Terms Of Values Research Articles

The Implications of Plantation Forest-Driven Land Use/Land Cover Changes for Ecosystem Service Values in the Northwestern Highlands of Ethiopia

In the northwestern Highlands of Ethiopia, a region characterized by diverse ecosystems, significant land use and land cover (LULC) changes have occurred due to a combination of environmental fragility and human pressures. The implications of these changes for ecosystem service values remain underexplored. This study quantifies the impact of LULC changes, with an emphasis on the expansion of plantation forests, on ecosystem service values in monetary terms to promote sustainable land management practices. Using Landsat images and the Random Forest algorithm in R, LULC patterns from 1985 to 2020 were analyzed, with the ecosystem service values estimated using locally adapted coefficients. The Random Forest classification demonstrated a high accuracy, with values of 0.97, 0.98, 0.96, and 0.97 for the LULC maps of 1985, 2000, 2015, and 2020, respectively. Croplands consistently dominated the landscape, accounting for 53.66% of the area in 1985, peaking at 67.35% in 2000, and then declining to 52.86% by 2020. Grasslands, initially the second-largest category, significantly decreased, while wetlands diminished from 14.38% in 1985 to 1.87% by 2020. Conversely, plantation forests, particularly Acacia decurrens, expanded from 0.4% of the area in 2000 to 28.13% by 2020, becoming the second-largest land cover type. The total ecosystem service value in the district declined from USD 219.52 million in 1985 to USD 39.23 million in 2020, primarily due to wetland degradation. However, plantation forests contributed USD 17.37 million in 2020, highlighting their significant role in restoring ecosystem services, particularly in erosion control, soil formation, nutrient recycling, climate regulation, and habitat provision. This study underscores the need for sustainable land management practices, including wetland restoration and sustainable plantation forestry, to enhance ecosystem services and ensure long-term ecological and economic sustainability.

Bulk Viscosity Analysis with New Holographic Dark Energy in f(R,T) theory

This paper represents the viscous circumstances to imitate new holographic dark energy behaviour in modified f(R, T ) gravity theory with a flat Friedmann-Robertson-Walker model with bulk viscosity. Here we assume bulk viscosity to be directly proportional to Hubble's parameter (ζ ∝ H), i.e., ζ = ζ0H, where ζ is assumed to be bulk viscosity coefficient and ζ0 is positive constant and H is Hubble’s parameter. In this particular model, we consider f(R, T ) = R + λT , where R represents the Ricci scalar, λ as a constant and T as trace of the energy-momentum tensor. The focus of this article majorly revolves around the concept that the negative pressure induced by bulk viscosity could potentially act as the driving force behind dark energy, contributing to the expansion of the universe. We precisely determine the scale factor’s primary solution and examine all possible conditions: deceleration as well as acceleration which contributes to the universe’s evolution. Depending on the values of the viscous terms, it has been observed that the model shows the decelerated period as well as the accelerated period. Later, we examine the diagnostic parameters, statefinder {r, s} to distinguish our model from the other existing dark energy models. Thus, a modified theory of gravity can explain the dark energy phenomenon in the presence of bulk viscosity.

Effect of Suction/Injection on Unsteady MHD Natural Convection Flow of Heat Mass Transfer in Porous Channel in the Presence of Soret Term

This research paper explores the effect of suction/injection on unsteady MHD natural convection flow of heat mass transfer in porous channel in the presence of Soret term. The governing partial differential equations are converted to non- dimensional forms and solved numerically by using unconditionally stable and convergent implicit finite difference method. A parametric study illustrating the influence of various physical parameters is performed. It is reported that the velocity profile increases as Soret term, Grashof number, Solutal Grashof number and Porous parameters values increase, while Magnetic field parameter decreases the velocity profile. The temperature profile rises by the influence in increasing values of Variable Thermal Conductivity and decreases by increasing values of Prandtl number and Radiation parameters. While concentration profile increase by the increasing values of Soret term and Chemical reaction. The dependence of the skin friction coefficient, rate of heat transfer and mass transfer on these parameter has been discussed.

