Astronomical Institute University of Bern 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt,...
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Transcript of Astronomical Institute University of Bern 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt,...
Astronomical Institute University of
Bern
31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany
Improved Space Object Observation Techniques using CMOS Detectors
T. Schildknecht, A. Hinze, J. Silha
Astronomical Institute, University of Bern, Switzerland
J. Peltonen, T. Säntti
Aboa Space Research Oy (ASRO), Turku, Finland
T. Flohrer
Space Debris Office, ESA/ESOC, Germany
Slide 2 Astronomical Institute University of
Bern
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CM
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Outline
1. Optical Space Object Observation Strategies requirement for new detector
2. CMOS Imaging Sensors potential benefits
3. Characterization of sCMOS Camera
4. Conclusion
Slide 3 Astronomical Institute University of
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Ground-Based Surveys
Ground-based GEO
Ground-based MEO/HEO
Ground-based LEO
Angular velocity
< 20"/s <100"/s 200"/s – 1800"/s
FoV dwell time(3° FoV)
540s @20"/s 108s @100"/s ~ 6s @1800"/s
Epoch accuracy(0.5")
25ms 5 ms 0.28ms
Exposure time 10 s ≥ 1s 10 s ≥ 1s 1s
Detector readout
few sec few sec1snon-
destructive
Processing streak det.
Electronic shutter
desired desired required
Slide 4 Astronomical Institute University of
Bern
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Space-Based Surveys
LEO sensor observing GEO/MEO/HEO similar to ground-based GEO/MEO/HEO
Short-range observations (small-size debris surveys) LEO to LEO, GEO to GEO, etc similar to ground-based LEO
Specific requirements mechanical shutters not advisable space-proof detector (cosmic ray
background!) on-board processing desirable
Slide 5 Astronomical Institute University of
Bern
T. S
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Generic Detector Requirements
Detection, astrometry, photometry high quantum efficiency Low read-out noise low dark current stable flat field (i.e. stable gain for each
pixel) stable bias or on-chip bias reduction limited number of dark/hot pixels
(“cosmetics”) no charge leakage from pixel to pixel limited enlargement of PSF in detector high full-well capacity
Slide 6 Astronomical Institute University of
Bern
T. S
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Requirements for New Detector
Electronic shutter required for space-based sensor required for precise epoch registration (surveys LEO) increased reliability for ground-based sensors
Faster read-out (large sensors!) improved duty cycle larger survey area are per time more observations per tracklet (FoV crossing)
improved orbit accuracy improved tracklet correlation
Extremely short exposures 1s required for ground-based LEO, space-based short
range non-destructive readout to “subdivide” streaks
On-chip processing spatial filtering image segmentation
Slide 7 Astronomical Institute University of
Bern
T. S
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Silicon Detector Technologies
Charge Coupled Devices (CCDs)
CMOS sensors or Active Pixel sensors
Hybrid Visible Sensors combining silicon photodiode detection with separate CMOS electronics
Slide 8 Astronomical Institute University of
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CCD Detectors
Basic structure/operation principle array of photodiodes sequential readout
(charge transfer) one (or few) readout
node(s) no electronic shutter
Alternative architectures “electronic shutter”
function
frame transfer
interline transfer
Slide 9 Astronomical Institute University of
Bern
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CMOS or Active Pixel Sensor
Basic structure /operation principle array of
photodiodes each pixel has own
amplifier (and storage area)
multiplexed readout
Slide 10 Astronomical Institute University of
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Hybrid Visible CMOS Imagers
Combination of matrix of photodiodes with matrix of CMOS multiplexers/amplifiers
Slide 11 Astronomical Institute University of
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On-chip processing in CMOS
In CMOS processing in a pixel-parallel fashion is possible
Back-illuminated circuits are needed in astronomy. More complex structures can be integrated on the front surface without too much reduction in the photoactive area
ROI (region of interest) detection: Background subtraction, filtering and simple (e.g. 1-bit) segmentation may be possible if a local pixel storage for reference values can be established.
Paralleled, application specific image pipelines can be integrated on the same chip outside the active area
Slide 12 Astronomical Institute University of
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Main Advantages/Disadvantages
CCD sCMOS Hybrid CMOS
Quantum Eff. (@500nm)
>90% (thinned)60% with
microlenses>90%
Read noise 6-10e- 1MHz
<2e- @560MHz 7-10e- @1MHz
Dynamic range
~1:10-20 000 1:16 000 ~1: 5 000
Uniformity good fair fair
p2p Cross-talk some some? some extra
Fast readout <1fps 30-60 fps 30-60 fps
Electronic shutter
(yes) rolling/global rolling
Radiation tol. fair/good ? good
Complex readout
norandom access;
non.-destructive
random access; non.-destructive
Processing no limited on-chip side-car
Slide 13 Astronomical Institute University of
Bern
T. S
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knech
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Microlenses: Cross-Talk
Problem if numerical aperture of optical system < numerical aperture of microlenses
Slide 14 Astronomical Institute University of
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sCMOS Camera Tests
Andor NEO sCMOS (CIS2051, former Fairchild Imaging) 11 bit intrinsic 16 "dual-gain" front-side QEmax 59 % microlenses
Slide 15 Astronomical Institute University of
Bern
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sCMOS: Readout Noise
2 single pixels (average of 1000 bias frames)
Slide 16 Astronomical Institute University of
Bern
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sCMOS: Readout Noise
Noise distribution of (512x512 pixels, best case)
CCD noise distribution
10x10 pixel area
manufacturer spec.
Slide 17 Astronomical Institute University of
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Non-Linearity
High gain < 4%(spec. <1%)
10 bit
11 bit
Slide 18 Astronomical Institute University of
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Non-Linearity
Low gain < 8%(spec. <1%)
11 bit
11 bit
Slide 19 Astronomical Institute University of
Bern
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Dual Gain
Slide 20 Astronomical Institute University of
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Non-Linearity
Dual gain
14 bit
16 bit
error in gate array?
Slide 21 Astronomical Institute University of
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Flat Field Pixel Variance
1000 flat fields, distrib. of single pixel variances (512x512 pixel area)
1/8 * 3.5!
Slide 22 Astronomical Institute University of
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Flat Field Pixel Variance
1000 flat fields, single pixel variances ~9% interpolated pixels (average of 9
pixels)!
Slide 23 Astronomical Institute University of
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Cross-Talk / MTF
2-d autocorrelation of difference of 2 flat fields
no explanation!.
Slide 24 Astronomical Institute University of
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Conclusions
Major challenges and design drivers for ground-based and space-based optical observation strategies are detection of faintest objects precise epoch registration electronic shutter short exposures 1s (LEO, space-based) high readout rate 1s for full frame (LEO, space-
based) on-chip processing (space based)
CMOS Active Pixel Sensors offer most of the required capabilities but have still disadvantages wrt. CCDs
• low quantum efficiency (no backside illuminated devices)• noise characteristics • high Pixel Response Non-Uniformity (PRNU) • low dynamic range• high percentage of dark/hot pixles
Slide 25 Astronomical Institute University of
Bern
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Conclusions
Andor NEO sCMOS (CIS2051) camera has been characterized by means of laboratory tests noise characteristics linearity, dynamic range cross-Talk / MTF
Scientific CMOS devices are rapidly evolving and some disadvantages may be overcome in near future