Principal Planes Research Articles

Improving the standard protocol for above-water reflectance measurements: 1. Estimating effective wind speed from angular variation of sunglint.

The standard above-water protocol for measurement of water reflectance uses a measurement of wind speed to estimate the air-water interface reflectance factor and, thus, remove reflected skylight from upwelling radiance. This aerodynamic wind speed measurement may be a poor proxy for the local wave slope distribution in cases such as fetch-limited coastal and inland waters and/or where there are spatial or temporal differences between the wind speed measurement and the location of reflectance measurements. Here, an improved method is proposed, with a focus on sensors mounted on autonomous pan-tilt units and deployed on fixed platforms, replacing the aerodynamic wind speed measurement by optical measurements of angular variation of upwelling radiance. Using radiative transfer simulations, it is shown that the difference between two upwelling (i.e.,water plus air-water interface) reflectances acquired at least 10° apart from each other in the solar principal plane is strongly and monotonically related to effective wind speed. The approach shows good performance in twin experiments using radiative transfer simulations. Limitations of the approach are identified, including difficulties for a very high Sun zenith angle (>60∘), very low wind speed (<2m s -1), and, potentially, cases in which nadir-pointing angles are limited by optical perturbations from the viewing platform.

A Machine Learning Approach to Derive Aerosol Properties from All-Sky Camera Imagery

We propose a methodology to derive the aerosol optical depth (AOD) and Angstrom exponent (AE) from calibrated images of an all-sky camera. It is based on a machine learning (ML) approach that establishes a relationship between AERONET measurements of AOD and AE and different signals derived from the principal plane radiance measured by an all-sky camera at three RGB channels. Gaussian process regression (GPR) has been chosen as machine learning method and applied to four models that differ in the input choice: RGB individual signals to predict spectral AOD; red signal only to predict spectral AOD and AE; blue-to-red ratio (BRR) signals to predict spectral AOD and AE; red signals to predict spectral AOD and AE at once. The novelty of our approach mostly relies on obtaining a cloud-screened and smoothed signal that enhances the aerosol features contained in the principal plane radiance and can be applied in partially cloudy conditions. In addition, a quality assurance criterion for the prediction has been also suggested, which significantly improves our results. When applied, our results are very satisfactory for all the models and almost all predictions are close to real values within ±0.02 for AOD and ±0.2 for AE, whereas the MAE is less than 0.005. They show an excellent agreement with AERONET measurements, with correlation coefficients over 0.92. Moreover, more than 87% of our predictions lie within the AERONET uncertainties (±0.01 for AOD, ±0.1 for AE) for all the output parameters of the best model. All the models offer a high degree of numerical stability with negligible sensitivities to the training data, atmospheric conditions and instrumental issues. All this supports the strength and efficiency of our models and the potential of our predictions. The optimum performance shown by our proposed methodology indicates that a well-calibrated all-sky camera can be routinely used to accurately derive aerosol properties. Together, all this makes the all-sky cameras ideal for aerosol research and this work may represent a significant contribution to the aerosol monitoring.

Simple and accurate method for determining lens focal length

A simple and accurate method for determining the focal length of a lens is presented. There is no need to know the distance between lens principal planes and can be performed with easily available and inexpensive hardware. Depending on the test lens (TL) f-number, the error on determining focal length can be in the order of 0.1% of the focal length. We discuss determining focal length with the Newton equation f2 = zz ′ , with the Bessel equation f = ( (L − PP)2 − D2 ) / 4 ( L − PP ) , with equation f2 = y ′ ( y + y ′ ) , or with equation f = ( y2 − PP2 ) / 4PP.

Structure and mobility of -type screw dislocation in presence of H in α-Ti from first-principles

Hydrogen has both negative and positive effects on the mechanical properties of titanium and titanium alloys. It has been reported that the plastic deformation of titanium is controlled by the <a>-type screw dislocation and the principal slip plane is the prismatic plane. Herein, we employ first-principles calculations to investigate the modification of the <a>-type screw dislocation core structures caused by addition of H and the interactions between them. It reveals that H is attracted to the pyramidal dislocation partial and tends to segregate to the dislocation region. Then, the slip paths of the <a> screw dislocations along different slip planes in the H inserted Ti system are studied. Furthermore, the mechanism on how H affects the strength and plasticity of Ti under different H concentrations through the change of dislocation mobility is discussed.