Diagnosis and management of Canine Renal Cell Carcinoma with special reference to Shear Wave Elastography

This report focuses on the diagnosis and surgical management of unilateral renal cell carcinoma in a 7-year-old male intact German Shepherd dog. The dog was presented with fever, haematuria, inappetence, infrequent bouts of emesis, and progressive weight loss. Palpation revealed a hard, round mass in the right cranial abdomen. A presumptive diagnosis of unilateral renal neoplasm was made based on clinical signs, haematobiochemical analysis, and radiography. B-mode ultrasound examination demonstrated an enlarged right kidney extending up to the ventral midline. The kidney exhibited heterogenous echotexture, loss of renal architecture, and only a small healthy portion at the caudal pole. Point Shear Wave Elastography analysis revealed elevated values both in terms Shear Wave Velocity (m/sec) and Young’s Modulus Stiffness Value (kPa), indicating the presence of renal malignancy. To treat the condition, unilateral nephroureterectomy was performed under general anaesthesia. Histopathological examination confirmed the diagnosis of renal cell carcinoma. Consequently, it can be concluded that B-mode ultrasonography, Point Shear Wave Elastography, and nephroureterectomy played crucial roles in the successful diagnosis and surgical management of unilateral renal cell carcinoma.

Method to discriminate between localized and chaotic quantum systems

We study whether a generic isolated quantum system initially set out of equilibrium can be considered as localized close to its initial state. Our approach considers the time evolution in the Krylov basis, which maps the system's dynamics onto that of a particle moving in a one-dimensional lattice where both the energy in the lattice sites and the tunneling from one lattice site to the next are inhomogeneous. By tying the dynamical propagation in the Krylov basis to that in the basis of microstates, we infer qualitative criteria that allow distinguishing systems that remain localized close to their initial state from systems that undergo quantum thermalization. These criteria are system-dependent and involve the expectation values and standard deviations of both the coupling strengths between Krylov states and their energy. We verify their validity by inspecting two cases: Anderson localization as a function of dimension and the out-of-equilibrium dynamics of a many-body dipolar spin system. We finally investigate the Wigner surmise and the eigenstate thermalization hypothesis that have both been proposed to characterize quantum chaotic systems. We show that when the average value of the nondiagonal terms in the Lanczos matrix is large compared to their fluctuations and to the fluctuations of the energy expectation values, which typically corresponds to delocalized quantum systems according to our criteria, there can be level repulsion of eigenenergies (also known as spectral rigidity), similar to that of the Wigner-Dyson statistics of energy levels; and we also demonstrate that in the same regime, the expectation values of typical local observables only weakly vary as a function of eigenstates, an important condition for the eigenstate thermalization hypothesis. Our demonstration assumes that, in the chaotic regime, the observable is sufficiently diagonal in the basis of Krylov states. Published by the American Physical Society 2024

Determining the constant diffusion coefficient by Fourier series solution of the diffusion equation

The purpose of this study was to obtain the diffusion coefficient by calculating directly from the Fourier series solution of the diffusion equation, which has not been studied so far. The Fourier series solution is the sum of a steady-state solution and a transient solution. The steady-state solution is a linear function of distance. The transient solution is the product of a distance function and a time function. The Fourier sine series solution, a function of distance only, is negative for the steady-state solution. For the sublimation diffusion of disperse dye in paste into polyethylene terephthalate (PET) film using the film-roll method, the constant surface concentration and the diffusion distance were determined from the quadratic regression curve for the concentration distribution at a long time. The concentration distribution of the transient solution is a downwardly convex curve with negative values. The concentration distribution of the Fourier series solution is also a downwardly convex curve. The diffusion coefficient in the exponential term, a function of time only, was determined from the value of the exponential term obtained by the surface concentration and the diffusion distance. The constant diffusion coefficients determined from the Fourier series solution are reliable because they are very similar to those obtained from the error function solution and have excellent linearity of the linear regression lines for their Arrhenius plots.

