Directional-hemispherical Reflectance Research Articles

Simultaneous estimation of leaf directional-hemispherical reflectance and transmittance from multi-angular canopy reflectance

Remote sensing retrieval of foliar biochemical traits via inversion of radiative transfer models is hampered by the uncertainties arising from the ill-posed problem of insufficient remote sensing information for the inversion. The use of leaf transmittance in addition to leaf reflectance in retrieving leaf traits could be a key step to alleviate this issue. To achieve this objective, our study introduces a novel theoretical framework for the simultaneous retrieval of leaf directional-hemispherical reflectance and transmittance, leveraging multi-angular optical observations at the canopy level. This framework partitions the canopy's spectral reflectance in the range of 400 nm to 2500 nm into two distinct components, each aligning with the contributions of 1st-order and multiple-order scatterings of radiation in the canopy. At a specific illumination-observation (IO) angle, these two scattering components are assumed to be determined by leaf hemispherical reflectance and scattering albedo (i.e., the sum of leaf reflectance and transmittance). The average leaf directional-hemispherical reflectance and transmittance can be estimated from combined canopy reflectance observed under different IO angles. The proposed framework was implemented using a single site data collected on August 19th, 2018, in Saihanba National Forest Park, Hebei, China. A comprehensive dataset was compiled, including hyperspectral images of a dense white birch canopy acquired at 8 different illumination-observation (IO) angles. This dataset was augmented with corresponding canopy structural traits, including leaf area index, diameter at breast height, crown radius, tree number, and domain size. Additionally, terrain features such as slope and aspect, along with leaf spectra and background spectra, were included in this extensive dataset. The geometrical-optical model GOST2 was utilized to establish the relationships between canopy reflectance and leaf reflectance and transmittance. Initially, the performance of GOST2 was evaluated, followed by the construction of a leaf spectral dataset generated by PROSPECT-D and input into GOST2 to construct the LUT. Subsequently, leaf reflectance and transmittance were estimated for different combinations of IO angles. The results demonstrated a close agreement between the canopy reflectance factors modelled by GOST2 and the observations obtained from UAV. Overall, leaf reflectance was more accurately retrieved than leaf transmittance across the entire spectrum of interest, primarily due to the significant influence of the 1st-order scattering in canopy reflectance. In the near-infrared region, where the magnitudes of 1st- and multiple-order scatterings were similar, the proposed framework produced satisfactory leaf transmittance with a relative error of <10% when compared to the measured reference data. Furthermore, the results indicated that the absolute error of model simulations should be less than half of the multiple-order scattering, which is particularly stringent for wavelengths characterized by strong absorption features. The proposed framework holds potential for reducing uncertainties in various fields, including global mappings of leaf biochemical traits.

Assessment of Directional-Hemispherical Reflectance of Tablets with Cefuroxime during Storage under Elevated Temperature and Ultraviolet Radiation.

Environmental conditions can lead to changes in the physical and chemical structures of drug products. In this study, the stability of cefuroxime tablets stored under adverse conditions was evaluated based on total directional-hemispherical reflectance (THR). The THR value was measured before and after the tablets' exposure to stress factors (temperature of 45 °C and UV radiation). Each measurement was performed three times within seven spectral bands at the beginning of the experiment (day 0), and then on days 1, 2, 3, 5, and 7. In addition, hyperspectral profiles (400-1030 nm) were analyzed on days 0 and 7. A significant decrease in THR values in all wavelength ranges was observed when day 7 vs. day 0 were compared, especially for spectral bands of 335-380 nm and 1700-2500 nm (Δ = 0.220, p < 0.001 and Δ = 0.171, p < 0.001, respectively). The hyperspectral analysis confirmed a decrease in the reflectance after the end of stress conditions in the visible light range (400-700 nm) compared to tablets before the experiment. This may indicate that more radiation entered the tablets. In conclusion, the THR of cefuroxime tablets decreases during the exposure to heat and UV radiation, which may result from some physicochemical changes that have occurred during storage.

