Incident Zenith Angle Research Articles

Determination of nitrogen and potassium content in greenhouse tomato leaves using a new spectro-goniophotometer

We assessed the feasibility of determining the nitrogen (N) and potassium (K) content of fresh, greenhouse-grown tomato leaves by using a new polarisation reflectance spectrum spectro-goniophotometer system developed by our research group and coupled with appropriate multivariate calibration methods. The main factors that affect the polarised reflectance characteristics of tomato leaves are discussed, including incident zenith angle, azimuth, detection zenith angle, and polariser angle. Orthogonal experiments and range analyses were performed to verify the optimum angle combination from the polarised reflectance parameters. Optimum angle combination experiments were then conducted to fine-tune the optimal parameters, which resulted in the following conditions: incident zenith angle, 60°; viewing zenith angle, 45°; polariser on light source, 0°; polariser on detector, 45°; and azimuth, 180°. On this basis, 122 fresh leaves of greenhouse-grown tomato were used to establish models of N and K content. Results showed that the performance of the iPLS-GA model under incident zenith angle 60° was superior to that of the other models. The optimal model for N was achieved with R = 0.9418 and root mean square error of prediction (RMSEP) = 0.519 in the prediction set; the optimal model for K was achieved with R = 0.8645 and RMSEP = 0.700 in the prediction set. The results show that it is feasible to measure the nutrient content of fresh, greenhouse-grown tomato leaves by polarisation reflectance spectroscopy with an appropriate multivariate calibration model under angle selection. This method allows for in-depth study of plant nutrient status and rapid detection at the single-leaf scale and has theoretical and practical significance.

Broadband optical absorption enhancement of hexagonal nanoconical frustum arrays texturing for c-Si film solarcells

In this paper, the optical properties of the silicon hexagonal nanoconical frustum (SiHNF) arrays are theoretically studied via simulation based on the Rigorous Coupled Wave Analysis (RCWA) in detail. The results show that the SiHNF bottom diameter (Dbot) should be equal to the array periodicity for efficient solar energy harvesting, and the optimized light absorption could be realized when the SiHNF height reaches 1000nm with Dtop equal to100nm. The optimal SiHNF arrays has the periodicity of 700nm, the top diameter of 100nm and the SiHNF height of 1000nm, yielding an ultimate efficiency of 30.54%, which is more than two times of a 2.33μm thick Si thin film solar cells. Comparing to nanopillar and square nanoconical frustum structures, the enhanced ultimate efficiency of SiHNF structure is less sensitive to the incident zenith angle and SiHNF top diameter. The possible physical mechanism behind the observation is also explored in thiswork.

Calibration of remote sensing image using BRDF model

A new bidirectional reflectance distribution function (BRDF) model of earth objects is established for the calibration of remote sensing image by the national metrology equipment. This model colligates the solar radiance, the atmosphere status, the object type, and the space camera parameter, etc. The output data of this model is the enter radiance data for the space camera. The remote sensing image can be appeared more “true” through this calibration. A kind of ground glass for architecture is measured and the correspond remote sensing image is simulated. After calibrated, the chromatism of this image is improved by 2 and the luminance contrast of that is improved by 3. OCIS codes: 120.0120, 280.0280, 290.0290. doi: 10.3788/COL201210.S11201. The aero camera receives different radiance and emit different wavelength light at the same time for the generation of the remote sensing image. Bidirectional reflectance distribution function (BRDF) combine these incident light, reflect light, and scatter light in one variable and it is the best variable to describe the space radiance performance of objects. The complex BRDF model for remote sensing image is based on the BRDF fundament equation, and colligates the solar radiance, the atmosphere status, the object type, and the space camera parameter, etc. In this model, the solar radiance and it’s change through atmosphere are considered in the incident variable of BRDF, and the proximity effect of atmosphere and the parameters of aero camera are considered for the reflect variable of BRDF, for example, the BRDF performance of aerosol [1] . Then the BRDF value of some typical objects are measured and calibrated. The absolute BRDF value are achieved and simulated using the complex BRDF model. Thus the remote sensing image which is calibrated is achieved. The whole procedure is shown in Fig.1. The basement equation of the complex BRDF model is established by the definition of BRDF as shown in Eq.(1) which defined as the ration of the reflect radiance and the incident irradiance on the appearance of the objects [2] . In Eq.(1), �i represents the incident zenith angle, 'i represents the incident azimuth angle, �r represents the incident zenith angle, 'r represents the incident azimuth angle, � the represents wavelength, Lr(�i,'i,�r,'r,�) represents the reflect radiance at specified angles and wavelength, Ei(�i,'i,�) represents the incident irradiance at specified angles and wavelength. Equation (1) is true in the controllable incident solid angle d i, which is shown in Fig.2. Under this condition, Lr(�i,'i,�r,'r,�) can be simplified to Lr(�r,'r,�). fr(�i,'i,�r,'r,�) = dLr(�i,'i,�r,'r,�) dEi(�i,'i,�) = Lr(�r,'r,�) Ei(�i,'i,�) .

