1 Access and Use of Auroral Imaging Data Harald U. Frey Space Sciences Laboratory University of California at Berkeley Credit: D. Hutchinson

2 Outline 1.Optical properties of the aurora 2.Relationship between precipitating particles and optical emissions 3.Principles of optical detectors 4.Instruments for observations from space 5.Instruments for observations from ground 6.Analyzing auroral images with examples

3 Aurora seen in different “light” X-Ray Visible Far Ultraviolet Extreme Ultraviolet

4 Aurora exists in other worlds too

5 The electromagnetic spectrum Energy of a photon: Visible: 2 eV Ultraviolet: 10 eV X-Ray: eV

6 The optical spectrum of aurora

7 Excited levels of oxygen (term scheme)

8 2. Relationship between precipitating particles and optical emissions Important quantities are: - Energy of precipitating particles - Altitude profile of emission - Spectral properties of resulting emission

9 B Oxygen atom specific photons, e.g. 630 nm Nitrogen molecule specific photons, e.g nm Electron aurora from space Aurora is created by energetic electrons Composition of atmosphere Electron is “lost” (precipitated) Oxygen atom specific photons, e.g

10 Green auroral arcs Credit: D. Hutchinson

11 The auroral spectrum Sensitivity of the human eye

12 Credit: S. Lichti Credit: NASA Different altitudes of colors

13 Extracting altitude and information about mean energy of electrons

14 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 Rayleigh 1 R = 10 6 photons cm -2 s -1 Solid angle Ω = A / r 2 (sr)

15 3. Principles of optical detectors Important quantities are: - Position information - Magnitude of signal (brightness)

16 For an electron to be excited from the valence band to the conduction band h  E g h = Planck constant (6.6  Joulesec) n = frequency of light (cycles/sec) = /c E g = energy gap of material (electron-volts) Principle of a Charged Coupled Device (CCD)

17 Transfer of charge

18 4. Instruments for observations from space Examples: - IMAGE

19 IMAGE WIC Camera

20 IMAGE Spectro- graphic Imager

21 Discreetness of light, Value of long exposures

22 5. Instruments for observations from ground Fisheye optics All-sky camera

23 Wide angle photography and distortions Focal length of optics: >80 mm: Telephoto 50 mm: Normal human perspective 30 mm: Wide angle 10 mm: Fisheye

24 Corona Credit: B. Walker Credit: T. Trondsen Credit: J. Curtis

25 Fisheye optics and all-sky camera

26 There is no point on Earth that is always under the auroral oval

27 Apparent motion of auroral oval over South Pole station South North

28 Apparent motion of auroral oval All-sky camera is looking up to the sky and sees from one to the other horizon

29 6. Analyzing auroral images First a few examples Later we do some analysis with IDL

30 Global view of Aurora from IMAGE Spacecraft

31 Spacecraft flight over auroral oval View like sitting in an airplane and looking out of window km

32 Spatial scale of aurora and resolution of observations seconds 1-5 seconds30 milliseconds

33 Small scale distortions

34 Movie of curls 40 km 30 km

35 Orientation of auroral images Looking down from space (IMAGE FUV) N S EW Looking up from the ground (all-sky) N S WE Default for THEMIS data presentation N S EW

36 Mapping of all-sky images Minimum elevation 0 o Minimum elevation 8 o WE N (poleward)

37 Tomography with 5 cameras of overlapping view

38 Tomographic reconstruction of optical emission

39 Substorm

40 Timing of substorm onset and East-West expansion East West Magnetic AE index

41 Speed of rays in auroral arc West East Mean speed: 4.5 km/sec

42 Now let’s do some real-time analysis If you have not done so already, please download all files and programs with anonymous ftp from: ftp sprite.ssl.berkeley.edu cd pub/hfrey/seminar mget *

43 Practice Session 1.Show basics of auroral arc with slicer_mod.pro and auroral_arc.pro; compile and run auroral_arc 2.Content of calibration file, show_skymap.pro 3.General THEMIS ASI software with thm_crib_asi.pro 4.Time analysis with time_analysis.pro 5.Generation of movie with make_movie.pro (change path) 6.Demonstration of pulsating aurora with pulsations.pro 7.Mark footprint of spacecraft in image with mark_satellite.pro; show movie fast_ _fsim.mpg and download fsim_ _ sav, compass.pro, fast_orbit_ sav and.txt 8.Flow analysis with flow_analysis_1.pro and flow_analysis_2.pro; download images.sav, inuv_image_f_*.dat