GEOG3051 Principles & Practice of Remote Sensing EM Radiation (Ii)

Total Page:16

File Type:pdf, Size:1020Kb

GEOG3051 Principles & Practice of Remote Sensing EM Radiation (Ii) UCL DEPARTMENT DEPARTMENT OF GEOGRAPHYOF GEOGRAPHY GEOGG141/ GEOG3051 Principles & Practice of Remote Sensing EM Radiation (ii) Dr. Mathias (Mat) Disney UCL Geography Office: 113, Pearson Building Tel: 7679 0592 Email: [email protected] http://www2.geog.ucl.ac.uk/~mdisney/teaching/GEOGG141/GEOGG141.html http://www2.geog.ucl.ac.uk/~mdisney/teaching/3051/GEOG3051.html UCL DEPARTMENT OF GEOGRAPHY EMR arriving at Earth • We now know how EMR spectrum is distributed • Radiant energy arriving at Earth’s surface • NOT blackbody, but close • “Solar constant” • solar energy irradiating surface perpendicular to solar beam • ~1373Wm-2 at top of atmosphere (TOA) • Mean distance of sun ~1.5x108km so total solar energy emitted = 4πr2x1373 = 3.88x1026W 8 • Incidentally we can now calculate Tsun (radius=6.69x10 m) from SB Law 4 26 2 •σ T sun = 3.88x10 /4π r so T = ~5800K 2 UCL DEPARTMENT OF GEOGRAPHY Departure from blackbody assumption • Interaction with gases in the atmosphere – attenuation of solar radiation 3 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: spatial relations • Now cover what happens when radiation interacts with Earth System • Atmosphere • On the way down AND way up • Surface • Multiple interactions between surface and atmosphere • Absorption/scattering of radiation in the atmosphere 4 UCL DEPARTMENT OF GEOGRAPHY Radiation passing through media • Various interactions, with different results From http://rst.gsfc.nasa.gov/Intro/Part2_3html.html 5 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: spatial relations • Definitions of radiometric quantities • Radiant energy emitted, transmitted of received per unit time is radiant flux (usually Watts, or Js-1) • Radiant flux density is flux per unit area (Wm-2) • Irradiance is radiant flux density incident on a surface (Wm-2) e.g. Solar radiation arriving at surface • Emittance (radiance or radiant exitance) (Wm-2) is radiant flux density emitted by a surface • For parallel beam, flux density defined in terms of plane perpendicular to beam. What about from a point? 6 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: point source Point source dω dF dA r • Consider flux dF emitted from point source into solid angle dω, where dF and dω very small • Intensity I defined as flux per unit solid angle i.e. I = dF/dω (Wsr-1) • Solid angle dω = dA/r2 (steradians, sr) 7 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: plane source dF ψ ω Plane source dS dS cos ψ • What about when we have a plane source rather than a point? • Element of surface with area dS emits flux dF in direction at angle ψ to normal • Radiant emittance, M = dF / dS (Wm-2) • Radiance L is intensity in a particular direction (dI = dF/ω) divided by the apparent area of source in that direction i.e. flux per unit area per solid angle (Wm-2sr-1) • Projected area of dS is direction ψ is dS cos ψ, so….. • Radiance L = (dF/ω) / dS cos ψ = dI/dS cos ψ (Wm-2sr-1) 8 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: radiance • So, radiance equivalent to: • intensity of radiant flux observed in a particular direction divided by apparent area of source in same direction • Note on solid angle (steradians): • 3D analog of ordinary angle (radians) • 1 steradian = angle subtended at the centre of a sphere by an area of surface equal to the square of the radius. The surface of a sphere subtends an angle of 4π steradians at its centre. 