Estimation of Oak Leaf Functional Traits for California Woodland Savannas and Mixed Forests: Comparison between Statistical, Physical, and Hybrid Methods Using Spectroscopy

Key leaf functional traits, such as chlorophyll and carotenoids content (Cab and Cxc), equivalent water thickness (EWT), and leaf mass per area (LMA), are essential to the characterization and monitoring of ecosystem function. Spectroscopy provides access to these four leaf traits by relying on their specific spectral absorptions over the 0.4–2.5 µm domain. In this study, we compare the performance of three categories of estimation methods to retrieve these four leaf traits from laboratory directional-hemispherical leaf reflectance and transmittance measurements: statistical, physical, and hybrid methods. To this aim, a dataset pooling samples from 114 deciduous and evergreen oak trees was collected on four sites in California (woodland savannas and mixed forests) over three seasons (spring, summer and fall) and was used to assess the performance of each method. Physical and hybrid methods were based on the PROSPECT leaf radiative transfer model. Physical methods included inversion of PROSPECT from iterative algorithms and look-up table (LUT)-based inversion. For LUT-based methods, two distance functions and two sampling schemes were tested. For statistical and hybrid methods, four distinct machine learning regression algorithms were compared: ridge, partial least squares regression (PLSR), Gaussian process regression (GPR), and random forest regression (RFR). In addition, we evaluated the transferability of statistical methods using an independent dataset (ANGERS Leaf optical properties database) to train the regression algorithms. Thus, a total of 17 estimations were compared. Firstly, we studied the PROSPECT leaf structural parameter N retrieved by iterative inversions and its distribution over our oak-specific dataset. N showed a more pronounced seasonal dependency for the deciduous species than for the evergreen species. For the four traits, the statistical methods trained on our dataset outperformed the PROSPECT-based methods. More particularly, statistical methods using GPR yielded the most accurate estimates (RMSE = 5.0 µg·cm−2; 1.3 µg·cm−2; 0.0009 cm; and 0.0009 g·cm−2 for Cab, Cxc, EWT, and LMA, respectively). Among the PROSPECT-based methods, the iterative inversion of this model led to the most accurate results for Cab, Cxc, and EWT (RMSE = 7.8 µg·cm−2; 2.0 µg·cm−2; and 0.0035 cm, respectively), while for LMA, a hybrid method with RFR (RMSE = 0.0030 g·cm−2) was the most accurate. These results showed that estimation accuracy is independent of the season. Considering the transferability of statistical methods, for the four leaf traits, estimation performance was inferior for estimators built on the ANGERS database compared to estimators built exclusively on our dataset. However, for EWT and LMA, we demonstrated that these types of statistical methods lead to better estimation accuracy than PROSPECT-based methods (RMSE = 0.0016 cm and 0.0013 g·cm−2 respectively). Finally, our results showed that more differences were observed between plant functional types than between species or seasons.

Micro-DRIFTS for small area hyper-black spectroscopy.

We have developed a low-cost micro-diffuse reflectance infrared Fourier transform spectroscopic (micro-DRIFTS) setup for measuring the reflectance of small area diffuse samples. The system performance is characterized and then demonstrated on small area vertically aligned carbon nanotube (VACNT) samples. We find that our system can measure samples with a spatial resolution of approximately 140 µm with sensitivities of 10s of ppm in the 2 µm - 18 µm spectral window. Our uncertainty budget is presented along with how our measured reflectance can be equated to directional-hemispherical reflectance.

Assessment of the photoprotection properties of hair cosmetics using the hemispherical directional reflectance method.

Solar radiation is responsible for changes in the structure of human hair, the damages include proteins (65%-95%), lipids, and melanin. The aim was to examine the effectiveness of sunscreen in hair cosmetics and whether hair color affects it. The study included nine women, divided according to hair color to three groups: light, dark, and gray hair. The 410-Solar reflectometer was used in five time points. The hair was divided into three strands, one product applied to each. Dark hair showed the highest absorption of radiation in all wavelength ranges, the reflectance before products application was significantly higher than the hair reflectance immediately after application. The effect of sunscreens on light hair reflectance was found at wavelengths 400 and 720nm and between 1000 and 2500nm, the reflectance before application was significantly higher than the reflectance after. The use of products on gray hair did not have a significant effect on hair reflectance at wavelengths 400-1100nm, the effect of sunscreens on the gray hair reflectance was observed in the UV and infrared range, the reflectance before application was significantly higher than immediately after. The results showed that the 410-Solar reflectometer is useful to assess the effectiveness of hair sunscreens. All three tested hair products do not show the expected protection properties. Dark hair showed the highest absorption of radiation in all wavelength ranges, suggesting that dark hair should be more protected against radiation than light and gray hair.