Study of Static Flexural Strength Anisotropy of Yttrium Calcium Oxyborate Crystals

As a promising optical and piezoelectric crystal, yttrium calcium oxyborate (YCOB) has been criticized for its easy fracture during both the cooling and machining processes. Herein, in order to evaluate the mechanical energy (G) required for crack propagation on one crystal plane, we measured the bending strength of the YCOB samples with different orientations via employing a three-point bending test. The surface topography of the polished sample was measured, and the average surface roughness is limited to 10 nm. Fracture surfaces were also observed and analyzed. The results showed that the bending strengths of Y-cut and Z-cut samples were higher than other cut directions in the XZ principal plane, showing obvious anisotropy. It can be found that the cleavage planes (2¯01) and (101) were always observed in fractured samples in multiple directions in the XZ principal plane. The contribution of the cleavage planes (2¯01) and (101) to the fracture of the specimens was discussed in detail by the theorem of energy minimum. Finally, based on the obtained scanning electron microscopy results, we propose the mechanism for crack advance in YCOB crystals. A perfectly brittle crack in a crystal prefers cleavage planes with low surface energy. It is believed that these findings may provide fresh ideas to overcome the cleavage fracture of larger size YCOB crystals.

Crystal orientation-dependent tensile mechanical behavior and deformation mechanisms of zinc-blende ZnSe nanowires

Crystal deformation mechanisms and mechanical behaviors in semiconductor nanowires (NWs), in particular ZnSe NWs, exhibit a strong orientation dependence. However, very little is known about tensile deformation mechanisms for different crystal orientations. Here, the dependence of crystal orientations on mechanical properties and deformation mechanisms of zinc-blende ZnSe NWs are explored using molecular dynamics simulations. We find that the fracture strength of [111]-oriented ZnSe NWs shows a higher value than that of [110] and [100]-oriented ZnSe NWs. Square shape ZnSe NWs show greater value in terms of fracture strength and elastic modulus compared to a hexagonal shape at all considered diameters. With increasing temperature, the fracture stress and elastic modulus exhibit a sharp decrease. It is observed that the {111} planes are the deformation planes at lower temperatures for the [100] orientation; conversely, when the temperature is increased, the {100} plane is activated and contributes as the second principal cleavage plane. Most importantly, the [110]-directed ZnSe NWs show the highest strain rate sensitivity compared to the other orientations due to the formation of many different cleavage planes with increasing strain rates. The calculated radial distribution function and potential energy per atom further validates the obtained results. This study is very important for the future development of efficient and reliable ZnSe NWs-based nanodevices and nanomechanical systems.

Ultrabroadband OPA in YCOB with a sub-ps Pump Source

We demonstrate the broadband optical parametric amplification of near-infrared laser pulses using a single yttrium calcium oxyborate (YCOB) crystal pumped in a noncollinear geometry by a sub-picosecond, milijoule-level source. The crystal uses an optimized orientation for phase matching outside of the principal planes, enabling ultrabroadband amplification (gain of ∼800) in the range of 750–950 nm and supporting down to 7 fs pulses.

