secchi consortium meeting, paris - march 2007 heliospheric imagers – instrument status chris eyles...

SECCHI Consortium Meeting, Paris - March 2007

Heliospheric Imagers – Instrument Status

Chris Eyles

Space Science & Technology Department (RAL)

Richard Harrison, Chris Davis, Danielle Bewsher, Steve Crothers and Jackie Davies (RAL)

Jean-Philippe Halain (Centre Spatiale de Liege)

Dan Moses and Jeff Newmark (Naval Research Laboratory)

Chris Eyles

Space Science & Technology Department

HI Design Requirements

• Geometrical requirements:– To view the Sun-Earth line

with unbroken coverage from Corona to Earth orbit

– Opening angle of 45º governed by average CME width over equator

• Brightness levels:– Need to achieve rejection to

< 3x10-13 and < 10-14 B/Bo to detect CME signal

– Have to contend with contributions from the F-Corona, planets, stars, the Earth and Moon

Chris Eyles


HI Specifications

HI-1 HI-2

Direction of centre of FOV 13.98º 53.68º

Angular field of view 20º 70º

Angular range 3.98º – 23.98º 18.68º – 88.68º

CCD pixel size 35 arcsec 2 arcmin

Image array (2x2 binning) 1024x1024 1024x1024

Image bin size 70 arcsec 4 arcmin

Spectral bandpass 630-730 nm 400-1000 nm

Nominal exposure time 12-20 s 60-90 s

Nominal exposures per image 70 50

Nominal image cadence 60 min 120 min

Brightness sensitivity (Bo = solar disk) 3 x 10-15 Bo 3 x 10-16 Bo

Straylight rejection (outer edge) 3 x 10-13 Bo 10-14 Bo

Chris Eyles


Early Mission Summary (1)

• Launched on 25 Oct 2006

– Decontamination Heaters switched on few hours later

• SECCHI Electronics and HI Cameras switched on 27 Oct

– Electronics checks, dark images, Cal LED images

• Outgassing until 22 Nov

– Decontamination Heaters switched off

– CCD cooling curves and dark charge measurements (see later)

– Cal LED and dark images

• HI-A Door deployment and first light on 13 Dec

• First Lunar swing-by and heliospheric insertion of STEREO-A on 15 Dec

– HI-2A images of Moon !!!

Chris Eyles


HI-A First Lights

Chris Eyles


HI-A Lunar Swingby

Chris Eyles



• HI-B Door deployment and first light on 11 Jan

– HI-1B images of Comet McNaught !!!

• Second Lunar swing-by and heliospheric insertion of STEREO-B on 21 Jan

• A reduced synoptic observing programme began late-Dec (for HI-A)

– Summed sequences of 25 x 24 sec exposures for HI-1 and 50 x 50 sec exposures for HI-2, both every 2 hours

– Interspersed with various calibration activities, including S/C off-points and rolls

• Various calibration and commissioning activities over period Dec – date

– HI straylight off-point calibrations (see later)

– SCIP stepped calibration rolls

– Open Door exposure time linearity sequences

– Open Door Cal LED images (LED + sky; sky only)

Chris Eyles


Comet McNaught (HI-1A 11-18 Jan 2007)

Chris Eyles


SCIP-B Stepped Calibration Roll

Chris Eyles



• Just starting routine synoptic observing programme (see later)

• HI-A/B calibration rolls planned for 13 and 15 Mar

– 90/270 deg simultaneous rolls; spacecraft are rolled so that HI-A and HI-B view same area of sky to North and South of ecliptic

– 180 deg rolls; each spacecraft in turn rolled so that HI-A and HI-B view same area of sky centred on ecliptic

Chris Eyles


HI CCD Cooling and Dark Charge

HI-1A CCD Dark Charge vs Temperature

0,01

0,10

1,00

10,00

100,00

1000,00

-80,00 -60,00 -40,00 -20,00 0,00 20,00

CCD Temperature (deg C)

Da

rk C

ha

rge

(D

N/p

ixe

l/se

c)Dark Charge (DN/pixel/sec)

HI-1A HI-2A HI-1B HI-2B e2v value*

+20ºC 505.7 392.0 496.5 402.0 1300

-80ºC 0.0018 0.0014 0.0017 0.0014 -

Fitted dark charge vs T relationship -

Idark = A T3 exp(6400/T) (T in deg K)