Residual-based reduced order models for parameterized Navier–Stokes equations with nonhomogeneous boundary condition

In this paper, we propose a residual-based reduced-order model (ROM) framework that utilizes available data to increase the ROM accuracy and stability. The available snapshots are utilized to obtain the original ROM systems and their projection coefficients by performing proper orthogonal decomposition. Then a time-parameter varying closure term is added to the original ROM systems to obtain the new ROM systems, and the values of the closure term at discrete time-parameter points with respect to snapshots are evaluated by computing the residual of the original ROM systems with projection coefficients. In an online testing stage, the values of the closure term at unknown time-parameter points are approximated by linear interpolation, and the new ROM systems are utilized to approximate solutions for unseen parameter values. In addition, the closure term in the new ROM systems is instead discarded when we predict systems' evolution outside the time interval with respect to snapshots. Numerical results show that the proposed method not only improves the prediction accuracy of original ROM but also extends the applicability of it.

Repeatability of a Combined Adaptive Optics Visual Simulator and Hartman-Shack Aberrometer in Pseudophakic Eyes With and Without Previous Corneal Refractive Surgery.

To evaluate the intrasession repeatability of wavefront aberrations obtained by a combined adaptive optics visual simulator and Hartman-Shack aberrometer in pseudophakic eyes with and without previous corneal refractive surgery. Three consecutive measurements were performed in one eye of each individual. Total ocular aberrations were recorded up to the 5th Zernike order for a 4.5-mm pupil. Repeatability was assessed by calculating the within-subject standard deviation (Sw), the repeatability limit (R), and the intraclass correlation coefficient (ICC). Vector analysis was performed to assess astigmatism variability between scans. The study enrolled 32 normal individuals and 24 individuals with a history of refractive surgery. In normal and eyes that had previous refractive surgery, respectively, the Sw values were 0.155 and 0.176 diopters (D) for sphere and 0.184 and 0.265 D for cylinder. The Sw values for all 3rd order terms ranged from 0.037 to 0.047 µm in normal eyes and 0.044 to 0.063 µm in eyes that had previous refractive surgery. The Sw for primary spherical aberration was 0.020 µm in normal eyes and 0.026 µm in eyes that had previous refractive surgery. ICC values for measurements of astigmatism yielded larger variability (ICC = 0.751 and 0.879). However, both groups demonstrated excellent repeatability (ICC > 0.9) for root mean square higher order aberrations (RMS-HOA) and total RMS values. In pseudophakic eyes, the adaptive optics Hartmann-Shack device demonstrated acceptable repeatability for measurement of sphere and 3rd and 4th order HOAs with higher variability for astigmatism measurements, especially in eyes with a prior history of corneal refractive surgery. [J Refract Surg. 2024;40(9):e645-e653.].

Predictors of a positive attitude towards rural practice in female osteopathic medical students.

