The Eddington Photometric Camera Working Group
Eddington System Studies WG meeting
ESA - HQ November 20th, 2002
revised on Nov. 28th
CAB
W G
Eddington SWG progress meeting ESA-HQ 20th November 2002 2
Contents
• Scientific Requirements analysis• Instrument configuration and operation• Example
Eddington SWG progress meeting ESA-HQ 20th November 2002 4
• Latest version “Eddington High level Science Requirements”Claude Catala and the ESTJuly 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
Scientific Requirements analysis: general
Eddington SWG progress meeting ESA-HQ 20th November 2002 5
• 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)
Scientific Requirements analysis: magnitude range
Eddington SWG progress meeting ESA-HQ 20th November 2002 6
• Integration time for saturation:
Bright stars saturation problem
Star Magnitud
e
Integration time for
saturation (sec)
5 0,17
6 0,50
7 1,25
8 3,25
9 7,75
10 19,25
11 48
12 120
13 301
14 760
15 1899
16 4771
17 11974
Saturation time for 16x16 defocusing
0,1
1
10
100
1000
10000
100000
0 5 10 15 20
Star MagnitudeIn
tegra
tion
time
(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.
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.
EddiSim Data
CCD 42-C0 Data Sheet
Readout time for different binnings
Eddington SWG progress meeting ESA-HQ 20th November 2002 7
Saturation time for 16x16 defocusing
0,1
1
10
100
1000
10000
100000
0 5 10 15 20
Star Magnitude
Inte
gra
tion
time
(sec
)AS PF
Readout time
Eddington SWG progress meeting ESA-HQ 20th November 2002 8
• PF:
No saturation problem within the required magnitude range
Potential saturation problems induced by bright stars present
in the FOV (magnitude below V=11)
Bright stars saturation problem
Eddington SWG progress meeting ESA-HQ 20th November 2002 9
• AS:
Scientific requirements are not accomplished.
Different options can be considered:
1. Larger defocusing
2. On chip binning: reduction of integration time
3. Smaller effective FOV: reduction of integration time
4. Use of two readout ports simultaneously
5. Use of integration times shorter than readout time
6. Different operations on one telescope, optimized for bright stars
7. Combination of some of the above options
Bright stars saturation range
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1. Larger defocusing: Maximum defocusing is constrained by the expected crowding
Bright stars saturation problem: options
Defocusing
(microns)
PSF box
V5 V6 V7
170 16x16 0,25 0,50 1,25
200 17x17 0,25 0,75 1,75
220 18x18 0,50 0,75 2,00
250 20x20 0,50 1,00 2,50
280 22x22 0,50 1,25 3,00
310 24x24 0,75 1,50 3,50
340 25x25 0,75 1,75 4,00
370 26x26 0,75 2,00 4,75
400 27x27 1,00 2,25 5,50
Integration time for saturation (sec)
Defocusing versus saturation time
0
1
2
3
4
5
6
100 200 300 400
Defocusing (microns)
Sa
tura
tio
n t
ime
(s
ec
)
V5V6V7
EddiSim Data
PROS:
•Longer integrations could be used without saturation
CONS:
•Crowding
•Photometry accuracy due to larger background contribution needs to be analysed
Eddington SWG progress meeting ESA-HQ 20th November 2002 11
Defocusing versus saturation time
0
1
2
3
4
5
6
100 200 300 400
Defocusing (microns)
Sa
tura
tio
n t
ime
(s
ec
)
V5
V6
V7
Eddington SWG progress meeting ESA-HQ 20th November 2002 12
2. Binning alternatives:
4x1
Bright stars saturation problem: options
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)
Eddington SWG progress meeting ESA-HQ 20th November 2002 13
2. Binning alternatives:
Bright stars saturation problem: options
EddiSim Data
Input image
CCD output 1x1 binning
CCD output 2x2 binning
CCD output 4x1 binning
Eddington SWG progress meeting ESA-HQ 20th November 2002 14
3. Smaller FOV (windowed readout):
Bright stars saturation problem: options
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
1650 pixels
625 pixels
2048 pixels
Claude Catala Proposal
Image area of 10,89 Mpixels instead of 37,8
Eddington SWG progress meeting ESA-HQ 20th November 2002 15
4. Use of two readout ports simultaneously:
Bright stars saturation problem: options
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:
PROS:
•Defocusing could be adapted for bright stars
• With a filter the integration time for saturation could be longer
CONS:
•If a filter is installed, redundancy between telescopes is lost
•Photometry accuracy for weak stars will be worse
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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:
Bright stars saturation problem: options
Defocusing Binning Integration time
16x16 2x2 2sec, continuously
1 of them optimized for bright stars (but also observing weak stars):
Defocusing Binning Integration time
18x18 2x2 0,5 sec integration + 3,5 sec integration efficiency: 66%
Eddington SWG progress meeting ESA-HQ 20th November 2002 17
• 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.