* Based on 20000 e/pixel/sec and 1 DN = 15 e

Chris Eyles


HI Thermal Status

CCD vs Lens Barrel Temperature Correlation

-85,0

-80,0

-75,0

-70,0

-65,0

-60,0

-30,0 -20,0 -10,0 0,0 10,0 20,0

Lens Barrel Temperature (deg C)

CC

D T

empe

ratu

re

(deg

C)

HI-1A

HI-2A

HI-1B

HI-2B

HI-A HI-B

Structure -70 to -23ºC

-68 to -29ºC

S/C Interface -1ºC 0ºC

HI-1 CCD -83ºC -80ºC

HI-2 CCD -80ºC -76ºC

HI-1 Lens Barrel

-15ºC -29ºC

HI-2 Lens Barrel

-15ºC -15ºC

CEB Internal -13ºC -13ºC

Wax Actuator -72ºC -71ºC

• All temperatures are well within operating limits• HI-1B Lens Barrels stabilized at -29ºC with Operational Bus Heater• CCD temperatures are very satisfactory

Chris Eyles


HI-A Straylight Off-Point Calibration (HI-1)

HI-1A Measured F-Corona Versus Off-Point Angle - 30 Jan 2007

1,0

10,0

100,0

1000,0

10000,0

2,0 6,0 10,0 14,0 18,0 22,0 26,0

Degrees from Sun Centre

DN

per

Bin

per

Sec

on

d

Nominal PointingFitted R^(-2.38)+1.0 deg Off-Point+0.5 deg Off-Point-0.25 deg Off-Point-0.5 deg Off-Point-0.75 deg Off-Point-1.0 deg Off-Point

• Spacecraft off-pointed in steps in HI pitch:

– 0.25º, 0.5º, 0.75º, 1.0º and 1.5º towards Sun

– 0.5º and 1.0º away from Sun

• Stars removed with median filter, then measured F-corona intensity at a number of points across centre-line of FOV

• Values plotted against angle from Sun centre allowing for off-point

• Rn profile fitted to nominal pointing values

• 1 DN/sec ~ 1.2 x 10-13 B/BO for HI-1

– Straylight rejection better than 2 x 10-13 B/BO over most of FOV

• Margin of at least 0.5º in off-pointing from Sun

HI-1A (Measured - Profile) Versus Off-Point Angle - 30 Jan 2007

-20,0

0,0

20,0

40,0

60,0

80,0

100,0

2,0 6,0 10,0 14,0 18,0 22,0 26,0


DN

per

Bin

per

Sec

on

d

Nominal Pointing

+1.0 deg Off-Point

+0.5 deg Off-Point

-0.25 deg Off-Point

-0.5 deg Off-Point

-0.75 deg Off-Point

-1.0 deg Off-Point

Chris Eyles


HI-A Straylight Off-Point Calibration (HI-2)

HI-2A Measured F-Corona Versus Off-Point Angle - 30 Jan 2007

1,0

10,0

100,0

1000,0

15,0 25,0 35,0 45,0 55,0 65,0 75,0


DN

per

Bin

per

Sec

on

d

Nominal PointingFitted R^(-1.85)+1.0 deg Off-Point+0.5 deg Off-Point-0.25 deg Off-Point-0.5 deg Off-Point-0.75 deg Off-Point-1.0 deg Off-Point

HI-2A (Measured - Profile) Versus Off-Point Angle - 30 Jan 2007

-10,0

0,0

10,0

20,0

15,0 25,0 35,0 45,0 55,0 65,0 75,0


DN

per

Bin

per

Sec

on

d

Nominal Pointing

+1.0 deg Off-Point

+0.5 deg Off-Point

-0.25 deg Off-Point

-0.5 deg Off-Point

-0.75 deg Off-Point

-1.0 deg Off-Point

• Rn profile fitted to nominal pointing values

– Value of n is very different for HI-1 and HI-2, 2.38 and 1.85 respectively, difference in spectral response?

