Albedo Measurements Research Articles

Night Thermal Unmixing for the Study of Microscale Surface Urban Heat Islands with TRISHNA-Like Data

Urban Heat Islands (UHIs) at the surface and canopy levels are major issues in urban planification and development. For this reason, the comprehension and quantification of the influence that the different land-uses/land-covers have on UHIs is of particular importance. In order to perform a detailed thermal characterisation of the city, measures covering the whole scenario (city and surroundings) and with a recurrent revisit are needed. In addition, a resolution of tens of meters is needed to characterise the urban heterogeneities. Spaceborne remote sensing meets the first and the second requirements but the Land Surface Temperature (LST) resolutions remain too rough compared to the urban object scale. Thermal unmixing techniques have been developed in recent years, allowing LST images during day at the desired scales. However, while LST gives information of surface urban heat islands (SUHIs), canopy UHIs and SUHIs are more correlated during the night, hence the development of thermal unmixing methods for night LSTs is necessary. This article proposes to adapt four empirical unmixing methods of the literature, Disaggregation of radiometric surface Temperature (DisTrad), High-resolution Urban Thermal Sharpener (HUTS), Area-To-Point Regression Kriging (ATPRK), and Adaptive Area-To-Point Regression Kriging (AATPRK), to unmix night LSTs. These methods are based on given relationships between LST and reflective indices, and on invariance hypotheses of these relationships across resolutions. Then, a comparative study of the performances of the different techniques is carried out on TRISHNA synthesized images of Madrid. Since TRISHNA is a mission in preparation, the synthesis of the images has been done according to the planned specification of the satellite and from initial Aircraft Hyperspectral Scanner (AHS) data of the city obtained during the DESIREX 2008 capaign. Thus, the coarse initial resolution is 60 m and the finer post-unmixing one is 20 m. In this article, we show that: (1) AATPRK is the most performant unmixing technique when applied on night LST, with the other three techniques being undesirable for night applications at TRISHNA resolutions. This can be explained by the local application of AATPRK. (2) ATPRK and DisTrad do not improve significantly the LST image resolution. (3) HUTS, which depends on albedo measures, misestimates the LST, leading to the worst temperature unmixing. (4) The two main factors explaining the obtained performances are the local/global application of the method and the reflective indices used in the LST-index relationship.

Spectral Albedo Estimation of Snow Covers in Pakistan Using Landsat Data

Accurate snow spectral albedo measurements from satellite data can essentially help to determine the changes over the snow surface area. In the current study, spectral snow albedo is measured over the northern region of Pakistan using spatio-temporal imagery datasets taken by Landsat satellite series equipped with TM and ETM+ sensors. An Automatic Cloud Cover Assessment (ACCA) algorithm is used to mask cloudy pixels from further processing. Furthermore, an image independent model, Second Simulation of the Satellite Signal in the Solar Spectrum (6S) is used in the current research work to atmospherically correct the satellite data. The snow cover albedo of northern Pakistan is estimated using pixel values prior to correction, ACCA output values, and 6S model output values. The results of the study show that highest albedo values are estimated using Landsat band 4 data with albedo model. The results of the study also show that the albedo values measured (band 4) in the year 1992 (0.989) are reduced in the year 2000 (0.931). It is expected that the results of the study could be utilized to predict climatic variations for spring runoff estimation.

Direct Comparison and Triple Collocation: Which Is More Reliable in the Validation of Coarse‐Scale Satellite Surface Albedo Products

AbstractA rigorous and reliable validation is the prerequisite and basis to properly understand the accuracy of satellite surface albedo products. However, the representativeness error of point scale in situ measurements, which mainly results from the spatial mismatch between in situ and satellite measurements as well as the surface heterogeneities, generally hinders an effective validation of satellite surface albedo products based on the conventional direct comparison method. Triple collocation technique has been recognized as a powerful tool to estimate the errors of satellite products without requiring the truth. Here, we evaluated the effectiveness of both the direct comparison and extended triple collocation (ETC) methods in tackling with the representativeness error of in situ measurements and characterizing the performances of satellite surface albedo products (MCD43A3 [V006], GLASS, and NPP VIIRS albedos) given whether the in situ‐based pixel‐scale albedo was available or not. The ETC method is shown to be advantageous over the direct comparison based on single “point” in situ measurements, because it is less affected by representativeness errors. However, it shall not substitute for the direct comparison method based on in situ‐based pixel‐scale albedo measurements, because its effectiveness in solving representativeness errors and estimating product errors is very limited and dependent on the choice of the data in the triplets. Furthermore, the ETC technique cannot be used to estimate the true physical errors of satellite surface albedo products.

