1. ACRIM Satellite TSI Observations, Scales and Traceability Active
in the context of the
NASA-NIST TSI Workshop Day2 Presentations and Discussion
ACRIM
Active
Cavity
Radiometer
Irradiance
Monitor
Experiments
ACRIM3 SCIENCE TEAM
Dr. Richard C. Willson
Principal Investigator
Columbia University
ACRIM3 INSTRUMENT TEAM
Roger S. Helizon
Instrument Scientist
ACRIMSAT Project Mgr.
Jet Propulsion Laboratory
ACRIMSAT/ACRIM3
AGU Fall Mtg 2005: SH33C
R C Willson - Columbia University

2. Constructing composite TSI time series: bridging the ACRIM ‘gap’
0.35 %
AGU Fall Mtg 2005: SH33C
R C Willson - Columbia University

3. Satellite TSI Observations, Scales and Traceability
TSI database sustained since 1980 by redundant, overlapping experiments
Precise traceability (relative precision) is the most important quality of the database
Sensor degradation calibration is the primary contributor to precise traceability
TSI monitoring experiments self-calibrate degradation using redundant sensors
TSI database traceability 1980 – 2005: ~ 100 ppm
Current state of the art: ~ 5 ppm/yr
TSI database cannot be sustained by measurement accuracy
TSI experiments self-calibrate in the International System of Units (SI)
Calibration is based on pre-flight sensor metrology
Scale differences result from systematic metrology errors
SI uncertainty varies among experiments but none are significantly less than ~ 0.1 %
R C Willson - Columbia University
AGU Fall Mtg 2005: SH33C

4. Rationale for ‘bridging’ the ACRIM Gap
and constructing a composite TSI time series
AGU Fall Mtg 2005: SH33C
R C Willson - Columbia University

5. AGU Fall Mtg 2005: SH33C
R C Willson - Columbia University

6. R C Willson - Columbia University
AGU Fall Mtg 2005: SH33C

7. Relative effects of ERB & ERBE ACRIM ‘gap’ ratios on TSI composites
AGU Fall Mtg 2005: SH33C
R C Willson - Columbia University

8. Paradigm Test of ERB and ERBE ACRIM ‘gap’ ratios
TSI variability paradigm:
TSI is proportional to solar magnetic activity on solar cycle time scales
During the ACRIM ‘gap’ the average solar magnetic activity level increased steadily
The Nimbus7/ERB upward trend during the ‘gap’ is compatible with the paradigm
The ERBS/ERBE downward trend during the ‘gap’ is incompatible with the paradigm
ERBE degradation during ACRIM ‘gap’ equals the ACRIM - PMOD trend difference
R C Willson - Columbia University
AGU Fall Mtg 2005: SH33C

9. NASA/NIST TSI Workshop Day2
A NASA/NIST TSI Workshop was convened in July 2005 with the following purposes:
Investigate the 0.35 % ACRIM3_VIRGO - TIM scale difference
Provide a state of the art assessment of TSI satellite monitoring
The Day2 discussions focused on the traceability of satellite TSI experiments’ launch calibrations throughout both their missions and the duration of the 27 year TSI database
R C Willson - Columbia University
AGU Fall Mtg 2005: SH33C

10. NASA/NIST TSI Workshop Day2: ACRIM Calibration Traceability
Instrument
Predicted SI Uncertainty (ppm)
Sensor agreement at launch (ppm)
Realizable SI Uncertainty (ppm)
Total mission
Degradation (ppm)
Degradation Uncertainty (ppm/yr)
ACRIM1
1000
1021
600
< 5
ACRIM2
4090
1500
ACRIM3
2068
360
< 3
AGU Fall Mtg 2005: SH33C
R C Willson - Columbia University

11. NASA/NIST TSI Workshop Day2: SOHO/VIRGO Calibration Traceability
Instrument
Predicted SI Uncertainty (ppm)
Sensor agreement at launch (ppm)
Realizable SI Uncertainty (ppm)
Total mission
Degradation (ppm)
Degradation Uncertainty (ppm/yr)
SOHO hiatus sensor change (ppm)
DIARAD
500
4100
366
tbd
200
PMO6V
1200
633
3000
300
SOHO gap
SOHO Hiatus
Attribution: C. Frohlich
NASA/NIST TSI Workshop
AGU Fall Mtg 2005: SH33C
R C Willson - Columbia University

12. NASA/NIST TSI Workshop Day2: SORCE/TIM Calibration Traceability
Instrument
Predicted SI Uncertainty (ppm)
Sensor agreement at launch (ppm)
Realizable SI Uncertainty (ppm)
Total mission
Degradation (ppm)
Degradation Uncertainty (ppm/yr)
TIM
100
660
~ 100 10
SOHO gap
AGU Fall Mtg 2005: SH33C
R C Willson - Columbia University

13. NASA/NIST TSI Workshop Day2 Conclusions
The 0.35 % ACRIM3_VIRGO - TIM scale difference cannot be explained
Additional experimental work is required:
Comparisons of ACRIM3, VIRGO and TIM sensor technology with NIST laboratory laser-based scale transfer standards
Real time comparisons of ACRIM3, VIRGO and TIM sensor technology using the sun as the source at the JPL Table Mtn. Solar Test Site
R C Willson - Columbia University
AGU Fall Mtg 2005: SH33C