Effect of Narrow-Band Ultraviolet B Therapy of Psoriasis Vulgaris on Skin Directional Reflectance, Skin Density and Epidermal Thickness

Psoriasis is an inflammatory dermatosis manifested by the appearance of brown-red papules on the body, covered with silver scales. One of the most common and effective treatments for psoriasis is narrow-band UVB phototherapy. Narrow-band UVB has a wavelength of 311 nm, which results in shallow skin penetration, is absorbed only by the epidermis and the superficial layers of the dermis. The aim of the study was to assess the effect of narrow-band UVB 311 nm phototherapy on skin covered with psoriatic scales and without psoriatic lesions in patients with psoriasis vulgaris on the total directional hemispherical reflectance (DHR) of the skin, skin density and epidermis thickness. For this purpose, a 410 Solar DHR reflectometer and high-frequency ultrasonography DUB SkinScanner were used. A total of 48 volunteers were enrolled. There was a difference in the reflectance of skin without psoriatic scales and psoriatic skin. Depending on the wavelength range, the skin was characterized by different reflectance values. During the course of phototherapy, the reflectance values decreased, both in the psoriatic skin and skin without psoriatic scales. After the phototherapy, the epidermis thickness and SLEB layer decreased and skin density increased in the area with psoriatic plaque. The density of the skin without psoriasis after a series of 20 irradiations increased, while the thickness of the epidermis did not change.

PIOSL: An improved version of PROSPECT model for simulating leaf optical properties by considering leaf internal structural variations

Leaf radiative transfer simulation is an important tool for studying the quantitative relationships between plant biochemical parameters and leaf spectra, at the leaf scale. This type of simulation can be used to investigate leaf structures and their biochemical parameters with regard to reflectance and transmittance, and can produce mathematical representations of the radiative transfers of leaves. Most current radiative transfer models represented by PROSPECT are based on the assumption that all leaf interiors are turbid and homogeneous, ignoring the impacts of leaf layer structures on their spectra. A leaf is composed of two heterogeneous layers, we assume that the optical properties of each layer are different. A PIOSL (PROSPECT considering the internal optical structure of leaves) model was proposed, with the assumption that a leaf is composed of two stacked plates with different biochemical parameters and structures. The PIOSL model was used to simulate the directional-hemispherical reflectance of plant leaves for four publicly available datasets. The structural parameters and biochemical contents of the two layers used in the simulation were determined using the bald eagle search optimization algorithm. The results showed that the structural parameters of the first layer were generally higher than those of the second layer in leaves of different plant species; chlorophyll was mainly distributed in the upper layer, while water and dry matter were concentrated in the lower layer—although some plant species showed different trends. PIOSL outperformed PROSPECT-4 to simulate leaf optical properties of various plant species.We therefore concluded that the PIOSL model better explains the responses of leaf biochemical parameters to leaf spectra, and provides a new strategy for modeling the leaf radiative transfer process.

Reflection of Solar Light from Surface Snow Loaded with Light-Absorbing Impurities: A Case Study of Black Carbon, Mineral Dust, and Ash.

Using a hemispherical directional reflectance factor instrument, spectral data of dirty snow containing black carbon (BC), mineral dust (MD), and ash was collected from multiple locations to investigate the impact of these light-absorbing impurities (LAIs) on snow reflectance characteristics. The findings revealed that the perturbation of snow reflectance caused by LAIs is characterized by nonlinear deceleration, indicating that the reduction in snow reflectance per unit ppm of LAIs declines as snow contamination increases. The reduction in snow reflectance caused by BC may reach saturation at elevated particle concentrations (thousands of ppm) on snow. Snowpacks loaded with MD or ash initially exhibit a significant reduction in spectral slope around 600 and 700 nm. The deposition of numerous MD or ash particles can increase snow reflectance beyond the wavelength of 1400 nm, with an increase of 0.1 for MD and 0.2 for ash. BC can darken the entire measurement range (350-2500 nm), while MD and ash can only affect up to 1200 nm (350-1200 nm). This study enhances our understanding of the multi-angle reflection characteristics of various dirty snow, which can guide future snow albedo simulations and improve the accuracy of LAIs' remote sensing retrieval algorithms.