Scientific Requirements analysis: photometric requirements
Eddington SWG progress meeting ESA-HQ 20th November 2002 18
• 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-1
telescope /Number of telescopes = SNR-1telescope / 2
Scientific Requirements analysis: photometric requirements
Eddington SWG progress meeting ESA-HQ 20th November 2002 19
• 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:
Scientific Requirements analysis: photometric requirements
EddiSim
(1 telescope)
S(for a given star
magnitude and type)
Noise (distributions of photon, readout,
background, etc.)
N times =
N samples of S*
(N around 400)
Calculation of:
*
S*
SNR-1telescope= */S*
SNR-1instrument= SNR-
1telescope /2
Eddington SWG progress meeting ESA-HQ 20th November 2002 20
• Results considering only photon noise:
Scientific Requirements analysis: photometric requirements
Instrument SNR-1
1,00E-06
1,00E-05
1,00E-04
1,00E-03
1,00E-02
1,00E-01
1 10 100 1000 10000 100000
Accumulated integration time (sec)
SNR-
1
V10
V11
V14
V15
V16
Star magnitude
1 telescope photons/s
1 telescope counts/s
4 telescopes counts/s
10 1,0E+6 6,8E+5 2,7E+6
11 4,0E+5 2,7E+5 1,1E+6
14 2,5E+4 1,7E+4 6,8E+4
15 1,0E+4 6,8E+3 2,7E+4
16 4,0E+3 2,7E+3 1,1E+4
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Instrument SNR-1
1,00E-06
1,00E-05
1,00E-04
1,00E-03
1,00E-02
1,00E-01
1 10 100 1000 10000 100000
Accumulated integration time (sec)
SNR-
1
V10
V11
V14
V15
V16
V 5
Eddington SWG progress meeting ESA-HQ 20th November 2002 22
• Results using EddiSim:
Scientific Requirements analysis: photometric requirements
V11 V16 V11 V16
5 4,29E-4 4,30E-3 4,22E-4 4,41E-3
10 3,03E-4 3,04E-3 2,82E-4 2,72E-3
30 1,75E-4 1,76E-3 1,56E-4 1,49E-3
100 9,59E-5 9,62E-4 8,18E-5 8,40E-4
600 3,91E-5 3,93E-4 3,53E-5 3,63E-4
1000 3,03E-5 3,04E-4 2,57E-5 2,51E-4
10000 9,59E-6 9,62E-5 8,59E-6 9,24E-5
Instrument SNR-1
Comparison between estimation and simulator results
1,00E-06
1,00E-05
1,00E-04
1,00E-03
1,00E-02
1,00E-01
1 10 100 1000 10000 100000
Accumulated integration time (sec)
SNR-
1
V11
V16
V11 EddiSim
V16 EddiSim
SNR-1instrument
Direct calculation
SNR-1instrument
Using EddiSimAcumulate
d integration time (sec)
EddiSim data have been obtained:
• considering only one integration and not taking into account the saturation
•for a PSF box of 16x16 pixels
Eddington SWG progress meeting ESA-HQ 20th November 2002 23
Instrument SNR-1
Comparison between estimation and simulator results
1,00E-06
1,00E-05
1,00E-04
1,00E-03
1,00E-02
1,00E-01
1 10 100 1000 10000 100000
Accumulated integration time (sec)
SNR-
1
V11
V16
V11 EddiSim
V16 EddiSim
Eddington SWG progress meeting ESA-HQ 20th November 2002 24
• 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)
Scientific Requirements analysis: photometric requirements
Eddington SWG progress meeting ESA-HQ 20th November 2002 25
• 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
Scientific Requirements analysis: number of stars and sampling time
Sampling time (sec)
Total Number of stars
30 20.000
600 100.000
Eddington SWG progress meeting ESA-HQ 20th November 2002 26
• 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
Scientific Requirements analysis: number of stars and sampling time
Sampling time (sec)
Total Number of stars
5 120
30 32400
Eddington SWG progress meeting ESA-HQ 20th November 2002 28
