DOCSLIB.ORG

The Metabolic Significance of Differential Absorption of Radiant Energy by Black and White Birds

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Metabolic Significance of Differential Absorption of Radiant Energy by Black and White Birds THE METABOLIC SIGNIFICANCE OF DIFFERENTIAL ABSORPTION OF RADIANT ENERGY BY BLACK AND WHITE BIRDS FRANK HEPPNERl Department of Zoology University of California Davis, California The surface color of homeotherms is com- The undyed birds exposed to radiant energy monly thought to have two possible functions: consumed a mean of 2.00 ml OJmin, while concealment (Cott 1957) and communication the dyed birds exposed to radiant energy had ( Lorenz 1935; Tinbergen 1948). Hamilton a mean consumption of 1.44 ml Oz/min. By and Heppner ( 1967) proposed a third possible assuming a thermal quotient of 4.8 Cal/ml 02 function for dark, or black, homeotherm color- (King and Famer 1961), the heat production ation: the reduction of the metabolic cost of of the blackened birds was 6.9 cal/min, and homeothermy by maximization of absorption the heat production of the white birds was of radiant solar energy. This hypothesis pro- 9.6 Cal/mm, a difference of 2.7 cal/min. It is posed that the integument o,f black animals this difference that must be accounted for in absorbs more of the visible and near infrared calculating the difference in the amount of components of solar energy than does the radiant energy absorbed by the blackened and integument of lighter-colored animals, and white birds. that this greater absorption may permit them to reduce their heat 108s~when ambient tem- DETERMINATION OF TOTAL AMOUNT peratures are below their lower critical tem- OF ENERGY FALLING ON SURFACE perature. As reported earlier, the rate of energy falling Hamilton and Heppner reported that black- on the surface of a bird in the metabolism dyed, white Zebra Finches (Poephilu castan- chamber was 1.23 cal/cm2-min, as determined Otis) demonstrated a significant metabolic by a 59junction Eppley pyroheliometer. The economy over undyed birds when both were metabolism chamber, which was made of exposed to artificial sunlight while in a mod- Plexiglas, had a lid fitted with an ultraviolet erately cold (10%) metabolism chamber. I transmitting glass filter. During a metabolism now report the results of experiments relating test, the chamber was submerged in a water the metabolic differences between blackened bath, with 1 cm of water over the top surface and white birds observed by Hamilton and of the chamber lid. Heppner to the difference in amount of radi- The spectrum of the light energy that fell on ant energy absorbed by the black and white a bird in the chamber, after passing through the birds in our experiments, and discuss a physi- lid and the water over the lid, was determined cal mechanism whereby dark-colored birds by employing a Beckman DK-2 spectrophoto,m- might achieve a metabolic advantage over eter set up in a spectroradiometry configura- lighter counterparts. tion. A Sylvania DWY “Sun-Gun” lamp, which was the artificial sun in the metabolism experi- DETERMINATION OF DIFFERENCES ment, was mounted over the entrance port of IN ABSORBED ENERGY the spectrophotometer. Spectrum measure- Of paramount importance is the quantitative ments were then made (fig. 1) over the range relationship between the difference in require- 0.359-2.960~ of: (A) the light of the lamp ments for chemical energy of the white and alone, (B ) the light passing through the lid blackened birds, and the different rates of of the metabolism chamber, which was energy absorption from the artificial sun. This mounted between the lamp and the spectro- relationship can be determined by comparing photometer, and (C) the light passing through the difference in heat production, expressed both the lid and a l-cm layer of tap water in calories, between the white and blackened which was created by making a rim of mask- birds, with the difference in the amount of ing tape around the edge of the chamber lid energy absorbed at the surface of birds in the and then pouring water on the lid. The area two color conditions. under the curves can be expressed as the amount of energy falling on‘ a unit of surface 1 Present address: Department of Zoology, University of Rhode Island, Kingston, Rhode Island 02881. per unit of time. The lid had little effect on The Condor, 72 :50-59, 1970 50 METABOLIC SIGNIFICANCE OF ABSORPTION OF RADIANT ENERGY 51 100 90 1 70- : 2 60- t, YI so- : ; 40- WAVELENGTH OJ,, 08 I I I I I, - .3 .5 .7 .9 1.1 I.3 1.5 1.7 1.9 2.1 2.3 2.5 FIGURE 1. Spectrum measurements of Sun-Gun WAVELENGTH I/L, artificial sun (A, Sun-Gun; B, Sun-Gun through filter; C, Sun-Gun through filter and water). FIGURE 2. Absorbance