ECE 583 Lecture 12. Mie Theory (cont.) Mie Theory. m( ) = n( )-ik( )

Transcription

1 ISSUES FOR AEROSOL DISTRIBUTION ECE 583 Lecture 12 Aerosol Size Distribution Retrieval Advanced Instrument Design Airborne Solar Photometers Solar Occultation from Space A given aerosol particle is characterized by its size, shape, phases, and chemical composition large number of variables! Measures of aerosol concentrations must be given in some integral form, by summing over all particles present in a given air volume that have a certain property Evolution of the aerosol size distribution involves nucleation/growth/coagulation and size characterization either through size bins or by volume condensation nucleation coagulation Typical aerosol size distributions by volume 2 Size Parameter d d - particle diameter - wavelength Mie Theory Complex Refractive Index m( ) = n( )-ik( ) n scattering term (refraction and reflection) k absorption term Q Mie Theory (cont.) Extinction Efficiency: light scattered and absorbed by particle light blocked by. particle cross tional area sec e Extinction Efficienc Size Parameter x m=1.13-i0.11; K=3585cm-1 m=1.46-i0.14; K=3180cm-1 m=1.29-i0.0003; K=4500cm-1 m=1.35-i0.43; K=592cm-1 Extinction efficiency of water in different part of the spectrum

2 Extinction as Function of Wavelength e 4 j e i Q ij N j d 2 j - extinction for the e i ith wavelength Q e - dimensionless extinction efficiencies ij N j - number density for the j th aerosol size d j - is the aerosol j th size class (diameter) ECE 583 Inversion of aerosol size distribution from sun photometer spectral optical thickness measurements 1. Early Work 2. Aeronet State of Art Retrievals (separate file) Herman, Browning and Reagan, JAM 1972 Shaw, Reagan and Herman, JAM 1973 Set of linear equation where g is the measurement vector, e measurement error, f the solution vector and A the kernal matrix Constrain to eliminate high frequency instabilities by replacing n(r) with h(r)f(r) rapidly and slowly varying functions with r. Pick the possible solutions that minimize the second derivative of the solution points. 20

3 Advances in Spectral Solar Radiometry Stratospheric Aerosol Layer (Spinhirne and King, 1985) The many advances and accomplishments in solar spectral radiometry/spectral sunphotometry over the past 30 to 40 years have been largely enabled by advances/progress in Silicon device technology, particularly the availability of highly reliable and efficient Silicon photodiodes (PD) and CCD and CMOS. Silicon operational amplifiers (op amps) and analog to digital converters (A/D)

4 Solar Radiometry in the 1-4 m region Detector Noise Noise occurs from Shot (photon) noise, Johnson noise, Thermal noise, Preamp noise. But overall it can be described (where i is current) as: i n2 = 2ei o f Where: i n is the RMS noise i o is signal plus dark current e is electron charge f is the signal bandwidth Signal to Noise S/N = i s / [2e f(i s +i d )] 1/2 Noise figures are obtained from manufactures specifications 58

5 Signal Noise Limitation 1. Minimize dark current, Johnson, preamp and thermal noise. The best detectors are quantum or shot noise limited only. 2. Minimize the measurement band width Filters. Low pass filters to eliminate higher frequencies Signal chopping and demodulation. The f is limited to a narrow bandwidth at the chopping frequency. Signal chopping and lock in amplifiers. A reference signal is applied to lock into the chopping frequency and phase to effect an extremely narrow effective bandwidth

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8 Traveling Spectral Sunphotometer Ground Traveling Sunphotometers Airborne/Spaceborne Sunphotometers Why would we want traveling spectral sunphotometer measurements? Answers To obtain spatial/global optical depth data. To obtain optical depth data in otherwise inaccessible places (Artic/Antartic regions). To obtain optical depth vs. height (i.e., extinction profiles). To remove or reduce atmospheric effects on Obtaining Calibrations Vo by flying above the atmosphere El Chichon Solar Photometer Experiment on NASA CV990 Airborne Laboratory 1982/1983 (Spinhirne and King, JGR 1985) Phil Russell NASA Ames A Collection of Slides on Ames Airborne Sunphotometry for John Reagan s Course SAGE II, III Volcanic Emissions AATS-14 Urban Pollution Terra, Aqua, Aura H 2 0 O 3 Desert Dust Biomass Smoke 1 10/8/2004 3:58:54 PM P. Russell, Ames Seminar, 24 January