9 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: solid angle • Cone of solid angle Ω = 1sr • Radiant intensity from sphere •Ω = area of surface A / radius2 From http://www.intl-light.com/handbook/ch07.html 10 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: terms and units 11 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: cosine law • Emission and absorption • Radiance linked to law describing spatial distn of radiation emitted by Bbody with uniform surface temp. T (total emitted flux = σT4) • Surface of Bbody then has same T from whatever angle viewed • So intensity of radiation from point on surface, and areal element of surface MUST be independent of ψ, angle to surface normal • OTOH flux per unit solid angle divided by true area of surface must be proportional to cos ψ 12 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: cosine law X Radiometer dA Y X Radiometer ψ Y dA/cos ψ • Case 1: radiometer ‘sees’ dA, flux proportional to dA • Case 2: radiometer ‘sees’ dA/cos ψ (larger) BUT T same, so emittance of surface same and hence radiometer measures same • So flux emitted per unit area at angle ψ ∝ to cos ψ so that product of emittance (∝ cos ψ ) and area emitting (∝ 1/ cos ψ) is same for all ψ • This is basis of Lambert’s Cosine Law Adapted from Monteith and Unsworth, Principles of Environmental Physics 13 UCL DEPARTMENT OF GEOGRAPHY Radiation Geometry: Lambert’s Cosine Law • When radiation emitted from Bbody at angle ψ to normal, then flux per unit solid angle emitted by surface is ∝ cos ψ • Corollary of this: • if Bbody exposed to beam of radiant energy at an angle ψ to normal, the flux density of absorbed radiation is ∝ cos ψ • In remote sensing we generally need to consider directions of both incident AND reflected radiation, then reflectivity is described as bi-directional Adapted from Monteith and Unsworth, Principles of Environmental Physics 14 UCL DEPARTMENT OF GEOGRAPHY Recap: radiance • Radiance, L dω • power emitted (dF) per unit of solid angle (d ) and per unit of the projected ω ψ surface (dS cosψ) of an extended widespread source in a given direction, ψ (ψ = zenith angle, ϕ= azimuth angle) Projected surface dS cos ψ • L = d2F / (dω dS cos ψ) (in Wm-2sr-1) • If radiance is not dependent on ψ i.e. if same in all directions, the source is said to be Lambertian. Ordinary surfaces rarely found to be Lambertian. Ad. From http://ceos.cnes.fr:8100/cdrom-97/ceos1/science/baphygb/chap2/chap2.htm 15 UCL DEPARTMENT OF GEOGRAPHY Recap: emittance • Emittance, M (exitance) • emittance (M) is the power emitted (dW) per surface unit of an extended widespread source, throughout an hemisphere. Radiance is therefore integrated over an hemisphere. If radiance independent of ψ i.e. if same in all directions, the source is said to be Lambertian. • For Lambertian surface • Remember L = d2F / (dω dS cos ψ) = constant, so M = dF/dS = • M = L π 2 π 2 π Lcosψdω = 2πL cosψ sinψdψ = πL ∫0 ∫0 16 Ad. From http://ceos.cnes.fr:8100/cdrom-97/ceos1/science/baphygb/chap2/chap2.htm € UCL DEPARTMENT OF GEOGRAPHY Recap: irradiance • Radiance, L, defined as directional (function of angle) • from source dS along viewing Direct angle of sensor (θ in this 2D case, but more generally (θ, ϕ) in 3D case) • Emittance, M, hemispheric • Why?? Diffuse • Solar radiation scattered by atmosphere • So we have direct AND diffuse components Ad. From http://ceos.cnes.fr:8100/cdrom-97/ceos1/science/baphygb/chap2/chap2.htm 17 UCL DEPARTMENT OF GEOGRAPHY Reflectance • Spectral reflectance, ρ(λ), defined as ratio of incident flux to reflected flux at same wavelength •ρ (λ) = L(λ)/I(λ) • Extreme cases: • Perfectly specular: radiation incident at angle ψ reflected away from surface at angle -ψ • Perfectly diffuse (Lambertian): radiation incident at angle ψ reflected equally in all angles 18 UCL DEPARTMENT OF GEOGRAPHY Interactions with the atmosphere From http://rst.gsfc.nasa.gov/Intro/Part2_4.html 19 UCL DEPARTMENT OF GEOGRAPHY Interactions with the atmosphere R4 R1 R2 R3 target target target target • Notice that target reflectance is a function of • Atmospheric irradiance • reflectance outside target scattered into path • diffuse atmospheric irradiance • multiple-scattered surface-atmosphere interactions 20 From: http://www.geog.ucl.ac.uk/~mdisney/phd.bak/final_version/final_pdf/chapter2a.pdf