characteristics of the sur- faces of white and black-dyed Zebra Finches (solid line, black bird; dashed line, white bird). the energy passing through it (curve 1B ) over the spectrum range measured, but the water cut off radiation beyond 1.406 p and shifted tions at the five locations were then averaged the energy peak to about 1.050 .U (curve 1C). at 0.100 ,Aintervals and a compo,site curve was This curve represents the spectrum of the hand drawn for each bird (fig. 2). light energy falling on the surface of a bird The shapes of both curves are generally sim- in the metabolism chamber. From the pyro- ilar, both birds tending to be “white” beyond heliometer measurements, it was known that 1.060 p, but there is a sharp difference in the energy falling on the bird had an absolute absorbance from 0.350 to 0.800 p, with the value of 1.23 cal/c&-min. This value is blackened bird absorbing more, as would be equivalent to the area under curve 1C. expected. If the fraction of energy absorbed by the In figure 3 the emission spectrum of the surface is determined for each wavelength, lamp is again shown with the curves produced and this fraction then multiplied by the frac- by multiplying the absorption fractions of the tion of total energy emitted by the source at black and white birds at 0.106 p intervals times that wave-length, a new curve will be ob- the height of the emission curve at the same tained, the area under which will be the wavelength. The area under these curves, energy absorbed by the surface. This area can compared with the area under the curve rep- be measured by a mechanical integrator (pla- resenting the energy falling on the bird, indi- nimeter), and compared with the area under cates what fraction of the energy falling on the curve of the emission spectrum, the ab- the bird is actually absorbed. solute value of which is known ( 1.23 cal/cms- The areas under the three curves were mea- min). The new value obtained will be the sured with a planimeter. It was found that energy absorbed by the surface of the bird. the area under the curve representing the en- The absorption characteristics of the birds ’ ergy absorbed by the black bird was 33.2 per surfaces were determined by setting up the cent of the total energy falling on the bird, Beckman DK-2 spectrophotometer in a spec- and the area under the curve for the white troreflectometer configuration. Live white bird, 16.0 per cent. Zebra Finches and newly dyed, blackened From the pyroheliometer measurements, Zebra Finches were anaesthetized with a gas the area under the curve representing energy anaesthetic and strapped to the sample port falling on the bird is equivalent to 1.23 cal/ of the integrating sphere of the spectrophotom- cm2-min. The black bird absorbed 33.2 per eter. The reflection and absorption charac- cent of this energy, or 0.41 cal/cm2-min, and teristics were compared to a white reference the white bird 16.0 per cent, or 0.20 cal/cm2- block of magnesium carbonate. Because there mm. were slight differences in absorption at differ- Finally, to determine the difference in total ent locations on the back, measurements were energy absorbed by the black and white birds, taken at five locations. The absorption frac- it is necessary to know the area upon which 52 FRANK HEPPNER 100 90 ;;e;;;Sfolling 80 . Energy absorbed 5 70 by black bird. ti Energy absorbed ; 60 by white bird. Ly g 50 f 40 4 / ‘, 1.23 cal/cm2Amin \ ff 30 20 WAVELENGTH (+L’ FIGURE 3. Energy falling on the surface of birds, and energy absorbed by black and white birds. the radiation is falling. This cannot be mea- conservative. The effective absorbing area sured precisely, because there are reflections of the birds is probably larger than the 14.7 from the bottom of the chamber that will ir- cm2 obtained by projecting the dorsal surface radiate the ventral surface of the bird, postural of the bird on a plane, since there will be some variations, and differences in feather erection reflections in the experimental universe that which will alter the effective area exposed to will impinge on all surfaces of the bird, direct radiation. An estimate can be obtained although the intensity of these reflections is by projecting the dorsal view of the bird on probably small. A larger surface area than a plane surface, and measuring the area of estimated here would increase the absolute this projection. The dorsal projected area of value of the difference in energy absorbed by three birds (excluding the tail) was 13.8, 15.2, black and white birds. Even with a conserva- and 15.2 cm2, or a mean of 14.7 cm2. These tive value, it appears that the difference in areas were obtained by measuring the pro- energy absorbed is sufficient to account for jected area with a planimeter.
