Albedo Values Research Articles

Approximate Relation Between Integral Albedo and Single-scattering Albedo of the Particulate Media

The radiative transfer model makes it possible to establish relationships between the single scattering albedo and the integral albedo of a medium consisting of particles. In this paper, an approximation is proposed for solving the inverse problem—calculating the albedo of a single scattering of a particle, based on the known value of the integral albedo. This approximation can be useful to all researchers involved in the photometry of solar system bodies with regolith-like surfaces.

Effects of phenological stages, growth and meteorological factor on the albedo of different crop cultivars

Albedo is a key component of the atmospheric, climatologic and remote sensing studies by means of global warming, energy balance, evapotranspiration, climate models, hydrological cycle etc. For these reasons, the accurate determination of surface albedo has become more important. In this study, the variation of measured albedo values of winter wheat, barley and sunflower cultivars according to phenological stages was investigated for the first time in the northwestern part of Turkey. Additonally, influences of leaf area index as growth indicator and rainfall as meteorological variable on albedo were also analyzed. The average albedo values of winter wheat, barley and sunflower in both growing periods varied from 0.176 to 0.190 for winter wheat, from 0.171 to 0.189 for sunflower and from 0.187 to 0.214 for barley cultivars. According to phenological stages, the minimum and maximum average albedo values were found for winter wheat as 0.121 between sowing and germination and 0.247 between stem formation and head emergence; for sunflower as 0.150 between sowing and germination and 0.212 between leaf initiation and immature bud; for barley as 0.144 sowing and germination and 0.261 between head emergence and flowering stages. Additionally, significant relationships were found between albedo and leaf area index for winter wheat, barley and sunflower as r2=0.87, r2=0.82 and r2=0.77, respectively.

Selection of time-dependent worst-case thermal environmental conditions for Low Earth Orbit spacecrafts

When facing the thermal analysis of a Low Earth Orbit satellite, selecting the worst-case orbit where the minimum and maximum temperatures are reached is essential for ensuring the success of the mission. Typical orbits have a non-constant Solar Beta Angle throughout the year providing a wide range of orbits with different heat loads and eclipses. It is possible to focus the analysis on a single orbit configuration by a rough analysis using a simple model. In order to achieve this, every potential orbit with their corresponding thermal environmental parameters must be analysed based on real data. The direct solar radiation, the albedo and the Earth Outgoing Longwave Radiation (OLR) characterize the thermal environment to be taken into account. However, their values have a wide variability which depend on many parameters. Based on the characteristics of the orbit and the system thermo-optical properties and characteristic time, it is possible to obtain particularized profiles of albedo and OLR that would lead the system to its maximum and minimum temperatures. The conventional criteria, which is studied here in depth, provides two constant values of albedo and OLR as the hot and cold worst-cases. This is suitable for massive system or cases in which the characteristics times of the system are high. For lighter elements or low characteristic times, temperatures throughout the orbit deviate considerably from the real behaviour. In contrast, the methodology here proposed provides a time-dependant profile that allows for the determination of a system temperature response closer to the real one, together with the potential minimum and maximum temperatures of the orbit, in order to optimize the design and avoid the oversizing.

Asteroid (3200) Phaethon: results of polarimetric, photometric, and spectral observations

