DOCSLIB.ORG

Lecture 9: Radiation Transfer Community Business — Check the Assignments HW #3 Due Next Wednesday

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Lecture 9: Radiation Transfer Community Business — Check the Assignments HW #3 Due Next Wednesday Atmospheric Sciences 321 Science of Climate Lecture 9: Radiation Transfer Community Business Check the assignments HW #3 due next Wednesday Questions? Radiative Transfer Equation For absorption and emission only dIv cosθ = ρakv (Bv (T ) − Iv ) dz Now define optical depth a little differently, from the surface up. z τ (z) = ρ k dz v ∫0 a v What is Optical Depth? It is a coordinate transformation. Instead of using physical distance (vertical or horizontal), we rescale to a dimensionless coordinate, where optical depth = 1 means that only e-1 = 0.368 of the energy is passed without being extincted (absorbed or scattered) in passing through one unit of optical depth. 1.2 1 z Exp(-tau) τ (z) = ρ k dz 0.8 v ∫0 a v 0.6 Exp(-tau) F( ) F e−τ 0.4 τ = ∞ 0.2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Tau = Optical Depth Example Suppose you look out the window of ATG 610 at the Space Needle on a clear day. The optical depth distance to the Space Needle is almost zero at visible wavelengths, you see it clearly even though it is almost 3 miles away SW. On a very foggy day the optical depth distance to the Space Needle might be effectively infinite. You have no chance of seeing the Space Needle, but the physical distance is the same. (the optical depth is the more relevant distance for seeing, or transmitting radiation.) In the infrared the optical distance in the middle of the 15 micron CO2 band might be quite large, since there is a lot of CO2 between here and the Space Needle. Two Photons Two Photons, 9.6Micron and 12Micron, arrive at 30km altitude on their way to space from Los Angeles. 12Micron has lots of friends with him, basically the whole group who left LA. 9.6Micron is alone, all his friends from LA were absorbed and became heat, but he picked up a few strangers who were emitted along the way. 12Micron says to 9.6Micron, “You 9.6Micron types are weak, my whole group made it from LA.” 9.6Micron says, “We actually have more energy than you 12Micron types, but we had to travel hundreds of optical depths to get here and you all had to travel less than one optical depth to get here.” Another Example: You are flying over the ocean. There is a small sand island in the sea below you, which has an albedo of 0.5 compared to the surrounding ocean albedo of 0.1. A cloud with an optical depth of 1 is between you and the surface. Can you see the island? The cloud transmits exp(-1) of the incident light and reflects back 1-exp(-1), assuming that which is not transmitted is reflected back by the cloud (no absorption) Cloud with unit optical depth I(1-e-1) I -2 0.1Ie 0.5Ie-2 -1 Ie -1 0.1Ie-1 0.5Ie Blue Water Island Island = I*(1-e-1+0.5*e-2)=0.6997*I Ocean = I*(1-e-1+0.5*e-2)=0.6455*I Difference is about 8%, probably detectable with human eye, but clearly might not be for optical depth = 2 Without cloud contrast is a factor of 5; 0.5 vs 0.1 Some formulas for Clouds and Radiation Combine our formula for liquid water content 4 LWC = πr 3ρ hN 3 L with our formula for optical depth τ = 2π h r 2 N To get a new formula for optical depth 3 LWC τ = 2 ρL r So the optical depth is proportional to the liquid water content and inversely proportional to the average particle radius. What Clouds do Cloud particle radius matters for solar reflection Twomey Effect Clouds are water collected on cloud condensation nuclei. So if I double the number of cloud condensation nuclei