Retrieval of the water ice column and physical properties of water-ice clouds in the martian atmosphere using the OMEGA imaging spectrometer

Using spectral images recorded by the OMEGA instrument on Mars Express (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité), we are able to derive physical properties of aerosols in water-ice clouds on Mars for a distribution of pixels over an observed cloud formation. These properties, mean effective radius, reff, and optical depth (at 0.67 μm), τi, were used to estimate the water ice-column (WIC), and we found an empirical relationship between the WIC and an ice cloud index (ICI). The overall mean of retrieved reff is ∼2.2 μm, with a standard deviation of 0.8 μm, and cloud formations with reff between 4.4 and 5.4 μm are observed. The optical depth varies between 0.2 and 2.0. The OMEGA spectra are primarily sensitive to water ice mass due to absorption, and we find that the ICI, very easy to compute, is a good proxy for the mass of the water-ice column (WIC) along the optical line of sight. Our retrieval of physical properties is limited in time (to before 2010) by the exhaustion of coolant for one of the OMEGA channels, and in space (to equatorial observations between 140∘W and 90∘E) by the availability of surface albedo measurements. However, we used the ICI to compute WIC values for the entire OMEGA data set, which has near-global coverage for Mars years 26–32, and we present a climatology of the WIC derived from the OMEGA data, which features enhancements on the order of 1.2–1.6 pr. μm over the aphelion cloud belt, and 1.5–2.5 pr. μm over the polar hoods. The data set analyzed is for observations between 140°W and 90°E, and between 35∘S and 35∘N. No restriction is placed on season, but the majority of cloudy observations were during the aphelion period from Ls 35∘ to 135∘. This work was motivated by the ability of the OMEGA instrument to observe the distribution of water-ice cloud physical properties, and by the availability of new a priori data sets, especially multi-spectral, aerosol-free surface albedo retrieved from a subset of the OMEGA data featuring a cloud-free sky. The main limitations of the retrieval algorithm are linked to the uncertainties on surface albedo, the dust opacity, and the quantity of water-ice suspended in the atmosphere, which can lead to spectral fits with lower accuracy or unrealistic results. We present distributions of each retrieved parameter, goodness of fit, ICI, and cloud mass, and our investigation of relationships between each parameter. Our approach was to maximize the amount of data analyzed, apply stringent data quality cuts and take a statistical approach to interpretation.

A UAV-Based Sensor System for Measuring Land Surface Albedo: Tested over a Boreal Peatland Ecosystem

A multiple sensor payload for a multi-rotor based UAV platform was developed and tested for measuring land surface albedo and spectral measurements at user-defined spatial, temporal, and spectral resolutions. The system includes a Matrice 600 UAV with an RGB camera and a set of four downward pointing radiation sensors including a pyranometer, quantum sensor, and VIS and NIR spectrometers, measuring surface reflected radiation. A companion ground unit consisting of a second set of identical sensors simultaneously measure downwelling radiation. The reflected and downwelling radiation measured by the four sensors are used for calculating albedo for the total shortwave broadband, visible band and any narrowband at a 1.5 nm spectral resolution within the range of 350–1100 nm. The UAV-derived albedo was compared with those derived from Landsat 8 and Sentinel-2 satellite observations. Results show the agreement between total shortwave albedo from UAV pyranometer and Landsat 8 (R2 = 0.73) and Sentinel-2 (R2 = 0.68). Further, total shortwave albedo was estimated from spectral measurements and compared with the satellite-derived albedo. This UAV-based sensor system promises to provide high-resolution multi-sensors data acquisition. It also provides maximal flexibility for data collection at low cost with minimal atmosphere influence, minimal site disturbance, flexibility in measurement planning, and ease of access to study sites (e.g., wetlands) in contrast with traditional data collection methods.