An accurate determination of the refractive indices of water and glass by smartphone photography

A smartphone can be used for many physics experiments by using the sensors built into the phone. The complementary metal oxide semiconductor (CMOS) (charge-coupled device, CCD) sensor of the camera records the images of objects photographed in pixels. The width of the image can be read off with micron level accuracy with the help of software available freely from the internet. If the dimensions of the object in the direction transverse to the viewing direction of the camera are known, the magnification of the object photographed can be determined accurately. A smartphone camera is a compound lens comprising a number of very thin lenses. A single thin lens is equivalent, as far as the transverse magnification is concerned, to a compound lens of the smartphone, when the thin lens has the same focal length as the effective focal length of the compound lens and is placed at its first principal plane. This property allows us to find experimentally the effective focal length of the compound lens of the camera accurately, using the thin lens equation. Once the focal length of the camera is known, the distance of an object can be determined by finding its magnification from the photograph. We have determined the refractive index of water accurately by photographing the apparent position of an object immersed in it. By determining the magnifications, we have found the real and apparent depths of the object. The ratio of these depths gives the refractive index. We have determined the refractive index of glass also using some thin glass slides.

The effects of surface roughness on the calculated, spectral, conical–conical reflectance factor as an alternative to the bidirectional reflectance distribution function of bare sea ice

Abstract. The conical–conical reflectance factor (CCRF) has been calculated as an alternative to the bidirectional reflectance distribution function (BRDF) for three types of bare sea ice with varying surface roughness (σ= 0.1–10) and ice thicknesses (50–2000 cm) over an incident solar irradiance wavelength range of 300–1400 nm. The comprehensive study of the CCRF of sea ice presented here is paramount for interpreting sea ice measurements from satellite imagery and inter-calibrating space-borne sensors that derive albedo from multiple multi-angular measurements. The calculations performed by a radiative-transfer code (PlanarRad) show that the CCRF of sea ice is sensitive to realistic values of surface roughness. The results presented here show that surface roughness cannot be considered independently of sea ice thickness, solar zenith angle and wavelength. A typical CCRF of sea ice has a quasi-isotropic reflectance over the hemisphere, associated with a strong forward-scattering peak of photons. Surface roughness is crucial for the location, size and intensity of the forward-scattering peak. As the surface roughness increases, a spreading of the CCRF peak is observed. The hemisphere was split in to 216 quadrangular regions or quads. The peak remains specular for the smaller surface roughnesses (σ=0.001 to σ=0.01), whereas for larger surface roughness features (above σ=0.05), the peak spreads out over multiple quads with a lower intensity than for smaller roughness features, and the highest value is displaced further out on the solar principal plane. Different types of sea ice have a similar pattern with wavelength: the CCRF increases by 30 % from first-year sea ice to multi-year sea ice at 400 nm and up to 631 % at 1100 nm, 32 % from melting sea ice to multi-year sea ice at 400 nm and a maximum of 98 % at 900 nm, and 11 % from melting sea ice to first-year sea ice at 400 nm and up to 86 % at 800 nm. The CCRF calculations presented in this study form the first set of complete CCRF values as an approximation of the BRDF for bare sea ice with a wide range of configurations.

Phosphate aggregation, diffusion, and adsorption on kaolinite in saline solutions by molecular dynamics simulation

Large amounts of phosphates are required for the survival of cells. However, undesirable algae overgrowth requires phosphorus levels to be kept under control. For large bodies of water, cost-effective and ecosystem-friendly ways to export phosphate are needed. The use of clays appears to be the most promising method in seawater. However, for a broader application, the mechanisms of phosphate adsorption on kaolinite, the conditions for effective flocculation, and the impact of salt must first be addressed. In this study, molecular dynamics simulations are used to determine the adsorption and anchoring mechanisms of two species of phosphates that predominate at neutral pH, the dihydrogen phosphate ion H2PO4− and the hydrogen phosphate ion HPO42−, in a 1:1 ratio, on each of the three kaolinite principal planes, the basal surfaces, octahedral gibbsite (001) and tetrahedral siloxane (001¯), and the edge sites (010), in aqueous NaCl at a concentration of 0.6 M to mimic seawater. Phosphate aggregation is enhanced by Na bridges, although at very high concentrations, the number of aggregates and the size of the largest cluster decrease. Calculated diffusion coefficients for both phosphate species drop sharply in hypersaline solutions, although the decay rate is higher for the HPO42− species. Diffusion results are in close agreement with experimental data. Phosphate adsorption on kaolinite occurs in clusters. The hydrophilic surface (001) adsorbs increasing amounts of each of the phosphate species as the salt concentration increases, more HPO42− than H2PO4−. The hydrophobic (001¯) surface remains non-reactive to any species. The hydrophilic (010) edge surface increases adsorption of H2PO4− and drastically decreases that of HPO42− as salt concentration increases. Bidentate adsorption of HPO42− on the much rougher edge surface, even if saturated with adsorbed Na ions, is sterically impeded. The dominant adsorption mechanism is through cationic bridges on the gibbsite surface and at the edges. The adsorption capacity of kaolinite, including all its surfaces, increases with salt concentration, reaching its highest value in synthetic seawater. The values are of the order, although lower than the experimental ones obtained with less-accessible clays with atomic substitutions. The use of clays to control phosphate content in coastal waters is expected to contribute to public health and sustainability of marine industrial activities.

