1. ISUAL Imager of Sprites and Upper Atmospheric Lightning (ISUAL). S. B. Mende UC Berkeley

2. ISUAL 6/18/012NCKU UCB Tohoku ISUAL Science objectives Major Science objectives: 1. Determine the location and timing of luminous phenomena above thunderclouds to investigate their spatial, temporal and spectral properties. 2. Obtain a global survey of upper atmospheric optical flash transients (sprites, elves, blue jets etc.) 3. Global observations of aurora and airglow

3. ISUAL 6/18/013NCKU UCB Tohoku ISUAL Science objectives 1. Detailed observation of individual sprites. –Pointing: Dip down to reduce range. –Location: Storms –Imager Wavelength: N 2 1st positive, 427.8 nm –Photometer Wavelength: UV bands, N 2 2nd positive, 427.8 nm, N 2 1st positive –Spatial Resolution:~2km –Time resolution: 1 - 30 msec (programmable) –Imager Mode: Burst Mode

4. ISUAL 6/18/014NCKU UCB Tohoku ISUAL Science objectives 2. Global survey of upper atmospheric optical flash transients (sprites, elves, blue jets etc.). –Pointing: Limb view (largest coverage possible, spatial separation between lightning and sprite). –Location: Storms –Imager Wavelength: N 2 1st positive, 427.8 nm –Photometer Wavelength: UV bands, N 2 2nd positive, 427.8 nm, N 2 1st positive –Spatial Resolution: ~2km –Time resolution: 1 - 30 msec (programmable) –Imaging Mode: Continuous Sprite Mode

5. ISUAL 6/18/015NCKU UCB Tohoku ISUAL Science objectives 3. Global survey of aurora and airglow –Pointing: Limb view. –Location: All –Imager Wavelength: All –Photometer Wavelength: All –Spatial Resolution: ~2km –Time resolution: 1 sec (programmable) –Mode: Continuous Aurora mode

6. ISUAL 6/18/016NCKU UCB Tohoku ISUAL Science Operations Strategy Instrument Mounted on ROCSAT2 S/C in 891 Km Polar Orbit Science Data Collected on Night Side of Orbit ROCSAT2 S/C reoriented to Point ISUAL at Limb or Somewhat Below at Beginning of Pass Pointing may be Either Along the Track or Cross Track Data are Stored and Compressed in on Board Memory and Transferred to the S/C Memory at the end of each Orbit After 14 Orbits, the Data are Telemetered from the S/C Memory to the Ground

7. ISUAL 6/18/017NCKU UCB Tohoku ISUAL viewing scenario

8. ISUAL 6/18/018NCKU UCB Tohoku ISUAL Operations Overview ROCSAT altitude = 891 km, Orbit = Sun sync. 10 a.m.10 p.m. Launch Date 8/31/2003

9. ISUAL 6/18/019NCKU UCB Tohoku ISUAL Instrument Complement Sprite Imager –Gated Intensified CCD camera –512 X 128 (was 80) pixel resolution –20 deg. X 5.0 (was 3.15) deg. Field of View –Filter wheel has six selectable filters Spectrophotometer –Six photometer modules are identical except for spectral characteristics –20 deg. X 5.0 (was 3.15) deg. Field of View –All photometers are boresighted in the same direction as the imager –All six channels are sampled at a 10 kHz rate

10. ISUAL 6/18/0110NCKU UCB Tohoku ISUAL Instrument Complement (con’t) Array Photometer –Two photometer units, identical except for optical filter bandpass –20 deg. X 3.15 deg. FOV divided into 16 channels –Selectable sample rate –Boresight same as other instruments Associated Electronics Package –Performs power distribution and control –Performs command decoding –Controls instrument and sensors –Performs compression of images –Stores 128 Mbytes in Mass Memory –Generates CCSDS telemetry packets

11. ISUAL 6/18/0111NCKU UCB Tohoku ISUAL System Electrical Block Diagram

12. ISUAL 6/18/0112NCKU UCB Tohoku ISUAL Operational Modes Sprite Continuous Mode –Imager is continuously taking images at a 100 frame/sec rate –Array Photometer is continuously sampled at a 20 or 2 kHz rate –Spectrophotometer is continuously sampled at a 10 kHz rate –All data are written into a series of circular memory buffers –Upon meeting trigger criteria on Spectrophotometer data, a selected block of data are saved in Mass Memory for compression and transfer to T/M –Selectable trigger parameters include channel, level, rise time, and pre-trigger block size and post-trigger block size Sprite Burst Mode –Same as continuous mode except sample rate is 650 Hz for a limited period –Price of high sample rate is ~80% dead time Auroral Mode –All instruments operate at a constant rate of 1 sample/second –All data saved, compressed, and transferred to S/C for downlink

13. ISUAL 6/18/0113NCKU UCB Tohoku Sprite Imager Mechanical Properties Volume: ~250 H x 240 W x 362 L (mm) Mass: 6.6 kg Max Power: 14.0 W

