werner schmutz pmod/wrc, switzerland tosca workshop berlin, may 14, 2012 measurements of tsi and ssi
TRANSCRIPT
Werner SchmutzPMOD/WRC, Switzerland
TOSCA WorkshopBerlin, May 14, 2012
Measurements of TSI and SSI
Werner Schmutz 2
Overview
14. May 2012
• Total Solar Irradiance
• Absolute calibration (first light PREMOS)
• Composites (relative calibration)
• Spectral Solar Irradiance (SSI)
• SIM/SORCE
• VIRGO/SOHO
PICARD
PREMOS – SOVAP – SODISM
Werner Schmutz 314. May 2012Total Solar Irradiance
Filter Radiometers
Werner Schmutz 4
TSI calibration
14. May 2012
PREMOS A is the first and only radiometer in space with a SI-traceable irradiance calibration in vacuum
Traceable to the irradiance calibration facility at LASP in Boulder (TRF)
Werner Schmutz 5
Traceability of PREMOS-TSI
14. May 2012
PREMOS B
Comparison to cryogenic rad.
(power in vacuum)
NPL
Comparison to cryogenic rad.
(power and irradiance in
vacuum)TRF @ LASPPREMOS A3
Werner Schmutz 6
Uncertainty of the calibration
14. May 2012
+ absolute uncertainty of TRF facility (70 ppm)
= uncertainty of TRF comparison (220 ppm)
PREMOS APREMOS A
TRF radiometerTRF radiometer
Werner Schmutz 7
Calibration uncertainty budget
14. May 2012
Traceable via TRF, LASP, Boulder to NIST
• Irradiance in vacuum PREMOS A uncertainty: ± 280 ppm
(± 0.4 W/m2)
Table compiled by Greg Kopp for an ISSI workshop March 2012
Flight-spare recalibrations
Werner Schmutz 814. May 2012
Comparison PREMOS – TIM
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Status of PREMOS-TSI
14. May 2012
„PREMOS is in excellent health“
o PREMOS-TSI is the most accurate absolute measurement;
±0.4 W/m2 or ±290 ppm
o After 2 years, PREMOS-TSI has at most 50 ppm relative deviation to TIM/SORCE.
The Future of TSI observations:Are relative observations sufficient?
Werner Schmutz 1014. May 2012
Werner Schmutz 11
There are three TSI composites
20.12.2011
TSI-composites normalized
Werner Schmutz 1220.12.2011
!normalized 2004-2005
DIARAD
PMOD, ACRIM
Composite 1996-2010
Werner Schmutz 1314. May 2012
!0.2 W/m2
± 0.2 W/m2 / 10-years
Werner Schmutz 14
Is there a long-term trend?
14. May 2012
Fröhlich 2009, A&AL 501, L27-L30
Werner Schmutz 15
Could we detect a long-term trend with a composite?
14. May 2012
Werner Schmutz 16
Requirements for a TSI monitoring
14. May 2012
„Any plan to rely on an unbroken chain of measurements is broken“
o Not only because of a potential gap;o But mainly because of the uncertainty
is continuously increasing with time !
Accurate absolute measurements are required !
Werner Schmutz 17
Requirements for a TSI monitoring
14. May 2012
Accurate absolute measurements are required: Nowadays possible !
But we certainly also want to assess the variations of TSI and therefore, we still need to aim for continues and overlapping data !
Werner Schmutz
TSI monitoring today …
1814. May 2012
Presently, 4 operational space experiments observing TSI:
- VIRGO (launched 1995)- ACRIM III (launched 2000)- TIM (launched 2003)- PREMOS (launched 2010)
Part II:Spectral Solar Irradiance
Werner Schmutz 1914. May 2012
Werner Schmutz 2014. May 2012
The open question !
Is the SIM observation really correct?
Or is it rather a degradation problem?
The bands 410-470 and 480-730 nm are anti-correlated to TSI variations
Compensated by larger (than TSI) UV variations
Werner Schmutz 2114. May 2012
Anti-correlation in models
Contrast between active and quite Sun (SSN 150 vs SSN 0)
Black: Bright+DarkRed: bright componentsBlue: dark components
Werner Schmutz 2214. May 2012
VIRGO and PREMOS bands
Werner Schmutz
215 nm PREMOS vs SOLSTICE
2314.05.2012
Independant correction of PREMOS
Strong correlation of13.5 and 27 days modulation
PREMOS sampling is faster Rotational modulation more accurate
PREMOS
SOLSTICE
PREMOS
NIST SSI workshop, February 2012
VIRGO SSI time series 1996 - now
Christoph Wehrli & VIRGO TeamPMOD/WRC Davos
An attempt to assess instrument degradation in a self consistent way by:
• referring operational measurements to occasional backup operations
• correcting the backup channel by initial ageing of operational channel
NIST SSI workshop, February 2012
VIRGO Sun Photometers
• Interference filter radiometer with 3 channels centered at 862nm, 500nm and 402nm (R,G,B); FWHM bandwidths 5nm; silicon PD detectors; rad-hard windows.