Orbital and radiative properties of wandering intermediate-mass black holes in the ASTRID simulation

ABSTRACT Intermediate-Mass Black Holes (IMBHs) of $10^3-10^6\, {\rm M_\odot }$ are commonly found at the centre of dwarf galaxies. Simulations and observations convincingly show that a sizeable population of IMBHs could wander off-centre in galaxies. We use the cosmological simulation ASTRID to study the orbital and radiative properties of wandering IMBHs in massive galaxies at z ∼ 3. We find that this population of black holes has large orbital inclinations (60° ± 22°) with respect to the principal plane of the host. The eccentricity of their orbits is also significant (0.6 ± 0.2) and decreases with time. Wandering IMBHs undergo spikes of accretion activity around the pericentre of their orbits, with rates 10−3 − 10−5 times the Eddington rate and a median accretion duty cycle of $\sim 12{{\ \rm per\ cent}}$. Their typical spectral energy distribution peaks in the infrared at $\sim 11 \, \mu \rm m$ rest-frame. Assuming a standard value of $10{{\ \rm per\ cent}}$ for the matter-to-energy radiative efficiency, IMBHs reach 2 − 10 keV X-ray luminosities $\gt 10^{37} \, \mathrm{erg\, s^{-1}}$ for $\sim 10{{\ \rm per\ cent}}$ of the time. This luminosity corresponds to fluxes $\gt 10^{-15} \, \mathrm{erg \, s^{-1} \, cm^{-2}}$ within 10 Mpc. They could be challenging to detect because of competing emissions from X-ray binaries and the interstellar medium. X-ray luminosities $\gt 10^{41} \, \mathrm{erg \, s^{-1}}$, in the hyper-luminous X-ray sources (HLXs) regime, are reached by $\sim 7{{\ \rm per\ cent}}$ of the IMBHs. These findings suggest that HLXs are a small subset of the wandering IMBH population, which is characterized by luminosities 103 − 104 times fainter. Dedicated surveys are needed to assess the demographics of this missing population of black holes.

Direct Elucidation of the Vibrationally Averaged Structure of Benzene: A Path Integral Molecular Dynamics Study.

Path integral molecular dynamics (PIMD) simulations for C6H6, C6D6, and C6T6 have been carried out to directly estimate the distribution of projected C-H(D,T) bond lengths onto the principal axis plane. The average values of raw C-H(D,T) bond lengths obtained from PIMD simulations are in the order of ⟨RC-H⟩ > ⟨RC-D⟩ > ⟨RC-T⟩ due to the anharmonicity of the potential energy curve. However, the projected C-H(D,T) bond lengths are almost the same as those reported by Hirano et al. [J. Mol. Struct. 2021, 1243, 130537]. Our PIMD simulations directly and strongly support the explanation by Hirano et al. for the experimental observations that almost the same projected C-H(D) bond lengths are found for C6H6 and C6D6. The PIMD simulations also predicted the same projected bond lengths for C6T6 as those of C6H(D)6. In addition to the previous local mode analysis, the present PIMD simulations predicted, for benzene isotopologues, that the vibrationally averaged structure is planar but non-flat.

