This photo, taken in February, 1978 at the Table Mtn. Observatory Solar Test Facility (TMOSTF) of the Jet Propulsion Laboratory (JPL) shows the personnel and instrumentation employed to perform pre-flight testing of the first Active Cavity Radiometer Irradiance Monitor (ACRIM I) experiment flown on the Solar Maximum Mission (SMM) satellite (1980 - 1989). The solar tracker on the left (white platform) contains international total solar irradiance (TSI) reference and sub-orbital rocket versions of instrumentation from JPL (PACRAD & ACRIM's), the Royal Meteorological Institute of Belgium (RMIB/CROM) and the Physical Meteorological Observatory at Davos, Switzerland (PMOD/PMO's). The solar tracker on the right (black box) contains the SMM/ACRIM I flight instrument.
The test compared the TSI observations of the reference instrumentation and the ACRIM I in real-time. The rocket versions of the instrumentation were then flown to make real-time comparative observations with the ACRIM I instrument. This type of test was primarily a health and sanity check on the flight instrumentation although more was originally expected from such comparisons. The limitations of applying the information on absolute radiation scale from this type of testing, even when performed under much more sophisticated conditions with the TMOSTF solar pointed vacuum chamber, became evident during the SMM/ACRIM I and subsequent Spacelab/ACRIM experiments. The absolute scale could not be reproduced with better than a few tenths percent accuracy, which from the SMM/ACRIM I observations, was found to be about the order of magnitude of the solar variability signal. The SMM/ACRIM I experiment showed that the flight observations, under optimum conditions, could be several orders of magnitude more precise. This led Willson to propose that an 'overlap strategy' in which seccesive solar monitoring experiments were directly compared in flight was required to sustain the long term TSI database with sufficient precision for investigation of solar-forced climate variability.
The participants of the 1978 TMOSTF SMM/ACRIM I pre-flight test and their
institution/instrumentation association and role shown in the photo are:
Kneeling (L to R):
Standing (L to R):
Jim Kendall was the PI for the sounding rocket PACRAD experiment. Dominique Crommelynck was PI for the URECA/CROM and recently terminated (?) SOHO/VIRGO/DIARAD experiments. Claus Frohlich was PI for the sounding rocket, EURECA and recently terminated (?) SOHO/VIRGO PMO experiments. Dick Willson was PI for the sounding rocket ACRIM, SMM/ACRIM I and Spacelab & ATLAS/ACRIM experiments. He is the PI for the on-going UARS/ACRIM II and the soon-to-be-launched EOS/ACRIM III experiments.
Not able to participate in this test but participants in other TMOSTF tests (either directly or indirectly) were significant contributors in this field: John Hickey of the Eppley Laboratory, Douglas Hoyt of NASA/GSFC and Lee Kyle (NASA/GSFC). Hickey was PI of the Nimbus7/ERB experiment which compiled the longest flight experiment record of TSI variability (1978 - 1993). Hoyt and Kyle assumed responsibility for the ERB database during the NIMBUS7 mission and their careful re-evaluation facilitated determination of the precise relationship of the non-overlapping ACRIM I and ACRIM II experiment results.