Load more

Recommended publications
  • Plant Lighting Basics and Applications
    9/18/2012 Keywords Plant Lighting Basics and Light (radiation): electromagnetic wave that travels through space and exits as discrete Applications energy packets (photons) Each photon has its wavelength-specific energy level (E, in joule) Chieri Kubota The University of Arizona E = h·c / Tucson, AZ E: Energy per photon (joule per photon) h: Planck’s constant c: speed of light Greensys 2011, Greece : wavelength (meter) Wavelength （nm） 380 nm 780 nm Energy per photon [J]: E = h·c / Visible radiation (visible light) mole photons = 6.02 x 1023 photons Leaf photosynthesis UV Blue Green Red Far red Human eye response peaks at green range. Luminous intensity (footcandle or lux Photosynthetically Active Radiation ) does not work (PAR, 400-700 nm) for plant light environment. UV Blue Green Red Far red Plant biologically active radiation (300-800 nm) 1 9/18/2012 Chlorophyll a Phytochrome response Chlorophyll b UV Blue Green Red Far red Absorption spectra of isolated chlorophyll Absorptance 400 500 600 700 Wavelength (nm) Daily light integral (DLI or Daily Light Unit and Terminology PPF) Radiation Photons Visible light •Total amount of photosynthetically active “Base” unit Energy (J) Photons (mol) Luminous intensity (cd) radiation (400‐700 nm) received per sq Flux [total amount received Radiant flux Photon flux Luminous flux meter per day or emitted per time] (J s-1) or (W) (mol s-1) (lm) •Unit: mole per sq meter per day (mol m‐2 d‐1) Flux density [total amount Radiant flux density Photon flux (density) Illuminance, • Under optimal conditions, plant growth is received per area per time] (W m-2) (mol m-2 s-1) Luminous flux density highly correlated with DLI.
    [Show full text]
  • Applied Spectroscopy Spectroscopic Nomenclature
    Applied Spectroscopy Spectroscopic Nomenclature Absorbance, A Negative logarithm to the base 10 of the transmittance: A = –log10(T). (Not used: absorbancy, extinction, or optical density). (See Note 3). Absorptance, α Ratio of the radiant power absorbed by the sample to the incident radiant power; approximately equal to (1 – T). (See Notes 2 and 3). Absorption The absorption of electromagnetic radiation when light is transmitted through a medium; hence ‘‘absorption spectrum’’ or ‘‘absorption band’’. (Not used: ‘‘absorbance mode’’ or ‘‘absorbance band’’ or ‘‘absorbance spectrum’’ unless the ordinate axis of the spectrum is Absorbance.) (See Note 3). Absorption index, k See imaginary refractive index. Absorptivity, α Internal absorbance divided by the product of sample path length, ℓ , and mass concentration, ρ , of the absorbing material. A / α = i ρℓ SI unit: m2 kg–1. Common unit: cm2 g–1; L g–1 cm–1. (Not used: absorbancy index, extinction coefficient, or specific extinction.) Attenuated total reflection, ATR A sampling technique in which the evanescent wave of a beam that has been internally reflected from the internal surface of a material of high refractive index at an angle greater than the critical angle is absorbed by a sample that is held very close to the surface. (See Note 3.) Attenuation The loss of electromagnetic radiation caused by both absorption and scattering. Beer–Lambert law Absorptivity of a substance is constant with respect to changes in path length and concentration of the absorber. Often called Beer’s law when only changes in concentration are of interest. Brewster’s angle, θB The angle of incidence at which the reflection of p-polarized radiation is zero.
