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

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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

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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

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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

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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

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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

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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

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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

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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

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Hybrid Visible CMOS Imagers

Combination of matrix of photodiodes with matrix of CMOS multiplexers/amplifiers

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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

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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

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Microlenses: Cross-Talk

Problem if numerical aperture of optical system < numerical aperture of microlenses

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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

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sCMOS: Readout Noise

2 single pixels (average of 1000 bias frames)

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sCMOS: Readout Noise

Noise distribution of (512x512 pixels, best case)

CCD noise distribution

10x10 pixel area

manufacturer spec.

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Non-Linearity

High gain < 4%(spec. <1%)

10 bit

11 bit

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Non-Linearity

Low gain < 8%(spec. <1%)

11 bit

11 bit

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Dual Gain

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Non-Linearity

Dual gain

14 bit

16 bit

error in gate array?

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Flat Field Pixel Variance

1000 flat fields, distrib. of single pixel variances (512x512 pixel area)

1/8 * 3.5!

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Flat Field Pixel Variance

1000 flat fields, single pixel variances ~9% interpolated pixels (average of 9

pixels)!

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Cross-Talk / MTF

2-d autocorrelation of difference of 2 flat fields

no explanation!.

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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

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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