14. ISUAL 6/18/0114NCKU UCB Tohoku ISUAL Imager

15. ISUAL 6/18/0115NCKU UCB Tohoku

16. ISUAL 6/18/0116NCKU UCB Tohoku Spectrophotometer Mechanical Properties Volume: ~187 (was 231) H x 156 (was 141) W x 244 (was 237) L (mm) Mass: 5.4 kg Max Power: 6.8 W

17. ISUAL 6/18/0117NCKU UCB Tohoku ISUAL photometer unit

18. ISUAL 6/18/0118NCKU UCB Tohoku Array Photometer Mechanical Properties Volume: ~290 H x 244 W x 395 L (mm) Mass: 11.0 kg Max Power: 16.4 W

19. ISUAL 6/18/0119NCKU UCB Tohoku ISUAL Science Data Handling Strategy AEP Collects Digital Data from each Instrument During each Nightside Pass Raw Data Stored in 128 Mbyte Memory Raw Data in Memory are Compressed by Dedicated DSP System Data Compression is pefrformed for a Portion of the Dayside Pass following Completion of Data Collection Compressed Data are Transferred to S/C Memory in 67,108,864 Bit Blocks of PVCF’s Packed with CCSDS Source Packets S/C Memory Stores up to 256 Kbytes of Compressed ISUAL Data Separate Channel for Real Time & Housekeeping Data S/C Memory Downlinked to Taiwan Twice per Day

20. ISUAL 6/18/0120NCKU UCB Tohoku ISUAL Cloud flash rejection A parent cloud to ground flash usually precedes the sprite event by a few (3 msec) [Rairden and Mende 1995] and can illuminate the thunderstorm cloud above with very high intensity light. The ISUAL instrument therefore uses four techniques to minimize the parent lightning interference. 1) Observing the flashes near the limb or on the limb to maximize spatial separation between the parent lightning and sprite. 2) With appropriate spectral filtering it is possible maximize the sprite induced spectral bands and cut down on the contamination produced by cloud to ground lightning. 3) A trigger photometer with suitable time delay can be used to remove some of the parent lightning intensity. 4) Using a CCD type which has anti-blooming gate will minimize the contamination of adjacent areas near a flash.

21. ISUAL 6/18/0121NCKU UCB Tohoku Optical Specifications Filters –1:660 - 900 nm notch at 756 - 790 –2:762 nm –3:427.8 nm –4:630 nm –5:557.7 nm –6:400 - 900 nm IR/thermal block

22. ISUAL 6/18/0122NCKU UCB Tohoku ISUAL Imager Filters Filter 1. N 2 1st positive band filter for observing Sprites. Removes the lightning induced 777.4 nm line minimizes the airglow 760 nm O 2 band contribution. This type of filter was qualified for Space use Filter 2. 762 nm O2 (0,0) atmospheric band for observing airglow (waves) and aurora Filter 3. 427.8 nm energetic electron induced emissions (sprites and aurora) Filter 4. 630 nm auroral and airglow emissions Filter 5. 557.7 nm auroral and airglow emissions. Filter 6. Broad band filter (no filter)

23. ISUAL 6/18/0123NCKU UCB Tohoku Spectrophotometer Optical Data SP Channels 1&2 1 -- Bandpass: 150 - 280 nm No filter used EMR type 541 PMT Rubidium Telluride photocathode Sapphire window 2 -- Bandpass: 250 - 390 nm Barr UG-5 glass filter EMR type 541 PMT Bi-alkali photocathode Magnesium Fluoride window

24. ISUAL 6/18/0124NCKU UCB Tohoku Spectrophotometer Optical Data SP Channels 3&4 3 -- Center: 337 nm Barr interference filter EMR type 741 PMT Bi-alkali photocathode Sapphire window 4 -- Center: 427.8 nm Barr interference filter EMR type 741 PMT Bi-alkali photocathode Sapphire window

25. ISUAL 6/18/0125NCKU UCB Tohoku Spectrophotometer Optical Data SP Channels 5&6 5 -- Bandpass: 665 - 900 nm Notch at 754 - 790 nm Barr interference filter EMR type 741 PMT Tri-alkali photocathode Sapphire window 6 -- Center: 777.4 nm Barr interference filter EMR type 741 PMT Tri-alkali photocathode Sapphire window

26. ISUAL 6/18/0126NCKU UCB Tohoku ISUAL Photometer Filters 1. Ultraviolet filter. Looking at N 2 LBH long wavelength bands. Upper state lifetime is 0.14 ms resulting in some quenching at lower altitudes. The altitude of unit optical depth is about 40 km in this range perhaps possible to see sprites while attenuating lightning. 2. Ultraviolet filter. It might be possible to see sprites and much attenuated lightning. 3. 337.0 nm N 2 2nd positive band requires higher electron energies therefore provides a particle energy “spectrometer”. 4. N 2 + 427.8 nm Energetic electron detector in sprites and aurora. 5. N 2 1st positive emission “bread and butter” sprite measurement. 6. 777.4 O lightning “perhaps trigger”.

