1 / 42

The Eddington Photometric Camera Working Group

The Eddington Photometric Camera Working Group. W G. CAB. Eddington System Studies WG meeting. ESA - HQ November 20 th , 2002 revised on Nov. 28th. Contents Scientific Requirements analysis Instrument configuration and operation Example. Scientific Requirements analysis.

brac
Download Presentation

The Eddington Photometric Camera Working Group

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Eddington Photometric Camera Working Group W G CAB Eddington System Studies WG meeting ESA - HQ November 20th, 2002 revised on Nov. 28th

  2. Contents • Scientific Requirements analysis • Instrument configuration and operation • Example ESA-HQ 20th November 2002

  3. Scientific Requirements analysis ESA-HQ 20th November 2002

  4. Scientific Requirements analysis: general • Latest version “Eddington High level Science Requirements” Claude Catala and the EST July 2002 • General comments: • There are some key requirements, which affect technical definition and are missing: • Maximum allowable defocusing (to avoid crowding) for AS and PF • Number of stars to be monitored for AS (could be derived from “Typical star densities for the Eddington mission” (Claude Catala; September 2002) • Color discrimination still TBC (?) for AS and PF • Photometric requirements should be clarified for the complete magnitude range and translated to directly measurable engineering parameters ESA-HQ 20th November 2002

  5. Scientific Requirements analysis: magnitude range • Requirement: • AS: 15 - 5 (goal 3) • PF: 17-11 • General considerations: • Bright stars produce saturation in the CCD • Weak stars can not reach the required photometric accuracy • INTA studies based on: • CCD E2V 42-C0: 3072x2048 pixels; full well capacity of 150.000e- • Astrium preliminary design • Defocusing: star box size 16x16 pixels (170 microns on the focal plane) ESA-HQ 20th November 2002

  6. Bright stars saturation problem • Integration time for saturation: EddiSim Data Readout time for different binnings CCD 42-C0 Data Sheet For Ti=50 µs ; Tr=500 ns = 2MHz • 1x1 => 3072(150 µs + 1049 µs) = 3,683 sec. • 2x1 (or 2x2) => 1536(200 µs + 1049 µs) = 1,918 sec. • 4x1 => 768(300 µs + 1049 µs) = 1,036 sec. For Ti=100 µs ; Tr=1 µs = 1MHz • 1x1 => 3072(300 µs + 2098 µs) = 7,366 sec. • 2x1 (or 2x2)=> 1536(400 µs + 2098 µs) = 3,837 sec. • 4x1 => 768(600 µs + 2098 µs) = 2,072 sec. ESA-HQ 20th November 2002

  7. PF AS Readout time ESA-HQ 20th November 2002

  8. Bright stars saturation problem • PF: • No saturation problem within the required magnitude range • Potential saturation problems induced by bright stars present in the FOV (magnitude below V=11) ESA-HQ 20th November 2002

  9. Bright stars saturation range • AS: • Scientific requirements are not accomplished.Different options can be considered: • Larger defocusing • On chip binning: reduction of integration time • Smaller effective FOV: reduction of integration time • Use of two readout ports simultaneously • Use of integration times shorter than readout time • Different operations on one telescope, optimized for bright stars • Combination of some of the above options ESA-HQ 20th November 2002

  10. Bright stars saturation problem: options 1. Larger defocusing:  Maximum defocusing is constrained by the expected crowding Integration time for saturation (sec) EddiSim Data • PROS: • Longer integrations could be used without saturation • CONS: • Crowding • Photometry accuracy  due to larger background contribution  needs to be analysed ESA-HQ 20th November 2002

  11. ESA-HQ 20th November 2002

  12. Bright stars saturation problem: options 2. Binning alternatives: 4x1 • PROS: • Readout time is reduced to 2 sec (1MHz) or 1sec (2MHz) • Data volume is reduced by 4 • CONS: • If working with CCD readout speed of 2MHz the electronic chain has to work at 2 MHz • Very poor PSF spatial sampling • Photometric accuracy due to higher background contribution 2x2 • PROS: • Data volume is reduced by 4 • PSF better sampled with 2x2 binning • It would allow to use a readout of 2MHz for the CCD and 1MHz for the electronic chain • CONS: • Readout time is reduced to only 3.8 sec (1MHz) or 2 sec (2MHz) ESA-HQ 20th November 2002

  13. Bright stars saturation problem: options 2. Binning alternatives: CCD output 1x1 binning CCD output 4x1 binning Input image CCD output 2x2 binning EddiSim Data ESA-HQ 20th November 2002

  14. Bright stars saturation problem: options 3. Smaller FOV (windowed readout): 625 pixels Claude Catala Proposal Image area of 10,89 Mpixels instead of 37,8 2048 pixels 1650 pixels • PROS: • Readout time is reduced • Data volume is reduced (smaller processing requirementS) • CONS: • FOV is reduced by a factor 4 (number of stars is reduced) • Strong constraints on the readout port; loss of redundancy ESA-HQ 20th November 2002