Characteristics of Commercial Effervescent Tablets Using Selected Pharmacopeial and Novel Analytical Methods

In the present study, we aimed to determine whether the shelf life of effervescent tablets may be assessed during storage using total directional hemispherical reflectance (THR). We also analyzed selected pharmacopeial parameters of the tablets and used X-ray microtomography to assess the internal structure of the tablets. Two types of effervescent tablets of one commercial product containing magnesium and vitamin B6 (expired and unexpired) were analyzed. In addition, randomly selected unexpired and expired tablets were dried in a vacuum oven for 24 h at 50 °C. The expired effervescent tablets disintegrated in a significantly shorter time than the unexpired tablets (68 s vs. 83 s, p = 0.016). The remaining pharmacopeial parameters did not differ between the two types of tablets. We observed that expired effervescent tablets showed lower mean values of THR in five spectral ranges, which indicates that a greater amount of radiation beam was transmitted into their inner structure than for unexpired tablets. The density of the inner structure assessed on the microtomographic scans differed significantly between all the analyzed tablets (p &lt; 0.001). The highest mean density was observed in the case of the unexpired tablets dried in a vacuum oven (1.273 g/cm3), while the lowest density was observed in the case of the expired tablets (1.261 g/cm3). The expired tablets had a larger pore diameter compared to the unexpired tablets (0.095 mm vs. 0.074 mm, respectively; p = 0.007). Additionally, the percentage of porosity was higher in the expired tablets compared to the unexpired tablets (p &lt; 0.001).

Use Directional-Hemispherical Reflectance to Identify Female Skin Features in Response of Microdermabrasion Treatment

Diamond microdermabrasion is one of the most popular cosmetological treatments in the field of mechanical, controlled abrasion of the stratum corneum corneocytes. In this study, the influence of micropeeling on the optical properties of the skin features was investigated. The directional reflectance of the skin was measured before and after the procedure. The study involved 15 women aged 23–26. The tests were performed on the surface of the skin in 15 spots—on the forearms, arms and lower legs. Post-treatment reflectance increased significantly in the wavelength range of 700–2500 nm. In the remaining ranges it also increased, except for the range 480–600 nm, in which it decreased, but insignificantly. It was found that the optical properties of the skin after microdermabrasion changed, the directional reflectance of the skin increased, especially in the infrared range. The main conclusion from the conducted research is that the directional-hemispherical reflectance method can be used to identify female skin features in response of microdermabrasion treatment.

Prediction of high-temperature infrared radiative properties of nickel foam ligaments

High-temperature radiative properties of open-cell foam ligaments are rather sparse due to measurement limitation. This study aims to numerically predict the infrared radiative properties of nickel foam ligaments at high temperatures. In this work, rough surfaces of ligaments are modeled with SEM scanning pictures, and optical properties of nickel components are simulated using ab initio molecular dynamics method at 298 K, 673 K, 873 K, 1073 K and 1273 K. The reflectivity of smooth surface is determined with empirical formulas at high temperatures. Moreover, the spectral radiative properties of nickel foam ligaments are predicted with finite difference time domain method at the waveband of 0.8–8.5 μm based on the modeled surfaces and high-temperature optical properties of components. It is found high temperature can marginally strengthen radiation scattering of the ligament surfaces, while having little effect on the distribution of radiation scattering. For instance, the directional-hemispherical reflectivity increases approximately linearly with temperature. As the incident wavelength grows, the directional-hemispherical reflectivity and proportion of specular reflection both show a rapid increase in the studied waveband, while the value of reflection main peak of directional-hemispherical reflectivity declines. With the growth of incident angle, the center position of main reflection peak is moving to the direction of increasing angles. Polynomial fit is applied to anticipate the relationship between proportion of specular reflection and incident wavelength with a RSME less than 0.02. This work demonstrates a practical method for obtaining the infrared radiative properties of open-cell metal foam ligaments at high temperatures.

