scholarly journals Accurately Quantifying Clear-Sky Radiative Cooling Potentials: A Temperature Correction to the Transmittance-Based Approximation

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1195
Author(s):  
Jyotirmoy Mandal ◽  
Xin Huang ◽  
Aaswath P. Raman
Keyword(s):  
Heat Loss ◽  
Theoretical Calculations ◽  
Temperature Correction ◽  
Meteorological Conditions ◽  
Radiative Cooling ◽  
Clear Sky ◽  
Long Wave ◽  
Continued Use ◽  
Sky Conditions ◽  
Long Wave Infrared

Theoretical calculations of the cooling potential of radiative cooling materials are crucial for determining their cooling capability under different meteorological conditions and evaluating their performance. To facilitate these calculations, accurate models of long-wave infrared downwelling atmospheric irradiance are needed. However, the transmittance-based cosine approximation, which is widely used to determine radiative cooling potentials under clear sky conditions, does not account for the cooling potential arising from heat loss to the colder reaches of the atmosphere itself. Here, we show that use of the approximation can lead to >10% underestimation of the cooling potential relative to MODTRAN 6 outputs. We propose a temperature correction to the transmittance-based approximation, which accounts for heat loss to the cold upper atmosphere, and significantly reduces this underestimation, while retaining the advantages of the original model. In light of the widespread and continued use of the transmittance-based model, our results highlight an important source of potential errors in the calculation of clear sky radiative cooling potentials and a means to correct for them.

scholarly journals Determination of Temperature Distributions for the Sky Based on the Results of Measurement with an Infrared Camera

2021 ◽  
Vol 25 (3) ◽  
pp. 57-63
Author(s):  
Tadeusz Kruczek
Keyword(s):  
Ambient Temperature ◽  
Heat Loss ◽  
Radiation Heat Transfer ◽  
Ground Surface ◽  
Infrared Camera ◽  
Quality Parameters ◽  
Long Wave ◽  
Long Wave Infrared ◽  
Insulation Quality

The surroundings of objects in an open atmospheric space usually consist of a hypothetical surface of the sky and the surface of the ground. The aim of thermovision examination of objects located in open atmospheric space, especially buildings, is to determine the amount of heat loss or to assess the insulation quality parameters of walls, roofs and other building partitions. The tested surfaces, including elements of the outer shell of buildings, are often located at different angles to the ground surface and the sky. For the needs of thermovision testing of the considered objects and calculations concerning the radiation heat transfer, it is necessary to know the radiation parameters of the sky. These parameters include the equivalent radiative ambient temperature needed for thermovision measurements (including the temperature of the sky and the ground) and the overall radiative ambient temperature, which determines the heat loss by radiation from the tested surface. The article describes the method of determining the values of these temperatures on the basis of measuring the temperature of the sky with the use of a long-wave infrared camera and calculations. In order to verify the developed method, the results obtained with the use of the above-mentioned method were compared with the results obtained with the use of a pyrgeometer. The verification comprised the comparison of the heat flux of radiation from the sky, calculated on the basis of infrared camera measurements, with the energy flux emitted by the sky and measured with a pyrgeometer. The result of the verification is satisfactory.

scholarly journals Seasonal and Regional Variability of Long-Wave Effective Radiation in China and Associated Modulating Factors

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Qianrong Ma ◽  
Jie Zhang ◽  
Yu Gu ◽  
Yujun Ma ◽  
Yu Cao
Keyword(s):  
Radiant Energy ◽  
Weather Conditions ◽  
Energy System ◽  
Northwest China ◽  
Wave Radiation ◽  
Regional Variability ◽  
Clear Sky ◽  
Long Wave ◽  
Sky Conditions ◽  
Effective Radiation

Variations in all-sky and clear-sky long-wave effective radiation (LER) in China during the period 2001–2016 were determined using monthly radiative datasets from the Clouds and the Earth’s Radiant Energy System (CERES). Annual and seasonal spatial distributions are found to be quite similar and show a decreasing trend from northwest to southeast, although highest values are found in spring. Mean LER under clear-sky conditions is approximately 20–30 Wm−2 higher than that under all-sky conditions. There is a consistent downward trend in annual and seasonal variations of LER under different weather conditions in China especially after 2007. In northwest China, the eastern Tibetan Plateau, and southeast and northeast China, LER is significantly reduced in two weather conditions and this is more pronounced in spring. However, decreases in clear-sky LER are more obvious. Empirical orthogonal function (EOF) results for LER differences between all-sky conditions and clear-sky conditions were used to analyze regional characteristics and modulating factors. The first mode shows that the LER differences of two weather conditions over China become larger and significant after 2007. The second mode reflects the spatial characteristics, and four climate regions are divided according to the second pattern. According to the definition of LER, regression analysis shows that downward long-wave radiation has a greater influence on LER. When considering cloud effects and other modulating factors, LER has higher correlation with relative humidity in climate regions 3 and 4. However, there are higher negative correlations with middle and high clouds in regions 1 and 2, which are modulated by cloud characteristics. When these factors influence LER together, their correlation is significant in all regions (correlation coefficients are on average higher than 0.7). In summary, changes of LER can well reflect the change of climate system.

scholarly journals Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions

2017 ◽  
Vol 4 (2) ◽  
pp. 160688 ◽  
Author(s):  
Gábor Horváth ◽  
Péter Takács ◽  
Balázs Kretzer ◽  
Szilvia Szilasi ◽  
Dénes Száz ◽  
...  
Keyword(s):  
Meteorological Conditions ◽  
Degree Of Polarization ◽  
The Sun ◽  
Polarization Pattern ◽  
Clear Sky ◽  
Solar Elevation ◽  
Cloud Coverage ◽  
Open Sea ◽  
Imaging Polarimetry ◽  
Sky Conditions

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d * for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d  >  d * is satisfied. Using full-sky imaging polarimetry, we measured the d -pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ . From the measured d -patterns of a given sky we determined the proportion P of the sky for which d  >  d *. We obtained that P is the largest at low solar elevations θ  ≈ 0° and under totally or nearly clear skies with cloud coverage ρ  = 0%, when the sun's position is already easily determined. If the sun is below the horizon (−5° ≤  θ  < 0°) during twilight, P  = 76.17 ± 4.18% for d min ∗ = 23 % under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes.