and keep the liquid water content the same, then the optical depth will do what? τ = 2π h r 2 N 4 3 LWC = πr ρ hN 3 L for fixed LWC 1 3 3 LWC ⎛ N1 ⎞ τ = r2 = r1 ⎜ ⎟ 2 ρL r ⎝ N2 ⎠ Twomey Effect Clouds are water collected on cloud condensation nuclei. So if I double the number of cloud condensation nuclei and keep the liquid water content the same, then the optical depth will do what? 4 3 3 LWC LWC = πr ρLhN τ = 3 2 ρL r Double 1 1 number, 3 3 ⎛ N1 ⎞ ⎛ N1 ⎞ radius r2 = r1 ⎜ ⎟ = r1 ⎜ ⎟ = 0.79 r1 decreases ⎝ N2 ⎠ ⎝ 2N1 ⎠ a little τ τ = 1 = 1.26τ Optical depth increases 26% 2 0.79 1 Aerosols and Cloud Reflection Ship Tracks and other pollution brighten clouds Remotely Sensed Cloud Droplet Radius Cloud droplet radius Aerosols and Cloud Reflection Ship Tracks and other pollution brighten clouds First indirect effect of aerosols: more aerosols reduce cloud particle radius, so for fixed LWC clouds reflect more solar radiation Second indirect effect of aerosols: More aerosols reduce cloud particle radius, so precipitation size particles less easily formed, LWC increases due to reduced precipitation. Aerosols and Cloud Reflection Ship Tracks and other pollution brighten clouds My FavoriteAEROSOL EFFECTS Image of smoke bright over land Aerosol Effectsdirect reflection by aerosols ship tracks first and second indirect effects smoke dark over clouds semi-direct effect Zoo of aerosol effects Tables from IPCC IN = Ice Nuclei - the small particles on which cloud ice can form Thermal Equilibrium in Realistic Model We have a one-dimensional (z-only) model of the global atmosphere that solves for the vertical distribution of temperature in radiative or thermal equilibrium. In radiative equilibrium all the radiative energy flux convergences add to zero. ∂T 1 ∂F | = − = 0.0 ∂t rad c ρ ∂z ρ In thermal equilibrium we add an adjustment process that moves energy vertically to conserve energy while keep the lapse rate at less than some value. ∂T 1 ∂F |rad = − + Convection = 0.0 ∂t cρ ρ ∂z Radiative and Thermal Equilibria - Global Here are four solutions, pure radiative, Dry adiabatic lapse rate, moist adiabatic lapse rate and global mean observed lapse rate We specified the water vapor, carbon dioxide and ozone profiles – no clouds Role of H20, CO2 and O3 You can see that water vapor only gets close Carbon dioxide warms about 10˚C and Ozone produces the stratosphere Heating Rates in Thermal Equilibrium Radiation cools the troposphere and the stratosphere is in radiative equilibrium The stratosphere is a balance by shortwave heating by ozone and longwave cooling from carbon dioxide 1-D Model: Total Solar Irradiance sensitivity Sensitivity depends on what we assume about humidity, Fixed absolute or fixed relative humidity Sensitivity to TSI more than doubles for fixed relative humidity compared to fixed absolute humidity 0.5 K/% for FAH 1.36 K/% for FRH These are clear-sky calculations, but surface albedo has been adjusted to make surface temperature close to observed for TSI/TSI0=1.0 1-D Model Cloudless CO2 Sensitivity Change CO2 concentration, Fixed Absolute and Fixed Relative Humidity. Temperature is not linear in CO2. Opacity of CO2 is more like log of concentration, not linear in concentration. Going from zero to 300 has a much bigger effect than going from 300 to 600 ppmv. Lines saturate. Clouds and Earth’s Temperature All the previous results were for clear skies, but clouds have a substantial effect on the TOA energy balance. Clouds in 1-D model Here are some clouds Clouds in 1-D model Here are some clouds. and their effects Clouds in 1-D model Here are some clouds. and their effects Clouds in 1-D model Here are some clouds. and