Surface Shadowing Research Articles

Validation of VEGETATION, MODIS, and GOES + SSM/I snow‐cover products over Canada based on surface snow depth observations

AbstractThe ability to map the areal depletion of snow accurately is important for operational decision making (e.g. reservoir management), for correct specification of boundary conditions in numerical weather‐prediction models, and for modelling atmospheric, hydrological and ecological processes. A number of satellite‐derived snow‐cover products are available in real time; however, these can differ considerably due to variations in sensor and platform characteristics, data pre‐processing methods, and the particular snow‐cover classification algorithms employed. This article evaluates the performance of three daily snow‐cover products over Canada: (1) Terra Moderate Resolution Imaging Spectroradiometer (MODIS) snow‐cover maps provided at 500 m spatial resolution for 2001; (2) National Oceanic Atmospheric Administration (NOAA) GOES + SSM/I snow maps provided at 4 km resolution for 2001 (∼30 km resolution SSM/I data were used for cloud‐covered areas); (3) SPOT‐4 VEGETATION (VGT) snow maps derived at 1 km resolution for 2000. An evaluation of the snow‐cover products with daily surface snow depth observations collected from almost 2000 meteorological stations across Canada revealed that the VGT snow product used in this study may not be suitable for snow mapping in Canada because of a significant bias towards mapping snow‐free conditions. The MODIS and NOAA products showed similar reasonable levels of agreement with ground data, ranging from approximately 80% to 100% on a monthly basis. Somewhat lower agreement was found in January, when solar zenith angles are large, suggesting that better correction for tree and surface shadow effects is needed in current snow‐cover mapping algorithms. The lowest agreement was seen during snowmelt, mainly in forest areas. Comparison of MODIS agreement statistics between sparse and dense conifer regions indicated that the effect of non‐representativenes of surface snow depth observations was on the order of 10% disagreement. The NOAA product was found to be the most consistent among land cover types and had the highest percentage of cloud‐free pixels. Copyright © 2004 John Wiley & Sons, Ltd.

Illumination from shadows

In this paper, we introduce a method for recovering an illumination distribution of a scene from image brightness inside shadows cast by an object of known shape in the scene. In a natural illumination condition, a scene includes both direct and indirect illumination distributed in a complex way, and it is often difficult to recover an illumination distribution from image brightness observed on an object surface. The main reason for this difficulty is that there is usually not adequate variation in the image brightness observed on the object surface to reflect the subtle characteristics of the entire illumination. In this study, we demonstrate the effectiveness of using occluding information of incoming light in estimating an illumination distribution of a scene. Shadows in a real scene are caused by the occlusion of incoming light and, thus, analyzing the relationships between the image brightness and the occlusions of incoming light enables us to reliably estimate an illumination distribution of a scene even in a complex illumination environment. This study further concerns the following two issues that need to be addressed. First, the method combines the illumination analysis with an estimation of the reflectance properties of a shadow surface. This makes the method applicable to the case where reflectance properties of a surface are not known a priori and enlarges the variety of images applicable to the method. Second, we introduce an adaptive sampling framework for efficient estimation of illumination distribution. Using this framework, we are able to avoid a unnecessarily dense sampling of the illumination and can estimate the entire illumination distribution more efficiently with a smaller number of sampling directions of the illumination distribution. To demonstrate the effectiveness of the proposed method, we have successfully tested the proposed method by using sets of real images taken in natural illumination conditions with different surface materials of shadow regions.

On reconstruction of surfaces by shadow contours

Abstract - The problem of reconstruction of surfaces based on a given plane by their shadow contours is considered. The optical projection of the surface point and shadow contours with respect to perpendicular and optical projection is introduced. Necessary and sufficient conditions of unique reconstruction of a plane curve by complete set of optical and perpendicular projections of their points are presented. A uniqueness result on the problem is obtained in the case of smooth hat-shaped surface. A uniqueness theorem for the problem of simultaneous reconstruction of two nonintersecting piecewise-smooth hat-shaped surfaces by complete set of their shadows is proved.