9 Ames Airborne Tracking Sunphotometers (AATS) 14-channel Ames Airborne Tracking Sunphotometer (AATS-14) AATS-14 AATS-6 33 Measures: Solar direct-beam transmission, T, at 14 wavelengths,, nm Data products Aerosol optical depth (AOD) at 13, nm Water vapor column content [using T(940 nm)] Aerosol extinction, nm Water vapor density When A/C flies vertical profiles 36 Sunphotometer channel wavelengths and atmospheric spectra 10 Years of Studies Comparing Airborne Sunphotometer and Satellite* Views of Aerosols Over the Ocean Phil Russell 1, John Livingston 2, Beat Schmid 3, Jens Redemann 4, Stephanie Ramirez 4, Qin Zhang 4 and many other contributors 1 NASA Ames Research Center 2 SRI International 3 Pacific Northwest National Laboratory 4 Bay Area Environmental Research Institute AGU Fall Meeting 15 Dec 2006 San Francisco, CA 37 *Nadir-viewing 38

10 Airborne Sunphotometer-Satellite* Comparisons Over Ocean TARFOX ACE-2 PRiDE SAFARI ACE-Asia CLAMS ADAM EVE INTEX -A -B Another Example: J31/King Air/C-130 (AATS-HSRL-HiGEAR) Aerosol Extinction Comparison C. Hostetler, R. Ferrare Satellite Instruments Compared To AATS AODs ATSR-2 MISR OMI AVHRR MAS # RSP # GMS-5 MODIS-Aqua SeaWiFS GOES-8 MODIS-Terra TOMS ~25 journal pubs *Nadir-viewing 39 # Airborne Simulator of Satellite Instrument One King Air/HSRL Goal: Evaluate/validate the HSRL retrieved profiles of aerosol extinction HSRL=High Spectral Resolution Lidar HiGEAR=Hawaii Group for Environmental Aerosol Research King Air Flight Track, 10 Mar 40 J31/AATS-14 Profiles of AOD and Aerosol Extinction Comparison of HSRL extinction/aot with other instruments from 10 Mar Flight Coordinated w King Air and C-130 J31/AATS-14 Spiral location for J31 & C130 AOD Extinction J31/King Air/C-130 (AATS-HSRL-HiGEAR) Aerosol Extinction Comparison Spiral location for J31 & C130 King Air Flight Track, 10 Mar J31 Track, 10 Mar 2006 Flight VER 5 J31/AATS: Redemann, Livingston, Russell et al. King Air/HSRL: Hostetler, Ferrare et al. Redemann, Livingston, Russell et al. 41 C-130/HiGEAR: Clarke et al. 42

11 ECE 583 Satellite Solar Occultation and Limb Scatter Remote Sensing SAGE Measurement Strategy Courtesy of L. Thomason, NASA Langley Research Center, Hampton, VA 45 Courtesy of M.P. McCormick, Hampton University, Hampton, VA 46

12 SAGE III INSTRUMENT Science Accomplishments O 3 Limb Scatter SAGE ozone retrievals are robust down to the tropopause and statistically indistinguishable from ozonesondes [Borchi et al., 2004; Cunnold et al, 2004] If take similar instrument and look at light scattered from the Earth s limb: Measurements are possible over entire sun lit portion of orbit. Vertical resolution ~1km. INSTRUMENT CLOUDS SOLAR RADIATION TANGENT HEIGHT SURFACE EARTH RADIUS LINE OF SIGHT Courtesy of L. Thomason, NASA Langley Research Center, Hampton, VA 49 Coverage from just 13 orbits of STS107 50

13 Limb Scattering SAGE Instrument Status SAGE II: instrument turned off (8/05) after over 20 years of operation. SAGE III/Meteor 3M: Space craft failed (3/06) due to charging system Instrument operated fine over 5 year period Courtesy of D. Rault, NASA Langley Research Center, Hampton, VA Comparison of SAGE III Limb Scatter O3 with correlative data Ozone Mapping Profiler Suite: OMPS Next generation of US spacebased ozone measurements onboard National Polarorbiting Operational Environmental Satellite System & NPOESS Preparatory Project (NPP). Nadir Total Ozone Mapper: TOMS Nadir Profiler: SBUV Limb Profiler (LP) Limb scatter measurements to provide primary ozone product nm spectral range 2 km vertical resolution 3 vertical slits across-track Aerosol extinction profile is an intermediate product. Courtesy of Ball Aerospace 53 OMPS Instrument Design Total Ozone Mapper UV Backscatter, grating spectrometer, 2-D CCD TOMS, SBUV(/2), GOME(-2), OMI, SCIAMACHY 110 deg. cross track, 300 to 380 nm spectral, 1 nm bandpass Limb Profiler UV/Visible Limb Scatter, quartz prism spectrometer, 2-D CCD array SOLSE/LORE, OSIRIS, SAGE III, SCIAMACHY Three 100-KM vertical slits, 290 to 1000 nm spectral, 2 nm to 40 nm bandpass Nadir Profiler UV Backscatter, grating spectrometer, 2-D CCD SBUV(/2), GOME(-2), SCIAMACHY, OMI Nadir view, 250 km cross track, 270 to 310 nm spectral, 1 nm bandpass The calibration concept uses working and reference solar diffusers. Courtesy of: - Larry Flynn, (NOAA/NESDIS, Suitland, MD) - Ball Aerospace 54