their effects Observed Cloud Fractions High Clouds (p<440mb) Max High Cloud in tropical rain areas Observed Cloud Fractions Low Clouds (p > 680mb) Max low cloud subtropical stratus Observed Cloud Fractions Total Clouds Max total cloud Midlatitude Oceans Cloud High Fractional Coverage Low Cloud Fractions High Low All Total Heuristic Model of Cloud Radiative Effect (CRE) a.k.a. Cloud Forcing TOA Energy Balance S0 ↑ RTOA = (1−α p ) − F (∞) 4 ΔR = R − R = ΔQ − ΔF ↑ (∞) TOA cloudy clear abs Cloud Radiative Effect – Add Clouds, what changes? S S ΔQ = 0 (1−α ) − 0 (1−α ) abs 4 cloudy 4 clear S0 S0 = (α cloudy −α clear ) = − Δα p 4 4 Heuristic Model of Cloud Radiative Effect (CRE) a.k.a. Cloud Forcing • Cloud Radiative Effect – Add Clouds, what changes? ΔR = R − R = ΔQ − ΔF ↑ (∞) TOA cloudy clear abs • Shortwave bit S S ΔQ = 0 (1−α ) − 0 (1−α ) abs 4 cloudy 4 clear S0 S0 = (α cloudy −α clear ) = − Δα p 4 4 • Longwave bit ΔF ↑ (∞) = F ↑ (∞) − F ↑ (∞) cloudy clear Heuristic Model of Cloud Radiative Effect (CRE) a.k.a. Cloud Forcing • Longwave bit ΔF ↑ (∞) = F ↑ (∞) − F ↑ (∞) cloudy clear • Expand using grey absorption integral equations T {z ,∞} ↑ 4 4 ct 4 ΔF (∞) = σTz T {zct ,∞}−σTs T {zs ,∞}− σT(z′) dT {z′,∞} ct ∫T {z ,∞} s • Assume cloud top is above most of water vapor, then OLR is emission from top of cloud T {zct ,∞}≈ 1.0 1 ΔF ↑ (∞) = σT 4 −σT 4T {z ,∞}− σT(z′)4 dT {z′,∞} zct s s ∫T {zs ,∞} ↑ 4 ↑ ΔF (∞) = σTz − Fclear (∞) ct Heuristic Model of Cloud Radiative Effect (CRE) a.k.a. Cloud Forcing • Putting the pieces together, ↑ ΔR = R − R = ΔQ − ΔF (∞) TOA cloudy clear abs • becomes S0 ↑ 4 ΔRTOA = − Δα p + Fclear (∞) −σTz 4 ct • The solar and longwave parts tend to be of opposite sign and we can calculate the cloud top temperature at which they will exactly cancel.
Load more

Recommended publications
  • Lecture 5. Interstellar Dust: Optical Properties
    Lecture 5. Interstellar Dust: Optical Properties 1. Introduction 2. Extinction 3. Mie Scattering 4. Dust to Gas Ratio 5. Appendices References Spitzer Ch. 7, Osterbrock Ch. 7 DC Whittet, Dust in the Galactic Environment (IoP, 2002) E Krugel, Physics of Interstellar Dust (IoP, 2003) B Draine, ARAA, 41, 241, 2003 1. Introduction: Brief History of Dust Nebular gas long accepted but existence of absorbing interstellar dust controversial. Herschel (1738-1822) found few stars in some directions, later extensively demonstrated by Barnard’s photos of dark clouds. Trumpler (PASP 42 214 1930) conclusively demonstrated interstellar absorption by comparing luminosity distances & angular diameter distances for open clusters: • Angular diameter distances are systematically smaller • Discrepancy grows with distance • Distant clusters are redder • Estimated ~ 2 mag/kpc absorption • Attributed it to Rayleigh scattering by gas Some of the Evidence for Interstellar Dust Extinction (reddening of bright stars, dark clouds) Polarization of starlight Scattering (reflection nebulae) Continuum IR emission Depletion of refractory elements from the gas Dust is also observed in the winds of AGB stars, SNRs, young stellar objects (YSOs), comets, interplanetary Dust particles (IDPs), and in external galaxies. The extinction varies continuously with wavelength and requires macroscopic absorbers (or “dust” particles). Examples of the Effects of Dust Extinction B68 Scattering - Pleiades Extinction: Some Definitions Optical depth, cross section, & efficiency: ext ext ext τ λ = ∫ ndustσ λ ds = σ λ ∫ ndust 2 = πa Qext (λ) Ndust nd is the volumetric dust density The magnitude of the extinction Aλ : ext I(λ) = I0 (λ) exp[−τ λ ] Aλ =−2.5log10 []I(λ)/I0(λ) ext ext = 2.5log10(e)τ λ =1.086τ λ 2.
