Session GC21B Dec. 14 2010 1

Traceability of Satellite TSI observationsand the significance for the TSI database

UARS/ACRIM2

ACRIMSAT/ACRIM3

ACRIM SCIENCE TEAM

Dr. Richard C. WillsonPrincipal Investigator

Roger HelizonACRIM3 Instrument Scientist

ACRIMSAT TEAM

Sandy KwanJet Propulsion Laboratory

ACRIMSAT/ACRIM3 Project Mgr.

SMM/ACRIM1

Session GC21B Dec. 14 2010 2

ACRIM3 Comparisons at the Laboratory for Astronomy and Space Physics (LASP)Total Solar Irradiance Radiometer Facility (TRF)

• ACRIM3 Engineering Model instrumentation comparisons with the LASP/TRF cryoradiometric scale

Diagnostic testing to discover source of ACRIMSAT/ACRIM3 – SORCE/TIM TSI scale differenceCompare ACRIM3 self-calibrations with TRF cryoradiometer through transfer laser systemTRF cryoradiometric scale traceable to NIST POWER cryoradiometric scale

• TRF laser coherent light source at 532 nm at full solar intensity level

Laser appears as point source from 800 metersSteerable mirror creates a filled circle or annular pattern

• Testing would alternate between the 2 instruments. The cryoradiometer would take measurements for 20 minutes and ACRIM3 engineering model for 24 minutes

Session GC21B Dec. 14 2010 3

LASP TRF Test Setup

532nm laser

Cryogenic Radiometer

Test ChamberMoveable Transfer Stage

Steering Mirror

Collimator

Session GC21B Dec. 14 2010 4

ACRIM3 Sensor Module

5mm Circular Beam 12HzUnderfill primary apertureBasic Power Measurement in SI Units

10.5mm Circular Beam 12HzOver-fill primary aperture, Under-fill BaffleCalibrates scattering in lower view limiting assembly

15mm Circular Beam 12HzOverfill View Limiting ApertureCalibrates total scattering + diffraction

• ACRIM3 Engineering Model TRF Results Summary

Session GC21B Dec. 14 2010 5

• ACRIM3 sensor scale within ~450 ppm of TRF and NIST cryoradiometer defined SI ‘absolute’ scale

• Scattering/diffraction in view-limiting assembly increases ACRIM3 TSI results

Most scattering occurs in lower VL assembly (~5000 ppm)Improper polish of primary apertures may be the cause of large scattering

Measurement(Relative performance toLASP/TRF Cryoradiometer)

Sensor A Sensor B

Power (5mm) 437 ppm 334 ppmScattering by VL assembly (10mm) 5632 ppm 4161 ppm

Total Flux (15mm) 7262 ppm 7053 ppmScatter+Diffraction by Baffle&VL 1193 ppm 2558 ppmScatter+Diffraction by VL aperture (11-15mm annular scan)

1206 ppm 2488 ppm

Net unaccounted for flux -13 ppm 71 ppm

Session GC21B Dec. 14 2010 6

ACRIM3 Comparisons at the Laboratory for Astronomy and Space Physics (LASP)Total Solar Irradiance Radiometer Facility (TRF)

• Precision apertures being replaced for 2nd TRF testing phase

ACRIM3 engineering model apertures made during the same period as ACRIM3 flight apertures will be used

Higher quality polished surfaces will reduce scattering in lower VL section

• Some scattering & diffraction correction will be required for ACRIM3 results

Comparisons with TRF scale in 2nd phase of testing will determine correction factor

Scale adjustment will likely put ACRIM3 observational scale at or below SORCE/TIM’s

Session GC21B Dec. 14 2010 7

Session GC21B Dec. 14 2010 8

Power spectra of sunspot activity and the TSI results ofACRIMSAT/ACRIM3, SORCE/TIM and SOHO/VIRGO experiments

during ACRIM3 mission (2003 – 2010). (N. Scafetta, 2010)

Session GC21B Dec. 14 2010 9

Power spectrum of sunspot number and TSI results for ACRIM3, VIRGO and TIM during the TIM mission (2003 – 2010)

• All three experiments see the same periodicities below 0.5 yr - ACRIM3 has more power at all frequencies

• ACRIM3 and VIRGO have a muted response at 0.5 yr - TIM does not detect this feature

• ACRIM3 responds strongly to the 1 yr periodicity – VIRGO has a muted response - TIM does not detect this feature

• VIRGO and TIM appear to have lower sensitivities - preventing the from detecting the smaller TSI variations during solar minima