    [Show full text]
  • CNT-Based Solar Thermal Coatings: Absorptance Vs. Emittance
    coatings Article CNT-Based Solar Thermal Coatings: Absorptance vs. Emittance Yelena Vinetsky, Jyothi Jambu, Daniel Mandler * and Shlomo Magdassi * Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel; [email protected] (Y.V.); [email protected] (J.J.) * Correspondence: [email protected] (D.M.); [email protected] (S.M.) Received: 15 October 2020; Accepted: 13 November 2020; Published: 17 November 2020 Abstract: A novel approach for fabricating selective absorbing coatings based on carbon nanotubes (CNTs) for mid-temperature solar–thermal application is presented. The developed formulations are dispersions of CNTs in water or solvents. Being coated on stainless steel (SS) by spraying, these formulations provide good characteristics of solar absorptance. The effect of CNT concentration and the type of the binder and its ratios to the CNT were investigated. Coatings based on water dispersions give higher adsorption, but solvent-based coatings enable achieving lower emittance. Interestingly, the binder was found to be responsible for the high emittance, yet, it is essential for obtaining good adhesion to the SS substrate. The best performance of the coatings requires adjusting the concentration of the CNTs and their ratio to the binder to obtain the highest absorptance with excellent adhesion; high absorptance is obtained at high CNT concentration, while good adhesion requires a minimum ratio between the binder/CNT; however, increasing the binder concentration increases the emissivity. The best coatings have an absorptance of ca. 90% with an emittance of ca. 0.3 and excellent adhesion to stainless steel. Keywords: carbon nanotubes (CNTs); binder; dispersion; solar thermal coating; absorptance; emittance; adhesion; selectivity 1.
    [Show full text]
  • Direct Insolation Models
    SERI/TR-33S-344 UC CATEGORY: UC-S9,61,62,63 DIRECT INSOLATION MODELS RICHARD BIRD ROLAND L. HULSTROM JANUARY 1980 PREPARED UNDER TASK No. 3623.01 Solar Energy Research Institute 1536 Cole Boulevard Golden. Colorado 80401 A Division of Midwest Research Institute Prepared for the U.S_ Department of Energy Contract No_ EG-77-C-01-4042 , '. Printed in the United States of America Available from: National Technical Information Service U.S. Departm ent of Commerce 5285 Port Royal Road Springfi e1dt VA 22161 Price: Microfiche $3.00 Printed Copy $ 5.25 NOTICE This report was prepared as an account of work sponsored by the United States Govern­ ment. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process dis closed, or represents that its us e would not infringe privately owned rights. S=�I TR-344 FOREWORD This re port documents wo rk pe rforme d by the SERI Energy Resource Assessment Branch for the Division of Solar Energy Technology of the U.S. De pa rtment of Energy. The re po rt compares several simple direct insolation models with a rigorous solar transmission model and describes an improved , simple, direct insolation model. Roland L. Hulstrom , Branch Chief Energy Resource Assessment , \ Approved for: SOLAR ENERGY RE SEARCH INSTITUTE for Research iii S=�I TR-344 TABLE OF CONTENTS 1.0 Introduction •••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1 2.0 Description of Models •••••••••••• .
    [Show full text]
  • Lighting: the Principles
    TECHNICAL GUIDE Cross Sector AHDB Fellowship CP 085 Dr Phillip Davis, Stockbridge Technology Centre Lighting: The principles Filmed over 3 weeks at Stockbridge Technology Centre SCAN WITH LAYAR APP 2 TECHNICAL GUIDE Lighting: The principles CONTENTS SECTION ONE LIGHT AND LIGHTING SECTION THREE LEDS IN HORTICULTURE 1.1 What is light? 6 3.1 Crop growth under red and blue LEDs 21 1.2 The natural light environment and its 3.2 The influences of other colours of impact on plant light responses 6 light on crop growth 22 1.3 The measurement of light 6 3.3 End of day, day extension and night interruption lighting 23 1.3.1 Photometric light measurement – lumens and lux 6 3.4 Interlighting 23 1.3.2 Radiometric light measurement – Watts per 3.5 Propagation 24 metre squared or Joules per metre squared 8 3.6 Improving crop quality 24 1.3.3 Photon counts – Moles 8 3.6.1 Improving crop morphology and reducing 1.3.4 Daily light integrals (DLI) 10 the use of plant growth regulators 24 1.4 Conversions between different 3.6.2 Improving pigmentation 25 measurement units 10 3.6.3 Improving flavour and aroma 26 1.5 Assessing light quality 10 3.7 Lighting strategies 26 1.6 Overview of light technologies 10 3.8 Other lighting techniques 27 1.6.1 Incandescent and halogen bulbs 10 3.9 Insect management under LEDs 27 1.6.2 Fluorescent tubes 10 3.10 Plant pathogens and their interactions 1.6.3 High intensity discharge lamps 11 with light 28 1.6.4 Plasma and sulphur lamps 12 3.11 Conclusions 28 1.6.5 LED technology 12 SECTION FOUR OTHER INFORMATION SECTION TWO PLANT LIGHT RESPONSES 4.1 References 30 2.1 Photosynthesis 15 2.2 Light stress – Photoinhibition 15 2.3 Sensing light quality 18 2.4 UVB light responses 18 2.5 Blue and UVA light responses 18 2.6 Green light responses 18 2.7 Red and far-red light responses 19 2.8 Hormones and light 19 3 TECHNICAL GUIDE Lighting: The principles GLOSSARY Cryptochrome A photoreceptor that is sensitive to blue and UVA light.