    [Show full text]
  • Aerosol Optical Depth Value-Added Product
    DOE/SC-ARM/TR-129 Aerosol Optical Depth Value-Added Product A Koontz C Flynn G Hodges J Michalsky J Barnard March 2013 DISCLAIMER This report was prepared as an account of work sponsored by the U.S. Government. Neither the United States nor any agency thereof, nor any of 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 disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof. DOE/SC-ARM/TR-129 Aerosol Optical Depth Value-Added Product A Koontz C Flynn G Hodges J Michalsky J Barnard March 2013 Work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research A Koontz et al., March 2013, DOE/SC-ARM/TR-129 Contents 1.0 Introduction .......................................................................................................................................... 1 2.0 Description of Algorithm ...................................................................................................................... 1 2.1 Overview
    [Show full text]
  • Retrieval of Cloud Optical Thickness from Sky-View Camera Images Using a Deep Convolutional Neural Network Based on Three-Dimensional Radiative Transfer
    remote sensing Article Retrieval of Cloud Optical Thickness from Sky-View Camera Images using a Deep Convolutional Neural Network based on Three-Dimensional Radiative Transfer Ryosuke Masuda 1, Hironobu Iwabuchi 1,* , Konrad Sebastian Schmidt 2,3 , Alessandro Damiani 4 and Rei Kudo 5 1 Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578, Japan 2 Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO 80309-0311, USA 3 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303-7814, USA 4 Center for Environmental Remote Sensing, Chiba University, Chiba 263-8522, Japan 5 Meteorological Research Institute, Japan Meteorological Agency, Tsukuba 305-0052, Japan * Correspondence: [email protected]; Tel.: +81-22-795-6742 Received: 2 July 2019; Accepted: 17 August 2019; Published: 21 August 2019 Abstract: Observation of the spatial distribution of cloud optical thickness (COT) is useful for the prediction and diagnosis of photovoltaic power generation. However, there is not a one-to-one relationship between transmitted radiance and COT (so-called COT ambiguity), and it is difficult to estimate COT because of three-dimensional (3D) radiative transfer effects. We propose a method to train a convolutional neural network (CNN) based on a 3D radiative transfer model, which enables the quick estimation of the slant-column COT (SCOT) distribution from the image of a ground-mounted radiometrically calibrated digital camera. The CNN retrieves the SCOT spatial distribution using spectral features and spatial contexts. An evaluation of the method using synthetic data shows a high accuracy with a mean absolute percentage error of 18% in the SCOT range of 1–100, greatly reducing the influence of the 3D radiative effect.
    [Show full text]
  • The Determination of Cloud Optical Depth from Multiple Fields of View Pyrheliometric Measurements
    The Determination of Cloud Optical Depth from Multiple Fields of View Pyrheliometric Measurements by Robert Alan Raschke and Stephen K. Cox Department of Atmospheric Science Colorado State University Fort Collins, Colorado THE DETERMINATION OF CLOUD OPTICAL DEPTH FROM HULTIPLE FIELDS OF VIEW PYRHELIOHETRIC HEASUREHENTS By Robert Alan Raschke and Stephen K. Cox Research supported by The National Science Foundation Grant No. AU1-8010691 Department of Atmospheric Science Colorado State University Fort Collins, Colorado December, 1982 Atmospheric Science Paper Number #361 ABSTRACT The feasibility of using a photodiode radiometer to infer optical depth of thin clouds from solar intensity measurements was examined. Data were collected from a photodiode radiometer which measures incident radiation at angular fields of view of 2°, 5°, 10°, 20°, and 28 ° • In combination with a pyrheliometer and pyranometer, values of normalized annular radiance and transmittance were calculated. Similar calculations were made with the results of a Honte Carlo radiative transfer model. 'ill!:! Hunte Carlo results were for cloud optical depths of 1 through 6 over a spectral bandpass of 0.3 to 2.8 ~m. Eight case studies involving various types of high, middle, and low clouds were examined. Experimental values of cloud optical depth were determined by three methods. Plots of transmittance versus field of view were compared with the model curves for the six optical depths which were run in order to obtain a value of cloud optical depth. Optical depth was then determined mathematically from a single equation which used the five field of view transmittances and as the average of the five optical depths calculated at each field of view.