The Use of Novel, Rapid Analytical Tools in the Assessment of the Stability of Tablets—A Pilot Analysis of Expired and Unexpired Tablets Containing Nifuroxazide

In the analysis of finished pharmaceutical products, numerous innovative analytical techniques are often used, i.e., Raman spectroscopy, scanning electron microscopy, computer microtomography, directional hemispherical reflectance, and hyperspectral analyses. These techniques allow for the identification of changes in solid phases. Many advantages over other techniques can be attributed to these techniques, e.g., they are rapid, non-destructive, and comprehensive. They allow for the identification of changes occurring in solid phases. However, the above-mentioned methods are still not standard procedures in pharmaceutical research. The present study aimed to assess the possible usefulness of total directional hemispherical reflectance (THR), hyperspectral imaging, and computer microtomography to evaluate the stability of tablets containing nifuroxazide during storage. In the study, expired and unexpired coating tablets containing nifuroxazide (n = 10 each) were analyzed. In addition, four unexpired tablets were stored at 40°C over 3 months (stressed tablets). Reflectance was determined with seven wavelength bands from 335 nm to 2500 nm using an SOC-410 Directional Hemispherical Reflectometer (Surface Optics Corporation, San Diego, CA, USA). A Specim IQ hyperspectral camera (Spectral Imaging Ltd., Oulu, Finland) was used with a wavelength range of 400–1030 nm. Tablets were also scanned using X-ray microtomography (Phoenix vǀtomeǀx, GE Sensing &amp; Inspection Technologies GmbH, Wunstorf, Germany). The results indicated that total reflectance was lower in expired tablets than in unexpired tablets in all spectral bands, except for 700–1100 nm and 1700–2500 nm. In turn, the stressed tablets showed higher THR values than expired tablets in all spectral bands, except for 1000–1700 nm. In addition, hyperspectral analysis of the homogeneity of the tablets, as well as X-ray microtomographic analysis of tablet density and coating thickness, indicated that these parameters differed significantly between the analyzed tablets.

Two-color pyrometry for backface temperature and emissivity measurement of burning materials

Two-color (2C) pyrometry has long been used for flame temperature and soot concentration studies and is now becoming more widely used to measure backface temperatures of burning materials. With the obvious advantage of being a contact-free method that requires only minimal optical access, 2C pyrometry combined with high-speed acquisition is a promising diagnostic tool to obtain exceptional temporal and spatial resolution of thermally degrading samples. However, its conceptual simplicity relies on a set of basic assumptions that when violated can result in large errors. In this work, we used an experimental configuration representative for fire resistance testing for aerospace and naval applications to analyze the impact of camera parameters and test setup on the accuracy of the surface temperature results obtained. Two types of fiber reinforced polymer composites and a steel plate are used to investigate material specific aspects that affect the measurements. An improved workflow for camera calibration is presented that takes into account the actual experimental setup. The temperature and emissivity mapping obtained through in-situ IR measurements is compared to data acquired through thermocouples and post-fire hemispherical directional reflectance measurements at room temperature. Excellent agreement is found for post-processed 2C pyrometry measurements and TC probe measurements with an uncertainty of 30 °C at 500 °C. In-situ emissivity mappings of burnt specimens are consistent with data from the literature for degraded composite samples and oxidized steel plates. Our results remind the importance of proper post-processing and demonstrate the potentials of 2C pyrometry for fire testing applications. We also present a detailed error budget and suggestions for calibration measurements to improve measurement accuracy.

Prediction of spectral radiative property based on the microscopic ligament morphology and pore-level structure of open-cell alumina foam

In this work, based on the complete structure model consisting of microscopic ligament morphology and pore-level structure, a trans-scale analysis method is presented for accurately predicting the spectral radiative properties of open-cell ceramic foams. The characteristic models of microscopic ligament morphologies are obtained by the SEM technique, while the network structure of ligaments is reconstructed by the μ-CT technique. According to the SEM data, the microscopic statistical models are developed for the rough surfaces and the internal porous media of ligaments. Additionally, based on the statistical models, the FDTD method is employed to analyze the spectral radiative transfer behaviors on the surfaces and inside the ligament media. The spectral directional-hemispherical reflectivity and specularity parameter for the ligament surface, as well as the extinction coefficient, the scattering albedo and the scattering phase function for the ligament medium are extracted from the FDTD simulations. The above parameters are used as the input data for the pore-level simulations of spectral radiative transfer inside the ligament network, where the Monte Carlo method is conducted. The apparent spectral absorptivity and reflectivity, as well as the equivalent volumetric spectral radiative properties of alumina foam sheets are predicted by the presented trans-scale analysis method. The trans-scale predicting method is verified and compared with the single pore-level simulations of radiative transfer inside alumina foams. The spectral radiative characteristics of alumina foams are analyzed for various wavelengths and incident angles. From the analysis, only when the specularity parameter is properly chosen, the pore-level simulation is also reliable for predicting the spectral radiative properties of ceramic foams.