    [Show full text]
  • Relation of Emittance to Other Optical Properties *
    JOURNAL OF RESEARCH of the National Bureau of Standards-C. Engineering and Instrumentation Vol. 67C, No. 3, July- September 1963 Relation of Emittance to Other Optical Properties * J. C. Richmond (March 4, 19G3) An equation was derived relating t he normal spcctral e mittance of a n optically in homo­ geneous, partially transmitting coating appli ed over an opaque substrate t o t he t hi ckncs and optical properties of t he coating a nd the reflectance of thc substrate at thc coaLin g­ SLI bstrate interface. I. Introduction The 45 0 to 0 0 luminous daylight r efl ectance of a composite specimen com prising a parLiall:\' transparent, spectrally nonselective, ligh t-scattering coating applied to a completely opaque (nontransmitting) substrate, can be computed from the refl ecta.nce of the substrate, the thi ck­ ness of the coaLin g and the refl ectivity and coefficien t of scatter of the coating material. The equaLions derived [01' these condi tions have been found by experience [1 , 2)1 to be of considerable praeLical usefulness, even though sever al factors ar e known to exist in real m aterials that wer e no t consid ered in the derivation . For instance, porcelain enamels an d glossy paints have significant specular refl ectance at lhe coating-air interface, and no r ea'! coating is truly spectrally nonselective. The optical properties of a material vary with wavelength , but in the derivation of Lh e equations refened to above, they ar e consid ered to be independent of wavelength over the rather narrow wavelength band encompassin g visible ligh t.
    [Show full text]
  • The Effects of Physical Parameters on the Absorption Coefficient of Natural Waters
    AN ABSTRACT OF THE THESIS OF W. Scott Pegau for the degree of Doctor of Philosophy in Oceanography presented on February 23, 1996. Title: The Effects of Physical Parameters on the Absorption Coefficient of Natural Waters. Abstract approved: Redacted for privacy J. Ronald V. Zaneveld The absorption coefficient is one of the fundamental parameters used for studies in hydrologic optics. The significance of this parameter makes it important to understand how to properly measure it and how the absorption of components, such as water, depend on physical parameters such as temperature and salinity. A discussion is provided of a majority of the techniques available for measuring the absorption coefficient. Results from a comparison of the techniques indicates that natural variability in the optical properties is an important factor to consider when comparing or reporting measured values of the absorption coefficient. The agreement between methods was found to be best at longer wavelengths where the absorption by water is a significant portion of the total absorption coefficient. In order to test the accuracy of measurements of the absorption coefficient a practical TOP closure equation is developed. Application of the equation to field measurements is limited by our ability to measure the volume scattering function. The dependence of the absorption coefficient of water on temperature and salinity is investigated. It was found that the absorption coefficient in the near infrared portion of the spectrum is strongly dependent on temperature and salinity. In the visible region the only portion with a temperature dependence > 0.00 1 m1/°C is in the neighborhood of 610 nm.