    [Show full text]
  • A Astronomical Terminology
    A Astronomical Terminology A:1 Introduction When we discover a new type of astronomical entity on an optical image of the sky or in a radio-astronomical record, we refer to it as a new object. It need not be a star. It might be a galaxy, a planet, or perhaps a cloud of interstellar matter. The word “object” is convenient because it allows us to discuss the entity before its true character is established. Astronomy seeks to provide an accurate description of all natural objects beyond the Earth’s atmosphere. From time to time the brightness of an object may change, or its color might become altered, or else it might go through some other kind of transition. We then talk about the occurrence of an event. Astrophysics attempts to explain the sequence of events that mark the evolution of astronomical objects. A great variety of different objects populate the Universe. Three of these concern us most immediately in everyday life: the Sun that lights our atmosphere during the day and establishes the moderate temperatures needed for the existence of life, the Earth that forms our habitat, and the Moon that occasionally lights the night sky. Fainter, but far more numerous, are the stars that we can only see after the Sun has set. The objects nearest to us in space comprise the Solar System. They form a grav- itationally bound group orbiting a common center of mass. The Sun is the one star that we can study in great detail and at close range. Ultimately it may reveal pre- cisely what nuclear processes take place in its center and just how a star derives its energy.
    [Show full text]
  • Simple Radiation Transfer for Spherical Stars
    SIMPLE RADIATION TRANSFER FOR SPHERICAL STARS Under LTE (Local Thermodynamic Equilibrium) condition radiation has a Planck (black body) distribution. Radiation energy density is given as 8πh ν3dν U dν = , (LTE), (tr.1) r,ν c3 ehν/kT 1 − and the intensity of radiation (measured in ergs per unit area per second per unit solid angle, i.e. per steradian) is c I = B (T )= U , (LTE). (tr.2) ν ν 4π r,ν The integrals of Ur,ν and Bν (T ) over all frequencies are given as ∞ 4 Ur = Ur,ν dν = aT , (LTE), (tr.3a) Z 0 ∞ ac 4 σ 4 c 3c B (T )= Bν (T ) dν = T = T = Ur = Pr, (LTE), (tr.3b) Z 4π π 4π 4π 0 4 where Pr = aT /3 is the radiation pressure. Inside a star conditions are very close to LTE, but there must be some anisotropy of the radiation field if there is a net flow of radiation from the deep interior towards the surface. We shall consider intensity of radiation as a function of radiation frequency, position inside a star, and a direction in which the photons are moving. We shall consider a spherical star only, so the dependence on the position is just a dependence on the radius r, i.e. the distance from the center. The angular dependence is reduced to the dependence on the angle between the light ray and the outward radial direction, which we shall call the polar angle θ. The intensity becomes Iν (r, θ). The specific intensity is the fundamental quantity in classical radiative transfer.
    [Show full text]
  • Optical-Depth Scaling of Light Scattering from a Dense and Cold Atomic 87Rb Gas
    Old Dominion University ODU Digital Commons Physics Faculty Publications Physics 2020 Optical-Depth Scaling of Light Scattering From a Dense and Cold Atomic 87Rb Gas K. J. Kemp Old Dominion University, [email protected] S. J. Roof Old Dominion University, [email protected] M. D. Havey Old Dominion University, [email protected] I. M. Sokolov D. V. Kupriyanov See next page for additional authors Follow this and additional works at: https://digitalcommons.odu.edu/physics_fac_pubs Part of the Atomic, Molecular and Optical Physics Commons, and the Quantum Physics Commons Original Publication Citation Kemp, K. J., Roof, S. J., Havey, M. D., Sokolov, I. M., Kupriyanov, D. V., & Guerin, W. (2020). Optical-depth scaling of light scattering from a dense and cold atomic 87Rb gas. Physical Review A, 101(3), 033832. doi:10.1103/PhysRevA.101.033832 This Article is brought to you for free and open access by the Physics at ODU Digital Commons. It has been accepted for inclusion in Physics Faculty Publications by an authorized administrator of ODU Digital Commons. For more information, please contact [email protected]. Authors K. J. Kemp, S. J. Roof, M. D. Havey, I. M. Sokolov, D. V. Kupriyanov, and W. Guerin This article is available at ODU Digital Commons: https://digitalcommons.odu.edu/physics_fac_pubs/420 PHYSICAL REVIEW A 101, 033832 (2020) Optical-depth scaling of light scattering from a dense and cold atomic 87Rb gas K. J. Kemp, S. J. Roof, and M. D. Havey Department of Physics, Old Dominion University, Norfolk, Virginia 23529, USA I. M. Sokolov Department of Theoretical Physics, Peter the Great St.-Petersburg Polytechnic University, 195251 St.-Petersburg, Russia and Institute for Analytical Instrumentation, Russian Academy of Sciences, 198103 St.-Petersburg, Russia D.
