Radiosity Overview 1 Radiometry
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Spectral Reflectance and Emissivity of Man-Made Surfaces Contaminated with Environmental Effects
Optical Engineering 47͑10͒, 106201 ͑October 2008͒ Spectral reflectance and emissivity of man-made surfaces contaminated with environmental effects John P. Kerekes, MEMBER SPIE Abstract. Spectral remote sensing has evolved considerably from the Rochester Institute of Technology early days of airborne scanners of the 1960’s and the first Landsat mul- Chester F. Carlson Center for Imaging Science tispectral satellite sensors of the 1970’s. Today, airborne and satellite 54 Lomb Memorial Drive hyperspectral sensors provide images in hundreds of contiguous narrow Rochester, New York 14623 spectral channels at spatial resolutions down to meter scale and span- E-mail: [email protected] ning the optical spectral range of 0.4 to 14 m. Spectral reflectance and emissivity databases find use not only in interpreting these images but also during simulation and modeling efforts. However, nearly all existing Kristin-Elke Strackerjan databases have measurements of materials under pristine conditions. Aerospace Engineering Test Establishment The work presented extends these measurements to nonpristine condi- P.O. Box 6550 Station Forces tions, including materials contaminated with sand and rain water. In par- Cold Lake, Alberta ticular, high resolution spectral reflectance and emissivity curves are pre- T9M 2C6 Canada sented for several man-made surfaces ͑asphalt, concrete, roofing shingles, and vehicles͒ under varying amounts of sand and water. The relationship between reflectance and area coverage of the contaminant Carl Salvaggio, MEMBER SPIE is reported and found to be linear or nonlinear, depending on the mate- Rochester Institute of Technology rials and spectral region. In addition, new measurement techniques are Chester F. Carlson Center for Imaging Science presented that overcome limitations of existing instrumentation and labo- 54 Lomb Memorial Drive ratory settings. -
Fundametals of Rendering - Radiometry / Photometry
Fundametals of Rendering - Radiometry / Photometry “Physically Based Rendering” by Pharr & Humphreys •Chapter 5: Color and Radiometry •Chapter 6: Camera Models - we won’t cover this in class 782 Realistic Rendering • Determination of Intensity • Mechanisms – Emittance (+) – Absorption (-) – Scattering (+) (single vs. multiple) • Cameras or retinas record quantity of light 782 Pertinent Questions • Nature of light and how it is: – Measured – Characterized / recorded • (local) reflection of light • (global) spatial distribution of light 782 Electromagnetic spectrum 782 Spectral Power Distributions e.g., Fluorescent Lamps 782 Tristimulus Theory of Color Metamers: SPDs that appear the same visually Color matching functions of standard human observer International Commision on Illumination, or CIE, of 1931 “These color matching functions are the amounts of three standard monochromatic primaries needed to match the monochromatic test primary at the wavelength shown on the horizontal scale.” from Wikipedia “CIE 1931 Color Space” 782 Optics Three views •Geometrical or ray – Traditional graphics – Reflection, refraction – Optical system design •Physical or wave – Dispersion, interference – Interaction of objects of size comparable to wavelength •Quantum or photon optics – Interaction of light with atoms and molecules 782 What Is Light ? • Light - particle model (Newton) – Light travels in straight lines – Light can travel through a vacuum (waves need a medium to travel in) – Quantum amount of energy • Light – wave model (Huygens): electromagnetic radiation: sinusiodal wave formed coupled electric (E) and magnetic (H) fields 782 Nature of Light • Wave-particle duality – Light has some wave properties: frequency, phase, orientation – Light has some quantum particle properties: quantum packets (photons). • Dimensions of light – Amplitude or Intensity – Frequency – Phase – Polarization 782 Nature of Light • Coherence - Refers to frequencies of waves • Laser light waves have uniform frequency • Natural light is incoherent- waves are multiple frequencies, and random in phase. -
Path Tracing
Path Tracing Steve Rotenberg CSE168: Rendering Algorithms UCSD, Spring 2017 Irradiance Circumference of a Circle • The circumference of a circle of radius r is 2πr • In fact, a radian is defined as the angle you get on an arc of length r • We can represent the circumference of a circle as an integral 2휋 푐푖푟푐 = 푟푑휑 0 • This is essentially computing the length of the circumference as an infinite sum of infinitesimal segments of length 푟푑휑, over the range from 휑=0 to 2π Area of a Hemisphere • We can compute the area of a hemisphere by integrating ‘rings’ ranging over a second angle 휃, which ranges from 0 (at the north pole) to π/2 (at the equator) • The area of a ring is the circumference of the ring times the width 푟푑휃 • The circumference is going to be scaled by sin휃 as the rings are smaller towards the top of the hemisphere 휋 2 2휋 2 2 푎푟푒푎 = sin 휃 푟 푑휑 푑휃 = 2휋푟 0 0 Hemisphere Integral 휋 2 2휋 2 푎푟푒푎 = sin 휃 푟 푑휑 푑휃 0 0 • We are effectively computing an infinite summation of tiny rectangular area elements over a two dimensional domain. Each element has dimensions: sin 휃 푟푑휑 × 푟푑휃 Irradiance • Now, let’s assume that we are interested in computing the total amount of light arriving at some point on a surface • We are essentially integrating over all possible directions in the hemisphere above the surface (assuming it’s opaque and we’re not receiving translucent light from below the surface) • We are integrating the light intensity (or radiance) coming in from every direction • The total incoming radiance over all directions in the hemisphere -
