2007 March 51 EUVI Early Observations Jean-Pierre Wuelser James Lemen Markus Aschwanden Nariaki Nitta

2007 March 52 Lunar Transit 2007 February 25

2007 March 53

4

5 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

2007 March 56 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

2007 March 57 ICER Performance - EUVI 171, 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

2007 March 58 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

2007 March 59 First 3D in 171

2007 March 510

2007 March 511 Observing Strategies - General Concept Synoptic program –Continuous coverage to catch all events – % 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

2007 March 512 Observing Strategies - Sequences (1) LMSAL proposed synoptic program: 2.5 min cadence, ICER6 –195, 284, 10 min cadence, ICER6 –171, 195, 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, 10 min cadence, ICER4 –171, 10 min cadence, ICER5 –Rationale: ICER4/5 for observing very faint structures far off-limb

2007 March 513 Observing Strategies - Sequences (2) Event program: –LMSAL: 50 sec cadence, ICER6 195, 284, 2.5 min cadence, ICER6 –NRL: 195, 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

2007 March 514

2007 March 515