Women outnumber men in medical school. Given the growing need for rural physicians and the underrepresentation of women in rural medicine, understanding predictors of rural practice among female students is imperative for addressing future healthcare workforce shortages in rural areas. Utilizing current evidence, medical schools should seek to admit students with a rural background and interest in pursuing a primary care specialty; however, whether this holds true for female osteopathic medical students is unknown. This study aims to determine if a rural background, a plan to practice family medicine, and motivation toward civic duty are associated with attitudes toward eventual practice of rural medicine in female osteopathic medical students. An anonymous online survey was administered to actively enrolled female students at Arkansas Colleges ofHealth Education College of Osteopathic Medicine. The survey assessed the respondents' presence of a rural background, degree of civic-mindedness, intention to practice family medicine, and attitudes to rural work and life. Demographics of ethnicity and year of study in medical school were also collected. In total, 129 students responded to the survey, with 97 complete responses for analysis. Hierarchical regression was utilized to compare nested models and interpret interactions. Of the 97 survey respondents, 34.0 % described themselves as first-year students, 37.1 % as second-year students, 16.5 % as third-year students, and 12.4 % as fourth-year students. Linear regression modeling indicated that for female medical students at Arkansas Colleges of Health Education, having a rural background had no relationship with their attitude toward practicing in a rural setting, β=-0.97, standard error (SE)=1.96, t=-0.49, p>0.05, CI [-4.86, 2.92]. Civic-mindedness had a positive relationship with their attitude toward practicing in a rural setting, β=0.17, SE=0.07, t=2.44, p=0.016, CI [0.03, 0.31], accounting for 4.57 % of its variance. Plan to practice family medicine was positively associated with a student's attitude toward practicing in a rural setting, β=4.38, SE=0.85, t=5.15, p<0.001, CI [2.69, 6.07], accounting for 20.25 % of its variance. Civic-mindedness appeared to moderate the relationship between planning to practice family medicine and attitudes toward practicing in a rural setting, F(1, 91) = 3.91, p=0.05, R 2=0.31. The p value for this interaction term was 0.05, but its effect size measure and graphical representation revealed a substantive effect. The regression analysis showed that, for thewomen in this study, the greater the student's civic-mindedness, the more favorable her attitude toward practicing in a rural setting. Additionally, the stronger thestudent's plan to practice family medicine, the more favorable her attitude toward eventual rural practice was. Lastly, the student's civic-mindedness influenced the predictive value of having a plan to practice family medicine.

Parameterization of vacancy production rate in phase-field models of fission gas bubble evolution in nuclear fuel

Phase-field modeling has increasingly been used to study microstructural evolution in fission gas bubbles in nuclear fuel to improve understanding of fission gas release. To improve computational efficiency, often only vacancies and gas atoms are included as defect species. In this case, the net effects of vacancy and interstitial production, recombination, and biased sink absorption are included as a net vacancy source, or net vacancy source combined with an effective sink. However, there has been a lack of clarity on what parameter values should be used for these approaches to best match the more complete physical picture that includes interstitials and vacancies. Here, we compare a phase-field model of void growth to analytical models for the source-only and source plus sink approach to gain insight into how the phase-field models can be parameterized effectively. The source-only approach provides greater flexibility to match growth rates determined from the full vacancy-interstitial picture. A strategy was developed for determining the value of the net vacancy source term by comparing to an analytical model that includes vacancy and interstitial production, recombination, and biased sink absorption. This strategy can be used to parameterize phase-field models of fission gas bubble growth.

Improving fake news detection on social networks through a novel machine learning approach

Recent years have seen an increase in societal information, such as commercial advertisements, celebrity information, political news, etc., due to the growth of online social networks. Some social media sites including Facebook, Instagram, and Twitter, were impacted by Fake News (FN) spread by their users. Nevertheless, some individuals propagate false information using words, images, and videos to increase their connections and reputation. The most current information is unreliable and misleads other members on an online social network. Because FN is circulated to encourage users to trust disinformation, it’s hard for detection algorithms to recognize false information according to uploaded material. In this research, we will provide an autonomous false news detection strategy called Grey Wolf optimized Adaptive Bidirectional Gated Recurrent Unit (GWO+ABi-GRU) that can identify FN on Twitter. The TF-IDF method translates textual material into a mathematical representation that accurately captures the value of terms and their context in the dataset. We improve the overall efficiency of the BiGRU by applying this GWO, which leads to increased accuracy when spotting false news. The experimental examination of real-world data shows that the proposed FN detection strategy GWO+ABi-GRU outperforms traditional approaches regarding recall, accuracy, F1 score, and precision. This enhanced performance proves essential in preventing the circulation of false news on social media, protecting the integrity of information sources, and mitigating the potential damage caused by false information.