Estimation of LAI and FAPAR by constraining the leaf and soil spectral characteristics in a radiative transfer model

We evaluated the estimation of the leaf area index (LAI) and the fraction of absorbed photosynthetically active radiation (FAPAR) of green plant canopies from top-of-the-canopy (TOC) spectral indices by using the PROSAIL model under the possible constraints of leaf and soil spectra. For the LAI estimation, the ratios (B1 – B3)/(B1 + B3) and B1/B3 provided fewer estimation errors than (B4 – B3)/(B4 + B3) or B4/B3 when the variation in the soil spectral reflectance was small or LAI was large. Here, B1, B3 and B4 denote the blue, red and near-infrared bands of Landsat ETM+, respectively. For the FAPAR estimation, the ratios (B5 – B7)/(B5 + B7) and B5/B7 provided fewer estimation errors than (NIR – R)/(NIR + R) or NIR/R for a FAPAR value of 0.3–0.7 when the variation in the soil spectral reflectance was large. Here, B5 and B7 denote the bands with wavelengths 1.55–1.75 and 2.09–2.35 μm, respectively. These were maintained for various conditions of the solar incident zenith angle (θs), leaf angle distribution (LAD), canopy hotspot parameter (s 1) and clumping index (Ω).

用于BSDF测量角度自动补偿装置设计及实验研究

When using a single reference to measure the bi-directional scattering distribution function (BSDF), the incident zenith angle of the tested sample must be identical to that of the reference. In order to get the hemisphere space scattering characteristic on the sample surface, usually a motor drives the sample tilting, then the incident zenith angle is changed and needs to be the compensated by another motor. We mathematically deduce the expression of compensation angle when the incident zenith angle is changed by the rotation of motor. After the incident angle is compensated, the scattering zenith angle and azimuth angle are deduced too. The uncertainty of the system is 0.75%. Scattering measurements are performed on copper sample with visible light under different temperatures.

Laboratory-based bidirectional reflectance distribution functions of radiometric tarps

Laboratory-based bidirectional reflectance distribution functions (BRDFs) of radiometric tarp samples used in the vicarious calibration of Earth remote sensing satellite instruments are presented in this paper. The results illustrate the BRDF dependence on the orientation of the tarps' weft and warp threads. The study was performed using the GSFC scatterometer at incident zenith angles of 0 degrees, 10 degrees, and 30 degrees; scatter zenith angles from 0 degrees to 60 degrees; and scatter azimuth angles of 0 degrees, 45 degrees, 90 degrees, 135 degrees, and 180 degrees. The wavelengths were 485 nm, 550 nm, 633 nm, and 800 nm. The tarp's weft and warp dependence on BRDF is well defined at all measurement geometries and wavelengths. The BRDF difference can be as high as 8% at 0 degrees incident angle and 12% at 30 degrees incident angle. The fitted BRDF data show a very small discrepancy from the measured ones. New data on the forward and backscatter properties of radiometric tarps are reported. The backward scatter is well pronounced for the white samples. The black sample has well-pronounced forward scatter. The provided BRDF characterization of radiometric tarps is an excellent reference for anyone interested in using tarps for radiometric calibrations. The results are NIST traceable.

Multi-factor Analysis of Reflection from Granite Surfaces

Many earlier experiments have shown that reflection from rock surfaces depends upon surface roughness, incidence zenith angle, viewing zenith angle, incidence azimuth and viewing azimuth. However, no research exists showing the interaction effects of these variables. Using granite as a model surface, we have designed an orthogonal, two level test having seven factors. Analysis of variance shows that surface roughness, relative viewing azimuth, and the interaction between these two factors are the largest sources of variance in our experiment. Hence we should include the interaction term in reflection models of granite.

Voxel-Based 3-D Modeling of Individual Trees for Estimating Leaf Area Density Using High-Resolution Portable Scanning Lidar

A method for accurate estimation of leaf area density (LAD) and the cumulative leaf area index (LAI) profiles of small trees ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Camellia sasanqua</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Deutzia crenata</i> ) under different conditions was demonstrated, which used precise voxel-based tree models produced by high-resolution portable scanning lidar. In this voxel-based canopy profiling (VCP) method, data for each horizontal layer of the canopy of each tree were collected from symmetrical azimuthal measurement points around the tree using optimally inclined laser beams. The data were then converted into a voxel-based three-dimensional model that reproduced the tree precisely, including within the canopy. This precise voxel model allowed the LAD and LAI of these trees, which have extremely dense and nonrandomly distributed foliage, to be computed by direct counting of the beam-contact frequency in each layer using a point-quadrat method. Corrections for leaf inclination and nonphotosynthetic tissues reduced the estimation error. A beam incident zenith angle near 57.5deg offered a good correction for leaf inclination without knowledge of the actual leaf inclination. Non-photosynthetic tissues were removed by image-processing techniques. The best LAD estimations showed errors of 17% at the minimum horizontal layer thickness and of 0.7% at the maximum thickness. The error of the best LAI estimations was also 0.7%

On possibility of the tau neutrino astronomy in GeV energies

We discuss the possibility of searching the galactic-plane tau neutrinos in GeV energies.