27. ISUAL 6/18/0127NCKU UCB Tohoku Observing Parameters Satellite Altitude891.00km View angle to solid earth tangent -28.68 Limb view to phenomena-27.5 Range at limb 3373.01km Height of observation60.00km

28. ISUAL 6/18/0128NCKU UCB Tohoku Imager Focal length61.8mm F number 1.56 Diameter of aperture 40 mm Area of aperture12.6 cm 2 Field of view per pix0.039 degree Etendu per pixel6 x 10 -6 Photon grasp 10 6 / (4  x 6 x 10 -6 = 6/ (4  ) = 0.5 photons/ R/sec/pix

29. ISUAL 6/18/0129NCKU UCB Tohoku ISUAL Imager Detector Number of pixels (vert.)128 Number of pixels (horiz)512 Pixel in microns at image intensifier43.00  m Image size (vert.)5.50mm (horiz.)22mm Pixel size at layer limb.2.14km Image size vertical.170km Image size horizontal.1093km Range to bottom pixel2201km

30. ISUAL 6/18/0130NCKU UCB Tohoku IMAGER SENSITIVITY Filter 1 2 3 4 5 6 Electrons696996 For 500kR SNR1.72.11.72.12.11.7

31. ISUAL 6/18/0131NCKU UCB Tohoku ISUAL Spectrophotometer Spectrophotometer FOV20 x 5.0 degrees Diameter of aperture 24 mm Area of aperture4.5 cm 2 Etendu (full field) 0.087 Sterad-cm 2 Photon grasp 10 6 / (4  x 0.0868 = 6/ (4  ) = 6,908 photons/ R/sec/pix

32. ISUAL 6/18/0132NCKU UCB Tohoku PHOTOMETER SENSITIVITY Sprite 30 x 10 kmExposure time = 0.0001 s Filter123456 Electrons 2448282892 For 500 kR SNR3.44.93.73.72.11

33. ISUAL 6/18/0133NCKU UCB Tohoku Imager Counting Rates/pixel

34. ISUAL 6/18/0134NCKU UCB Tohoku ISUAL Photometer Counting Rates

35. ISUAL 6/18/0135NCKU UCB Tohoku Photometer counting rate (Airglow/aurora)

36. ISUAL 6/18/0136NCKU UCB Tohoku Photometer counting rate (Airglow/aurora )

37. ISUAL 6/18/0137NCKU UCB Tohoku Windowed Compression Technique. S. P. Geller and S. B. Mende

38. ISUAL 6/18/0138NCKU UCB Tohoku Windowed Compression In the ISUAL experiment one of the major hurdles is how to store and down link the data. Windowed Compression will provide routinely compressions > 30.

39. ISUAL 6/18/0139NCKU UCB Tohoku To verify the method of “windowed compression” experiment data from the Tether Optical Phenomena investigation was used while the STS-76 (TSS-1R) shuttle orbiter was flying over stroms. 30 frames per second video data were processed to verify the method. The data were summed into “tiles”. Each consecutive image is compared to the one prior and regions in which tiles show a positive step intensity change are captured in the data stream. Once a region is captured then the same region from a subsequent set of images are captured.

40. ISUAL 6/18/0140NCKU UCB Tohoku Flash, captured as difference Tiling = 8x8 pixels Display radius = 3 tiles around qualifying pixel

41. ISUAL 6/18/0141NCKU UCB Tohoku Flash-2

42. ISUAL 6/18/0142NCKU UCB Tohoku Flash-1

43. ISUAL 6/18/0143NCKU UCB Tohoku Flash

44. ISUAL 6/18/0144NCKU UCB Tohoku

45. ISUAL 6/18/0145NCKU UCB Tohoku

46. ISUAL 6/18/0146NCKU UCB Tohoku

47. ISUAL 6/18/0147NCKU UCB Tohoku

48. ISUAL 6/18/0148NCKU UCB Tohoku Multiple Objects Two simultaneous flashes

49. ISUAL 6/18/0149NCKU UCB Tohoku Flash-3

50. ISUAL 6/18/0150NCKU UCB Tohoku Flash-2

51. ISUAL 6/18/0151NCKU UCB Tohoku Flash-1

52. ISUAL 6/18/0152NCKU UCB Tohoku Flash

53. ISUAL 6/18/0153NCKU UCB Tohoku Eliminating non-Flash objects Lightning flash with city, star

54. ISUAL 6/18/0154NCKU UCB Tohoku Flash-2

55. ISUAL 6/18/0155NCKU UCB Tohoku Flash-1

56. ISUAL 6/18/0156NCKU UCB Tohoku Flash