access and use of auroral imaging dataimaging data · 2010. 2. 24. · 6 anal ing a roral images6....
TRANSCRIPT
Access and Use of Auroral Imaging DataImaging Data
Credit:D. Hutchinson
Harald U. Frey
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Space Sciences LaboratoryUniversity of California at Berkeley
Outline
1. Optical properties of the aurora2. Relationship between precipitating
particles and optical emissionsp p3. Principles of optical detectors4 Instruments for observations from space4. Instruments for observations from space5. Instruments for observations from ground6. Analyzing auroral images with examples
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Aurora seen in different “light”
X-RayE t Ult i l tExtreme Ultraviolet
3VisibleFar Ultraviolet
Aurora exists in other worlds too
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The electromagnetic spectrum
Energy of a photon: /hcE Visible: 2 eV
l i l 105
Ultraviolet: 10 eVX-Ray: 10000 eV
The optical spectrum of aurora
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Excited levels of oxygen (term scheme)
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2. Relationship between i it ti ti l dprecipitating particles and
optical emissions
Important quantities are:E f i i i i l- Energy of precipitating particles
- Altitude profile of emission- Spectral properties of resulting emissionp p p g
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Aurora is created by energetic electrons
Oxygen atom specific h t 630
Composition of atmosphere
photons, e.g. 630 nm
Oxygen atom specific photons, e.g. 557.7
Electron aurorafrom space
BNitrogen molecule specifich t 427 8
from space
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B photons, e.g. 427.8 nm
Electron is “lost” (precipitated)
Green auroral arcs
C di D H hiCredit: D. Hutchinson
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The auroral spectrumSensitivity of the human eye
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Different Credit: S. Lichti
altitudes of colorscolors
Credit: NASA
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Extracting altitudeExtracting altitude and information about meanabout mean energy of electronselectrons
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The photometric unit Rayleigh
Radiance L (apparent surface brightness) is given in: Photons cm-1 s-1 sr-1
4 π L is then given in Rayleighg y g1 R = 106 photons cm-2 s-1
lid l / 2 ( )Solid angle Ω = A / r2 (sr)
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3 Principles of optical detectors3. Principles of optical detectors
Important quantities are:P i i i f i- Position information
- Magnitude of signal (brightness)
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Principle of a Charged CoupledCharged Coupled Device (CCD)
For an electron to be excited from thevalence band to the conduction band
h Eg
h = Planck constant (6 610 34 Joule•sec)
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h = Planck constant (6.610-34 Joule•sec) = frequency of light (cycles/sec) = /c Eg = energy gap of material (electron-volts)
Transfer of charge
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4 Instr ments for obser ations from space4. Instruments for observations from space
Examples:IMAGE- IMAGE
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IMAGE WIC Camera
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IMAGE Spectro-graphic g pImager
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Discreetness of light, Value of long exposures
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5 Instr ments for obser ations from gro nd5. Instruments for observations from ground
Fisheye opticsAll kAll-sky camera
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Wide angle photography and distortionsFocal length of optics:Focal length of optics:>80 mm: Telephoto50 mm: Normal human perspective30 mm: Wide angle10 mm: Fisheye
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Corona
Credit: B. Walker
Credit: J Curtis
24Credit: T. Trondsen
Credit: J. Curtis
Fisheye optics and all-sky camera
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There is no point on Earth that is always d th l lunder the auroral oval
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Apparent motion of auroral oval over South Pole station
South
North
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Apparent motion of auroral oval
All-sky camera is looking up to the sky and sees from
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yone to the other horizon
6 Anal ing a roral images6. Analyzing auroral images
First a few examplesLater we do some analysis with IDL
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Global view of Aurora from IMAGEGlobal view of Aurora from IMAGE Spacecraft
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Spacecraft flight over auroral oval
1000 km
View like sitting in an airplane and looking out of window.
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Spatial scale of aurora and resolution of observations
30-120 seconds 1-5 seconds 30 milliseconds
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Small scale distortions
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Movie of curls
30 km
3440 km
Orientation of auroral images
Looking down from space(IMAGE FUV)
Looking up from the ground( ll k )
Default for THEMIS data
t ti(IMAGE FUV)
N
(all-sky)
N
presentation
N
EW WE EW
S S S
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Mapping of all sky images
N (poleward)
Mapping of all-sky imagesW E
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Minimum elevation 0o Minimum elevation 8o
Tomography with 5 cameras of overlapping view
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Tomographic reconstruction ofreconstruction of optical emission
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SubstormSubstorm
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Timing of b
Magnetic AE index
substorm onset and East-West
iWest
expansion
East40
East
Speed of rays in auroral arcWest East
Mean speed: 4.5 km/sec
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Now let’s do some real time analysisNow let s do some real-time analysis
If you have not done so already, please download all files and programs with anonymous ftp from:p g y p
ftp sprite.ssl.berkeley.educd pub/hfrey/seminarcd pub/hfrey/seminarmget *
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Practice Session1. Show basics of auroral arc with slicer_mod.pro and
auroral_arc.pro; compile and run auroral_arc2. Content of calibration file, show_skymap.pro3. General THEMIS ASI software with thm_crib_asi.pro4. Time analysis with time analysis.proy _ y p5. Generation of movie with make_movie.pro (change path)6. Demonstration of pulsating aurora with pulsations.pro7 Mark footprint of spacecraft in image with mark satellite pro;7. Mark footprint of spacecraft in image with mark_satellite.pro;
show movie fast_2008-03-09_fsim.mpg and downloadfsim_20080309_040000.sav, compass.pro, f bi dfast_orbit_20080309.sav and .txt
8. Flow analysis with flow_analysis_1.pro and flow analysis 2.pro; download images.sav,
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_ y _ p ; g ,inuv_image_f_*.dat