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EUVI Instrument and Calibration Status. Jean-Pierre Wuelser James Lemen Markus Aschwanden Nariaki Nitta. Outline. Commissioning activities First light images Performance Entrance Filters Comparison A/B, EIT Fine pointing system Flat fielding Pointing and roll Image compression - PowerPoint PPT Presentation
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2007 March 5 1
EUVI Instrument andCalibration Status
Jean-Pierre Wuelser
James Lemen
Markus Aschwanden
Nariaki Nitta
2007 March 5 2
Outline
• Commissioning activities• First light images• Performance
– Entrance Filters– Comparison A/B, EIT– Fine pointing system
• Flat fielding• Pointing and roll• Image compression• Observing strategies• Lunar transit• First 3D
2007 March 5 3
Commissioning Activities (1)
• Commissioning activities still ongoing– Much of the calibration data still need to be analyzed
• Guide Telescope commissioning– Initial GT gain calibration based on intensities
• Still used on orbit, absolute accuracy about 10 percent
– First use of GT as S/C fine sun sensor went smoothly– GT fine calibration: compare GT signal with sun center in EUVI
during offpoints• Results implemented in software for updating EUVI FITS keywords
• Plan to provide software for updating FITS header of CORs
– GT signal is very low noise• Signal fluctuations reflect true S/C attitude motions
• S/C jitter decreased substantially over course of S/C commissioning
2007 March 5 4
GT-A Signal Example: 2 Sec Ave/StdDev
2007 March 5 5
Commissioning Activities (2)
• EUVI closed door commissioning– Darks– LED images
• 2 LEDs in spider:
• Blue (470 nm)
• Purple (400 nm)
• 1 LED in FPA
– Primarily a performance baseline
2007 March 5 6
First Light AHEAD : December 4, 2006
2007 March 5 7
First Light BEHIND : December 13, 2006
2007 March 5 8
First Light
• First Light went smoothly on both S/C– Initial images with open filter wheel at all 4 wavelengths– Comprehensive set of images at all filter wheel / wavelength
combinations with lossless compression– Images to test tip/tilt mirror Fine Pointing System (FPS)
• Open filter wheel images showed that entrance filters survived launch in pristine condition
• Image intensity levels within factor 2 of expectations• Images well in focus• FPS performed very well without any tuning
2007 March 5 9
Entrance Filter Performance (1)
• Entrance filters have a very small bulk transmission (less than 1e-8)• Images in the filter wheel “open” position show a small visible light
component, in particular at the (fainter) 284 wavelength
EUVI-A 284 OPEN EUVI-A 284 S1
2007 March 5 10
Entrance Filter Performance (2)
• A few weeks after launch, two entrance filters on the EUVI-A developed a small pinhole
• Pinholes are tiny, imaging in the “open” position is still possible
• No practical impact as we always planned to observe with additional filter in the filter wheel.