The effect of cross-section geometry on the lateral–torsional behavior of thin-walled beams: Analytical and numerical studies

In this paper, the elastic lateral–torsional behavior of simple beams is discussed by presenting a novel analytical solution and performing numerical studies. The motivation of the presented research is the observation that classic analytical prediction and finite element prediction are, typically, significantly different when the second-order nonlinear behavior of beams with initial imperfections is analyzed. To understand and explain the observed differences, a novel analytical model is worked out for the geometrically nonlinear analysis of beams with initial geometric imperfections. The advancement in the presented analytical solution is the explicit consideration of the changing geometry as the load increases. The most important steps of the derivations are summarized, and the resulting formulae are briefly discussed. The derivations are done for general cross-sections, however, the bending is assumed to act in one of the principal planes. Numerical studies are also presented, focusing on mono-symmetric cross-sections. As part of the numerical studies, first, the results of the new analytical formulae are compared to those from shell finite element analysis. The results suggest that the new formulae can capture the most essential elements of the behavior observed in the shell finite element calculations, justifying that the cross-section shape might have a significant effect on the nonlinear lateral–torsional behavior of beams. Then the effect of the lateral–torsional buckling is predicted by calculating buckling reduction factors, using the results of the geometrically nonlinear finite element calculations. The capacity prediction results, again, justify that the cross-section shape, as well as the sign of the assumed geometric imperfection, might have a non-negligible effect on the buckling reduction factors, and on the capacity of the member.

A novel method for the characterization of through-thickness shear constitutive behavior of composites

This work presents a novel experimental method to characterize the through-thickness shear response for fiber-reinforced polymer composite materials. A sandwich short-beam shear specimen with a thin 0° laminated face sheet bonded with a thick 90° laminated core is proposed. A combination of a finite element model-based stress calculation and a full-field surface strain measurement in a custom sandwich specimen under bending is used in the method. An entire interlaminar shear response in the 2–3 principal material plane has been generated using a regression of FEM-calculated shear stress and DIC-measured shear strain. The measured 23-plane interlaminar shear stress–strain response was very close to the 23-plane Iosipescu test and the plate-twist shear test, but a higher ultimate shear strain was achieved. Transverse tensile failure with a 45° fracture angle originated from the transverse shear stress on the neutral surface. A full set of the three-dimensional stress–strain constitutive relations has been assessed using one short-beam-shear test method, and identical nonlinear shear stress–strain responses with distinct ultimate shear strengths have been observed in the three principal material planes for the generic FRP tape material in this work for the first time.

Impact of sun-view geometry on canopy spectral reflectance variability

UAS-based remote sensing has been rapidly growing in numerous fields, including agriculture and environmental studies. However, the lack of a practical and reliable quantitative method independent of the experiment condition has limited the translation of remote sensing models to another time and space since the results are barely generalizable. Several error sources severely affect the UAS-based remote sensing data; one of the most important ones is the sun-camera geometry. This study investigates the effect of sun-camera geometry on the reflectance of several specialty crops, including citrus, almond, and grape, quantifies the magnitude of the effect, and introduces a practical approach to account for these effects. We learned that a minimal variation of 2° in view angle causes a significantly different reflectance for similar canopies. Due to the directional solar radiation, the canopy reflectance measured from different view angles in the cameras' Field of View (FOV) could vary more than ± 50 % of the nadir view. Despite widely practiced assumptions in the literature, results show that these variations are not negligible, and the practical use of remote sensing imagery requires compensation for directional effects. We developed a model based on the Laplacian distribution function that estimates the variations in aerial images in two directions: principal plane and cross-plane. The nadir reflectance of each canopy can be calculated from other view angles using the developed model with r2 of up to 0.88 based on the band, crop, and other variables. The 4Sail radiative transfer model was used as a benchmark to evaluate the model’s performance. We leveraged the output of this study to determine the optimum flight time as a function of date, the camera’s FOV, and the site’s location latitude, which will facilitate the correction of the solar angle effect and help avoid unreliable data collections.

