ACRIM I / Solar Maximum Mission (SMM) TSI source notes

Dataset: SMM ACRIM-I daily TSI (Solar Maximum Mission, 1980-1989)
Instrument: ACRIM (Active Cavity Radiometer Irradiance Monitor) I on SMM
Platform: Solar Maximum Mission (SMM) satellite

Raw file URL (HTTPS via Wayback Machine):
http://web.archive.org/web/20210109004518id_/ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SOLAR_IRRADIANCE/SMM.PLT

Original FTP source (blocked on this network):
ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SOLAR_IRRADIANCE/SMM.PLT

NCEI landing page:
https://www.ncei.noaa.gov/products/space-weather/legacy-data/total-solar-irradiance

Local raw file:
tsi_raw/acrim_smm/raw/SMM.PLT

Coverage: 1980-02-16 to 1989-06-01 (3053 daily value rows)
File format: space-separated "YYYY MM DD TSI uncertainty"
  Rows with fewer than 4 fields are blank/missing-data placeholders.

Scale note:
  TSI values are on the old SMM/ACRIM-I absolute scale (~1367-1368 W/m^2), which is
  approximately +6-7 W/m^2 higher than the modern SI-traceable scale from TIM instruments.
  This is a known systematic offset (see e.g. Kopp & Lean, GRL 2011). The plot and CSV
  include a prominent note about the scale offset. No re-scaling is applied here.

Attribution:
  NOAA National Centers for Environmental Information (NCEI) / NGDC solar data archive.
  Original instrument PI: Dr. Richard C. Willson (ACRIM Science Team).
  Reference: Willson, R.C. (1979) Active Cavity Radiometer Type IV, Appl. Opt. 18, 179.

Downloaded: 2026-06-04 via Wayback Machine HTTPS copy of NOAA NGDC FTP file