Analytical modeling of desublimation of a phase change material (PCM) in a porous medium with temperature-dependent volumetric heat sink and convection due to air-mixed vapor

The desublimation phase change heat and mass transfer process in a porous medium occurs during the conversion of vapor into solid form, which has several applications in chemical deposition and industrial coating. For economic feasibility, reducing the operating time of the conventional desublimation technique is of much interest. Toward this goal, current work presents a mathematical model for desublimation that accounts for a volumetric heat sink connected with temperature. A linear profile of the volumetric heat sink varying with temperature is modeled within the frozen region. Further, the rate of water vaporization (with mixed air) produces a convective term, which is also accounted for in the frozen region. Despite previous studies on desublimation phase change process, there is still insufficient mathematical modeling of this particular phenomena. The solution to the governing set of dimensionless partial differential equations is obtained analytically by employing the space-time transformation. Results indicate that the rate of desublimation process becomes faster with increasing the strength of the volumetric heat sink, which results in the reduction of the total operating time to desublimate of a phase change material. Higher values of the dimensionless temperature parameters also accelerate the desublimation process. On the other hand, a larger value of the convective term is found to slow down the desublimation process. The dimensionless moisture concentration profile in the vapor region increases with increasing the value of the Luikov number. Observations from this study are expected to aid in the fundamental design of processes including industrial coating, preservation of biological products, and evaporative deposition where desublimation plays a key role.

Study on load rejection test of pumped storage units

Abstract The rise rate of rotating speed, the maximum inlet pressure of the spiral casing and the minimum inlet pressure of the draft tube cone of unit 2 in Jinzhai pumped storage power station were analyzed when 50% and 100% of the rated load were rejected in this paper. The low pass filtering method (cut off frequency is 0.2 times of the frequency) was used to process the pressure data at the inlet of the spiral casing and the draft tube cone to retain the trend term. The peak to peak values (97% confidence) of the pressure pulsation term under different data durations were studied, which provided technical support for rational and accurate calculation of the maximum inlet pressure of the spiral casing and the minimum inlet pressure of the draft tube cone, and provided an example reference for the load rejection test analysis of pumped storage units.

Bond behavior of deformed rebar in concrete containing recycled brick aggregate and waste rubber

The reuse of aggregates and crumb rubber (CR) in concrete is gaining interest globally for reducing the adverse effects on the environment and maintaining construction sustainability. The bond strength of reinforcing rebars in such concrete is one of the key issues to be addressed before their practical application, particularly in structural elements. Pull-out tests were performed on 80 specimens to assess the bond performance of deformed rebars in rubberized recycled brick aggregate concrete (RRBAC). After investigating the strength properties of RRBAC, pull-out tests were performed on two sizes of cylindrical specimens. RBA%, CR%, rebar diameter (d), embedment length (le), and concrete cover-to-rebar diameter ratio (c/d) were among the test variables in this bond behavior investigation. Bond stress-slip relationships were obtained, examined, and average bond strengths were compared with the available codes. Concrete split failure was observed in 79% of the tested specimens, whereas rebar fracture was not seen in any of the tests. The bond strength was found to be decreased with the inclusion of RBAs and CRs though relative improvement was observed for higher percentage RBAs. Additionally, regression analysis was performed on the experimental data to produce a closed-form equation for forecasting the bond strength for RRBAC. With a strong coefficient of determination (R2 = 0.97) and low values of error terms, the predicted bond strengths were seen to be a good agreement with the test results.

Metricizing policy texts: Comprehensive dataset on China’s Agri-policy intensity spanning 1982–2023

Due to the lack of direct assessment metrics, existing studies on the intensity of agricultural policies often utilize indicators such as Gross Domestic Product (GDP) of agriculture or the quantity of agricultural policies as measures. Optimizing methods for analyzing the intensity of agricultural policies will significantly impact parameter selection in agricultural policy research and the evaluation of policy effectiveness. In this study, we constructed a Chinese Agricultural Policy Corpus using agricultural policies released by various governmental agencies at the national level in China from 1982 to April 2023. We quantified the values of agricultural domain terms in the corpus and evaluated the intensity of each agricultural policy document. The validation results of this study indicate a strong correlation between the intensity of agricultural policies and agricultural GDP. The trend in agricultural GDP changes lags behind policy intensity by 2.5 years (at a 95% confidence level), thus validating the rationality of our constructed corpus, agricultural policy scoring dataset, and methodology.