The Use of Hemispherical Directional Reflectance to Evaluate the Interaction of Food Products with Radiation in the Solar Spectrum.

Food product packaging should block light to protect nutrients, color and active ingredients in functional food from degradation. Currently, packages are not optimized in terms of the solar radiation impact on the products they contain. The aim of this study was to develop a method of quantifying the interaction of food products with solar radiation, which would enable the optimization and selection of packaging that would protect the product from the spectral range specifically absorbed by it. In order to determine the reflectance of chocolate, the total reflectance ratio was measured. For this purpose, a SOC 410 Solar DHR reflectometer from Surface Optics Corporation, San Diego, CA, USA was used. Directional reflectance was measured for seven discrete spectral ranges from 335 to 2500 nm, which correspond to the spectrum of solar radiation. The value of total reflectance for chocolate differed significantly in the studied spectral ranges. The highest reflectance ratio, averaged for all the tested chocolate, was recorded for the spectral range 700–1100 nm and the lowest for the 335–380 nm range. The total reflectance was significantly correlated with the cocoa content and the brightness of the chocolate. The proposed method of hemispheric directional reflectance enables the measurement of the total reflectance of food products. It can be used as a measure of exposure to radiation. Thus, it is possible to design a package that will protect the product from the spectral range that is most harmful for it.

Temperature-dependent spectral emittance of bauxite and silica particle beds

ABSTRACT Bauxite and silica particles are candidate materials for solar thermal energy storage at high temperatures. The temperature-dependent emittance of packed beds with bauxite and silica particles was measured using a newly upgraded emissometer at wavelengths 2 μm ≤ λ ≤ 16 μm and temperatures up to ~730 K. The room-temperature emittance was obtained from the measured directional-hemispherical reflectance. A fused silica disc was used to test the emissometer by comparing the measured spectral emittance with the calculated emittance from a fitted Lorentz oscillator model. For the polycrystalline silica particles and the fused silica disc, the measured emittance increases with temperature in the mid-infrared region. The underlying mechanism is interpreted as the temperature-dependent damping coefficient in the Lorentz oscillator model. Two types of bauxite particles with different compositions and sizes were investigated. For λ > 10 μm, the measured emittance at elevated temperatures is higher than that at room temperature. In the region 2 μm < λ < 6 μm, the temperature dependence varies for different types of particles. The total emittance of bauxite particle beds was calculated by spectral integration using Planck’s distribution at the prescribed temperature. The calculated total emittance is between 0.89 and 0.96, but it does not change monotonically with temperature.

Airborne measurements of directional reflectivity over the Arctic marginal sea ice zone

Abstract. The directional reflection of solar radiation by the Arctic Ocean is mainly shaped by two dominating surface types: sea ice (often snow-covered) and open ocean (ice-free). In the transitional zone between them, the marginal sea ice zone (MIZ), the surface reflection properties are determined by a mixture of the reflectance of both surface types. Retrieval methods applied over the MIZ need to take into account the mixed directional reflectivity; otherwise uncertainties in the retrieved atmospheric parameters over the MIZ may occur. To quantify these uncertainties, respective measurements of reflection properties of the MIZ are needed. Therefore, in this case study, an averaged hemispherical–directional reflectance factor (HDRF) of the inhomogeneous surface (mixture of sea ice and open ocean) in the MIZ is derived using airborne measurements collected with a digital fish-eye camera during a 20 min low-level flight leg in cloud-free conditions. For this purpose, a sea ice mask was developed to separate the reflectivity measurements from sea ice and open ocean and to derive separate HDRFs of the individual surface types. The respective results were compared with simulations and independent measurements available from the literature. It is shown that the open-ocean HDRF in the MIZ differs from homogeneous ocean surfaces due to wave attenuation. Using individual HDRFs of both surface types and the sea ice fraction, the mixed HDRF describing the directional reflectivity of the inhomogeneous surface of the MIZ was retrieved by a linear weighting procedure. Accounting for the wave attenuation, good agreement between the average measured HDRF and the constructed HDRF of the MIZ was found for the presented case study.