• Active (SPM-A) and Backup (SPM-B) instruments– SPM-A: exposed continuously for helioseismology
application– SPM-B: exposed rarely for solar spectral irradiance
measurements• Calibrated by EG&G FEL lamps, NBS 1973
traceable
NIST SSI workshop, February 2012
VIRGO SPM: Level1 data
1996 1998 2000 2002 2004 2006 2008 2010 20120
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
spec
tral
irra
dia
nce
[W
m-2
nm
-1]
VIRGO SPM-A
70%
20%
5%
Sen
sitivity after 5825 days
1996 1998 2000 2002 2004 2006 2008 2010 20120
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
spec
tral
irra
dia
nce
[W
m-2
nm
-1]
VIRGO SPM-B
Number of Backups 178Total exposure time 2.6 days
SPM-B:Number of backups 178Total exposure time 2.6 days
NIST SSI workshop, February 2012
1996 1998 2000 2002 2004 2006 2008 2010 20120.990
0.992
0.994
0.996
0.998
1.000
1.002
1.004
1.006
1.008
1.010
rel.
Var
iati
on
(T
SI*
5)
VIRGO SPM-B and TSI
Raw variations of SPM-B
VIRGO-SPM-B changes are about 5 times larger than the (real) solar variations in TSI.
Solar cycle 24 SSI variation is not obvious (smaller), hidden in instrumental ageing.
5*(TSI/<TSI>) - 4
NIST SSI workshop, February 2012
Initial ageing of SPM-A
Steep degradation during first hours!
17.Jan 18.Jan 19.Jan 20.Jan0.990
0.995
1.000
1.005
1.010
1.015
1.020
1.025
1.030
1.035
Date 1996
rel.
Var
iatio
n
VIRGO SPM-A First Light
Linear degradation during first month
{Commissioning activities until 29.03.1996}
28.Jan 04.Feb 11.Feb 18.Feb 25.Feb 03.Mar0.990
0.995
1.000
1.005
1.010
1.015
Date 1996
rel.
Var
iatio
n [T
SI*
100]
VIRGO SPM-A Operational
∂TSI (*100)
NIST SSI workshop, February 2012
Ageing of SPM-A and SPM-B versus exposure time
0 0.5 1 1.5 2 2.50.985
0.990
0.995
1.000
1.005
1.010
1.015
exposure time [d]
rel.
Var
iatio
n
VIRGO SPM A & B
polynomial fit SPM-A
NIST SSI workshop, February 2012
SPM-B corrected by operational degradation of SPM-
A
Instrumental effects dominating over solar cycle
1995 1997 2000 2002 2005 2007 2010
0.992
0.994
0.996
0.998
1.000
1.002
1.004
1.006
1.008
rel.
Var
iatio
n
VIRGO SPM-B corrected for SPM-A operational degradation
1%
NIST SSI workshop, February 2012
Empirical Approach
• SSI timeseries represent a mixture of Solar Cycle and instrumental effects
• Active & Backup SPM degrade differently in time or exposure time
• Linear correction accounts for probable decline of SSI, i.e. first order estimation of instrumental effect.
• Exponential correction eliminates most of solar cycle variation as well
2000 2002 2004 2006 2008 2010 20121.815
1.820
1.825
1.830
SP
M-B
500
[Wm
-2n
m-1
]
VIRGO SSI
0.5%
NIST SSI workshop, February 2012
Linear vs. Exponential Detrending: what does it to
TSI ?
1000 2000 3000 4000 5000 6000
1363.0
1364.0
1365.0
1366.0
1367.0
1368.0
MissionDay
TS
I
1000 2000 3000 4000 5000 6000
-3.0
-2.0
-1.0
+0.0
+1.0
+2.0
MissionDay
TS
I (re
sid
ual
s)
1363 1364 1365 1366 1367 1368-2.5
-2.0
-1.5
-1.0
-0.5
+0.0
+0.5
+1.0
+1.5
TSI
TS
I (re
sid
ual
s)
Lslope 0.54 [ 0.47 0.62]Eslope 0.32 [ 0.27 0.36]
NIST SSI workshop, February 2012
Linear Detrending 2000-2012
1000 2000 3000 4000 5000 60001362
1364
1366
1368
MissionDay
TS
I
1000 2000 3000 4000 5000 6000-5
0
5
MissionDay
SS
I500
(res
)
1363 1364 1365 1366 1367 1368-5
-4
-3
-2
-1
0
1
2
3
TSI
SS
I500
(res
idu
als)
slope 1.20 [ 1.02 1.38] [1/µm]
NIST SSI workshop, February 2012
Summary
Normalization of SPM-A by SPM-B:– Larger than expected variations of Backup channel
“instrumental effects”• Rapid initial degradation in Active channelversus• ‘Early increase’ of Backup (not observed in operational
channel)
Empirical correction of SPM-B: fitting degradation in time with:
– Linear or exponential detrending yields positive correlation with solar cycle (TSI) in
all 3 visible channels !!!
None of VIRGOS’s wavelength bands 862 nm, 500 nm, 402 nm
isanti-correlated to TSI variations
Thank you for your attention
Werner Schmutz 3514. May 2012
PREMOS PICARD
NIST SSI workshop, February 2012
Alternative analysis including proxies
(C. Fröhlich, EGU 2011)
Empiric correction versus Time (double exponential), Temperature (linear + Boltzmann), TSI and Mg-II Index.
SORCE