• 1 DN/sec ~ 2 x 10-14 B/BO for HI-2

– Straylight rejection better than 2 x 10-14 B/BO over most of FOV

• Margin of at least 0.5º in off-pointing from Sun

Chris Eyles


Synoptic Observing Programme (1)

HI-1 HI-2

Exposure Time 24 sec 50 sec

Exposure Cadence 30 sec 60 sec

Number of Images in Summed Sequence 50 99

Duration of Exposure Sequence 25 min 99 min

Summed Sequence Cadence 40 min 2 hr

Observing Duty Cycle 50% 67%

• In addition take full-resolution single images at regular intervals– One every 2 days for HI-1– One every 4 days for HI-2

Chris Eyles


Synoptic Observing Programme (2)

• Exposure times selected on dynamic range considerations

– 24 sec exposure for HI-1 gives maximum F-corona signal ~ 60% of dynamic range; very few saturated stars in HI-1 (~ 0 – 1)

– 50 sec exposure for HI-2 gives ~ 3 – 6 saturated stars

• Exposures at multiples of 30 sec simplifies scheduling

• Duration of exposure sequence results in drift of stars by ~ 1 bin

– Minimal smearing of star images

• Summed sequence cadences constrained by telemetry allocation but matched to respective plate scales and typical velocity of coronal ejecta

Chris Eyles


HI Instrument Health and Status

• The HI instruments are performing superbly

• HI CEB and other electronics performance entirely nominal

• Thermal performance nominal

– All temperatures within operating temperature limits

– CCDs operating at ~ -80ºC; dark charge negligible, high tolerance against radiation damage effects

• No new issues or problems since launch

• Calibrations of flat fields, pointing offsets, etc proceeding well

Chris Eyles


HI Instrument Issues

Three issues were known about pre-launch:

• Thermal leak in HI-1B Lens Barrel

– Very minor, requires operating set-point of HI-1B Optics to be -29ºC rather than -15ºC

– No impact on performance whatsoever

• Off-axis PSRF of HI-2B inferior to HI-2A

– Also minor, issue was found late in programme

– No significant impact on Level 1 science; star removal from images will be more challenging

• Bright Earth in HI-B

– Issue arises from fundamental orbital mechanics and the consequent (and inevitable) mission design.

– Dynamic range of cameras is excellent

Chris Eyles


• First solutions from fitting to star-fields show plate-scales, distortion parameters, etc consistent with pre-launch values

• PSFs consistent with pre-launch values

Values in pixels –

• Tests during AIV showed that HI-2B PSF problem is not a simple focus setting error– No significant impact on Level 1 science– Star subtraction more challenging; stellar photometry may be somewhat

compromised– Images not so photogenic

HI Imaging Performance

Pre-Launch PSF On-Orbit PSF

FWHM HEW FWHM est

HI-1A 3 – 4 3 – 4 ~ 3 – 4

HI-2A 3 – 6 3 – 6 ~ 3 – 8

HI-1B 3 – 4 3 – 4 ~ 3 – 4

HI-2B 3 – 10 3 – 12 ~ 3 – 12

Chris Eyles


HI-B Bright Earth Issues (HI-1)

• Earth first produced significant stray light effect on HI-1B on day 98 (Jan 30)– Sun-Earth angle was 34.5º

• Earth will leave HI-1B FOV (Sun-Earth angle 24º) around day 150 (Mar 23)• Sun-Earth angle will return to 34.5º around day 169 (Apr 11)

– Guarantees that Earth will cease to be an issue for HI-1B by mid-Apr– In fact will be significantly earlier because Earth irradiance is more than an order

of magnitude lower than on day 98

A recent HI-1B image (25 Feb):

Surface brightness < 10% of F-corona locally

Chris Eyles


HI-B Bright Earth Issues (HI-2)

• Earth signal is ~ 5 x 1010 photoelectrons per pixel (in 10 sec)– ~ 2.5 x 105 x CCD full-well depth!!!– Also ~ 2.5 x 105 x system dynamic range

• By mid-June Earth irradiance will be order of magnitude lower– Spacecraft separation still only 13º– Success of on-going modeling and background subtraction studies will determine

how much earlier Earth will cease to be an issue.

HI-2B image (10 sec exposure) from 6 Feb:

Surface brightness < 10% of F-corona locally

Chris Eyles


The Lunar Transit in HI-B

19 Feb 2007

0100 UT(full-res image)

28 Feb 2007

0100 UT(full-res image)

Chris Eyles


HI Instrument Status Conclusions

• The performance of the instruments is excellent

• No new issues or problems since launch

• The Bright Earth will cease to be an issue for HI-1B by mid-April or earlier and for HI-2B by mid-June or earlier

• Excellent progress with calibrations– First flat-fielding results– First star-field fitting results– Pointing information being implemented in FITS headers

(CRPIX, CRVAL, PCj_i, PV2_1, initially with nominal off-points, soon with updated values from star fields)

• HI is well placed for start of mission science phase

secchi consortium meeting, paris - march 2007 heliospheric imagers – instrument status chris eyles...

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