A New Method to Estimate the Leaf Chlorophyll Content From Multiangular Measurements: Anisotropy Index

Anisotropy index (ANIX), which is defined as the ratio between the maximum and minimum reflectance factors in the principal plane, has been applied in characterizing the optical properties of vegetation. But it is seldom used to estimate the chlorophyll content in leaf level. In this study, we found the leaf spectral anisotropy index (ANIX) depended on the variation of leaf chlorophyll content (LCC). Newly proposed indices, (ASRI: A750/A720 and ANDI: (A750-A720)/(A750+A720), A is the modified ANIX (mANIX=ANIX-1)), were derived from the format of the existing reflectance-based vegetation indices: simple ratio (SR) and normalized difference (ND) indices. The diffuse reflection, closely related to LCC, can be extracted from the two new indices (or directly obtained as the minimum bidirectional reflectance factor). They have strong linear relationships with LCC (R2=0.88 and 0.89), and have good estimation accuracy using an independent dataset (RMSE=6.39 μg/cm2 and 6.10 μg/cm2). We also found the ASRI (ANDI) had similar LCC estimation accuracy as the range-ASRIs or range-ANDIs (RANDIs or RANDIs), which were calculated by the random combination of reflectance factors in the forward scattering directions (ranged from -30° to -50°) and near the backward scattering directions (ranged from 0° to 20°). The wide and effective ranges of viewing angles strengthen the usability of ASRI and ANDI to estimate LCC in the practical measurements.

PRINCIPAL COMPONENT ANALYSIS AND CLASSIFICATION OF SUGARCANE PRODUCTION DATA IN BURUNDI

This study aims at identifying groupings of individuals (years) from sugarcane production data in Burundi by applying Principal Component Analysis (PCA) and classification, and computing clusters’ distances between centroids. These data were obtained from the Ministry of Environment, Agriculture and Livestock in Burundi and cover a period from 2000 to 2019, i.e. 20 years. The variables used are mean sugarcane yield, sugar production, cultivated area, sugarcane production, molasses production, herbicide inputs, mean temperature and cost of sugar production. R software version 3.6.1 was used to analyze data. This study shows that the years 2002 and 2013 are opposed by the first factorial axis while the years 2001 and 2017 are opposed by the second one. The years 2000, 2002, 2008, 2012, 2013 and 2017 are better represented on the principal factorial plane. The years 2017 and 2019 are characterized by high values of herbicide inputs and cultivated area while the years 2011, 2012 and 2013 are characterized by high values of mean temperature and mean sugarcane yield. The year 2015 is characterized by high values of sugar production, sugarcane production, cost of sugar production and molasses production.

Cutting force modeling in the electrical discharge assisted milling of Ti-6Al-4V in a multi-hybrid energy field based on finite volume method

Previous studies have confirmed that electrical discharge machining assisted milling (EDAM) is an effective method for machining titanium alloys precisely and efficiently. However, there is little research on the precise control of machined surface quality in EDAM through theoretical models. Hence, in this research, a cutting force model of EDAM under a multi-hybrid energy field, including the discharge thermal temperature field (DTTF) and the cutting thermal temperature field (CTTF), was developed. Further, the DTTF was numerically analyzed using the finite volume method (FVM). In particular, through the theoretical derivation of the classical cutting temperature model, classical cutting force model, and Johnson-Cook (J-C) constitutive model, the temperature of the principal shear plane and the shear flow stress under different discharge energies were obtained in this analysis. In particular, the analysis showed that when the capacitance was 100,000 pF, the heat distribution on the workpiece was relatively uniform, and the temperature of the workpiece was the highest among those from the analyses under different capacitances, respectively. Subsequently, the validity of the cutting force model under many aspects was verified by conducting EDAM of Ti-6Al-4 V. Specifically, the experiment was carried out based on the optimal discharge capacitance (100,000 pF) found from the cutting force model and demonstrated that the EDAM, compared to conventional milling (CM), could significantly improve the machined surface quality and reduce tool wear. Hence, the cutting force model provided important theoretical support for parameter selection in EDAM. • The cutting force model for EDAM is developed under a multi-hybrid energy field. • The multi-hybrid energy field, including the discharge thermal temperature field and the cutting thermal temperature field. • The finite volume method is used to analyze the multi-pulse discharge heat transfer random model for discharge thermal. • A good agreement of cutting force model has been obtained between theoretical and experimental results. • The optimal discharge capacitance (100000 pF) is found by simulating the cutting force model.