Extraction Optimization, Structure Analysis and Antioxidant Activity of Polysaccharide from Sanghuangporus baumii

Introduction: In this study, we optimized the extraction process, analyzed the structure and assessed the antioxidant activity of Sanghuangporus baumii polysaccharide (SBP). The present results provide important information for the Sanghuangporus baumii polysaccharides in potential natural antioxidant effects. Background: The extraction and structural analysis of polysaccharides from Sanghuangporus has gained significant attention in the fields of chemistry, medicine, and life sciences. There is great significance in maximizing the extraction of polysaccharides from Sanghuangporus and developing their potential products in a scientific and rational manner. Objective: The study was designed to establish an efficient and practical extraction process for SBP, and then investigated the structure and the antioxidant activity. Methods: The Response Surface Methodology (RSM) based on Box-Behnken design was used to explore the ultrasound-assisted extraction of SBP, and the structure of SBP was studied by ultraviolet spectroscopy, infrared spectroscopy and other instrumental analysis methods. The total antioxidant capacity of SBP was studied by the Ferric Reducing Ability of Plasma (FRAP) method, and the scavenging capacity of ABTS+·, DPPH· and OH· was carried out as the index to investigate its antioxidant activity in vitro. Results: The statistical analysis results showed that the optimal conditions for extracting SBP were an ultrasound time of 20.74 min, ultrasound power of 268.40 W and material-liquid ratio of 1:25.71. Under optimal conditions, the experimental yield of SBP was 3.36 ± 0.01%. The RSM optimization process was applied to the experiment of complex enzyme extraction of SBP, and the yield increased to 4.72 ± 0.03%. Structural analysis showed that SBP mainly consisted of glucose, a small amount of mannose and galactose, and the molecular weight distribution was uneven, mainly concentrating in the three parts of 24.5,6.4,2.5 kDa. Moreover, SBP exhibited dose-dependent and strong reducing power and radical scavenging activity. For DPPH·, ABTS+· and OH· radical scavenging assays, IC50 values were 1.505 ± 0.050 mg/ml, 0.065 ± 0.036 mg/ml and 0.442 ± 0.007 mg/ml, respectively. Conclusion: In the present study, a β-linked heteroglucan (SBP) was extracted using the optimized process combining enzymes from the fruiting bodies of Sanghuangporus baumii. SBP exhibited effective and dose-dependent antioxidant activities. Our findings were of great value in terms of developing polysaccharides with potential natural antioxidants.

Cosmological constraints on time-varying cosmological terms: A study of FLRW universe models with [formula omitted]CDM cosmology

This paper explores models of the FLRW universe that incorporate a time-varying cosmological term Λ(t). Specifically, we assume a power-law form for the cosmological term as a function of the scale factor: Λ(t)=Λ0a(t)-α, where Λ0 represents the present value of the cosmological term. Then, we derive an exact solution to Einstein’s field equations within the framework of Λ(t)CDM cosmology and determine the best-fit values of the model parameters using the combined H(z) + SNe Ia dataset and MCMC analysis. Moreover, the deceleration parameter demonstrates the accelerating behavior of the universe, highlighting the transition redshift ztr, at which the expansion shifts from deceleration to acceleration, with confidence levels of 1-σ and 2-σ. In addition, we analyze the behavior of the Hubble parameter, jerk parameter, and Om(z) diagnostic. Our analysis leads us to the conclusion that the Λ(t)CDM model is consistent with present-day observations.