Evaluation of net shortwave radiation over China with a regional climate model

2020 ◽  
Vol 80 (2) ◽  
pp. 147-163
Author(s):  
X Liu ◽  
Y Kang ◽  
Q Liu ◽  
Z Guo ◽  
Y Chen ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Climate Model ◽  
Regional Climate ◽  
Radiant Energy ◽  
Energy System ◽  
Radiation Budget ◽  
Shortwave Radiation ◽  
Monsoon Region ◽  
Clear Sky ◽  
Sky Conditions

The regional climate model RegCM version 4.6, developed by the European Centre for Medium-Range Weather Forecasts Reanalysis, was used to simulate the radiation budget over China. Clouds and the Earth’s Radiant Energy System (CERES) satellite data were utilized to evaluate the simulation results based on 4 radiative components: net shortwave (NSW) radiation at the surface of the earth and top of the atmosphere (TOA) under all-sky and clear-sky conditions. The performance of the model for low-value areas of NSW was superior to that for high-value areas. NSW at the surface and TOA under all-sky conditions was significantly underestimated; the spatial distribution of the bias was negative in the north and positive in the south, bounded by 25°N for the annual and seasonal averaged difference maps. Compared with the all-sky condition, the simulation effect under clear-sky conditions was significantly better, which indicates that the cloud fraction is the key factor affecting the accuracy of the simulation. In particular, the bias of the TOA NSW under the clear-sky condition was <±10 W m-2 in the eastern areas. The performance of the model was better over the eastern monsoon region in winter and autumn for surface NSW under clear-sky conditions, which may be related to different levels of air pollution during each season. Among the 3 areas, the regional average biases overall were largest (negative) over the Qinghai-Tibet alpine region and smallest over the eastern monsoon region.

RxCADRE 2008: Wildfire Airborne Sensor Program - Lite uncalibrated long wave infrared image mosaics

2016 ◽  
Author(s):  
Andrew T. Hudak ◽  
Benjamin C. Bright ◽  
Robert L. Kremens ◽  
Matthew B. Dickinson ◽  
Matthew G. Alden
Keyword(s):  
Infrared Image ◽  
Long Wave ◽  
Long Wave Infrared

scholarly journals A Bi-Spectral Microbolometer Sensor for Wildfire Measurement

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3690
Author(s):  
Denis Dufour ◽  
Loïc Le Noc ◽  
Bruno Tremblay ◽  
Mathieu N. Tremblay ◽  
Francis Généreux ◽  
...  
Keyword(s):  
Low Resource ◽  
Long Wave ◽  
Radiative Power ◽  
Infrared Radiances ◽  
Moderate Scale ◽  
Long Wave Infrared ◽  
Detector Type ◽  
Experimental Burns ◽  
Fire Radiative Power

This study describes the development of a prototype bi-spectral microbolometer sensor system designed explicitly for radiometric measurement and characterization of wildfire mid- and long-wave infrared radiances. The system is tested experimentally over moderate-scale experimental burns coincident with FLIR reference imagery. Statistical comparison of the fire radiative power (FRP; W) retrievals suggest that this novel system is highly reliable for use in collecting radiometric measurements of biomass burning. As such, this study provides clear experimental evidence that mid-wave infrared microbolometers are capable of collecting FRP measurements. Furthermore, given the low resource nature of this detector type, it presents a suitable option for monitoring wildfire behaviour from low resource platforms such as unmanned aerial vehicles (UAVs) or nanosats.

Efficient downscaling of satellite oceanographic data with convolutional neural networks

2021 ◽  
Vol 12 (3) ◽  
pp. 46-47
Author(s):  
Nikita Saxena
Keyword(s):  
Neural Networks ◽  
Deep Learning ◽  
Convolutional Neural Networks ◽  
Super Resolution ◽  
Sea Surface ◽  
Clear Sky ◽  
Oceanographic Data ◽  
Computationally Expensive ◽  
Sky Conditions ◽  
Data Inference

Space-borne satellite radiometers measure Sea Surface Temperature (SST), which is pivotal to studies of air-sea interactions and ocean features. Under clear sky conditions, high resolution measurements are obtainable. But under cloudy conditions, data analysis is constrained to the available low resolution measurements. We assess the efficiency of Deep Learning (DL) architectures, particularly Convolutional Neural Networks (CNN) to downscale oceanographic data from low spatial resolution (SR) to high SR. With a focus on SST Fields of Bay of Bengal, this study proves that Very Deep Super Resolution CNN can successfully reconstruct SST observations from 15 km SR to 5km SR, and 5km SR to 1km SR. This outcome calls attention to the significance of DL models explicitly trained for the reconstruction of high SR SST fields by using low SR data. Inference on DL models can act as a substitute to the existing computationally expensive downscaling technique: Dynamical Downsampling. The complete code is available on this Github Repository.

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