Anisotropic crystal orientations dependent mechanical properties and fracture mechanisms in zinc blende ZnTe nanowires.

The orientations of crystal growth significantly affect the operating characteristics of elastic and inelastic deformation in semiconductor nanowires (NWs). This work uses molecular dynamics simulation to extensively investigate the orientation-dependent mechanical properties and fracture mechanisms of zinc blende ZnTe NWs. Three different crystal orientations, including [100], [110], and [111], coupled with temperatures (100 to 600 K) on the fracture stress and elastic modulus, are thoroughly studied. In comparison to the [110] and [100] orientations, the [111]-oriented ZnTe NW exhibits a high fracture stress. The percentage decrease in fracture strength exhibits a pronounced variation with increasing temperature, with the highest magnitude observed in the [100] direction and the lowest magnitude observed in the [110] direction. The elastic modulus dropped by the largest percentage in the [111] direction as compared to the [100] direction. Most notably, the [110]-directed ZnTe NW deforms unusually as the strain rate increases, making it more sensitive to strain rate than other orientations. The strong strain rate sensitivity results from the unusual short-range and long-range order crystals appearing due to dislocation slipping and partial twinning. Moreover, the {111} plane is the principal cleavage plane for all orientations, creating a dislocation slipping mechanism at room temperature. The {100} plane becomes active and acts as another fundamental cleavage plane at increasing temperatures. This in-depth analysis paves the way for advancing efficient and reliable ZnTe NWs-based nanodevices and nanomechanical systems.

Optimizing the Protocol of Near-Surface Remote Sensing Experiments Over Heterogeneous Canopy Using DART Simulated Images

Optical canopy models that connect land surface properties and satellite-observed radiance must be validated before being used. These models include the bidirectional reflectance distribution function (BRDF) models in the visible and near-infrared domains, and directional brightness temperature (DBT) models in the thermal infrared domain. Near-surface experiments have been extensively conducted to evaluate the modeling accuracy, including ground-, tower-, and aircraft-based measurements. Indeed, it should be noted that in situ measured BRDF/DBT results are sensitive to the experiment protocol, such as sensor moving orientation, flight height, and sampling frequency. A practical tool for optimizing the in situ measurement protocols is needed in the community of remote sensing modeling. For that, we devised a virtual experiment framework based on the discrete anisotropic radiative transfer (DART) 3-D radiative transfer model that is capable of simultaneously simulating both the BRDF/DBT pattern and the images acquired by in situ cameras. Here, as an optimization case, we use it to determine the optimal sensor flight orientation over heterogeneous vegetated canopies (a row-planted scene with three solar angles and a discrete scene with three solar angles) for measuring their DBT distribution. Results showed considerable errors (i.e., image-extracted DBT minus DART-simulated DBT) exist for sensor flight orientation along the canopy rows ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> = 0.24 and root mean square error (RMSE) = 4.32 K), and they become much smaller ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> = 0.94 ~ 0.98 and RMSE = 0.82 ~ 1.03 K) in other typical orientations (e.g., cross row plane, solar principal plane, and cross solar principal plane). The critical azimuth offset relative to the row direction that can ensure an acceptable RMSE < 1 K is quantified as atan(3*Unitwidth/Scenesize) based on a series of intensive simulations by this new tool. However, the RMSE of the discrete scene is not sensitive to the flight orientation. Such accuracy differences in various protocols were experimentally verified over row-planted maize using a 4-D tower in Huailai, Hebei, China. The result highlights the great potential of this newly designed DART-based virtual experiment to optimize near-surface experiment protocols.