ABSTRACT We present results of polarimetric, photometric, and spectral observations of the near-Earth asteroid (3200) Phaethon carried out at the 6-m BTA telescope of the Special Astrophysical Observatory and the 2.6-m and 1.25-m telescopes of the Crimean Astrophysical Observatory over a wide range of phase angles during its close approach to the Earth at the end of 2017 (α = 19°–135°) and in 2020 at α = 52.2°. Using our and other available in literature data, we found that the maximum degree of linear polarization of Phaethon in the V band is Pmax = (45 ± 1) per cent at the phase angle αmax = 124.0° ± 0.4°, whereas the inversion angle αinv = 21.4° ± 1.2° and polarimetric slope is h = (0.326 ± 0.027) per cent per degree. Using the dependence ‘polarimetric slope – albedo,’ we have found the geometric albedo of asteroid Phaethon to be pv = 0.060 ± 0.005. This value falls into the lower range of albedo values for asteroids determined by different methods. The mean colour indices U–B = 0.207 m ± 0.053 m and B–V = 0.639 m ± 0.054 m of the asteroid are derived at heliocentric and geocentric distances 1.077 au and 0.102 au, respectively, and phase angle α = 23.78°. The absolute magnitude of Phaethon is V(1,1,0) = 14.505 m ± 0.059 m. The effective diameter of Phaethon is estimated from obtained absolute magnitude and geometrical albedo, it is equal to 6.8 ± 0.3 km. The best fit to the observed polarimetric data was obtained with the Sh-matrix model of conjugated random Gaussian particles composed of Mg-rich silicate (90 per cent) and amorphous carbon (10 per cent).

Surface albedo retrieval based on high spatial resolution data

The paper aims to compare the accuracy of three methods of solving the atmospheric correction problem for a Lambertian surface using high spatial resolution remotely sensed data. Three couples of formulas are presented. Each couple contains a formula for expressing the reflectance in a target pixel at the upper boundary of the atmosphere via albedo in target and adjacent pixels of the surface and a formula for the surface albedo in a target pixel via reflectances. The derivation of each couple of formulas is given. Derivation conditions are presented. Formulas of only one couple are found by solving the radiation transport equation in 1D geometry. Formulas of two other couples include values obtained by solving the transport equation in 3D geometry. Results of testing the accuracy of all formulas when solving an atmospheric correction problem on data of high (30 m) spatial resolution are given. Problems with aerosol optical depths from 0.2 to 2 for a wavelength of (lambda)=0.55(mu)m for all possible albedo values (from 0.1 to 0.9) in target and adjacent pixels are considered. It is shown that only one couple of formulas out of the three gives high accuracy under any condition. Formulas of the two other couples give sufficient accuracy (with less than 10 % error) only for a small value of the aerosol optical depth and a small difference of the albedo of the target and adjacent pixels.

On the mitigation potential of higher urban albedo in a temperate oceanic metropolis

The urban overheating calls for the implementation of mitigation actions. The article aims at demonstrating the advantages and the risks associated with the increase of the city albedo in Melbourne (Australia), through high resolution numerical analyses based on a detailed urban land use. The Weather Research and Forecasting model was used to calculate the spatial and temporal local climate change for three increased albedo scenarios and three different urban densities. In the scenario with highest albedo, the ambient temperature decreases of about 1.6°C in the middle and high density zones and 0.9°C in the low density zones. The sea breeze extends the thermal benefit due to the albedo increase to non-urban areas, despite it is slightly weakened by the diminished land-sea temperature contrast. The pollutant levels are expected to increase, due to a combination of slower winds (drops up to 0.19 ms−1) and decreased planetary boundary layer heights (drops from 175 m up to 291 m). High and low density classes have the highest and lowest risk of stagnation, respectively. Due to the contrasting results in terms of thermal mitigation and pollution risks, the study calls for the identification of comprehensive metrics to asses optimal values of urban albedo.

Impacts of Land Surface Parameterizations on Simulations over the Arid and Semiarid Regions: The Case of the Loess Plateau in China

Abstract The arid and semiarid areas of the Loess Plateau are extremely sensitive to climate change. Land–atmosphere interactions of these regions play an important role in the regional climate. However, most present land surface models (LSMs) are not reasonable and accurate enough to describe the surface characteristics in these regions. In this study, we investigate the effects of three key land surface parameters including surface albedo, soil thermal conductivity, and additional damping on the Noah LSM in simulating the land surface characteristics. The observational data from June to September from 2007 to 2009 collected at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) station in northwest China are used to validate the Noah LSM simulations. The results suggest that the retrieved values of surface albedo, soil thermal conductivity, and additional damping based on observations are in closer agreement with those of the MULT scheme for surface albedo, the J75_NOAH scheme for soil thermal conductivity, and the Y08 scheme for additional damping, respectively. Furthermore, the model performance is not obviously affected by surface albedo parameterization schemes, while the scheme of soil thermal conductivity is vital to simulations of latent heat flux and soil temperature and the scheme of additional damping is crucial for simulating net radiation flux, sensible heat flux, and surface soil temperature. A set of optimal parameterizations is proposed for the offline Noah LSM at the SACOL station when the MULT scheme for surface albedo, the J75_NOAH scheme for soil thermal conductivity, and the Y08 scheme for additional damping are combined simultaneously, especially in the case of sensible heat flux and surface soil temperature simulations.

