Refractive Index Dependent Bidirectional Scattering Distribution Functions

Wir untersuchen die Wirkung des Eintauchens von realen Materialien in Medien mit unterschiedlichem Brechindex. In der Theorie sollte das Reflektanz-Verhalten eines Materials, das in den umgebenden Medien mit unterschiedlichen Brechungsindizes eingetaucht wird,durch die Fresnel-Gleichungen vorhergesagt werden. Wie wir jedoch zeigen, folgt nur eine Unterklasse von Materialien diesem theoretischen Modell. In der Realität zeigen viele Materialien unerwartete Effekte wie stärker lokalisierte Highlights oder eine deutliche Zunahme von spekularer Reflexion durch Mikrogeometrie. In unseren Experimenten haben wir herausgefunden, dass diese Effekte ziemlich stark variieren, und keines der bestehenden BRDF-Modelle das realistisch wiedergeben. Wir schlagen ein neues, parametrisches Modell vor, dass den Brechungsindex berücksichtigt. Wir fitten unsere Messergebnisse an das Modell und erhalten so Parameter zur Beschreibung der Reflektanz verschiedener Medien.We investigate the effect of immersing real-world materials into media of different refractive indices. In theory, the reflective and transmissive behavior of a material that is immersed into surrounding media with different refractive indices should be predicted by the Fresnel equations. However, as we show, %\todo{Ivo}{} only a subclass of materials follows this theoretical model. In reality, many materials exhibit unexpected effects such as stronger localized highlights or a significant increase in the glossy reflection due to microgeometry. In our experiments we found that the variation of these effects can be quite strong, and none of the existing BRDF models realistically reproduce these effects seen in reality. We propose a new, parametric model that takes refractive index changes into account. We fit measurements of different materials and present results to demonstrate the importance of BRDF changes for submerged objects

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle Spectropolarimetric Imager

Accurate characterization of surface reflection is essential for retrieval of aerosols using downward-looking remote sensors. In this paper, observations from the Ground-based Multiangle SpectroPolarimetric Imager (GroundMSPI) are used to evaluate a surface polarized bidirectional reflectance distribution function (PBRDF) model. GroundMSPI is an eight-band spectropolarimetric camera mounted on a rotating gimbal to acquire pushbroom imagery of outdoor landscapes. The camera uses a very accurate photoelastic-modulator-based polarimetric imaging technique to acquire Stokes vector measurements in three of the instrument's bands (470, 660, and 865 nm). A description of the instrument is presented, and observations of selected targets within a scene acquired on 6 January 2010 are analyzed. Data collected during the course of the day as the Sun moved across the sky provided a range of illumination geometries that facilitated evaluation of the surface model, which is comprised of a volumetric reflection term represented by the modified Rahman-Pinty-Verstraete function plus a specular reflection term generated by a randomly oriented array of Fresnel-reflecting microfacets. While the model is fairly successful in predicting the polarized reflection from two grass targets in the scene, it does a poorer job for two manmade targets (a parking lot and a truck roof), possibly due to their greater degree of geometric organization. Several empirical adjustments to the model are explored and lead to improved fits to the data. For all targets, the data support the notion of spectral invariance in the angular shape of the unpolarized and polarized surface reflection. As noted by others, this behavior provides valuable constraints on the aerosol retrieval problem, and highlights the importance of multiangle observations.NASAJPLCenter for Space Researc

Hybrid analytical/numerical coupled-mode modeling of guided-wave devices

A general version of coupled-mode-theory for frequency domain scattering problems in integrated optics is proposed. As a prerequisite a physically reasonable field template is required, that typically combines modes of the optical channels in the structure with coefficient functions of in principle arbitrary coordinates. Upon 1-D discretizations of these amplitude functions into finite elements, a Galerkin procedure reduces the problem to a system of linear equations in the element coefficients, where given input amplitudes are included. Smooth approximate solutions are obtained by solving the system in a least squares sense. The versatility of the approach is illustrated by means of a series of 2-D examples, including a perpendicular crossing of waveguides, and a grating-assisted rectangular resonator. As an appendix, we show that alternatively a similar procedure can be derived by variational means, i.e. by restricting a suitable functional representation of the full 2-D/3-D vectorial scattering problem (with transparent influx boundary conditions for inhomogeneous exterior) to the respective field templates.\u

Research relative to angular distribution of snow reflectance/snow cover characterization and microwave emission