    [Show full text]
  • Radiometry and Photometry
    Radiometry and Photometry Wei-Chih Wang Department of Power Mechanical Engineering National TsingHua University W. Wang Materials Covered • Radiometry - Radiant Flux - Radiant Intensity - Irradiance - Radiance • Photometry - luminous Flux - luminous Intensity - Illuminance - luminance Conversion from radiometric and photometric W. Wang Radiometry Radiometry is the detection and measurement of light waves in the optical portion of the electromagnetic spectrum which is further divided into ultraviolet, visible, and infrared light. Example of a typical radiometer 3 W. Wang Photometry All light measurement is considered radiometry with photometry being a special subset of radiometry weighted for a typical human eye response. Example of a typical photometer 4 W. Wang Human Eyes Figure shows a schematic illustration of the human eye (Encyclopedia Britannica, 1994). The inside of the eyeball is clad by the retina, which is the light-sensitive part of the eye. The illustration also shows the fovea, a cone-rich central region of the retina which affords the high acuteness of central vision. Figure also shows the cell structure of the retina including the light-sensitive rod cells and cone cells. Also shown are the ganglion cells and nerve fibers that transmit the visual information to the brain. Rod cells are more abundant and more light sensitive than cone cells. Rods are 5 sensitive over the entire visible spectrum. W. Wang There are three types of cone cells, namely cone cells sensitive in the red, green, and blue spectral range. The approximate spectral sensitivity functions of the rods and three types or cones are shown in the figure above 6 W. Wang Eye sensitivity function The conversion between radiometric and photometric units is provided by the luminous efficiency function or eye sensitivity function, V(λ).
    [Show full text]
  • Principles of the Measurement of Solar Reflectance, Thermal Emittance, and Color
    Principles of the Measurement of Solar Reflectance, Thermal Emittance, and Color Contents Roof Heat Transfer Electromagnetic Radiation Radiative Properties of Surfaces Measuring Solar Radiation Measuring Solar Reflectance Measuring Thermal Emittance Measuring Color 1. Roof Heat Transfer 3 Roof surface is heated by solar absorption, cooled by thermal emission + convection Radiative Cooling Convective Solar Cooling Absorption Troof Insulatio n T Qin = U (Troof – inside Tinside) Most solar heat gain is dissipated by convective and radiative cooling… ...because the conduction heat transfer coefficient is much less than those for convection & radiation 2. Electromagnetic Radiation 7 The electromagnetic spectrum spans radio waves to gamma rays This includes sunlight (0.3 – 2.5 μm) and thermal IR radiation (4 – 80 μm) (0.4 – 0.7 All surfaces emit temperature-dependent electromagnetic radiation • Stefan-Boltzmann law • Blackbody cavity is a perfect absorber and emitter of radiation • Total blackbody radiation [W m-2] = σ T 4, where – σ = 5.67 10-8 W m-2 K-4 – T = absolute temperature [K] • At 300 K (near room temperature) σ T 4 = 460 W m-2 Higher surface temperatures → shorter wavelengths Solar radiation from sun's surface (5,800 K) peaks near 0.5 μm (green) Thermal radiation from ambient surfaces (300 K) peaks near 10 μm (infrared) Extraterrestrial sunlight is attenuated by absorption and scattering in atmosphere Global (hemispherical) solar radiation = direct (beam) sunlight + diffuse skylight Pyranometer measures global (a.k.a. Pyranometer hemi-spherical) sunlight on with horizontal surface sun-tracking shade Pyrheliometer measures measures direct (a.k.a. collimated, diffuse beam) light from sun skylight Let's compare rates of solar heating and radiative cooling Spectral heating rate of a black roof facing the sky on a 24-hour average basis, shown on a log scale.