Radiosity Radiosity
Radiosity Radiosity Motivation: what is missing in ray-traced images? Indirect illumination effects Color bleeding Soft shadows Radiosity is a physically-based illumination algorithm capable of simulating the above phenomena in a scene made of ideal diffuse surfaces. Books: Cohen and Wallace, Radiosity and Realistic Image Synthesis, Academic Press Professional 1993. Sillion and Puech, Radiosity and Global Illumination, Morgan- Kaufmann, 1994. Indirect illumination effects Radiosity in a Nutshell Break surfaces into many small elements Light source Formulate and solve a linear system of equations that models the equilibrium of inter-reflected Eye light in a scene. Diffuse Reflection The solution gives us the amount of light leaving each point on each surface in the scene. Once solution is computed, the shaded elements can be quickly rendered from any viewpoint. Meshing (partition into elements) Radiosity Input geometry Change geometry Form-Factors Change light or colors Solution Render Change view 1 Radiometric quantities The Radiosity Equation Radiant energy [J] Assume that surfaces in the scene have been discretized into n small elements. Radiant power (flux): radiant energy per second [W] Assume that each element emits/reflects light Irradiance (flux density): incident radiant power per uniformly across its surface. unit area [W/m2] Define the radiosity B as the total hemispherical Radiosity (flux density): outgoing radiant power per flux density (W/m2) leaving a surface. unit area [W/m2] Let’’s write down an expression describing the total flux (light power) leaving element i in the Radiance (angular flux dedensity):nsity): radiant power per scene: unit projected area per unit solid angle [W/(m2 sr)] scene: total flux = emitted flux + reflected flux The Radiosity Equation The Form Factor Total flux leaving element i: Bi Ai The form factor Fji tells us how much of the flux Total flux emitted by element i: Ei Ai leaving element j actually reaches element i. -
About SI Units
Units SI units: International system of units (French: “SI” means “Système Internationale”) The seven SI base units are: Mass: kg Defined by the prototype “standard kilogram” located in Paris. The standard kilogram is made of Pt metal. Length: m Originally defined by the prototype “standard meter” located in Paris. Then defined as 1,650,763.73 wavelengths of the orange-red radiation of Krypton86 under certain specified conditions. (Official definition: The distance traveled by light in vacuum during a time interval of 1 / 299 792 458 of a second) Time: s The second is defined as the duration of a certain number of oscillations of radiation coming from Cs atoms. (Official definition: The second is the duration of 9,192,631,770 periods of the radiation of the hyperfine- level transition of the ground state of the Cs133 atom) Current: A Defined as the current that causes a certain force between two parallel wires. (Official definition: The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 Newton per meter of length. Temperature: K One percent of the temperature difference between boiling point and freezing point of water. (Official definition: The Kelvin, unit of thermodynamic temperature, is the fraction 1 / 273.16 of the thermodynamic temperature of the triple point of water. Amount of substance: mol The amount of a substance that contains Avogadro’s number NAvo = 6.0221 × 1023 of atoms or molecules. -
Black Body Radiation and Radiometric Parameters
Black Body Radiation and Radiometric Parameters: All materials absorb and emit radiation to some extent. A blackbody is an idealization of how materials emit and absorb radiation. It can be used as a reference for real source properties. An ideal blackbody absorbs all incident radiation and does not reflect. This is true at all wavelengths and angles of incidence. Thermodynamic principals dictates that the BB must also radiate at all ’s and angles. The basic properties of a BB can be summarized as: 1. Perfect absorber/emitter at all ’s and angles of emission/incidence. Cavity BB 2. The total radiant energy emitted is only a function of the BB temperature. 3. Emits the maximum possible radiant energy from a body at a given temperature. 4. The BB radiation field does not depend on the shape of the cavity. The radiation field must be homogeneous and isotropic. T If the radiation going from a BB of one shape to another (both at the same T) were different it would cause a cooling or heating of one or the other cavity. This would violate the 1st Law of Thermodynamics. T T A B Radiometric Parameters: 1. Solid Angle dA d r 2 where dA is the surface area of a segment of a sphere surrounding a point. r d A r is the distance from the point on the source to the sphere. The solid angle looks like a cone with a spherical cap. z r d r r sind y r sin x An element of area of a sphere 2 dA rsin d d Therefore dd sin d The full solid angle surrounding a point source is: 2 dd sind 00 2cos 0 4 Or integrating to other angles < : 21cos The unit of solid angle is steradian. -