    [Show full text]
  • Transfer of Radiation
    TRANSFER OF RADIATION Under LTE (Local Thermodynamic Equilibrium) condition radiation has a Planck (black body) distribution. Radiation energy density is given as 8πh ν3dν U dν = , (LTE), (tr.1) r,ν c3 ehν/kT − 1 and the intensity of radiation (measured in ergs per unit area per second per unit solid angle, i.e. per steradian) is c I = B (T )= U , (LTE). (tr.2) ν ν 4π r,ν The integrals of Ur,ν and Bν (T ) over all frequencies are given as ∞ 4 Ur = Ur,ν dν = aT , (LTE), (tr.3a) Z 0 ∞ ac 4 σ 4 c 3c B (T )= Bν (T ) dν = T = T = Ur = Pr, (LTE), (tr.3b) Z 4π π 4π 4π 0 4 where Pr = aT /3 is the radiation pressure. Inside a star conditions are very close to LTE, but there must be some anisotropy of the radiation field if there is a net flow of radiation from the deep interior towards the surface. We shall consider intensity of radiation as a function of radiation frequency, position inside a star, and a direction in which the photons are moving. We shall consider a spherical star only, so the dependence on the position is just a dependence on the radius r, i.e. the distance from the center. The angular dependence is reduced to the dependence on the angle between the light ray and the outward radial direction, which we shall call the polar angle θ. The intensity becomes Iν (r, θ). Let us consider a change in the intensity of radiation in the direction θ at the radial distance r when we move along the beam by a small distance dl = dr/ cos θ.
    [Show full text]
  • Lecture 3: Emission and Absorption
    Lecture 3: Emission and absorption Senior Astrophysics 2018-03-09 Senior Astrophysics () Lecture 3: Emission and absorption 2018-03-09 1 / 35 Outline 1 Optical depth 2 Sources of radiation 3 Blackbody radiation 4 Sources of radiation: Atomic processes 5 Next lecture Senior Astrophysics () Lecture 3: Emission and absorption 2018-03-09 2 / 35 Radiative transfer equation Last lecture we derived an expression for how radiation intensity changes with pure absorption: dI ν = −α I ds ν ν If the absorption coecient is a constant (e.g. uniform density gas of ionised hydrogen), then −αν ∆s Iν(∆s) = I0e i.e. specic intensity after distance ∆s = initial intensity × radiation exponentially absorbed with distance Lecture 3: Emission and absorption Optical depth 3 / 35 Absorption: Macroscopic version Imagine radiation travelling into a cloud of absorbing gas. The exponential term denes a scale over which radiation is attenuated. When −αν∆s = 1 the intensity will be reduced to 1=e of its original value. Lecture 3: Emission and absorption Optical depth 4 / 35 Absorption: Macroscopic version We dene the optical depth τ as Z s 0 0 τν(s) = αν∆s [more generally: τν(s) = αν(s )ds ] s0 A medium is optically thick at a frequency ν if the optical depth for a typical path through the medium satises τν 1 Medium is optically thin if instead τν 1 We take τν = 1 to be just optically thick. Lecture 3: Emission and absorption Optical depth 5 / 35 An optically thin medium is one which a typical photon of frequency ν can pass through without being absorbed.