Experimentation and Modeling of Laser Radiation Scattering Through Carbon Fiber Reinforced Polymers

With the prevalence of carbon fiber reinforced polymers (CFRPs) in aerospace platforms, there is a need to better understand radiative heat transport through the material. A laboratory experiment was constructed and computational Monte Carlo (MC) model optimized to quantify and understand the laser-scattering properties of CFRPs. The transmission data were analyzed by a zonal MC (ZMC) method to determine the material’s albedo and extinction coefficient, which can then be used for platform-level aerospace models to predict heat transfer more accurately through CFRP structures. This paper considers the effects of nodal, substrate, and detector plane sizing, as well as laser beam parameters, on matching albedo and extinction coefficient predictions from the ZMC method to experimental test data. Average albedo values for IM7/977-3 CFRP using the anchored ZMC method are 0.78 and 0.81 with one-ply and two-ply samples, respectively, having standard deviations of 0.11 and 0.09. Extinction coefficient predictions are 109.4 and with standard deviations of 28.3 and for one-ply and two-ply samples.

Study on the solar albedo characteristics of pavement and embankment slope surfaces in permafrost regions

Roadways built in permafrost regions are more sensitive to the thermal disturbance caused by the natural environment and engineering construction activities. The construction of the embankment changes the albedo characteristics of the natural ground surfaces. Dark asphalt pavement absorbs a huge amount of solar radiation into the permafrost embankment, which leads to the thawing of frozen soil and freezing-thawing diseases of the embankment. Besides, the south-facing slope of the high-fill embankment is exposed to longer and stronger insolation than the north-facing slope annually. It gives rise to the thermal asymmetrical problem and differential settlement across the embankment. To solve above problems and further improve the thermal stability of permafrost embankment, we study the solar albedo characteristics of pavement and embankment slope surfaces in permafrost regions. In this study, an albedo measurement method is proposed for both pavement surface and slope surfaces. The method is validated by in-situ experiments and compared with traditional albedo measurement methods. Meanwhile, we measure the albedo values of the permafrost embankment surfaces along the G109 Highway in high latitude permafrost regions by using the proposed method. The results show that these embankment surfaces absorb a lot of solar radiation for a long time due to the low albedo. Comparing the measured results and remote sensing data, we carry out a comprehensive analysis of the albedo characteristics of permafrost embankment surfaces. Based on these findings, a preliminary solution is put forward to improve the thermal stability of permafrost embankment and decrease embankment diseases.

Firefly Algorithm-Based Optimization of the Additional Energy Yield of Bifacial PV Modules

A solar bifacial photovoltaic (PV) module is designed so that it permits the addition of the back electrode to the prevailing silicon PV on the front side. Hence, it has the ability to harvest energy using its front and back faces. This study presents an optimization model for calculating the extra energy yield (EY) that can be harvested from the backside of a bifacial PV module using the Firefly Algorithm (FA). Mathematical modelling of the various parameters that influence the extra EY of the backside of a bifacial module was carried out using SIMULINK. Moreover, the mathematical model of the EY of the module was also carried out and then optimized using FA. The optimization model was confined to two orientation states namely the vertical south–north and vertical east–west at Ogbomosho (8.1227° N, 4.2436° E), Nigeria, with different values of albedo and mounting heights. The simulation result shows that the vertical east–west oriented modules outperform the vertical south–north oriented modules in terms of the EY generated. The result also showed that the maximum value of the EY is harvested at a mounting height of 1 m above the ground with row spacing of 2.5 m and a tilt angle of 25 degrees. Therefore, an optimal selection of the mounting surface (albedo) and mounting elevation values can harvest an extra EY of 5 to 45 per cent and help minimize the cost of energy generated using bifacial PV modules for electricity generation.