UCL DEPARTMENT OF GEOGRAPHY Interactions with the atmosphere: refraction • Caused by atmosphere at different T having different density, hence refraction • path of radiation alters moving from medium of one density to another (different velocity) • index of refraction (n) is ratio of speed of light in a vacuum (c) to speed cn in another medium (e.g. Air) i.e. n = c/cn • note that n always >= 1 i.e. cn <= c • Examples • nair = 1.0002926 • nwater = 1.33 21 UCL DEPARTMENT OF GEOGRAPHY Refraction: Snell’s Law Incident • Refraction described by Snell’s Law radiation • For given freq. f, n1 sin θ1 = n2 sin θ2 n1 •where and are the angles from the θ 1 θ1 θ2 Optically normal of the incident and refracted waves less dense respectively Optically more • (non-turbulent) atmosphere can be θ 2 n2 dense considered as layers of gases, each with a Path Optically θ 3 unaffected different density (hence n) less dense by n • Displacement of path - BUT knowing 3 atmosphere Path affected by Snell’s Law can be removed atmosphere 22 After: Jensen, J. (2000) Remote sensing of the environment: an Earth Resources Perspective. UCL DEPARTMENT OF GEOGRAPHY Interactions with the atmosphere: scattering • Caused by presence of particles (soot, salt, etc.) and/or large gas molecules present in the atmosphere • Interact with EMR anc cause to be redirected from original path. • Scattering amount depends on: •λ of radiation • abundance of particles or gases • distance the radiation travels through the atmosphere (path length) 23 After: http://www.ccrs.nrcan.gc.ca/ccrs/learn/tutorials/fundam/chapter1/chapter1_4_e.html UCL DEPARTMENT OF GEOGRAPHY Atmospheric scattering 1: Rayleigh • Particle size << λ of radiation • e.g. very fine soot and dust or N2, O2 molecules • Rayleigh scattering dominates shorter λ and in upper atmos. • i.e. Longer λ scattered less (visible red λ scattered less than blue λ) • Hence
Recommended publications
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • 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).
    [Show full text]
  • Reflectance IR Spectroscopy, Khoshhesab
    11 Reflectance IR Spectroscopy Zahra Monsef Khoshhesab Payame Noor University Department of Chemistry Iran 1. Introduction Infrared spectroscopy is study of the interaction of radiation with molecular vibrations which can be used for a wide range of sample types either in bulk or in microscopic amounts over a wide range of temperatures and physical states. As was discussed in the previous chapters, an infrared spectrum is commonly obtained by passing infrared radiation through a sample and determining what fraction of the incident radiation is absorbed at a particular energy (the energy at which any peak in an absorption spectrum appears corresponds to the frequency of a vibration of a part of a sample molecule). Aside from the conventional IR spectroscopy of measuring light transmitted from the sample, the reflection IR spectroscopy was developed using combination of IR spectroscopy with reflection theories. In the reflection spectroscopy techniques, the absorption properties of a sample can be extracted from the reflected light. Reflectance techniques may be used for samples that are difficult to analyze by the conventional transmittance method. In all, reflectance techniques can be divided into two categories: internal reflection and external reflection. In internal reflection method, interaction of the electromagnetic radiation on the interface between the sample and a medium with a higher refraction index is studied, while external reflectance techniques arise from the radiation reflected from the sample surface. External reflection covers two different types of reflection: specular (regular) reflection and diffuse reflection. The former usually associated with reflection from smooth, polished surfaces like mirror, and the latter associated with the reflection from rough surfaces.
