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EUVI Early Observations

EUVI Early Observations

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EUVI Early Observations

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  1. EUVI Early Observations Jean-Pierre Wuelser James Lemen Markus Aschwanden Nariaki Nitta

  2. Lunar Transit 2007 February 25

  3. Image Compression - ICER • Almost all EUVI images are ICER compressed on-board • ICER was developed at JPL and used on the Mars Rovers • The main parameter for ICER is the desired size of the compressed image (in Byte) • SECCHI uses 12 sets of compression parameters, including • ICER0 : 2 MByte (usually lossless for EUVI images) • ICER4 : 400 kByte • ICER5 : 300 kByte • ICER6 : 200 kByte • ICER7 : 100 kByte • Choosing compression level essentially involves trading image quality versus image cadence • ICER4 instead of ICER6 means half the image cadence • There is an ongoing debate on how much the EUVI images should be compressed

  4. ICER Performance - EUVI 195 • Analysis of an EUVI image with various levels of ICER • Plot shows average compression error as a function of intensity • Horizontal axis is square root scaled • Poisson noise limit is a straight line (dotted) • Top: ICER7 • Bottom: ICER4 • All curves are below the single pixel Poisson noise limit

  5. ICER Performance - EUVI 171, 284, 304 • 284 compresses very well • 304 compresses the least, with ICER7 exceeding the Poisson limit • All wavelengths compress below the Poisson limit for up to ICER6 • Most EUVI observations to date use ICER6

  6. ICER Faint areas: • ICER adjusts spatial resolution to match the noise level by summing faint areas into superpixels • Areas at the noise level show “blocky” appearance • Loss of true information is small • Left to right: • ICER6 • ICER4 • Lossless

  7. First 3D in 171

  8. Observing Strategies - General Concept • Synoptic program • Continuous coverage to catch all events • 85 - 90 % of available telemetry • Moderate cadence • Event buffer program • Observes into ring buffer (“SSR2”) • On-board event detection algorithm on Cor2 images stops observations when triggered by CME • Ring buffer has 3-4 hour capacity of high cadence observations • Allows for some “well observed” events • Ongoing discussion on cadence versus compression ratio

  9. Observing Strategies - Sequences (1) • LMSAL proposed synoptic program: • 171 @ 2.5 min cadence, ICER6 • 195, 284, 304 @ 10 min cadence, ICER6 • 171, 195, 304 @ ICER4, once every hour • Rationale: • 171 shows the most structures suitable for 3D reconstruction • Many transients last less than 10 min, requiring a cadence of at least 2.5 min • NRL proposed synoptic program: • 195, 304 @ 10 min cadence, ICER4 • 171, 284 @ 10 min cadence, ICER5 • Rationale: • ICER4/5 for observing very faint structures far off-limb

  10. Observing Strategies - Sequences (2) • Event program: • LMSAL: • 171 @ 50 sec cadence, ICER6 • 195, 284, 304 @ 2.5 min cadence, ICER6 • NRL: • 195, 304 @ 2.5 min cadence, ICER4 • Approach for choosing best program: • Take observations with both proposed observing programs • For a limited time (one week?): • Run NRL program on Ahead • Run LMSAL program on Behind • Re-evaluate