A stratified environmental reference system for better understanding of the relationship between remote sensing observations and ground monitoring of karst rocky desertification

AbstractQuickly and accurately monitoring karst rocky desertification via remote sensing could assist in its mitigation. Yet this is limited by high environmental heterogeneity that introduces uncertainty into satellite observations' relationships with ground‐based karst rocky desertification. Influenced by variations of environmental factors, the relevance of satellite data for karst rocky desertification is questionable, especially at a large geographic scale. Here a novel stratified degradation reference system was built to describe this complex relationship. The method was applied in Guizhou–Guangxi Karst Mountainous Region, a typical karst region in China undergoing severe karst rocky desertification. A stratified procedure of elevation‐based initial division and sub‐division of lithology and land use was designed using moderate resolution imaging spectroradiometer (MODIS) data. MODIS values of surface vegetation, albedo, and temperature products were standardized by percentiles to reveal their relevance for evaluating each environmental stratification of land degradation. We found a substantial spatial variation of MODIS observations across elevation gradients and different land uses. This was corrected using our proposed reference method, wherein standardized MODIS observations show a nonlinear but clear downward trend with increasing karst rocky desertification intensities. Most areas affected by karst rocky desertification had lower MODIS values. Using the stratified environmental reference approach between MODIS observations and karst rocky desertification can enable the cost‐effective screening of high‐heterogeneity karst areas, to better support monitoring and identify desertification hotspots.

Glass beads retro-reflective coating for building application: albedo assessment in urban canyon configurations

Materials for urban pavements and building coatings have a direct impact on urban thermal environment: low-reflective and highly absorptive materials, in fact, could contribute to the exacerbation of the Urban Heat Island (UHI) phenomenon, which negatively affects building energy consumptions and indoor and outdoor thermal comfort. These effects could be worsened especially in Urban Heat Canyon configurations, where the inter-building effect becomes more relevant. As regards UHI mitigation strategies, high-reflective (HR) and retro- reflective (RR) materials have been studied for their application as urban coatings, in order to provide a cooling effect inside urban canyons. In this framework, this study aims at comparing the albedo performance of HR and RR materials applied on a small scale urban canyon facility. To this aim, an in-field experimental campaign was conducted in two days during summer 2020. Different canyon coating combinations and height/width (H/W) ratios were investigated and compared in terms of albedo. Results show that an albedo worsening occurs when the RR coating was applied to the canyon’s surfaces, because of the lower global reflectance of the RR with respect to the HR. Nevertheless, the application of RR coating on walls, coupled with HR paint on pavement, lead to higher albedo values of up to 4.7%, with respect to the opposite mixed coating combination. Future developments may concern the investigation of the optimum design of a glass bead RR material for building application, by studying the correlation between its optical capabilities and the dimensions and density of the glass beads.

Study on the Aridity in the North-Western (NW) Part of Bangladesh through Combined Application of Remote Sensing, GIS and Geophysical Data

In the present paper, hydro-environmental behaviour of two adjacent but characteristically different land areas of (i) semi-arid Barind Tract and (ii) Ganges flood plain situated in the north-western part of Bangladesh have been studied and possible mechanisms of variability in the two study sites have been investigated. Time series remote sensing data supplemented with climatic, geophysical and groundwater data and other ancillary information have been analysed for the purpose. Coupling of Landsat TM derived vegetation cover information with meteorological data depicts higher sensitivity of Barind Tract than the other study site towards vegetation cover changes in response to rainfall amount. Temporal sequence of albedo value as derived from Landsat TM data manifests appropriate seasonal trend that is consistent with field observations. Analysis of rainfall data over a period of about 50 years depicts substantially higher rainfall in both the study sites as compared to a typical semiarid region. However, temporal distribution of rainfall events is mostly concentrated within very short period of time in the year. Lithological information on the subsurface configuration depicts the existence of a relatively impermeable clayey layer near the top surface in these areas. Relatively higher thickness of this impermeable clayey layer over the semiarid Barind areas has been noticed that slows down the infiltration process significantly as compared to that in adjacent floodplain areas. Analysis of drainage network exhibits relatively higher drainage density in the Barind Tract area as compared to that in floodplain area. The drainage pattern shows predominantly unidirectional and distributary nature of drainage in the Barind Tract area and in general, distribution is oriented towards basin direction and most of the branches of the drainage system. Ultimately, relatively higher elevation, steeper slope result in relatively quicker surface runoff to carry out excess rain water to the nearest basins, results in decreased infiltration of rainwater. Eventually, the conversion efficiency of Barind Tract area to transform intercepted rainwater into underground reservoir water through infiltration seems to be lower as compared to that of floodplain areas.