    [Show full text]
  • Principles of Radiation Measurement
    Principles of Radiation Measurement This report presents a comprehensive summary of the terminology and units used in radiometry, photometry, and the measurement of photosynthetically active radiation (PAR). Measurement errors can arise from a number of sources, and these are explained in detail. Finally, the conversion of radiometric and photometric units to photon units is discussed. In this report, the International System of Units (SI) is used unless noted otherwise.9 Radiometry component of sunlight plus the diffuse component of skylight received together on a horizontal surface). This Radiometry1 is the measurement of the properties of physical quantity is measured by a pyranometer such as radiant energy (SI unit: joule, J), which is one of the many the LI-200R. Unit: W m-2. interchangeable forms of energy. The rate of flow of radi- ant energy, in the form of an electromagnetic wave, is Direct Solar Radiation is the radiation emitted from the called the radiant flux (unit: watt, W; 1 W = 1 J s-1). Radi- solid angle of the sun’s disc, received on a surface per- ant flux can be measured as it flows from the source (the pendicular to the axis of this cone, comprising mainly sun, in natural conditions), through one or more reflect- unscattered and unreflected solar radiation. This physical -2 ing, absorbing, scattering and transmitting media (the quantity is measured by a pyrheliometer. Unit: W m . Earth’s atmosphere, a plant canopy, etc.) to the receiving Diffuse Solar Radiation (sky radiation) is the downward surface of interest (e.g. a photosynthesizing leaf).8 scattered and reflected radiation coming from the whole hemisphere, with the exception of the solid angle sub- Terminology and Units tended by the sun’s disc.
    [Show full text]
  • Principles and Techniques of Remote Sensing
    EE/Ae 157a Introduction to the Physics and Techniques of Remote Sensing Week 2: Nature and Properties of Electromagnetic Waves 2-1 TOPICS TO BE COVERED • Fundamental Properties of Electromagnetic Waves – Electromagnetic Spectrum, Maxwell’s Equations, Wave Equation, Quantum Properties of EM Radiation, Polarization, Coherency, Group and Phase Velocity, Doppler Effect • Nomenclature and Definition of Radiation Quantities – Radiation Quantities, Spectral Quantities, Luminous Quantities • Generation of Electromagnetic Radiation • Detection of Electromagnetic Radiation • Overview of Interaction of EM Waves with Matter • Interaction Mechanisms Throughout the Electromagnetic Spectrum 2-2 ELECTROMAGNETIC SPECTRUM 2-3 MAXWELL’S EQUATIONS B E t D H J t B 0r H D 0 rE E 0 B 0 2-4 WAVE EQUATION From Maxwell’s Equations, we find: E H 0 r t 2E 0 r 0 r t 2 E E 2E 2E 2E 0 0 r 0 r t2 This is the free-space wave equation 2-5 SOLUTION TO THE WAVE EQUATION For a sinusoidal field, the wave equation reduces to 2 2 E 2 E 0 cr The solution to this equation is of the form E Aei kr t The speed of light is given by 1 c0 cr 0 r 0r r r 2-6 QUANTUM PROPERTIES OF EM RADIATION • Maxwell’s equations describe mathematically smooth motion of fields. • For very short wavelengths, it fails to describe certain significant phenomena when the wave interacts with matter. • In those cases, a quantum description is more appropriate. • In this description, the EM radiation is presented by a quantized burst with energy Q proportional to the
    [Show full text]
  • On Kirchhoff's Law and Its Generalized Application to Absorption and Emission by Cavities *
    JOURNAL OF RESEARCH of the National Bureau of Standards-B. Mathematics and Mathematical Physics Vol. 69B, No.3, July-September 1965 On Kirchhoff's Law and Its Generalized Application to Absorption and Emission by Cavities * Francis J. Kelly (March 15, 1965) Severa l a uthurs have ma de the assumption that Kirc hhoff's Law holds fur the apparent local s pec­ tral e mittance and apparent lo cal s pectral absorptance of a ny point on the inte rior s urface of a cavity. The correctness of this assumption is de monstrate d under cert ain general cunditiuns, and it s practi cal appli cati on to the calc ul ation of the tota l Aux a bsorbed by a cavit y or s pacecraft is di scussed. A fur­ ther app li cation to the case of a nunisothe rmal cavity ur spacecraft is de rived. By this de rivati on a n easy methud fur determining the total Au x e mitt ed fru lll s uc h a nonisothe rmal cavity is found when the di s tribution of the appare nt lucal s pectral e mittance uf the is uthermal c avity is known. T he economy and versatility of this methud is s hown by the calc ulation of the total Au x e mitt ed from a noni solhermal cylindrical cavit y for several a rbitra ry cases of te mpe rature di s tribution on the int e rior s urface of the c avity. Finally, the int egra l eq uation for a diffuse cav it y whose wall e mittance varies with position on the wall is tra nsformed to an e quation havi ng a symme tric kernel.
    [Show full text]