  15. Bright stars saturation problem: options 4. Use of two readout ports simultaneously: • PROS: • Readout time is reduced • CONS: • Duplicated readout chain • Loss of redundancy 5. Use of integration times shorter than readout time: • PROS: • Integration time could be adapted to the required value • CONS: • Gaps between integrations required to read the image and “clean” the CCD; effective observation time is reduced • Photometry accuracy for weak stars could not be acceptable due to the loss of effective integration time 6. Optimization of one telescope for bright stars: • CONS: • If a filter is installed, redundancy between telescopes is lost • Photometry accuracy for weak stars will be worse • PROS: • Defocusing could be adapted for bright stars • With a filter theintegration time for saturation could be longer ESA-HQ 20th November 2002

  16. Bright stars saturation problem: options 7. Combination of some/all of the above options: • There are lot of possibilities • It is recommended that the operational solution: • Does not reduce redundancy • Maintains the same HW configuration for the four telescopes; differences should be only in the operation • Example: • 4 identical telescopes • 3 of them with operations optimized for weak stars: • 1 of them optimized for bright stars (but also observing weak stars): ESA-HQ 20th November 2002

  17. Scientific Requirements analysis: photometric requirements • Requirement: • AS: Noise level in amplitude Fourier space  1.5ppm in 30d for mv= 11 in frequency range 0.001-100mHz • PF: noise level in the light curve  1e-5 in 39 hrs (average 3 transits) = 6.3e-5 in 1hr for late-type dwarfs • Both requirements should be translated into measurable instrument parameters and should be expressed for the whole magnitude range. ESA-HQ 20th November 2002

  18. Scientific Requirements analysis: photometric requirements • We have assumed the following definition: SNR-1telescope = Noise/Signal = / signal For one single measurement with the telescope the accuracy of this single measurement is given by: Smeasured   SNR-1instrument= SNR-1telescope /Number of telescopes =SNR-1telescope / 2 ESA-HQ 20th November 2002

  19. Scientific Requirements analysis: photometric requirements • How is SNR-1instrument calculated?: • Directly considering only photon noise: SNR-1telescope = Noise/Signal =1 /  counts per telescope SNR-1instrument = 1 / 2 counts per telescope • Using EddiSim: Noise (distributions of photon, readout, background, etc.) Calculation of: * S* SNR-1telescope= */S* SNR-1instrument= SNR-1telescope /2 EddiSim (1 telescope) S (for a given star magnitude and type) N times = N samples of S*(N around 400) ESA-HQ 20th November 2002

  20. Scientific Requirements analysis: photometric requirements • Results considering only photon noise: ESA-HQ 20th November 2002

  21. V 5 ESA-HQ 20th November 2002

  22. Scientific Requirements analysis: photometric requirements • Results using EddiSim: Acumulated integration time (sec) SNR-1instrument Using EddiSim SNR-1instrument Direct calculation • EddiSim data have been obtained: • considering only one integration and not taking into account the saturation • for a PSF box of 16x16 pixels ESA-HQ 20th November 2002

  23. ESA-HQ 20th November 2002

  24. Scientific Requirements analysis: photometric requirements • Photometric accuracy could be improved by: • Increasing the telescope aperture (worsening of the saturation problem) • Implementing more telescopes (not realistic) • Increasing the accumulated integration time (longer sampling time, still compatible with the detection of transits) ESA-HQ 20th November 2002

  25. Scientific Requirements analysis: number of stars and sampling time • Requirements: • PF: • Time sampling:  600 sec (bottomline)  30 sec (goal) • Number of stars to monitor > 20.000 late-type dwarfs with PF1 S/N > 100.000 all types with lower S/N • Assumed by INTA studies ESA-HQ 20th November 2002

  26. Scientific Requirements analysis: number of stars and sampling time • Requirement: • AS: • Time sampling:  30 sec (baseline)  5 sec (for some targets) • Number of stars to monitor not included; estimation could be done with “Typical star densities for the Eddington mission” – Claude Catala, Sep.02 • Assumed by INTA studies ESA-HQ 20th November 2002

  27. Instrument configuration and operation ESA-HQ 20th November 2002

  28. Instrument configuration and operation: • General comments • In order to start the instrument definition and preliminary sizing it is necessary to establish an instrument configuration and operation baseline for both science modes: AS and PF • The parameters that should be set are the following: ESA-HQ 20th November 2002

  29. Instrument configuration and operation: • How do these parameters affect the instrument definition and sizing? Some examples: • Defocusing/binning: determine the number of pixels in which the information is contained  number of pixels to be processed required processing capability • Image area and binning: affects directly the required onboard memory • Number of stars: gives the number of photometric points to be processed required processing capability • Sampling time:it constraints the time in which the processing has to be done required processing capability ESA-HQ 20th November 2002

  30. Instrument configuration and operation: • In addition, the scientific proocessing algorithm has to be defined to dimension the instrument. ESA-HQ 20th November 2002