Estimation of the effects of aerosol optical properties on peatland production in Rzecin, Poland

The productivity response of a peatland ecosystem in Rzecin, Poland, was determined based on varying aerosols abundant in the atmosphere. The study was done with the use of a multifactorial model that combined atmospheric and ecosystem modules to describe plant photosynthetic ability from different perspectives. The Gross Ecosystem Production (GEP) was calculated for real conditions in the period from May through September 2018. This period was characterized by increased air temperatures (1.4 °C) and reduced precipitation(17%), when compared to the long-term averages (1981–2010) for the studied area. This also aligned with expected direction of climate change predictions.The multifactorial model was used to show that, depending on the aerosol situation, the peatland ecosystem may react with an average increase (8.2%) as well as a decrease (6%) of GEP during the growing season. The modification of atmospheric optical properties with a step-wise increase of aerosol optical depth (AOD) by 0.2 in relation to the observed value, resulted in the increase of diffuse index (DI) of circa 22%, the decrease of photosynthetic photon flux density (PPFD) of circa 5%, and the increase of GEP of circa 8% in each of analyzed months.The GEP reduction (6%) was caused by the absorbing aerosol presence characterized by low single scattering albedo (SSA) value. Consequently, the CO2 uptake process could not be maximized by the ecosystem due to reduced levels of available radiant energy. Conversely, the effect of non-absorbing aerosols presence on GEP was found negligible due to the continental clean aerosols prevailed in the air mass during the study period. Generally speaking, the estimation of the effects of aerosol optical properties on Rzecin peatland production shows that more absorbing aerosols occurrence cause GEP reduction while AOD rise results in GEP gain.

Filling gaps of black-sky surface albedo of the Arctic sea ice using gradient boosting and brightness temperature data

Surface albedo is a necessary parameter for climate studies and modeling. There is a need for a full spatial coverage of albedo data, but clouds and high solar zenith angle cause missing values to the optical satellite products, especially around the polar areas. Therefore, our motivation is to develop gap filling models. For that purpose, we will apply monthly gradient boosting (GB) based models to the Arctic sea ice area of the 34 years long albedo time series of the Satellite Application Facility on Climate Monitoring (CM SAF) project. We demonstrate the ability of the GB models to accurately fill missing data using albedo monthly mean, brightness temperature, and sea ice concentration as model inputs. Monthly GB models produce the most unbiased, precise, and robust estimates when compared to alternative estimates presented, such as monthly mean albedo values or estimates from monthly linear regression (LR) models. The mean relative differences between GB based estimates and original pentad values vary from −20% to 20% with RMSE being 0.048, compared to relative differences varying from −20% to over 60% with RMSE varying from 0.054 to 0.074 between other estimates and original pentad values. Pixelwise mean differences and standard deviations (std) over the whole Arctic sea ice area show that GB based estimates are more accurate (mean differences from −0.02 to 0.02) and more precise (std from 0.02 to 0.08) than other estimates (mean differences varying between −0.05 to over 0.05, and std varying from around 0.03 to over 0.1). Also, albedo of the melting sea ice is predicted better by the GB model, with negligible mean differences, compared to the LR model. Based on these results, we show that GB method is a useful technique to fill missing data, and the brightness temperature and sea ice concentration are useful additional model input data sources.