Surface evolution of ultrahigh vacuum magnetron sputter deposited amorphous SiO2 thin films

The surface morphology evolution of amorphous SiO2 thin films deposited by ultrahigh vacuum radio-frequency magnetron sputtering was studied by atomic force microscopy. The results show that: (1) the surface roughness of the deposited films reduces with increased substrate temperatures; (2) the surface roughness increases with higher deposition pressures; and (3) there is a roughening transition at the critical thickness of ∼ 90 nm for the substrate temperature of 713 K. The results also show that the surface roughness at the early stages of growth evolves according to a power law. Further growth beyond the critical thickness leads to a sharp increase in roughness. The experimental results are compared with the previous theoretical and experimental studies on surface evolution during sputter deposition, and discussed in terms of the competition between surface diffusion and shadowing.

Generating cloudmasks in spatial high-resolution observations of clouds using texture and radiance information

The detection of clouds in measurements taken by airborne and spaceborne remote sensing sensors in the visible and near-infrared is often difficult due to the high albedo of underlying surfaces such as snow- and ice-covered surfaces as well as sunglint regions of water surfaces. The authors show that the measured intensity of the reflected solar radiation together with texture information is effective in detecting clouds over water surfaces which are affected by sunglint. An automated cloud-masking technique for images measured by a compact airborne spectrographic imager ( casi ) during the ACE-2 CLOUDYCOLUMN experiment has been developed based on supervised learning of an artificial neural network. The neural network has been trained on radiances, texture features, and gradient-filtered radiances. The radiances were measured at a single wavelength but with high spatial resolution so that characteristic spatial features within an image can be used to discriminate clouds from sunglint, cloud shadow and ocean surface. The accuracy of the cloudmask-generating algorithm was investigated on the basis of the testing set for the neural network. Maximum errors of 3.4% and 1% occur for detecting cloudy and cloud-free pixels, respectively. The performance of the network was compared with a second network trained on radiances alone. The second network is up to 44% less efficient for cloud detection which demonstrates the improvement arising from the use of texture information together with spatial high-resolution observations.

The potential information in the temperature difference between shadow and sunlit of surfaces and a new way of retrieving the soil moisture

The thermal inertia and plant water stress index are often adopted to estimate soil moisture available for crops or plants. However, it is not very easy to obtain two temporal temperatures for thermal inertia model and air temperature for the plant water stress mode. Shadows of ground objects are often referred to noise on visible and near infrared remote sensing. But the difference of temperature between shadows and sunlit contains rich information concerning with heat-water status for soil. This paper presented a new way to excavate just by temperature difference usually between shadow and sunlit surface. Experiments validated the ideal. We can adopt thermal camera to measure the differences in the field measurements. However, we must use inversion based on multianglar thermal infrared remote sensing data in airborne and spaceborne. An inverting model was also presented by using Monte-Carlo and the least square method. Results show that this way is feasible.

Sidewall-angle effect on the bottom etch profile in SiO2 etching using a CF4 plasma

The dependence of the bottom etch profile on the sidewall angle in the CF4 plasma etching of an SiO2 film was investigated using a Faraday cage, which allowed ions to impinge on the sidewall at specified angles. The bottom etch profile obtained at −500 V was not affected by the sidewall when the angle between the sidewall and the bottom surface was 45° but showed microtrenching when the angle was greater than 60°. The microtrench depth increased until the angle reached 80°, beyond which the local etch rate was drastically reduced to allow the corner rounding of the bottom profile. As the sidewall angle increases, the etch rate of the bottom surface near the corner is controlled by two opposing factors. The decreasing number of incident ions on the sidewall surface and the increasing shadowing of the bottom surface from ions and neutrals by the sidewall contribute to the reduced etch rate, whereas the increasing kinetic energy and the narrower ion-angular distribution of the ions reflected from the sidewall contribute to the enhancement of the etch rate. In addition to these factors, the enhanced roughness of the sidewall surface due to the fluorocarbon film deposition plays the critical role of suppressing the microtrench formation. Microtrenching was not observed when the sidewall surface was covered with rough fluorocarbon film but was observed when the surface was smooth due to the energy transferred by ions higher than the threshold energy for the fluorocarbon film sputtering.