A Method for Landsat and Sentinel 2 (HLS) BRDF Normalization

The Harmonized Landsat/Sentinel-2 (HLS) project aims to generate a seamless surface reflectance product by combining observations from USGS/NASA Landsat-8 and ESA Sentinel-2 remote sensing satellites. These satellites’ sampling characteristics provide nearly constant observation geometry and low illumination variation through the scene. However, the illumination variation throughout the year impacts the surface reflectance by producing higher values for low solar zenith angles and lower reflectance for large zenith angles. In this work, we present a model to derive the bidirectional reflectance distribution function (BRDF) normalization and apply it to the HLS product at 30 m spatial resolution. It is based on the BRDF parameters estimated from the MODerate Resolution Imaging Spectroradiometer (MODIS) surface reflectance product (M{O,Y}D09) at 1 km spatial resolution using the VJB method (Vermote et al., 2009). Unsupervised classification (segmentation) of HLS images is used to disaggregate the BRDF parameters to the HLS spatial resolution and to build a BRDF parameters database at HLS scale. We first test the proposed BRDF normalization for different solar zenith angles over two homogeneous sites, in particular one desert and one Peruvian Amazon forest. The proposed method reduces both the correlation with the solar zenith angle and the coefficient of variation (CV) of the reflectance time series in the red and near infrared bands to 4% in forest and keeps a low CV of 3% to 4% for the deserts. Additionally, we assess the impact of the view zenith angle (VZA) in an area of the Brazilian Amazon forest close to the equator, where impact of the angular variation is stronger because it occurs in the principal plane. The directional reflectance shows a strong dependency with the VZA. The current HLS BRDF correction reduces this dependency but still shows an under-correction, especially in the near infrared, while the proposed method shows no dependency with the view angles. We also evaluate the BRDF parameters using field surface albedo measurements as a reference over seven different sites of the US surface radiation budget observing network (SURFRAD) and five sites of the Australian OzFlux network.

Evaluating the Estimation of Net Radiation Based on MODIS Data and CoLM: A Case Study in the Tibetan Plateau

Estimation of net radiation is essential for characterization of the land–atmosphere energy and water exchange processes of the Tibetan Plateau. Two methods are commonly used to estimate the net radiation. Method 1 relies on ground measurements and earth satellite observations, and method 2 relies on the use of a land surface model. Currently, there is no consensus on regarding which of these two methods is the most accurate. In this study, we evaluated net radiation calculated by MODIS land surface temperature products, combined with ground-based incoming shortwave and longwave radiation and albedo measurements, and compare this to performance of the common land model for modeling surface net radiation for the Muztaga site located in the northwest of the Tibetan Plateau at three timescales (half-hourly, hourly, and daily). The results show that the two methods provide similar results, and both methods provide estimates that are notably higher than ground-measured net radiation validations at three different timescales. Estimates of net radiation obtained at half-hourly and hourly timescales closely match the fluctuations in the reference data. However, the daily timescale is too coarse to capture the short-term fluctuations. Thus, this study demonstrates that the shorter timescales are preferred in determining surface net radiation. In addition, compared with method 2, method 1 is more accurate for each of the different timescales.

Field and laboratory measurement of albedo and heat transfer for pavement materials

Albedo is an important indicator of the radiation reflectance of pavement surface and commonly measured using the field albedometer. In this study, factors affecting the field measurement of albedo including solar radiation intensity, incident angle and surrounding conditions were investigated. A new albedometer for laboratory testing of albedo and internal temperature at different depths in compacted asphalt mixture/Portland cement concrete (PCC) slabs was developed to overcome the negative effects of field measurements. Laboratory measurements of albedo were performed on three types of asphalt mixture (e.g. AC-13, SMA-13 and OGFC-13) and PCC with different surface textures using the developed albedometer. Three types of coating materials were prepared by mixing base material of transparent epoxy glue and the filler of Nano-TiO2, Micro-TiO2 and Nano-ZnO, respectively. The albedo and internal temperature of asphalt mixtures with coating materials were also measured and compared to those without coating materials. Results show that the developed laboratory albedometer can synchronously measure the accurate albedo and internal temperature of pavement materials. The albedo of three types of asphalt mixtures have a range of 5.46%–6.11%, while the albedo of PCC with different surface textures ranges from 22.8% to 26.4%. The gradation of asphalt mixture has little impact on the albedo. Rougher PCC surface reflect less solar radiation and produce a higher internal temperature. The filler of Micro-TiO2 in pavement coating has the better reflectance than Nano-TiO2 and Nano-ZnO.