Multiple linear and non-linear regression analyses of various soil and terrain indices with regard to their efficiency in the determination of temporal changes in LST values within Trichy district of Tamil Nadu, India.

Land surface temperature (LST) of the terrain is the result of thermal energy received from the sun as the source. The study site was Trichy district of Tamil Nadu state in India wherein the LST values pertaining to all the belonging pixels have been calculated using generalized split window (GSW) algorithm from the Landsat-8 satellite images on two different dates with a gap of 5years between them. Along with the LST calculation on these 2 dates, corresponding NDWI, NDVI, NDBI, NDMI, BSI, DBI, DBSI, LSE, and albedo values have also been calculated. Then, changes in the dependent variable (LST) and in the each of the respective explanatory or independent variables have been undergone through the process of multiple linear and non-linear regression analysis to find out the best-fitting model set of explanatory variables that best describes the variation in LST values at a location. In this research, it has been found that a non-linear model set comprising five independent variables like change in BSI, LSE, NDWI, NDBI, and albedo seem to be the best-fitting model for predicting the variations in the dependent variable to the maximum degree and also with acceptable redundancy. Also, it has been observed that changes in LSE or albedo values at any place within the study-site could play the most significant role in having an influence in the LST value change that could be recorded in the same over any given time period, thus proving the vastness of the effect that could be made by an increase in urbanization or structural development on the extent of positive change in LST.

Hyperspectral Satellite Remote Sensing of Aerosol Parameters: Sensitivity Analysis and Application to TROPOMI/S5P

Precise knowledge about aerosols in the lower atmosphere (optical properties and vertical distribution) is particularly important for studying the Earth’s climatic and weather conditions. Measurements from satellite sensors in sun-synchronous and geostationary orbits can be used to map distributions of aerosol parameters in global or regional scales. The new-generation sensor Tropospheric Monitoring Instrument (TROPOMI) onboard the Copernicus Sentinel-5 Precursor (S5P) measures a wide variety of atmospheric trace gases and aerosols that are associated with climate change and air quality using a number of spectral bands between the ultraviolet and the shortwave infrared. In this study, we perform a sensitivity analysis of the forward model parameters and instrument information that are associated with the retrieval accuracy of aerosol layer height (ALH) and optical depth (AOD) using the oxygen (O2) A-band. Retrieval of aerosol parameters from hyperspectral satellite measurements requires accurate surface representation and parameterization of aerosol microphysical properties and precise radiative transfer calculations. Most potential error sources arising from satellite retrievals of aerosol parameters, including uncertainties in aerosol models, surface properties, solar/satellite viewing geometry, and wavelength shift, are analyzed. The impact of surface albedo accuracy on retrieval results can be dramatic when surface albedo values are close to the critical surface albedo. An application to the real measurements of two scenes indicates that the retrieval works reasonably in terms of retrieved quantities and fit residuals.

Half-space albedo problem for the Anlı-Güngör scattering function

Abstract One speed, time-independent and homogeneous medium neutron transport equation is solved for second order scattering using the Anlı-Güngör scattering function which is a recently investigated scattering function. The scattering function depends on Legendre polynomials and the t parameter which is defined on the interval [−1, 1]. A half-space albedo problem is examined with the FN method and the recently developed SVD method. Albedo values are calculated with two methods and tabulated. Thus, the albedo values for the Anlı-Güngör scattering are compared with these methods. The behaviour of the scattering function is similar to İnönü’s scattering function according to calculated results.