    [Show full text]
  • Improving Remote Sensing of Aerosol Optical Depth Over Land by Polarimetric Measurements at 1640 Nm: Airborne Test in North China
    Remote Sens. 2015, 7, 6240-6256; doi:10.3390/rs70506240 OPEN ACCESS remote sensing ISSN 2072-4292 www.mdpi.com/journal/remotesensing Article Improving Remote Sensing of Aerosol Optical Depth over Land by Polarimetric Measurements at 1640 nm: Airborne Test in North China Lili Qie 1, Zhengqiang Li 1,*, Xiaobing Sun 2,3, Bin Sun 2,3, Donghui Li 1, Zhao Liu 1,4,†, Wei Huang 1,4,†, Han Wang 2,3, Xingfeng Chen 1, Weizhen Hou 1 and Yanli Qiao 2,3 1 State Environmental Protection Key Laboratory of Satellite Remote Sensing, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China; E-Mails: [email protected] (L.Q.); [email protected] (D.L.); [email protected] (Z.L.); [email protected] (W.H.); [email protected] (X.C.); [email protected] (W.H.) 2 Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031 , China; E-Mails: [email protected] (X.S.); [email protected](B.S.); [email protected] (H.W.); [email protected] (Y.Q.) 3 Key Laboratory of Optical Calibration and Characterization, Chinese Academy of Sciences, Hefei 230031, China 4 University of Chinese Academy of Sciences, Beijing 100049, China † These authors contributed equally to this work. * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +86-10-6485-7437; Fax: +86-10-6480-6225. Academic Editors: Richard Müller and Prasad S. Thenkabail Received: 18 February 2015 / Accepted: 13 May 2015 / Published: 19 May 2015 Abstract: An improved aerosol retrieval algorithm based on the Advanced Multi-angular Polarized Radiometer (AMPR) is presented to illustrate the utility of additional 1640-nm observations for measuring aerosol optical depth (AOD) over land using look-up table approaches.
    [Show full text]
  • Lecture 6: Radiation Transfer
    Atmospheric Sciences 321 Science of Climate Lecture 6: Radiation Transfer Community Business Check the assignments Moving on to Chapter 3 of book HW #2 due next Wednesday Brief quiz at the end of class on Monday on Chapters 1 and 2. Questions? Energy takes many forms A molecule has many kinds of energy E = E + E + E + E + E total translational rotational vibrational electronic bonding For infrared radiative transfer we are mostly concerned with translational energy (temperature), rotational energy of the molecule and vibrational energy of the molecule. Interaction of molecules with radiation depends on molecular structure. Polyatomic molecules have the best chance of absorbing and emitting thermal infrared radiation. N2 and O2 are not able to absorb much of these relatively low energy photons, but really high energy photons can break O2 apart – photodissociation. N2 and O2 have no permanent or temporary dipole moment like polyatomic molecules such as H2O, CO2 and O3, which are able to absorb and emit thermal infrared radiation. Molecular Structure and absorption and emission of photons H2O and O3 are the best, since they are bent triatomic molecules. CH4, CO2, N2O are also very good They have three modes of vibration and also absorb and emit IR by changing rotational energy levels. Observed CO radiance vs 2 wavenumber O3 Wavenumber is H O the inverse of 2 wavelength Looking down you see colder temps in the line centers Looking up you CO Planck Curves see warmer 2 temps in the line O H O centers 3 2 Radiative Transfer Extinction only Consider solar radiation coming in and being absorbed.
    [Show full text]
  • Estimating Cloud Optical Depth from Surface Radiometric Observations: Sensitivity to Instrument Noise and Aerosol Contamination
    NOVEMBER 2005 B E A ULNE ET AL. 4095 Estimating Cloud Optical Depth from Surface Radiometric Observations: Sensitivity to Instrument Noise and Aerosol Contamination ALAIN BEAULNE Canadian Meteorological Centre, Meteorological Service of Canada, Dorval, Québec, Canada HOWARD W. BARKER Meteorological Service of Canada, Downsview, Ontario, Canada JEAN-PIERRE BLANCHET Université du Québec à Montréal, Montréal, Québec, Canada (Manuscript received 21 October 2003, in final form 30 January 2005) ABSTRACT The spectral-difference algorithm of Barker and Marshak for inferring optical depth ␶ of broken clouds has been shown numerically to be potentially useful. Their method estimates cloud-base reflectance and ␶ using spectral radiometric measurements made at the surface at two judiciously chosen wavelengths. Here it is subject to sensitivity tests that address the impacts of two ubiquitous sources of potential error: instrument noise and presence of aerosol. Experiments are conducted using a Monte Carlo photon transport model, cloud-resolving model data, and surface albedo data from satellite observations. The objective is to analyze the consistency between inherent and retrieved values of ␶. Increasing instrument noise, especially if uncorrelated at both wavelengths, decreases retrieved cloud fraction and increases retrieved mean ␶.As with all methods that seek to infer ␶ using passive radiometry, the presence of aerosol requires that threshold values be set in order to discriminate between cloudy and cloud-free columns. A technique for estimating
    [Show full text]