Surface topography of microtubule walls decorated with monomeric and dimeric kinesin constructs.

The surface topography of opened-up microtubule walls (sheets) decorated with monomeric and dimeric kinesin motor domains was investigated by freeze-drying and unidirectional metal shadowing. Electron microscopy of surface-shadowed specimens produces images with a high signal/noise ratio, which enable a direct observation of surface features below 2 nm detail. Here we investigate the inner and outer surface of microtubules and tubulin sheets with and without decoration by kinesin motor domains. Tubulin sheets are flattened walls of microtubules, keeping lateral protofilament contacts intact. Surface shadowing reveals the following features: (i) when the microtubule outside is exposed the surface relief is dominated by the bound motor domains. Monomeric motor constructs generate a strong 8 nm periodicity, corresponding to the binding of one motor domain per alpha-beta-tubulin heterodimer. This surface periodicity largely disappears when dimeric kinesin motor domains are used for decoration, even though it is still visible in negatively stained or frozen hydrated specimens. This could be explained by disorder in the binding of the second (loosely tethered) kinesin head, and/or disorder in the coiled-coil tail. (ii) Both surfaces of undecorated sheets or microtubules, as well as the inner surface of decorated sheets, reveal a strong 4 nm repeat (due to the periodicity of tubulin monomers) and a weak 8 nm repeat (due to slight differences between alpha- and beta-tubulin). The differences between alpha- and beta-tubulin on the inner surface are stronger than expected from cryo-electron microscopy of unstained microtubules, indicating the existence of tubulin subdomain-specific surface properties that reflect the surface corrugation and hence metal deposition during evaporation. The 16 nm periodicity visible in some negatively stained specimens (caused by the pairing of cooperatively bound kinesin dimers) is not detected by surface shadowing.

Consideration of local shadowing and ion beam voltage effects in the prediction of a surface evolving under ion milling

Ion milling applications in the micro-electronics industry are becoming more challenging due to decreasing feature sizes and increasing aspect ratios. A simulation of the milling problem which is capable of predicting surface evolution in the presence of high aspect ratios where local shadowing of the substrate surface becomes an important issue is described. A method of characteristics solution based on surface inclination angles is derived for a three-dimensional surface evolution model. An algorithm is developed to account for local shadowing effects, where raised areas of the substrate surface (i.e., the photomask) prevent the ion beam from reaching hidden or shadowed portions of the surface. The yield (sputtering) function is modified to account for beam voltage as well as the angle of beam incidence. Yield function parameters are determined experimentally for Al2O3, Ti, permalloy (83/17 wt % Ni–Fe) and postbaked AZ P4400 photoresist. Model predictions are in good agreement with experimental results for the surface evolution of a photopatterned Al2O3 substrate.

Part-based 3D descriptions of complex objects from a single image

Volumetric, 3D, part-based descriptions of complex objects in a scene can be highly beneficial for many tasks such as generic object recognition, navigation, and manipulation. However, it has been difficult to derive such descriptions from image data. There has been some progress in getting such descriptions from range data or from perfect contours, but analysis of a real intensity image presents many difficulties. The object and part boundaries do not completely correspond to image boundaries. The detected boundaries are often fragmented and many boundaries due to surface markings, shadows, and noise are present. In addition, inference of 3D from a 2D image is difficult. The paper describes a method to compute the desired descriptions from a single image by exploiting projective properties of a class of generalized cylinders and of possible joints between them. Experimental results on some examples are given.

Shadows on a Planetary Surface and Implications for Photometric Roughness

We advocate the use of fractal surface statistics as a simple, quantitative, and general model for planetary surface roughness. We determine the shadowing behavior of a wide range of fractal surfaces using computer simulations, and present an empirical function that reproduces their observed behavior within statistical uncertainties. We compare the shadowing behavior of fractal surfaces to four analytic shadowing models for random surfaces and find that three of these, including the Hapke (1984,Icarus59, 41–59) model, are well approximated by specific cases of a general fractal surface model. In addition, we demonstrate that a fractal surface model provides a way of quantitatively verifying and extending previous interpretations of the Hapke (1984) roughness parameter. We hypothesize that the scale which dominates surface shadowing, and by extension photometric roughness, is the smallest surface scale for which shadows exist and that this scale is a function of intrinsic physical parameters such as the single scattering albedo and particle phase function. If correct, a major implication of this hypothesis is that photometric roughness may have different physical meanings on different surfaces.