    [Show full text]
  • 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.
    [Show full text]
  • RADIANCE® ULTRA 27” Premium Endoscopy Visualization
    EW NNEW RADIANCE® ULTRA 27” Premium Endoscopy Visualization The Radiance® Ultra series leads the industry as a revolutionary display with the aim to transform advanced visualization technology capabilities and features into a clinical solution that supports the drive to improve patient outcomes, improve Optimized for endoscopy applications workflow efficiency, and lower operating costs. Advanced imaging capabilities Enhanced endoscopic visualization is accomplished with an LED backlight technology High brightness and color calibrated that produces the brightest typical luminance level to enable deep abdominal Cleanable splash-proof design illumination, overcoming glare and reflection in high ambient light environments. Medi-Match™ color calibration assures consistent image quality and accurate color 10-year scratch-resistant-glass guarantee reproduction. The result is outstanding endoscopic video image performance. ZeroWire® embedded receiver optional With a focus to improve workflow efficiency and workplace safety, the Radiance Ultra series is available with an optional built-in ZeroWire receiver. When paired with the ZeroWire Mobile battery-powered stand, the combination becomes the world’s first and only truly cordless and wireless mobile endoscopic solution (patent pending). To eliminate display scratches caused by IV poles or surgical light heads, the Radiance Ultra series uses scratch-resistant, splash-proof edge-to-edge glass that includes an industry-exclusive 10-year scratch-resistance guarantee. RADIANCE® ULTRA 27” Premium Endoscopy
    [Show full text]
  • The International System of Units (SI)
    NAT'L INST. OF STAND & TECH NIST National Institute of Standards and Technology Technology Administration, U.S. Department of Commerce NIST Special Publication 330 2001 Edition The International System of Units (SI) 4. Barry N. Taylor, Editor r A o o L57 330 2oOI rhe National Institute of Standards and Technology was established in 1988 by Congress to "assist industry in the development of technology . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . and to facilitate rapid commercialization ... of products based on new scientific discoveries." NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen U.S. industry's competitiveness; advance science and engineering; and improve public health, safety, and the environment. One of the agency's basic functions is to develop, maintain, and retain custody of the national standards of measurement, and provide the means and methods for comparing standards used in science, engineering, manufacturing, commerce, industry, and education with the standards adopted or recognized by the Federal Government. As an agency of the U.S. Commerce Department's Technology Administration, NIST conducts basic and applied research in the physical sciences and engineering, and develops measurement techniques, test methods, standards, and related services. The Institute does generic and precompetitive work on new and advanced technologies. NIST's research facilities are located at Gaithersburg, MD 20899, and at Boulder, CO 80303.
    [Show full text]
  • Ikonos DN Value Conversion to Planetary Reflectance Values by David Fleming CRESS Project, UMCP Geography April 2001
    Ikonos DN Value Conversion to Planetary Reflectance Values By David Fleming CRESS Project, UMCP Geography April 2001 This paper was produced by the CRESS Project at the University of Maryland. CRESS is sponsored by the Earth Science Enterprise Applications Directorate at NASA Stennis Space Center. The following formula from the Landsat 7 Science Data Users Handbook was used to convert Ikonos DN values to planetary reflectance values: ρp = planetary reflectance Lλ = spectral radiance at sensor’s aperture 2 ρp = π * Lλ * d ESUNλ = band dependent mean solar exoatmospheric irradiance ESUNλ * cos(θs) θs = solar zenith angle d = earth-sun distance, in astronomical units For Landsat 7, the spectral radiance Lλ = gain * DN + offset, which can also be expressed as Lλ = (LMAX – LMIN)/255 *DN + LMIN. The LMAX and LMIN values for each of the Landsat bands are given below in Table 1. These values may vary for each scene and the metadata contains image specific values. Table 1. ETM+ Spectral Radiance Range (W/m2 * sr * µm) Low Gain High Gain Band Number LMIN LMAX LMIN LMAX 1 -6.2 293.7 -6.2 191.6 2 -6.4 300.9 -6.4 196.5 3 -5.0 234.4 -5.0 152.9 4 -5.1 241.1 -5.1 157.4 5 -1.0 47.57 -1.0 31.06 6 0.0 17.04 3.2 12.65 7 -0.35 16.54 -0.35 10.80 8 -4.7 243.1 -4.7 158.3 (from Landsat 7 Science Data Users Handbook) The Ikonos spectral radiance, Lλ, can be calculated by using the formula given in the Space Imaging Document Number SE-REF-016: 2 Lλ (mW/cm * sr) = DN / CalCoefλ However, in order to use these values in the conversion formula, the values must be in units of 2 W/m * sr * µm.
