the eddington photometric camera working group eddington system studies wg meeting esa - hq november...

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


Scientific Requirements analysis


• 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


• 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


• 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


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


• 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


• 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


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


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


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)


2. Binning alternatives:


EddiSim Data

Input image

CCD output 1x1 binning




3. Smaller FOV (windowed readout):


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


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:

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


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:


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%


• 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


• 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



• 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:


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


• Results considering only photon noise:


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


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


SNR-

1

V10

V11

V14

V15

V16

V 5


• Results using EddiSim:


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


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


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


SNR-

1

V11

V16

V11 EddiSim

V16 EddiSim


• 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)



• 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


• 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


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:

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


• 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



• In addition, the scientific proocessing algorithm has to be

defined to dimension the instrument.



Example of instrument dimensioning


• 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)


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


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


• 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


• 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.


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


• 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.



• 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.



• 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!



• 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


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


OMC first light 5ºx5º image (limit magnitude 13)

Each star spreads over around 50”, similar to a 16x16 pixels PSF on Eddington

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