• The filters continue to meet light and heat rejection requirements
• Affected quadrants: 171 & 304 on Ahead• All other quadrants, including all
quadrants on EUVI-B continue to be in pristine condition as of mid January 2007
2007 March 5 11
Fine Pointing System Performance
• Early in the commissioning phase, the FPS dramatically improved the quality of the EUVI images– Images below were taken during EUVI-A first light
• S/C jitter performance has substantially improved since, making the effect more subtle
FPS off FPS on
2007 March 5 12
Response Comparison Ahead vs. Behind
• Histograms of simultaneous images in A/B
– Blue: Ahead– Red: Behind
• Response very similar
• Largest difference in 171:
– Approx. 10 %– EUVI A & B have
slightly different response ratio 171 / 175
2007 March 5 13
EUVI A / B Spectral Response (Prelaunch)
2007 March 5 14
Comparison EUVI - EIT (Qualitative)• EUVI has higher resolution, and similar S/N as EIT• Images below displayed with same contrast setting• Raw EIT images have reduced dynamic range due to CCD damage
– Degree of damage: strongest at limb, smallest far off limb– Artificially enhances features far off limb, and on disk– Prepping EIT compensates most of this effect
• EUVI images have appearance of being “less sensitive” in faint areas
EUVI (raw) EIT preppedEIT raw
2007 March 5 15
Flat Fielding (1)
Approach:• Large scale (S/C controlled) offpoints for vignetting function
– 6 positions– Up to +/- 12 arcmin
• Small (SECCHI controlled) offpoints for flat field– 14 random positions– Up to +/- 1.5 arcmin
• All observations use tip/tilt mirror to artificially blur images
2007 March 5 16
Flat Fielding (2)
Status• Large scale offpoints complete
– A: 2007-02-15, B: 2007-02-05
– See Figures on the right
• Small scale offpoints:– A-171 & 304: 2007-02-21
– B-171 & 304: 2007-02-04
– 195 & 284 not done yet
• Data analysis pending
2007 March 5 17
EUVI Pointing and Roll : Status
• Goal: Header of Level 0.5 FITS images will include proper attitude information (pointing and roll)– CRPIXi indicate sun center pixel, CRVALi=0, PCij point to Solar N
– CDELTi indicate proper plate scale
• Current status of Level 0.5 FITS images– Pointing is not yet correct (generic CRPIXi values)
– Roll reflects S/C roll, EUVI specific roll offset not yet implemented• S/C roll is probably within a couple degrees of EUVI roll
– Assumes identical plate scale for EUVI-A and EUVI-B
2007 March 5 18
EUVI Pointing and Roll : euvi_point.pro
• SSW routine euvi_point.pro adds preliminary attitude information to FITS header:
• Uses GT data for pointing• Absolute sun center location currently accurate to a few
arcsec• Relative pointing (jitter) accurate to subarcsecond level• Does not change roll of EUVI-B• Adjusts roll of EUVI-A to reflect the recently determined
roll difference between EUVI-A and EUVI-B (1.245 deg)• Adjusts plate scale of EUVI-A to reflect the recently
determined plate scale difference between A and B– Pixels of EUVI-A are about 0.9986 times smaller than on EUVI-B– Plate scale of EUVI-B remains at 1.590 arcsec/pixel
2007 March 5 19
EUVI Pointing and Roll : Near-term Plan
• Future Level 0.5 FITS header to incorporate the attitude information from euvi_point.pro
• Improve accuracy of absolute pointing to subarcsec level– Improved modeling of GT non-linearities in euvi_point.pro
• Use lunar transit observations to determine absolute roll offset of EUVI-B
• Use lunar transit observations to recalibrate plate scale of EUVI-B
• Reprocess Level 0.5 FITS files with best available attitude data
2007 March 5 20
EUVI Pointing and Roll - The FPS and Jitter
• FPS mode of operation:– The FPS is turned on/off for each image– At the beginning of the exposure, an offset is added to the GT
signal to minimize the motion of the tip/tilt mirror– The offset is chosen in integer increments of the EUVI pixel size
• Effect on EUVI raw images– The sun center location may jump around from image to image– The amplitude of the jumps is in full pixel increments
• The exact amplitude may be a few percent off a full pixel increment
• The exact amplitude is given in the (corrected) CRPIXi values
– Movies, overlays, or difference images can be made with images that are shifted in full pixel increments
• Sub-pixel interpolation is not necessary
2007 March 5 21
2007 March 5 22
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 5 23
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 5 24
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
2007 March 5 25
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 5 26
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
2007 March 5 27
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
2007 March 5 28
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 (essentially this week?):
• Run NRL program on Ahead• Run LMSAL program on Behind
– Re-evaluate
2007 March 5 29
Lunar Transit 2007 February 25
2007 March 5 30
2007 March 5 31
2007 March 5 32
First 3D in 171
2007 March 5 33
2007 March 5 34
2007 March 5 35