1. 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

2. Slide 2 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Outline 1.Optical Space Object Observation Strategies  requirement for new detector 2.CMOS Imaging Sensors  potential benefits 3.Characterization of sCMOS Camera 4.Conclusion

3. Slide 3 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany 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"/s108s @100"/s~ 6s @1800"/s Epoch accuracy (0.5") 25ms5 ms0.28ms Exposure time 10 s ≥ 1s  1s Detector readoutfew sec  1s non-destructive Processingstreak det. Electronic shutter desired required

4. Slide 4 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany 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

5. Slide 5 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany 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

6. Slide 6 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany 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

7. Slide 7 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Silicon Detector Technologies Charge Coupled Devices (CCDs) CMOS sensors or Active Pixel sensors Hybrid Visible Sensors combining silicon photodiode detection with separate CMOS electronics

8. Slide 8 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany 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

9. Slide 9 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany CMOS or Active Pixel Sensor Basic structure /operation principle  array of photodiodes  each pixel has own amplifier (and storage area)  multiplexed readout

10. Slide 10 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Hybrid Visible CMOS Imagers Combination of matrix of photodiodes with matrix of CMOS multiplexers/amplifiers

11. Slide 11 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany 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

12. Slide 12 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Main Advantages/Disadvantages CCDsCMOSHybrid CMOS Quantum Eff. (@500nm) >90% (thinned) 60% with microlenses >90% Read noise6-10e - 1MHz<2e - @560MHz7-10e - @1MHz Dynamic range~1:10-20 0001:16 000~1: 5 000 Uniformity goodfair p2p Cross-talksomesome?some extra Fast readout<1fps30-60 fps Electronic shutter (yes)rolling/globalrolling Radiation tol.fair/good?good Complex readout no random access; non.-destructive Processingnolimited on-chipside-car

13. Slide 13 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Microlenses: Cross-Talk Problem if numerical aperture of optical system < numerical aperture of microlenses

14. Slide 14 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany sCMOS Camera Tests Andor NEO sCMOS (CIS2051, former Fairchild Imaging)  11 bit intrinsic  16 "dual-gain"  front-side  QE max 59 %  microlenses

15. Slide 15 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany sCMOS: Readout Noise 2 single pixels (average of 1000 bias frames)

16. Slide 16 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany sCMOS: Readout Noise Noise distribution of (512x512 pixels, best case) CCD noise distribution 10x10 pixel area manufacturer spec.

17. Slide 17 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Non-Linearity High gain  < 4% (spec. <1%) 10 bit 11 bit

18. Slide 18 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Non-Linearity Low gain  < 8% (spec. <1%) 11 bit

19. Slide 19 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Dual Gain

20. Slide 20 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Non-Linearity Dual gain 14 bit 16 bit error in gate array?

21. Slide 21 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Flat Field Pixel Variance 1000 flat fields, distrib. of single pixel variances (512x512 pixel area) 1/8 * 3.5! 

22. Slide 22 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Flat Field Pixel Variance 1000 flat fields, single pixel variances  ~9% interpolated pixels (average of 9 pixels)!

23. Slide 23 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany Cross-Talk / MTF 2-d autocorrelation of difference of 2 flat fields no explanation!.

24. Slide 24 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany 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

25. Slide 25 Astronomical Institute University of Bern T. Schildknecht: Improved Space Object Observation Techniques using CMOS Detectors 31th IADC Meeting, April 17 - 19, 2013, ESOC, Darmstadt, Germany 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