On Possible Changes in the Physical Characteristics of the Aerosol in the Deep Layers of the Atmosphere of Saturn

This study is dedicated to determining the values of the physical parameters of cloud particles in the deep layers of Saturn’s atmosphere using the data from remote measurements of the solar radiation field diffusely reflected by the giant planet. In the previous studies, using the effective optical depth method, from the spectral measurements of the geometric albedo of Saturn in 1993 in the wavelength range of 300–1000 nm, a pressure dependence of the aerosol scattering component of the optical depth, i.e., a change in its value with altitude in the atmosphere, was obtained. The analysis of the initial data was performed in the long-wave part of the spectrum in the methane absorption lines of different levels of absorption with the centers at wavelengths of λ = 619, 727, 842, 864, and 887 nm. At certain altitude levels in the deep layers of the atmosphere of the giant planet, the indicated dependence shows the features that possibly reflect changes in the physical characteristics of aerosol. Therefore, the aim of this work was to determine the possible values of the physical parameters of aerosol particles in the deep layers of Saturn’s atmosphere at altitudinal levels with the features noted above. As a result, an increase in the effective radius of cloud particles was observed in the transition from the outer to the deeper layers of the atmosphere: from 1.4 μm in the upper part of atmosphere to 1.83 μm in the altitudinal region with a pressure of 1.0–1.25 bar and up to 2.2–2.4 μm in the region with a pressure of 1.5–2.0 bar. In the latter segment, a decrease by 3.5% was revealed in the real part of the refractive index of aerosol particles. A possible reason for this decrease is the change in the phase state of aerosol particles in the lower and warmer atmospheric layers of Saturn due to the presence of ammonium hydroxide in their composition at a sufficient high concentration.

A Coupled Glacier‐Hydrology Model and Its Application in Eastern Pamir

AbstractAn energy‐balance glacier‐melt scheme was coupled with the Variable Infiltration Capacity hydrology model (VIC‐glacier). The coupled model was setup at 30 m × 30 m grids and applied in the Muji basin in eastern Pamir. The model was validated with field measurements of albedo, glacier mass balance, and river runoff. The VIC‐glacier model showed a good correspondence with the observations in incoming shortwave radiation and albedo, with R2 of 0.70 and 0.32, respectively, during August–October 2012. Simulated glacier mass balance exhibited overall good agreements with the observations in ablation seasons, with R2 of 0.89 and root‐mean‐square error of 162.12 mm w.e. during 2011–2015. The model also reproduced discharge records, with R2 of 0.70–0.84, Nash‐Sutcliffe efficiency of 0.56–0.81, root‐mean‐square error of 0.29–0.45 m3/s, and negative relative error of 13.73–18.76% in melt seasons of 2014–2015. The glaciers in Muji basin had a low mean net radiation of 40 W/m2, large negative latent heat fluxes of −32 W/m2, and low melt energy of −21 W/m2 in ablation seasons, resembling the energy partitioning generally found in continental climates. About 60% of the positive energy supply was consumed by latent heat fluxes on the glaciers in Muji basin, while only about 40% of the positive energy supply was used for melting. Glaciers in the Muji basin experienced a mass balance of −812.18 mm over 2011–2015, corresponding to a water release of 4.42 × 106 m3.The VIC‐glacier model has a good potential of broader utility for the large basins with limited meteorological observations.

Reconstruction of Remotely Sensed Snow Albedo for Quality Improvements Based on a Combination of Forward and Retrieval Models