    [Show full text]
  • Application Note (A2) LED Measurements
    Application Note (A2) LED Measurements Revision: F JUNE 1997 OPTRONIC LABORATORIES, INC. 4632 36TH STREET ORLANDO, FLORIDA 32811 USA Tel: (407) 422-3171 Fax: (407) 648-5412 E-mail: www.olinet.com LED MEASUREMENTS Table of Contents 1.0 INTRODUCTION ................................................................................................................. 1 2.0 PHOTOMETRIC MEASUREMENTS.................................................................................... 1 2.1 Total Luminous Flux (lumens per 2B steradians)...................................................... 1 2.2 Luminous Intensity ( millicandelas) ........................................................................... 3 3.0 RADIOMETRIC MEASUREMENTS..................................................................................... 6 3.1 Total Radiant Flux or Power (watts per 2B steradians)............................................. 6 3.2 Radiant Intensity (watts per steradian) ..................................................................... 8 4.0 SPECTRORADIOMETRIC MEASUREMENTS.................................................................. 11 4.1 Spectral Radiant Flux or Power (watts per nm)....................................................... 11 4.2 Spectral Radiant Intensity (watts per steradian nm) ............................................... 13 4.3 Peak Wavelength and 50% Power Points............................................................... 15 LED MEASUREMENTS 1.0 INTRODUCTION The instrumentation selected to measure the output of an LED
    [Show full text]
  • Radiometry of Light Emitting Diodes Table of Contents
    TECHNICAL GUIDE THE RADIOMETRY OF LIGHT EMITTING DIODES TABLE OF CONTENTS 1.0 Introduction . .1 2.0 What is an LED? . .1 2.1 Device Physics and Package Design . .1 2.2 Electrical Properties . .3 2.2.1 Operation at Constant Current . .3 2.2.2 Modulated or Multiplexed Operation . .3 2.2.3 Single-Shot Operation . .3 3.0 Optical Characteristics of LEDs . .3 3.1 Spectral Properties of Light Emitting Diodes . .3 3.2 Comparison of Photometers and Spectroradiometers . .5 3.3 Color and Dominant Wavelength . .6 3.4 Influence of Temperature on Radiation . .6 4.0 Radiometric and Photopic Measurements . .7 4.1 Luminous and Radiant Intensity . .7 4.2 CIE 127 . .9 4.3 Spatial Distribution Characteristics . .10 4.4 Luminous Flux and Radiant Flux . .11 5.0 Terminology . .12 5.1 Radiometric Quantities . .12 5.2 Photometric Quantities . .12 6.0 References . .13 1.0 INTRODUCTION Almost everyone is familiar with light-emitting diodes (LEDs) from their use as indicator lights and numeric displays on consumer electronic devices. The low output and lack of color options of LEDs limited the technology to these uses for some time. New LED materials and improved production processes have produced bright LEDs in colors throughout the visible spectrum, including white light. With efficacies greater than incandescent (and approaching that of fluorescent lamps) along with their durability, small size, and light weight, LEDs are finding their way into many new applications within the lighting community. These new applications have placed increasingly stringent demands on the optical characterization of LEDs, which serves as the fundamental baseline for product quality and product design.
    [Show full text]