Analyzing Lower Limb Dynamics in Human Gait Using Average Value-Based Technique

The motivation of this study is to develop effective and economical assistive technologies for people with physical disabilities. The novelty in this manuscript is the application of the average value-based technique to accurately represent the involved biomechanics of the lower limb joints during the human gait cycle. This mathematical formulation of lower limb joints’ biomechanics forms the first objective for modeling and final exoskeleton prototype development. To account for modeling the characteristics of human locomotion, the nth-order linear differential equation with constant coefficients is considered with appropriate modification. The physical characteristics of an individual are represented by the constant coefficients (P0, P1, P2, and P3) of the modified infinite series, which are obtained by processing experimental data collected using an optical technique. The differential terms of the infinite series are replaced by difference terms (δbavg, δ2bavg, and δ3bavg) since the data were captured as a set of digital values. The work presented here is based on the experimental results of individuals suitably categorized according to their physical nature like age and other physical structure. The optically monitored positional values of the lower limb joints of the individual subjects while they are completing the gait cycles are used for getting values of different terms of the model. The data collected through the conduct of experiments are used for finding the values of the terms of the differential equation. The model is effectively validated through experimental results. It was determined that the representation’s accuracy fell within the ±5% acceptable tolerance limit. The model is prepared for healthy as well as disabled persons, through which the disability is quantified. The resulting model can be used to develop assistive devices for people with physical disabilities. This results in the rehabilitation process and thereby helps the reintegration into society, subsequently allowing them to lead a normal life.

Short-term creep approach to redefining the role of 17-4PH stainless steel for high-temperature applications

The creep response of the 17-4PH martensitic age-hardening steel in H1150 state was investigated at 427 and 482 °C. Hardness measurements of the heads of the creep samples demonstrated that the material underwent additional age hardening during the high-temperature exposure. Microstructural investigations confirmed that the additional precipitation of carbides and the G-phase occurred at the lowest temperature. A set of constitutive equations previously developed to describe the creep response of particle-strengthened alloys was successfully used to obtain a comprehensive description of the experimental data. The value of the particle strengthening term was obtained from the hardness measurements and corresponded to the Orowan stress. The model accurately described the observed minimum creep rate dependence on the applied stress and explained the occurrence of lower values of the minimum strain rate observed during variable-load experiments.

An improved BRDF hotspot model and its use in VLIDORT for studying the impact of atmospheric scattering on hotspot directional signatures in the atmosphere

Abstract. The term “hotspot” refers to the sharp increase in the reflectance occurring when incident (solar) and reflected (viewing) directions almost coincide in the backscatter direction. The accurate simulation of hotspot directional signatures is important for many remote sensing applications. The RossThick–LiSparse–Reciprocal (RTLSR) bidirectional reflectance distribution function (BRDF) model is widely used in radiative transfer simulations, and the hotspot model mostly used is from Maignan–Bréon, but it typically requires large values of numerical quadrature and Fourier expansion terms in order to represent the hotspot accurately for its use coupled with atmospheric radiative transfer modeling (RTM). In this paper, we have developed a modified version based on the Maignan–Bréon's hotspot BRDF model that converges much faster numerically, making it more practical for use in the RTMs that require Fourier expansion of BRDF to simulate the top-of-atmosphere (TOA) hotspot signatures, such as in the RTM models using the Doubling–Adding or discrete ordinate method. Using the vector linearized discrete ordinate radiative transfer model (VLIDORT), we found that reasonable TOA–hotspot accuracy can be obtained with just 23 Fourier terms for clear atmosphere and 63 Fourier terms for atmosphere with aerosol scattering. In order to study the impact of molecular and aerosol scattering on hotspot signatures, we carried out a number of hotspot signature simulations with VLIDORT. We confirmed that (1) atmospheric molecule scattering and the existence of aerosol tend to smooth out the hotspot signature at the TOA and that (2) the hotspot signature at the TOA in the near-infrared is larger than in the visible, and its impact by surface reflectance is more significant. As the hotspot amplitude at the TOA with aerosol scattering included is smaller than that with molecular scattering only, the amplitude of hotspot signature at the surface is likely underestimated in the previous analysis based on the POLDER measurements, where the atmospheric correction was based on a single-scatter Rayleigh-only calculation. This modified model can calculate the amplitude of the hotspot accurately, and, as it agrees very well with the original RossThick model away from the hotspot region, this model can be simply used in conditions with and without hotspots. However, there are some differences in this modified model compared to the original Maignan–Bréon model for the scattering angles close to the hotspot point; thus, it may not be appropriate for those who need an exact representation of the hotspot angular signature.