Correction to “Near‐grazing illumination and shadowing of rough surfaces” by Donald E. Barrick

Radio ScienceVolume 33, Issue 3 p. 633-633 CorrectionsFree Access Correction to “Near-grazing illumination and shadowing of rough surfaces” by Donald E. Barrick First published: 01 May 1998 https://doi.org/10.1029/98RS00657AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References Barrick, D. E., Grazing behavior of scatter and propagation above any rough surface, IEEE Trans. Antennas Propag., 461, 73– 83, 1998. Volume33, Issue3May-June 1998Pages 633-633 ReferencesRelatedInformation

High-resolution imaging of electronic devices using line modified-asymmetric crystal topography (LM-ACT)

X-ray topographic measurements are reported for implantation and superstructure details in an otherwise perfect, parametric, single-crystal device. Image contrast in topographs is attributed to the combined effects of device implantation or deposition strains in the host crystal, X-ray absorption, and surface shadowing or edge enhancement of the X-ray beam and, also, perfection of the lattice at the atomic scale. Stereo-pair images have been obtained to provide depth measurements. Sequential topographs have been utilized after various steps in device fabrication, ultimately, to monitor processing procedures. Comparison is made with dynamical theory calculations. The X-ray penetration depth and micrometer size of the thin-film nuclear emulsions used to record the diffraction images are shown to be important factors in limiting spatial resolution.

Near‐grazing illumination and shadowing of rough surfaces

A simple and computationally efficient methodology is demonstrated for treating the interaction of radio waves near grazing above rough surfaces. We apply it to the sea from HF through the microwave. Results using actual finite seawater conductivity depart significantly from those of a perfectly conducting profile for vertical polarization; for horizontal polarization there is essentially no difference. Shadowing behind wave crests is surprisingly shallow for vertical polarization even when the occluded depth is tens of wavelengths. This methodology gives expressions for the effective surface impedance at grazing as modified by the roughness when height scales greatly exceed the radio wavelength, augmenting prior expressions valid at HF for the sea obtained from perturbation theory. These effective impedances can then be used in formulations for radiation and surface wave propagation/diffraction at and below the horizon.

Oceanographic, topographic, and sediment interactions in deep water acoustic propagation. Part II. Gulf Stream simulations

Interacting low-frequency acoustic propagation effects of range-dependent oceanographic sound-speed profiles and range varying topography, with a fluid sediment layer, are modeled in the Gulf Stream region using a parabolic approximation to the Helmholtz equation. Oceanographic frontal effects, monotonically upsloping and downsloping topographic effects are identified in propagation between reciprocally chosen points on either side of the Gulf Stream at frequencies of 25, 50, and 100 Hz. For propagation from Slope to Sargasso water, surface shadow zone formation is documented, and ensonification of the shadow zone due to low-frequency diffraction. In propagation from Sargasso to Slope water, increased surface ensonification results. Topographic effects include truncation/reflection of deep propagation paths for upsloping topography, and increased depth for water column refraction for downsloping topography. Frequency and source depth-dependent oceanographic and topographic interaction effects are documented for two major propagation regimes: one containing primarily water-column refracting patterns, and one in which bottom-glancing propagation paths dominate sound fields for mid to long ranges.

An Investigation of Nucleating Flows of Steam in a Cascade of Turbine Blading

During the course of expansion in turbines steam first supercools and then nucleates to become a wet mixture. To reproduce turbine nucleating conditions realistically requires a supply of supercooled vapor. This can be achieved under blow-down conditions and an experimental facility for such studies has been constructed. The results of the first experimental investigation of nucleating flows of steam in a cascade of nozzle blading using the equipment are presented. The experimental results presented consist of surface pressure measurements, Mach-Zehnder and shadow photography. Comparisons with theoretical solutions show reasonable agreement.