Adjoints and Importance in Rendering: an Overview
IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 9, NO. 3, JULY-SEPTEMBER 2003 1 Adjoints and Importance in Rendering: An Overview Per H. Christensen Abstract—This survey gives an overview of the use of importance, an adjoint of light, in speeding up rendering. The importance of a light distribution indicates its contribution to the region of most interest—typically the directly visible parts of a scene. Importance can therefore be used to concentrate global illumination and ray tracing calculations where they matter most for image accuracy, while reducing computations in areas of the scene that do not significantly influence the image. In this paper, we attempt to clarify the various uses of adjoints and importance in rendering by unifying them into a single framework. While doing so, we also generalize some theoretical results—known from discrete representations—to a continuous domain. Index Terms—Rendering, adjoints, importance, light, ray tracing, global illumination, participating media, literature survey. æ 1INTRODUCTION HE use of importance functions started in neutron importance since it indicates how much the different parts Ttransport simulations soon after World War II. Im- of the domain contribute to the solution at the most portance was used (in different disguises) from 1983 to important part. Importance is also known as visual accelerate ray tracing [2], [16], [27], [78], [79]. Smits et al. [67] importance, view importance, potential, visual potential, value, formally introduced the use of importance for global -
Reflectometers for Absolute and Relative Reflectance
sensors Communication Reflectometers for Absolute and Relative Reflectance Measurements in the Mid-IR Region at Vacuum Jinhwa Gene 1 , Min Yong Jeon 1,2 and Sun Do Lim 3,* 1 Institute of Quantum Systems (IQS), Chungnam National University, Daejeon 34134, Korea; [email protected] (J.G.); [email protected] (M.Y.J.) 2 Department of Physics, College of Natural Sciences, Chungnam National University, Daejeon 34134, Korea 3 Division of Physical Metrology, Korea Research Institute of Standards and Science, Daejeon 34113, Korea * Correspondence: [email protected] Abstract: We demonstrated spectral reflectometers for two types of reflectances, absolute and relative, of diffusely reflecting surfaces in directional-hemispherical geometry. Both are built based on the integrating sphere method with a Fourier-transform infrared spectrometer operating in a vacuum. The third Taylor method is dedicated to the reflectometer for absolute reflectance, by which absolute spectral diffuse reflectance scales of homemade reference plates are realized. With the reflectometer for relative reflectance, we achieved spectral diffuse reflectance scales of various samples including concrete, polystyrene, and salt plates by comparing against the reference standards. We conducted ray-tracing simulations to quantify systematic uncertainties and evaluated the overall standard uncertainty to be 2.18% (k = 1) and 2.99% (k = 1) for the absolute and relative reflectance measurements, respectively. Keywords: mid-infrared; total reflectance; metrology; primary standard; 3rd Taylor method Citation: Gene, J.; Jeon, M.Y.; Lim, S.D. Reflectometers for Absolute and 1. Introduction Relative Reflectance Measurements in Spectral diffuse reflectance in the mid-infrared (MIR) region is now of great interest the Mid-IR Region at Vacuum. -
Guide for the Use of the International System of Units (SI)
Guide for the Use of the International System of Units (SI) m kg s cd SI mol K A NIST Special Publication 811 2008 Edition Ambler Thompson and Barry N. Taylor NIST Special Publication 811 2008 Edition Guide for the Use of the International System of Units (SI) Ambler Thompson Technology Services and Barry N. Taylor Physics Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 (Supersedes NIST Special Publication 811, 1995 Edition, April 1995) March 2008 U.S. Department of Commerce Carlos M. Gutierrez, Secretary National Institute of Standards and Technology James M. Turner, Acting Director National Institute of Standards and Technology Special Publication 811, 2008 Edition (Supersedes NIST Special Publication 811, April 1995 Edition) Natl. Inst. Stand. Technol. Spec. Publ. 811, 2008 Ed., 85 pages (March 2008; 2nd printing November 2008) CODEN: NSPUE3 Note on 2nd printing: This 2nd printing dated November 2008 of NIST SP811 corrects a number of minor typographical errors present in the 1st printing dated March 2008. Guide for the Use of the International System of Units (SI) Preface The International System of Units, universally abbreviated SI (from the French Le Système International d’Unités), is the modern metric system of measurement. Long the dominant measurement system used in science, the SI is becoming the dominant measurement system used in international commerce. The Omnibus Trade and Competitiveness Act of August 1988 [Public Law (PL) 100-418] changed the name of the National Bureau of Standards (NBS) to the National Institute of Standards and Technology (NIST) and gave to NIST the added task of helping U.S. -
Analyzing Reflectance Data for Various Black Paints and Coatings