• 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:
Instrument configuration and operation:
Telescope operation
Identical or different operation
Defocusing
Integration time
Number of stacking areas
Image area size
Binning
CCD readout frequency + readout port (1 or 2)
Sampling time
Number of stars to be monitored
Telescope Configuration
Identical or different (filter for example))
Number of CCDs per telescope
CCDs type and characteristics
Eddington SWG progress meeting ESA-HQ 20th November 2002 29
• 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
Instrument configuration and operation:
Eddington SWG progress meeting ESA-HQ 20th November 2002 30
• In addition, the scientific proocessing algorithm has to be
defined to dimension the instrument.
Instrument configuration and operation:
Eddington SWG progress meeting ESA-HQ 20th November 2002 32
• Instrument configuration and operation baseline:
Example
Telescope Configuration
Identical telescopes
6 CCDS per telescope
CCDs 42-C0 type (3072 x 2048 pixels in the image area)
Telescope operation
Identical operation
Defocusing 16 x 16 pixels (170 microns)
Integration time = 2 sec
Number of stacking areas = 2
Image area size = 3072 x 2048 pixels
Binning = 2x2
CCD readout frequency: 2MHz1 readout port readout time = 1.9 sec
Sampling times: AS: 6 + 30 sPF: 30 + 600 s
Number of stars:AS: 120 (6s) + 32400 (30s)PF: 20.000 (30s) + 100.000 (600s)
Eddington SWG progress meeting ESA-HQ 20th November 2002 33
Example: instrument data flow configuration
CCD
ADC
Binning 2x2
1 read-out port
Integration time 2 sec
16 bits ADC per binned pixel (availability TBC option suggested by MSSL with 2 x12 bits ADCs)
3 Bytes per binned pixel
4 Bytes per binned pixel
Spacewire bus (100Mbits/s)
1.5 MBytes/s
Adder 1 Adder 2
DPU
Intermediate buffer
9MBytes
Pre-processor
STACK 16s/30s
4.5MBytes
STACK 230s/600s 4.5MByte
s
Image area
Storage area
6.3 Mpix
6.3 Mpix
3.15 Mpix
2 MHz
2 MHz
1.575 Mpix/2sec1 MHz
Output Registe
r
Readout time 1.9 sec 2sec
Readout
Amplifier
1 MHz
4.5 Mbytes per CCD image
3 Mbytes per CCD image
6 MBytes per CCD image
Eddington SWG progress meeting 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
Eddington SWG progress meeting ESA-HQ 20th November 2002 35
• 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:
Example: scientific processing strategy
Eddington SWG progress meeting ESA-HQ 20th November 2002 36
• 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.
Example: scientific processing strategy
0 0 0 0 0 0 0 0
0 0 1 1 1 1 0 0
0 1 1 1 1 1 1 0
0 1 1 0 0 1 1 0
0 1 1 0 0 1 1 0
0 1 1 1 1 1 1 0
0 0 1 1 1 1 0 0
0 0 0 0 0 0 0 0
Eddington SWG progress meeting ESA-HQ 20th November 2002 37
• 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.
Example: scientific processing strategy
Eddington SWG progress meeting ESA-HQ 20th November 2002 38
• 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.
Example: scientific processing strategy
Eddington SWG progress meeting ESA-HQ 20th November 2002 39
• 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!
Example: scientific processing strategy
Eddington SWG progress meeting ESA-HQ 20th November 2002 40
• 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
Example: system simulations
Eddington SWG progress meeting 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