Snow albedo plays an important role in the global climate system. There are notable missing data and error uncertainties in the current remote sensing snow albedo products that are attributed to the limits of remote-sensing technology. Due to the uncertainties of meteorological factors and the differences in various forward model simulation methods, snow albedo forward simulations also have considerable uncertainties. This paper suggests a long-time-series reconstruction of snow albedo utilizing a forward radiation-transferring model and a remote-sensing retrieval model together with multisource remotely sensed data and meteorological data. The key to this paper is to estimate snow information for areas lacking data utilizing a forward model for snow albedo with clear physical mechanisms. The estimated snow information can be used as reliable data for snow albedo reconstructions. The results indicate that the long time series of snow albedo data obtained by coupling the snow albedo retrieval model and forward simulation model is highly accurate. The mean absolute error, root mean square error, Pearson’s correlation coefficient (R), and Nash–Sutcliffe efficiency coefficient of the observed and reconstructed snow albedos are 0.11, 0.14, 0.79, and 0.69, respectively. The reconstructed snow albedo data are underestimated by only 11% relative to the in situ snow surface albedo measurements. In the alpine mountain regions, the proposed method has a simulation accuracy that is 6% greater than that of the MOD10A1 SAD. This paper provides an effective reconstruction solution that improves the accuracy of estimations of snow albedo and fills gaps in the data.

The influence of photochemical aging on light absorption of atmospheric black carbon and aerosol single-scattering albedo

Abstract. Coating enhancement of black carbon (BC) light absorption (Eabs) is a large uncertainty in modelling direct radiative forcing (DRF) by BC. Reported Eabs values after atmospheric aging vary widely and the mechanisms responsible for enhancing BC absorption remain elusive. Here, we report on the direct field measurement of size-resolved mixing state, Eabs, and aerosol single-scattering albedo (SSA) at λ = 532 nm at a rural site in east China from June to July 2016. Strong diurnal variability of Eabs, SSA, and Ox (Ox = NO2 + O3, a proxy for atmospheric photochemical aging) was observed. A method that combined Eabs and SSA was developed to retrieve the fraction contribution of BC absorption (fBC), lensing-driven enhancement (fLens), as well as the fractional contribution of coating absorption (fraction absorption contribution (fShell), the coated shell diameter (DShell) and the imaginary part of the complex refractive index (CRI) of the shell (kShell)). Parameterization of Eabs and SSA captures much of the influence of BC coating and the particle absorption. In our measurements at this site, the results showed that the absorption amplification depended on the coating thickness and the absorption of coating materials, and photochemistry plays a role in modifying the absorption of BC-containing particles. The lensing-driven enhancement was reduced by light absorption of the shell. One implication of these findings is that the contribution of light-absorbing organic compounds (brown carbon, BrC) at a longer aging time should be included in climate models.

Development of a Multispectral Albedometer and Deployment on an Unmanned Aircraft for Evaluating Satellite Retrieved Surface Reflectance over Nevada's Black Rock Desert.

Bright surfaces across the western U.S. lead to uncertainties in satellite derived aerosol optical depth (AOD) where AOD is typically overestimated. With this in mind, a compact and portable instrument was developed to measure surface albedo on an unmanned aircraft system (UAS). This spectral albedometer uses two Hamamatsu micro-spectrometers (range: 340–780 nm) for measuring incident and reflected solar radiation at the surface. The instrument was deployed on 5 October 2017 in Nevada’s Black Rock Desert (BRD) to investigate a region of known high surface reflectance for comparison with albedo products from satellites. It was found that satellite retrievals underestimate surface reflectance compared to the UAS mounted albedometer. To highlight the importance of surface reflectance on the AOD from satellite retrieval algorithms, a 1-D radiative transfer model was used. The simple model was used to determine the sensitivity of AOD with respect to the change in albedo and indicates a large sensitivity of AOD retrievals to surface reflectance for certain combinations of surface albedo and aerosol optical properties. This demonstrates the need to increase the number of surface albedo measurements and an intensive evaluation of albedo satellite retrievals to improve satellite-derived AOD. The portable instrument is suitable for other applications as well.

Preliminary assessment of 20-m surface albedo retrievals from sentinel-2A surface reflectance and MODIS/VIIRS surface anisotropy measures