  31. Example of instrument dimensioning ESA-HQ 20th November 2002

  32. Example • Instrument configuration and operation baseline: ESA-HQ 20th November 2002

  33. Example: instrument data flow configuration 16 bits ADC per binned pixel (availability TBC option suggested by MSSL with 2 x12 bits ADCs) CCD Readout 3 Mbytesper CCD image Integration time 2 sec 6.3 Mpix Image area 1.5 MBytes/s 2 MHz ADC 1 MHz Pre-processor 6.3 Mpix 2 MHz Storage area 1.575 Mpix/2sec Adder 2 Adder 1 Output Register Amplifier 3.15 Mpix 1 MHz 3 Bytes per binned pixel Binning 2x2 STACK 2 30s/600s 4.5MBytes STACK 1 6s/30s 4.5MBytes 4.5Mbytes per CCD image 1 read-out port Readout time 1.9 sec 2sec Intermediate buffer 9MBytes 4 Bytes per binned pixel 6MBytesper CCD image Spacewirebus (100Mbits/s) DPU ESA-HQ 20th November 2002

  34. Example: DPU configuration • Based on the design developed by CRISA for PACS on Herschel • Constituted by: + CCD I/F interface module, based on SMCS332 Spacewire links at 100 Mbps+ scientific processing unit, based on 1 TSC21020E processor at 20 MHz+ extended memory boards + instrument control unit, with an independent processor+ OBDH I/F module based on the 1553B bus at 100 kbps+ monitoring, synchronization and power supply modules This DPU is already being built and is fully compatible with the Herschel bus ESA-HQ 20th November 2002

  35. Example: scientific processing strategy • At the beginning of each observing period (once per month), a reference image (binning 1x1) is obtained by combining different integrations during around 1 hour. • The reference image is downloaded to ground using the highest available TM (10 minutes per CCD at 300 kbps without compression). • The reference image is processed on ground, obtaining the reference photometric value for each star of interest. • A table containing the identification of the stars to be monitored, as well as several bits indicating the kind of processing to be performed, is uplinked to the spacecraft. The table will include also the photometric mask to be used for each star: ESA-HQ 20th November 2002

  36. Example: scientific processing strategy • The photometric mask contains 1 bit per position (64 bits for 8x8 PSF box). • Depending on the bit information, the corresponding binned pixel will be added or rejected. • The masks will allow to minimize the impact of overlapping stars, CCD edges, defect pixels or columns, ... • They will be obtained on ground from the reference images, in order to optimize the results. ESA-HQ 20th November 2002

  37. Example: scientific processing strategy • The DPU will add only the pixels marked with 1 in each PSF box. • The value so obtained will be subtracted from the reference value, computed on ground from the reference image with the same algorithm: the reference background is computed on the same pixels than the star itself!. • This difference will be sent to ground with 4 bytes per value. • The values will be mostly zero or very small numbers, allowing for a high degree of compression. ESA-HQ 20th November 2002

  38. Example: scientific processing strategy • In addition, a TBD number of complete windows (8x8 pixels) will be sent to ground to monitor the evolution of the background and the health of the CCDs. • The real photometric value will be reconstructed on ground. • Cross-correlation of the 4 photometric series on ground will allow to discard the effect of cosmic rays. • Computations with the EddiCam simulator show that for V < 16 the images stacked up to 600 s effective integration time (300 frames) remain photon noise limited. ESA-HQ 20th November 2002

  39. Example: scientific processing strategy • The preliminary estimated TM requirements are the following (assuming all values sent to Earth with 3 bytes coding): AS: 105.6 kbps for stars (+ 30.7 kbps for 100 background windows)every 30 s: (32.400 + 5x120) stars/telescope + (6x100) 8x8 windows (33.000x3)x4 telescopes + (600x64x3) = 396.000 + 115.200 bytes PF: 81.9 kbps for stars (+ 5.4 kbps for 100 background windows)every 600 s: (120.000 + (20x20.000)) stars/teles + (21x100) bkg windows (520.000x3)x4 telescopes + (2.100x64x3) = 6.240.000 + 403.200 bytes  Well within the Herschel TM capabilities ( 100 kbps sustained rate), assuming some moderate data compression! ESA-HQ 20th November 2002

  40. Example: system simulations • Processing analysis tool support: • DEIMOS Space S.L. is supporting INTA with the processing requirements dimensioning • Emulations of Eddington image processing are being done using TSIM Professional host simulation tools • Processors under study: • ERC32 (TSC695E) with 32 Mbytes RAM, at 20 MHz AS:  22 % CPU load PF:  26 % CPU load  A single DPU can handle the 6 CCDs of each telescope • TSC 21020 at 20-25 MHz under evaluation, but similar results expected ESA-HQ 20th November 2002

  41. Conclusions • Not all the present scientific requirements can be accomplished simultaneously with the present Eddington mission concept • Major problems with saturation vs crowding vs large dynamical range • But feasible instrument configurations would allow to comply with most of the requirements • The fine tuning of the present designs requires the agreement on which scientific drivers should be optimized: a task for the EST ESA-HQ 20th November 2002

  42. Each star spreads over around 50”, similar to a 16x16 pixels PSF on Eddington OMC first light 5ºx5º image (limit magnitude 13) ESA-HQ 20th November 2002

More Related