific technical aspects (constructive and functional) and novelty in the field of torque motors with limited angle. These types of motors are recommended for applications where both volume and weight are critical requirements. The applications of DC-LATM are diverse: in the fields of aerospace, military technique, medical etc. For special applications (eg aerospace) a redundant motor solution is required [7]. The motor is designed for applications that require rotation over a certain angular range, (the working domain of this motor is 45 ÷ 135°). The space industry is a field of maximum interest from a scientific, economic and strategic point of view. Compared to other fields, its growth in recent years is extraordinary, as evidenced by the availability of telecommunications services. The requirements of the motor given by the application in which it is used including the environmental conditions in which the motor operates will determine the input data of the heat transfer problem. There are two categories of requirements that are equally important: general (mechanical, thermal, electrical) and environmental (stability to vacuum and radiation, resistance to AO - atomic oxygen) etc. Also, several aspects must be considered, such as: environmental effects (LEO - Low Earth Orbit or GEO - Geostationary Orbit), constraints applicable to materials (temperature, vacuum, thermal cycles, chemical - corrosion, galvanic compatibility, atomic oxygen , moisture absorption / desorption, fluid compatibility), if materials will degrade over time, the system in which the product will be integrated, interfaces [8]. The heat transfer analysis addressed in this paper establishes the DC-LATM behavior from a thermal point of view in space conditions."

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Ma, Jing, Ya-Song Sun, and Ben-Wen Li. "Completely Spectral Collocation Solution of Radiative Heat Transfer in an Anisotropic Scattering Slab With a Graded Index Medium." Journal of Heat Transfer 136, no. 1 (October 25, 2013). http://dx.doi.org/10.1115/1.4024990.

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A completely spectral collocation method (CSCM) is developed to solve radiative transfer equation in anisotropic scattering medium with graded index. Different from the Chebyshev collocation spectral method based on the discrete ordinates method (SP-DOM), the CSCM is used to discretize both the angular domain and the spatial domain of radiative transfer equation. In this approach, the angular derivative term and the integral term are approximated by the high order spectral collocation scheme instead of the low order finite difference approximations. Compared with those available data in literature, the CSCM has a good accuracy for a wide range of the extinction coefficient, the scattering albedo, the scattering phase function, the gradient of refractive index and the boundary emissivity. The CSCM can provide exponential convergence for the present problem. Meanwhile, the CSCM is much more economical than the SP-DOM. Moreover, for nonlinear anisotropic scattering and graded index medium with space-dependent albedo, the CSCM can provide smoother results and mitigate the ray effect.

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Manwadkar, Viraj, Barak Kol, Alessandro A. Trani, and Nathan W. C. Leigh. "Testing the flux-based statistical prediction of the three-body problem." Monthly Notices of the Royal Astronomical Society, June 12, 2021. http://dx.doi.org/10.1093/mnras/stab1689.

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Abstract We present an extensive comparison between the statistical properties of non-hierarchical three-body systems and the corresponding three-body theoretical predictions. We perform and analyse 1 million realizations for each different initial condition considering equal and unequal mass three-body systems to provide high accuracy statistics. We measure 4 quantities characterizing the statistical distribution of ergodic disintegrations: escape probability of each body, the characteristic exponent for escapes by a narrow margin, predicted absorptivity as a function of binary energy and binary angular momentum, and, finally, the lifetime distribution. The escape probabilities are shown to be in agreement down to the 1 per cent level with the emissivity-blind, flux-based theoretical prediction. This represents a leap in accuracy compared to previous three-body statistical theories. The characteristic exponent at the threshold for marginally unbound escapes is an emissivity-independent flux-based prediction, and the measured values are found to agree well with the prediction. We interpret both tests as strong evidence for the flux-based three-body statistical formalism. The predicted absorptivity and lifetime distributions are measured to enable future tests of statistical theories.

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Journal articles on the topic 'Angular emissivity'

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