Airborne Measurements of Surface Albedo and Leaf Area Index of Snow‐Covered Boreal Forest

AbstractHelicopter based simultaneous measurements of broadband surface albedo and the effective leaf area index (LAIeff) were carried out in subarctic area of Finnish Lapland in spring 2008, 2009, and 2010 under varying illumination and snow cover conditions. Vertical profile measurements show that the found relationship between albedo and LAIeff seems to be rather independent of the flight altitude and therefore the footprint scale. Actually, flights above 500 m in altitude revealed low variations of the surface albedo approaching an aerial average at 1 km, meaning that a footprint of 20 km is representative of the landscape. The albedo of the area was beta distributed, and without LAIeff values below 0.25, the average albedo value of the area would decrease from 0.49 to 0.44 showing the albedo sensitivity to sparse vegetation. The results agreed with the photon recollision probability based model PARAS and the MODIS satellite albedo product MCD43A3. However, differences between satellite based and airborne albedo values were noticed, which could be explained by a difference in footprint size and/or the strong local heterogeneity as certain flights were operated on specific targets.

Balanço de Radiação no Bioma Caatinga no Semiárido Alagoano

O conhecimento da dinâmica do Balanço de radiação é imprescindível para determinação das trocas de energia que ocorrem no sistema Terra-Atmosfera. Este estudo objetivou estudar a dinâmica do comportamento dos componentes do balanço de radiação numa Caatinga. Esta pesquisa foi realizada em uma área com vegetação de Caatinga na Fazenda Mourão (09º42,664’ S; 37º25,008’ W ; 165m) no município de Pão de Açúcar, Alagoas, Sertão Alagoano, Nordeste do Brasil. Para a realização do monitoramento micrometeorológico foi instalada uma torre de 6,5 metros de altura no período de abril/2019 a outubro/2020, no qual a irradiância solar incidente (Rg), refletida pela superfície (Rr), radiação de onda longa incidente (Ra), onda longa emitida pela superfície (Rs) e balanço de radiação (Rn) foram medidas pelo saldo radiômetro modelo CNR1 da Kipp e Zonen (Delft, Holanda). A variação diária, horária e sazonal de cada elemento do balanço de radiação foi avaliada. A atmosfera se apresentou 66,47% parcialmente nublada anualmente. Foi detectada pouca variação nos valores médios mensais diários de albedo entre as estações seca e chuvosa. A Rn foi estimada da Rg com muito boa acuracidade independentemente da época do ano. O saldo de radiação foi dominado pelo Rg, mas se revelou sazonal: maior na estação seca e menor na chuvosa. A variação estacional das componentes de ondas curtas (Rg, Rr, BOC) dependem mais da transmissividade atmosférica e pouco do albedo superficial, enquanto as de ondas longas (Ra, Rs e BOL) dependem da emissividade efetiva da atmosfera (Ra) e da temperatura do solo (Rs).Palavras-chave: Saldo de radiação; Sazonalidade; Nordeste do Brasil. Radiation Balance in the Caatinga Biome in the Semi-arid of Alagoas, BrazilA B S T R A C TKnowing of the Net Radiation dynamic is crucial to determine the exchanges of energy that happen in the surface-atmosphere system. This research aimed to study the net radiation components dynamic pattern above a Caatinga vegetation. The study was carried out in a Caatinga vegetation area in the Mourão Farm (09º42,664’ S; 37º25,008’ W ; 165m) in Pão de Acúcar municipality, State of Alagoas, Northestern of Brazil. To carry out the micrometeorological monitoring a 6.5m height tower was installed throughout period from April/2019 to October/2020, in which the incoming solar radiation (Rg), reflected solar radiation (Rr), atmospheric long wave radiation and surface long wave radiation were measured by a CNR1 of Kipp e Zonen (Delft, Holanda) net radiometer. The hourly, daily and seasonal oscillation for each component of the net radiation were evaluated. The atmosphere had shown 66.47% partly cloudy through the experimental year. The values of albedo have shown small variation of its daily monthly average values among the dry and wet season. The Rn was estimated from Rg with good accuracy regardless of the year period. The Rn was dominated by the Rg, but had presented seasonal: higher during the dry season and lower in the wet season. The seasonal variation of the short wave components (Rg, Rr, BOC) depend on the atmospheric transmissivity and less from the surface albedo, meanwhile the long waves (Ra, Rs and BOL) depend on the effective emissivity of the atmosphere and the soil temperature (Rs).Keywords: Net radiation; Seasonality; Northeastern of Brazil.