The effect of atmospheric attenuation on inclined cosmic ray air showers

The increasing cosmic ray statistics collected by present experiments and the future prospects with new large arrays demand accurate calculations of the extensive air shower (EAS) parameters. The energy of the primary particle is estimated by ground arrays fitting a lateral distribution function (LDF) to the particle densities at a given observing level. However, the lack of appropriate parameterization for these distributions, able to reproduce the data collected from all arrival directions, makes the experimental analysis difficult. We propose a method to parametrize particle density distributions of EAS at any incident zenith angle. Starting from analytical LDF for vertical showers we present a detailed study of the atmospheric depth dependence of the shower parameters. The results obtained are used to calculate the corresponding LDF for non-vertical showers including for the first time both, geometrical and atmospheric attenuation effects. We check the method analysing electron and muon LDF generated by Monte Carlo simulations from incident cosmic ray particles at different zenith angles. A comparison of the proposed LDF with experimental results, as well as MC data including detector effects, is also presented.

Momentum and Angular Momentum Transfer in Oblique Impacts: Implications for Asteroid Rotations

We conducted a series of high velocity oblique impact experiments (0.66–6.7 km/s) using polycarbonate (plastic) projectiles and targets made of mortar, aluminum alloy, and mild steel. We then calculated the efficiencies of momentum transfer for small cratering impacts. They are η = (M′Vn′)/(mvn) and ζ = (M′Vt′)/(mvt), wheremandvare the mass and velocity of a projectile, andM′ andV′ represent those of a postimpact target. Subscripts “n” and “t” denote the components normal and tangential to the target surface at the impact point, respectively. The main findings are: (1) η increases with increasing impact velocity; (2) η is larger for mortar than for ductile metallic targets; (3) ζ for mortar targets seems to increase with the impact velocity in the velocity range less than about 2 km/s and decrease with it in the higher velocity range; (4) ζ for the aluminum alloy targets correlates negatively with incident zenith angle of the projectile. In addition to these findings on the momentum transfer, we show theoretically that “ζL” can be expressed by η and ζ for small cratering impact. Here, ζLis the spin angular momentum that the target acquires at impact divided by the collisional angular momentum due to the projectile. This is an important parameter to study the collisional evolution of asteroid rotation. For a spherical target, ζLis shown to be well approximated by ζ.

Incident angle dependence of photographic darkness on X-ray films exposed in emulsion chambers

X-ray films of two different grain sizes have been exposed to the electron beam of an accelerator at different incident zenith angles with the aim of studying the influence of the angle on the measured optical density of the spot left by the beam on the films. Such study is motivated by the need to use optical means in the energy measurement of eletromagnetic showers in high energy collision events detected in emulsion chamber experiments. We conclude from this study that the dependence under investigation effectively exists, that it is more pronounced for finer-grained films, and that the absolute value of the darkness density does not influence the found results.

Defocusing characteristics of auroral X-ray images observed at balloon altitudes.

The purpose of the present paper is to estimate defocusing characteristics of auroral X-ray images observed at balloon altitudes, on the basis of propagation properties of photons from the top to deep in the atmosphere. A Monte Carlo simulation of the X-ray propagation down to a selected atmospheric depth between 6 and 14g/cm2 was carried out to deduce the spatial dispersion of the initial source photons with different functions of energy and incident direction. The simulation results obtained can be summarized as follows: 1) the horizontal dispersion at a depth is amplified with increasing energy and incident zenith angle of source photons; 2) a fractional contribution of the upward scattering photons amounts to about one-third of the downward moving photons; 3) the omni-directional X-ray detector provides the defocusing of ±10-12km at balloon altitudes for any spectral type of isotropic photon; and 4) the collimated detector with a limited field of view reduces the dispersion widths, say ±10° in collimation angle, to about one-third of case 3. An example demonstrates defocused images of a ring-shaped photon source, as functions of incident direction, collimation angle and atmospheric depth.

Calibration of METEOSAT Infrared Radiometer using Split Window Channels of NOAA AVHRR

A multispectral/multiangular procedure is proposed to calibrate the infrared channel of METEOSAT-2 IR 1 (760–980 cm−1), using the radiances of NOAA-7 AVHRR channels 4 (870–980 cm−1) and 5 (795–885 cm−1). The METEOSAT radiance can be successfully simulated by using one or both AVHRR infrared channels. The calibration coefficients are strongly influenced by the airmass (propagation paths) or incident zenith angles (θi). With one AVHIRR channel, the best results are obtained at θM<θN for channel 4 and at θM>θN for channel 5. With both AVHRR channels, the best results are found at θM = θN; however, an overall accuracy of less than 0.2 K is achievable at almost any viewing geometry. Application of the procedure to real data shows that the calibration factor for the METEOSAT-2 IR 1 channel can be accurately estimated from the NOAA AVHRR data on the same date and zone. The method can easily be automated and used to calculate or adjust the calibration factors for METEOSAT-2.