Laboratory intercomparison of solar absorptance and thermal emittance measurements at room temperature

Solar thermal absorber coatings play an important role in the opto-thermal efficiency of receivers in Concentrated Solar Power (CSP). Two standard figures of merit are the solar absorptance αsol and thermal emittance εth, derived from spectral directional hemispherical reflectance measurements at room temperature. These two figures of merit allow comparing coating formulations in terms of performance and durability. In this study, a black coating and a solar selective coating are optically characterized by different laboratories to compare spectral datasets, solar absorptance αsol and thermal emittance εth calculations. The comparison includes various benchtop spectrophotometers operating in the UV-VIS-NIR and Infrared spectral ranges as well as three commercial portable reflectometers/emissometers. A good agreement is found between the nine parties participating in this intercomparison campaign. The black coating αsol value is 96.6 ± 0.2%, while the solar selective coating αsol value is 94.5 ± 0.4%. For the thermal emittance, spectral data is concatenated and integrated from 0.3 to 16 μm. The black coating εth value calculated at 650 °C is 80.8 ± 3.8%, while the solar selective coating εth value calculated at 650 °C is 25.0 ± 0.5%.

PROSPECT-PMP+: Simultaneous Retrievals of Chlorophyll a and b, Carotenoids and Anthocyanins in the Leaf Optical Properties Model.

The PROSPECT leaf optical radiative transfer models, including PROSPECT-MP, have addressed the contributions of multiple photosynthetic pigments (chlorophyll a and b, and carotenoids) to leaf optical properties, but photo-protective pigment (anthocyanins), another important indicator of vegetation physiological and ecological functions, has not been simultaneously combined within a leaf optical model. Here, we present a new calibration and validation of PROSPECT-MP+ that separates the contributions of multiple photosynthetic and photo-protective pigments to leaf spectrum in the 400–800 nm range using a new empirical dataset that contains multiple photosynthetic and photo-protective pigments (LOPEX_ZJU dataset). We first provide multiple distinct in vivo individual photosynthetic and photo-protective pigment absorption coefficients and leaf average refractive index of the leaf interior using the LOPEX_ZJU dataset. Then, we evaluate the capabilities of PROSPECT-MP+ for forward modelling of leaf directional hemispherical reflectance and transmittance spectra and for retrieval of pigment concentrations by model inversion. The main result of this study is that the absorption coefficients of chlorophyll a and b, carotenoids, and anthocyanins display the physical principles of absorption spectra. Moreover, the validation result of this study demonstrates the potential of PROSPECT-MP+ for improving capabilities in remote sensing of leaf photosynthetic pigments (chlorophyll a and b, and carotenoids) and photo-protective pigment (anthocyanins).

Spectral Radiative Properties of Polydispersed SiO2 Particle Beds

The focus of this work is on the measurement and analysis of the radiative properties of polycrystalline particle beds with various layer thicknesses. The particles are polydispersed with average diameters of 222, 150, and . The spectral, directional–hemispherical reflectance and transmittance of the particle bed are measured at wavelengths from 0.4 to using a monochromator, and the reflectance measurement is extended to using a Fourier-transform infrared spectrometer. Particles are closely packed between two transparent windows for measuring the radiative properties. In the visible and near-infrared region up to , the inverse adding–doubling method yields the effective absorption and scattering coefficients. The results suggest that short wavelength absorption needs to be included in modeling the behavior of particle beds due to multiple scattering. A discrete-scale Monte Carlo ray-tracing method is developed to model the radiative properties by assuming monodispersed spherical particles, and the simulated results compare well with measurements. The effective absorption and scattering coefficients of the particle beds obtained from the independent scattering theory are compared to those from the inverse method. The impact of dependent scattering on the packed beds is observed for smaller-sized particles.