Satellite-based retrievals of land surface albedo at 20-m resolution are generated by coupling the surface reflectances from the recently launched Sentinel-2A satellite with surface anisotropy information (as described by Bidirectional Reflectance Distribution Function, BRDF) from either the MODerate-resolution Imaging Spectroradiometer (MODIS) or the Visible Infrared Imaging Radiometer Suite (VIIRS). The intrinsic black-sky albedo (BSA) and white-sky albedo (WSA) values of the surface are derived at the six shortwave spectral bands of Sentinel-2A's Multi Spectral Instrument (MSI). A specific set of narrow-to-broadband conversion coefficients is derived from radiative transfer simulations and presented for the generation of broadband albedos. Initial evaluation uses well-calibrated ground-based albedo measurements by pyranometers mounted on the towers at seven sites of the Surface Radiation Network (SURFRAD). Over those sites where pyranometer measurement footprints are not spatially representative of the landscape covered by the satellite pixels (i.e., spatially nonrepresentative) at the grid scales (500 m to 1 km) of the MODIS and VIIRS products, the finer-resolution Sentinel-2A albedos manifested a pronounced decrease in root mean squared error (RMSE) and mean bias in the evaluation against the ground-based data as compared to the coarser resolution albedo products of MODIS and VIIRS. This decrease occurs because the 20-m Sentinel-2A albedo values are better able to resolve the spatial details of surface albedo within the ground-based instrument footprints than the coarser resolution sensors. This preliminary evaluation also demonstrates the consistency of the Sentinel-2A albedo results whether using the MODIS BRDF or the VIIRS BRDF products for the surface anisotropy information. The RMSEs and mean biases of the Sentinel-2A albedos over all the seven validation sites are both within the accuracy requirement of ±0.05 absolute albedo units for satellite derived albedo products. This study, to generate Sentinel-2A MSI albedo with either MODIS or VIIRS BRDFs, extends previous efforts of Landsat TM, ETM+ and OLI albedo and enhances the continuity of finer-resolution albedo data. Such long-term and higher resolution records of surface albedo improve the investigations into the changes and drivers of local/regional surface energy balance over heterogeneous regions and increasingly fragmented landscapes across the globe due to natural and human-induced land cover changes.

Characterization of Remote Sensing Albedo Over Sloped Surfaces Based on DART Simulations and In Situ Observations

AbstractIn situ albedo measurement over sloped surfaces is pivotal to a wide range of remote sensing applications, such as the estimation and evaluation of surface energy budget at regional and global scales. However, existing albedo measurements over rugged terrain are limited and controversial and remain a major challenge. In this paper, two commonly measured broadband albedos, which depend on incoming/outgoing geometric conditions, were characterized over sloped surfaces and illustrated. These albedos are the horizontal/horizontal sloped surface albedo (HHSA) and inclined/inclined sloped surface albedo (IISA). The 3‐D Discrete Anisotropic Radiative Transfer (DART) model simulations over varying slopes were utilized to quantify differences in the albedos. In particular, the effects of the slope, aspect, the solar zenith angle, and the proportion of diffuse skylight were investigated. The results show that absolute (relative) biases between HHSA and IISA are significant, reaching up to 0.026 (61.8%), 0.134 (62.4%), and 0.114 (62.3%) in the visible, near‐infrared, and shortwave broadbands, respectively. In addition, the diurnal cycle differences between HHSA and IISA were also compared using DART simulations and in situ observations over four typical slopes. Comparisons reveal that topographic parameters (e.g., slope and aspect) and atmospheric conditions (e.g., diffuse skylight and atmospheric visibility) are the primary factors, while the optical and structural parameters have a smaller effect.

Novel Measurements of Fine-Scale Albedo: Using a Commercial Quadcopter to Measure Radiation Fluxes

Remote sensing of radiative indices must balance spatially and temporally coarse satellite measurements with finer-scale, but geographically limited, in-situ surface measurements. Instruments mounted upon an Unmanned Aerial Vehicle (UAV) can provide small-scale, mobile remote measurements that fill this resolution gap. Here we present and validate a novel method of obtaining albedo values using an unmodified quadcopter at a deciduous northern hardwood forest. We validate this method by comparing simultaneous albedo estimates by UAV and a fixed tower at the same site. We found that UAV provided stable albedo measurements across multiple flights, with results that were well within the range of tower-estimated albedo at similar forested sites. Our results indicate that in-situ albedo measurements (tower and UAV) capture more site-to-site variation in albedo than satellite measurements. Overall, we show that UAVs produce reliable, consistent albedo measurements that can capture crucial surface heterogeneity, clearly distinguishing between different land uses. Future application of this approach can provide detailed measurements of albedo and potentially other vegetation indices to enhance global research and modeling efforts.

Would LEED-UHI greenery and high albedo strategies mitigate climate change at neighborhood scale in Cairo, Egypt?

