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Imager of Sprites and Upper Atmospheric Lightning (ISUAL).

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

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Imager of Sprites and Upper Atmospheric Lightning (ISUAL).

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

  2. 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 NCKU UCB Tohoku

  3. ISUAL Science objectives • 1. Detailed observation of individual sprites. • Pointing: Dip down to reduce range. • Location: Storms • Imager Wavelength: N2 1st positive, 427.8 nm • Photometer Wavelength: UV bands, N2 2nd positive, 427.8 nm, N2 1st positive • Spatial Resolution:~2km • Time resolution: 1 - 30 msec (programmable) • Imager Mode: Burst Mode NCKU UCB Tohoku

  4. 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: N2 1st positive, 427.8 nm • Photometer Wavelength: UV bands, N2 2nd positive, 427.8 nm, N2 1st positive • Spatial Resolution: ~2km • Time resolution: 1 - 30 msec (programmable) • Imaging Mode: Continuous Sprite Mode NCKU UCB Tohoku

  5. 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 NCKU UCB Tohoku

  6. 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 NCKU UCB Tohoku

  7. ISUAL viewing scenario NCKU UCB Tohoku

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

  9. 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 NCKU UCB Tohoku

  10. 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 NCKU UCB Tohoku

  11. ISUAL System Electrical Block Diagram NCKU UCB Tohoku

  12. 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 NCKU UCB Tohoku

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

  14. ISUAL Imager NCKU UCB Tohoku

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  16. 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 NCKU UCB Tohoku

  17. ISUAL photometer unit NCKU UCB Tohoku

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

  19. 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 NCKU UCB Tohoku

  20. 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. NCKU UCB Tohoku

  21. 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 NCKU UCB Tohoku

  22. ISUAL Imager Filters • Filter 1. N2 1st positive band filter for observing Sprites. Removes the lightning induced 777.4 nm line minimizes the airglow 760 nm O2 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) NCKU UCB Tohoku

  23. Spectrophotometer Optical Data • SP Channels 1&2 • 1 -- Bandpass: 150 - 280 nm • No filter used • EMR type 541 PMT • Rubidium Telluridephotocathode • Sapphire window • 2 -- Bandpass: 250 - 390 nm • Barr UG-5 glass filter • EMR type 541 PMT • Bi-alkali photocathode • Magnesium Fluoridewindow NCKU UCB Tohoku

  24. 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 NCKU UCB Tohoku

  25. 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 NCKU UCB Tohoku

  26. ISUAL Photometer Filters 1. Ultraviolet filter. Looking at N2 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 N2 2nd positive band requires higher electron energies therefore provides a particle energy “spectrometer” . 4. N2 + 427.8 nm Energetic electron detector in sprites and aurora. 5. N2 1st positive emission “bread and butter” sprite measurement. 6. 777.4 O lightning “perhaps trigger”. NCKU UCB Tohoku

  27. Observing Parameters • Satellite Altitude 891.00 km • View angle to solid earth tangent -28.68 • Limb view to phenomena -27.5 • Range at limb 3373.01 km • Height of observation 60.00 km NCKU UCB Tohoku

  28. Imager • Focal length 61.8 mm • F number 1.56 • Diameter of aperture 40 mm • Area of aperture 12.6 cm2 • Field of view per pix 0.039 degree • Etendu per pixel 6 x 10 -6 • Photon grasp 10 6 / (4p) x 6 x 10 -6 = 6/ (4p ) = 0.5 photons/ R/sec/pix NCKU UCB Tohoku

  29. ISUAL Imager Detector • Number of pixels (vert.) 128 • Number of pixels (horiz) 512 • Pixel in microns at image intensifier 43.00 m • Image size (vert.) 5.50 mm • (horiz.) 22 mm • Pixel size at layer limb. 2.14 km • Image size vertical. 170 km • Image size horizontal. 1093 km • Range to bottom pixel 2201 km NCKU UCB Tohoku

  30. IMAGER SENSITIVITY Filter 1 2 3 4 5 6 Electrons 6 9 6 9 9 6 For 500kR SNR 1.7 2.1 1.7 2.1 2.1 1.7 NCKU UCB Tohoku

  31. ISUAL Spectrophotometer Spectrophotometer • FOV 20 x 5.0 degrees • Diameter of aperture 24 mm • Area of aperture 4.5 cm2 • Etendu (full field) 0.087 Sterad-cm2 • Photon grasp 10 6 / (4p) x 0.0868 = 6/ (4p ) = 6,908 photons/ R/sec/pix NCKU UCB Tohoku

  32. PHOTOMETER SENSITIVITY Sprite 30 x 10 km Exposure time = 0.0001 s Filter 1 2 3 4 5 6 Electrons 24 48 28 28 9 2 For 500 kR SNR 3.4 4.9 3.7 3.7 2.1 1 NCKU UCB Tohoku

  33. Imager Counting Rates/pixel NCKU UCB Tohoku

  34. ISUAL Photometer Counting Rates NCKU UCB Tohoku

  35. Photometer counting rate (Airglow/aurora) NCKU UCB Tohoku

  36. Photometer counting rate (Airglow/aurora) NCKU UCB Tohoku

  37. Windowed Compression Technique. S. P. Geller and S. B. Mende NCKU UCB Tohoku

  38. 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. NCKU UCB Tohoku

  39. 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. NCKU UCB Tohoku

  40. Flash, captured as difference • Tiling = 8x8 pixels • Display radius = 3 tiles around qualifying pixel NCKU UCB Tohoku

  41. Flash-2 NCKU UCB Tohoku

  42. Flash-1 NCKU UCB Tohoku

  43. Flash NCKU UCB Tohoku

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  48. Multiple Objects • Two simultaneous flashes NCKU UCB Tohoku

  49. Flash-3 NCKU UCB Tohoku

  50. Flash-2 NCKU UCB Tohoku

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