Access and Use of Auroral Imaging DataImaging Data

Credit:D. Hutchinson

Harald U. Frey

1

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

2

Aurora seen in different “light”

X-RayE t Ult i l tExtreme Ultraviolet

3VisibleFar Ultraviolet

Aurora exists in other worlds too

4

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

6

Excited levels of oxygen (term scheme)

7

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

8

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

9

B photons, e.g. 427.8 nm

Electron is “lost” (precipitated)

Green auroral arcs

C di D H hiCredit: D. Hutchinson

10

The auroral spectrumSensitivity of the human eye

11

Different Credit: S. Lichti

altitudes of colorscolors

Credit: NASA

12

Extracting altitudeExtracting altitude and information about meanabout mean energy of electronselectrons

13

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)

14

3 Principles of optical detectors3. Principles of optical detectors

Important quantities are:P i i i f i- Position information

- Magnitude of signal (brightness)

15

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)

16

h = Planck constant (6.610-34 Joule•sec) = frequency of light (cycles/sec) = /c Eg = energy gap of material (electron-volts)

Transfer of charge

17

4 Instr ments for obser ations from space4. Instruments for observations from space

Examples:IMAGE- IMAGE

18

IMAGE WIC Camera

19

IMAGE Spectro-graphic g pImager

20

Discreetness of light, Value of long exposures

21

5 Instr ments for obser ations from gro nd5. Instruments for observations from ground

Fisheye opticsAll kAll-sky camera

22

Wide angle photography and distortionsFocal length of optics:Focal length of optics:>80 mm: Telephoto50 mm: Normal human perspective30 mm: Wide angle10 mm: Fisheye

23

Corona

Credit: B. Walker

Credit: J Curtis

24Credit: T. Trondsen

Credit: J. Curtis

Fisheye optics and all-sky camera

25

There is no point on Earth that is always d th l lunder the auroral oval

26

Apparent motion of auroral oval over South Pole station

South

North

27

Apparent motion of auroral oval

All-sky camera is looking up to the sky and sees from

28

yone to the other horizon

6 Anal ing a roral images6. Analyzing auroral images

First a few examplesLater we do some analysis with IDL

29

Global view of Aurora from IMAGEGlobal view of Aurora from IMAGE Spacecraft

30

Spacecraft flight over auroral oval

1000 km

View like sitting in an airplane and looking out of window.

31

Spatial scale of aurora and resolution of observations

30-120 seconds 1-5 seconds 30 milliseconds

32

Small scale distortions

33

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

35

Mapping of all sky images

N (poleward)

Mapping of all-sky imagesW E

36

Minimum elevation 0o Minimum elevation 8o

Tomography with 5 cameras of overlapping view

37

Tomographic reconstruction ofreconstruction of optical emission

38

SubstormSubstorm

39

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

41

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 *

42

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,

43

_ y _ p ; g ,inuv_image_f_*.dat