Remote sensing has been applied in recent years to monitoring snow cover properties for applications in hydrologic and energy balance modeling. In addition, snow cover has been recently shown to exert a considerable local influence on weather variables. Of particular importance is the potential of sensors to provide data on the physical properties of snow with high spatial and temporal resolution. Visible and near-infrared measurements of upwelling radiance can be used to infer near-surface properties through the calculation of albedo. Microwave signals usually come from deeper within the snow pack and thus provide depth-integrated information, which can be measured through clouds and does not relay on solar illumination.Fundamental studies examining the influence of snow properties on signals from various parts of the electromagnetic spectrum continue in part because of the promise of new remote sensors with higher spectral and spatial accuracy. Information in the visible and near-infrared parts of the spectrum comprise nearly all available data with high spatial resolution. Current passive microwave sensors have poor spatial resolution and the data are problematic where the scenes consist of mixed landscape features, but they offer timely observations that are independent of cloud cover and solar illumination

Effects of aerosols and surface shadowing on bidirectional reflectance measurements of deserts

Desert surfaces are probably one of the most stable of the Earth's natural targets for remote sensing. The bidirectional reflectance properties of the Saudi Arabian desert was investigated during the Summer Monsoon Experiment (Summer Monex). A comparison of high-altitude with near-surface measurements of the White Sands desert showed significant differences. These discrepancies have been attributed to forward scattering of the dust-laden atmosphere prevalent during Summer Monex. This paper is concerned in general with modeling the effects of atmospheric aerosols and surface shadowing on the remote sensing of bidirectional reflectance factors of desert targets, and in particular with comparing the results of these models with flight results. Although it is possible to approximate the latter, it is felt that a surface reflectance model with a smaller specular component would have permitted using a more realistic set of atmospheric conditions in the simulations

Study on Optical Microfiber Probes for Nanoparticle Manipulation

早稲田大学博士(工学)早大学位記番号:新9437doctoral thesi

Optimisation of the key SOA parameters for amplification and switching

Wireless Sensor Networks (WSN) are composed of small, low cost, resource-constrained computing nodes equipped with low power wireless transceivers. Generally, they are embedded in their environment to perform some specific monitoring and/or control function. Unlike wired networks that have dedicated routers for network connectivity and message forwarding, every node in a WSN can act as a router in a multi-hop network. A WSN can offer a cheap, applicationspecific solution in a variety of situations including military and disaster response scenarios, where other approaches are not viable. Due to their unattended nature and deployment in possibly hostile environmental conditions, there are many challenges in ensuring that a WSN is formed effectively and survives long enough to fulfil its function. Securing a WSN against attack is a particular challenge. Traditional encryption mechanisms are resource hungry and are not sufficient alone to provide a complete solution. This project is concerned with secure routing protocols. Formal methods are used to model and analyse the design of existing protocols and to demonstrate some previously unreported weaknesses

Method for predicting whispering gallery mode spectra of spherical microresonators

A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simulate the whispering gallery modes of a microsphere in the vicinity of a dipole source. This provides a guide for experiments that rely on efficient coupling to the modes of microspheres. The resultant spectra are compared to those of analytic models used in the field. In contrast to the analytic models, the FDTD method is able to collect flux from a variety of possible collection regions, such as a disk-shaped region. The customizability of the technique allows one to consider a variety of mode excitation scenarios, which are particularly useful for investigating novel properties of optical resonators, and are valuable in assessing the viability of a resonator for biosensing.Comment: Published 10 Apr 2015 in Opt. Express Vol. 23, Issue 8, pp. 9924-9937; The FDTD toolkit supercomputer scripts are hosted at: http://sourceforge.net/projects/npps/files/FDTD_WGM_Simulator

Pluto's global surface composition through pixel-by-pixel Hapke modeling of New Horizons Ralph/LEISA data

On July 14th 2015, NASA's New Horizons mission gave us an unprecedented detailed view of the Pluto system. The complex compositional diversity of Pluto's encounter hemisphere was revealed by the Ralph/LEISA infrared spectrometer on board of New Horizons. We present compositional maps of Pluto defining the spatial distribution of the abundance and textural properties of the volatiles methane and nitrogen ices and non-volatiles water ice and tholin. These results are obtained by applying a pixel-by-pixel Hapke radiative transfer model to the LEISA scans. Our analysis focuses mainly on the large scale latitudinal variations of methane and nitrogen ices and aims at setting observational constraints to volatile transport models. Specifically, we find three latitudinal bands: the first, enriched in methane, extends from the pole to 55deg N, the second dominated by nitrogen, continues south to 35deg N, and the third, composed again mainly of methane, reaches 20deg N. We demonstrate that the distribution of volatiles across these surface units can be explained by differences in insolation over the past few decades. The latitudinal pattern is broken by Sputnik Planitia, a large reservoir of volatiles, with nitrogen playing the most important role. The physical properties of methane and nitrogen in this region are suggestive of the presence of a cold trap or possible volatile stratification. Furthermore our modeling results point to a possible sublimation transport of nitrogen from the northwest edge of Sputnik Planitia toward the south.Comment: 43 pages, 7 figures; accepted for publication in Icaru