Neighborhood has always been of significant interest to built environment stockholders as a basic planning unit. However, any discussion in these concerns, without drawing attention to sustainable microclimate approaches, would still in a mess at a time of increasing population and climate change. Emergence of the sustainable development concept at the mid-20th century and its emphasis led to increasing crucial role that the urban green infrastructure along with reflective materials can play in mitigating neighborhood microclimate’s symptoms of climate change. Considering the lack of studies for urban heat island (UHI) in hot arid regions, particularly in Egypt and the limited number of studies concerning the numerical simulation of all mitigation strategies incorporated, this research studies the mitigation of UHI phenomenon in a case study in Cairo in present and future (2020, 2050 and 2080) through applying the criteria of tree lines, green roofs, high albedo pavements and shading structures within the neighborhood sustainability assessment tool (Leadership in Energy and Environmental Design for Neighborhood; LEED-ND). The microclimatic numerical CFD simulations of ENVI-met 4.0 was used following the measurement of LAI and Albedo of selected Egyptian trees to assess UHI through air and radiant temperature differences before and after applying mitigation strategies. Results demonstrate a considerable ability to acclimatize the microclimate in terms of better conditions in present and future.

Measuring the albedo of limited-extent targets without the aid of known-albedo masks

Albedo is a non-dimensional parameter used to quantify the proportion of solar radiation reflected by a surface. While a couple of methods are available for measuring the albedo of limited-extent targets, these methods require known-albedo mask(s) for calibration, which interrupt the measurement by manual intervention and make continuous albedo measurements difficult. Here we propose a mask-free method for measuring the albedo of limited-extent diffuse targets without the aid of known-albedo masks for calibration. The albedo of a limited extent target can be measured by leveling an albedometer over the target and assembling a baffle around the lower detector of the albedometer to make the detector receive reflected radiation from the target only. The view factor from the detector through the baffle to the target is found by leveling the albedometer over a large open field with uniform background and then dividing the reflected radiation at the baffle-on case from that at the baffle-off case. Albedos of seven 1 m × 1 m flexible uniform sheets with different colors were measured using the proposed mask-free method and the methods with known-albedo masks for calibration. The results indicated that the mask-free method measured the albedo of limited extent targets as accurately as the methods with known-albedo masks for calibration.

A New SEBAL Approach Modified with Backtracking Search Algorithm for Actual Evapotranspiration Mapping and On-Site Application

Actual evapotranspiration is one of the most important component for efficient water management and planning. Until recently, evapotranspiration computations and measurements have been performed locally. But, in recent years, actual evapotranspiration computations can be calculated regionally thanks to improvements on remote sensing discipline and satellites. Surface Energy Balance Algorithm for Land (SEBAL) is one of the most commonly preferred technics for actual evapotranspiration mapping. However, this algorithm has some difficulties such as mismatch with Landsat 8 and hot–wet pixel selection which require expert knowledge. In this paper, a novel SEBAL based approach (SEBAL-BSA), which can use Landsat 8 images as data and can automatically perform hot–wet pixel selection using Backtracking Search Algorithm (BSA) with ground control points, has been proposed. SEBAL-BSA was developed and tested using January 22–2015, April 28–2015 and July 01–2015 dated Landsat 8 images in Akarsu Irrigation Water User Association command area in the Cukurova Region of Turkey and actual evapotranspiration mapping was realized without albedo measurements. Accuracy of SEBAL-BSA has been examined by comparing values of predefined ground truth points and values obtained from proposed approach. According to results of parametric matched pairs T test and nonparametric Wilcoxon sign rank test, SEBAL-BSA is highly successful. Applications also show that the SEBAL-BSA is a user-friendly approach for institutions and organizations related to water authorization and management.

Calculation of thermal neutron albedo for mono-material and bi-material reflectors

Thermal neutron albedo has been investigated for different thicknesses of mono-material and bi-material reflectors. An equation has been obtained for a bi-material reflector by considering the neutron diffusion equation. The bi-material reflector consists of binary combinations of water, graphite, lead, and polyethylene. An experimental measurement of thermal neutron albedo has also been conducted for mono-material and bi-material reflectors by using a 241Am–Be (5.2 Ci) neutron source and a BF3 detector. The maximum value of thermal neutron albedo was obtained for a polyethylene–water combination (0.95 ± 0.02).