Analyzing Reflectance Data for Various Black Paints and Coatings Mimi Huynh US Army NVESD UNITED STATES OF AMERICA [email protected] ABSTRACT The US Army NVESD has previously measured the reflectance of a number of different levels of black paints and coatings using various laboratory and field instruments including the SOC-100 hemispherical directional reflectometer (2.0 – 25 µm) and the Perkin Elmer Lambda 1050 (0.39 – 2.5 µm). The measurements include off-the-shelf paint to custom paints and coatings. In this talk, a number of black paints and coatings will be presented along with their reflectivity data, cost per weight analysis, and potential applications. 1.0 OVERVIEW Black paints and coatings find an important role in hyperspectral imaging from the sensor side to the applications side. Black surfaces can enhance sensor performance and calibration performance. On the sensor side, black paints and coatings can be found in the optical coatings, mechanical and enclosure coating. Black paints and coating can be used inside the sensor to block or absorb stray light, preventing it from getting to the detector and affecting the imagery. Stray light can affect the signal-to-noise ratio (SNR) as well introduce unwanted photons at certain wavelengths. Black paints or coatings can also be applied to a baffle or area around the sensor in laboratory calibration with a known light source. This is to ensure that no stray light enter the measurement and calculations. In application, black paints and coatings can be applied to calibration targets from the reflectance bands (VIS- SWIR) and also in the thermal bands (MWIR-LWIR). -
Extraction of Incident Irradiance from LWIR Hyperspectral Imagery Pierre Lahaie, DRDC Valcartier 2459 De La Bravoure Road, Quebec, Qc, Canada
DRDC-RDDC-2015-P140 Extraction of incident irradiance from LWIR hyperspectral imagery Pierre Lahaie, DRDC Valcartier 2459 De la Bravoure Road, Quebec, Qc, Canada ABSTRACT The atmospheric correction of thermal hyperspectral imagery can be separated in two distinct processes: Atmospheric Compensation (AC) and Temperature and Emissivity separation (TES). TES requires for input at each pixel, the ground leaving radiance and the atmospheric downwelling irradiance, which are the outputs of the AC process. The extraction from imagery of the downwelling irradiance requires assumptions about some of the pixels’ nature, the sensor and the atmosphere. Another difficulty is that, often the sensor’s spectral response is not well characterized. To deal with this unknown, we defined a spectral mean operator that is used to filter the ground leaving radiance and a computation of the downwelling irradiance from MODTRAN. A user will select a number of pixels in the image for which the emissivity is assumed to be known. The emissivity of these pixels is assumed to be smooth and that the only spectrally fast varying variable in the downwelling irradiance. Using these assumptions we built an algorithm to estimate the downwelling irradiance. The algorithm is used on all the selected pixels. The estimated irradiance is the average on the spectral channels of the resulting computation. The algorithm performs well in simulation and results are shown for errors in the assumed emissivity and for errors in the atmospheric profiles. The sensor noise influences mainly the required number of pixels. Keywords: Hyperspectral imagery, atmospheric correction, temperature emissivity separation 1. INTRODUCTION The atmospheric correction of thermal hyperspectral imagery aims at extracting the temperature and the emissivity of the material imaged by a sensor in the long wave infrared (LWIR) spectral band. -
RADIATION HEAT TRANSFER Radiation
MODULE I RADIATION HEAT TRANSFER Radiation Definition Radiation, energy transfer across a system boundary due to a T, by the mechanism of photon emission or electromagnetic wave emission. Because the mechanism of transmission is photon emission, unlike conduction and convection, there need be no intermediate matter to enable transmission. The significance of this is that radiation will be the only mechanism for heat transfer whenever a vacuum is present. Electromagnetic Phenomena. We are well acquainted with a wide range of electromagnetic phenomena in modern life. These phenomena are sometimes thought of as wave phenomena and are, consequently, often described in terms of electromagnetic wave length, . Examples are given in terms of the wave distribution shown below: m UV X Rays 0.4-0.7 Thermal , ht Radiation Microwave g radiation Visible Li 10-5 10-4 10-3 10-2 10-1 10-0 101 102 103 104 105 Wavelength, , m One aspect of electromagnetic radiation is that the related topics are more closely associated with optics and electronics than with those normally found in mechanical engineering courses. Nevertheless, these are widely encountered topics and the student is familiar with them through every day life experiences. From a viewpoint of previously studied topics students, particularly those with a background in mechanical or chemical engineering, will find the subject of Radiation Heat Transfer a little unusual. The physics background differs fundamentally from that found in the areas of continuum mechanics. Much of the related material is found in courses more closely identified with quantum physics or electrical engineering, i.e. Fields and Waves.