Describing and Segmenting Scenes from Imperfect and Incomplete Data

Usually shape description systems assume that a scene has been segmented into objects and that object boundaries are given. This, however, is not realistic when working with intensity images. Such images do not, in general, yield silhouettes corresponding to objects. The boundaries from such images are fragmented and contain surface markings and shadow and noise boundaries. The system we describe works with such input and computes shape descriptions of complex objects. Scene segmentation takes place through shape description. We use ribbons or 2D analogs of generalized cones for the basic shape representation. The key idea in our approach is the Finiteness Observation, which says that an object/object part is not infinite in extent, rather that it is terminated by a boundary or another object part. This observation is embodied in the Principle of Termination developed specifically for ribbons. We also develop the Same-sidedness and the Non-overlapping Observations to obtain parts of compound objects from imperfect and incomplete data. We exploit these observations and principle in the system that we develop. We show results for several synthetic and real intensity images of objects (simple and compound) with broken boundaries in the presence of shadows, reflectance boundaries, texture, and occlusion. The output of our system is useful for object recognition, learning new models, stereo and motion correspondence and navigation, inference of 3D orientation from a single 2D image, and grasping for robot hand-eye coordination.

Aortogenic embolic stroke: a transesophageal echocardiographic approach.

We studied the frequency and grade of atherosclerotic changes in the thoracic aorta and their significance as embologenic lesions in patients with stroke. Using transesophageal echocardiography, we evaluated complicated lesions in the thoracic aortas of 62 patients who met our clinical criteria for embolic stroke. A complicated lesion was defined as a raised lesion with an irregular surface or acoustic shadow based on a comparative study of echocardiographic and histopathologic findings. The results were compared with plain radiographic findings and in some cases with computed tomographic or aortographic findings. Twenty-six patients (42%) showed complicated aortic arch lesions on echocardiogram. Transesophageal echocardiography brought us more abundant information than other techniques. Aortic knob calcification by plain radiography correlated well with the presence of echocardiographically complicated lesions, suggesting its utility for rough screening of atherosclerotic changes. Fifty-two patients had other potential embolic sources in the heart or cervical arteries. Among the remaining 10 patients without extra-aortic embolic sources, three showed complicated lesions and were diagnosed as having aortogenic embolic stroke. Aortic atherosclerosis should be recognized as an embolic source of stroke and the advantage of transesophageal echocardiography recognized in its evaluation.

Energy-density distribution inside large nonabsorbing spheres by using Mie theory and geometrical optics

Mie theory and geometrical-optics ray tracing are used to obtain the distribution of electric energy density inside a nonabsorbing micrometer-sized sphere illuminated by a polarized plane wave. The Mie solution shows the multiply reflected geometrical-optics rays inside a sphere having a diameter of ~ 150 free-space wavelengths (size parameter = circumference/wavelength = 500). The geometrical-optics result shows the major features of the Mie solution and provides a physical interpretation of the electromagnetic interactions that result in the observed energy-density distributions. Both solutions show internal on-axis energy-density maxima inside the shadow surface of the sphere. The region of greatest enhanced energy density is approximately one internal wavelength in diameter and approximately twenty internal wavelengths in length.

High-intensity ultraviolet laser interaction with a metallic filament

Results of research conducted on interaction of high-intensity ultraviolet pulsed KrF laser radiation with a metallic filament in atmospheric air are reported. Experimental results are presented on the time dependent material ejection dynamics associated with pulsed single shot focused excimer laser beams interacting with a small diameter wire. Copper wire 75 μm in diameter was illuminated with a KrF (λ=248 nm, pulse duration =17 ns full width at half-maximum) excimer laser at an irradiance of 80 GW/cm2. Interaction dynamics were recorded using both real-time and double-strobed ultraviolet laser imaging techniques. Temporal and spatial evolutions of both vaporized and molten material are reported. Material observed, during two-dimensional shadow imaging, on the side opposite the incident beam (shadow side) was shown to originate from the front ablating surface without spallation of material on the shadow surface. Several spatial material emission velocities are reported utilizing two different imaging techniques. A maximum velocity of 1500 m/s was obtained for material ejected in a direction toward the ablating laser.