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Instrument: ACRIM II : Active Cavity Radiometer Irradiance Monitor II
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The objective of the Active Cavity Radiometer (ACR) Irradiance Monitor (ACRIM) is to measure the total solar irradiance with state-of-the-art accuracy and precision. The ACRIM instrument was first flown on the Solar Maximum Mission (SMM/ACRIM I) satellite and was flown on all three Atmospheric Laboratory for Applications and Science (ATLAS) missions and the Spacelab 1 misson from the Space Shuttle. In addition, ACRIM was flown as a flight-of-opportunity instrument on the Upper Atmosphere Research Satellite (UARS/ACRIM II) and is scheduled to fly as a flight-of-opportunity mission during NASA's Earth Observation System (EOS) program (ACRIMSAT/ACRIM III) The principal role of the ACRIM is to support extended solar irradiance experiments on free-flying satellites and establishment of the radiation scale at the solar total flux level through direct intercomparison with other experiments. The total solar irradiance (TSI) from far ultraviolet through far infrared is measured by three Type V active-cavity radiometer sensors. These detectors are electrically self-calibrated, cavity pyrheliometers each capable of defining the absolute radiation scale with an uncertainty of +/- 0.1% SI units. The single sample irradiance precision is +/-0.012 %. The three sensors are independently shuttered and their measurement cycles are different so that the three sensors can be used in various combinations to provide periodic cross references on the system's performance. For more information about the UARS/ACRIM II and current data availability see:

For information about the latest ACRIM III instrument which was
launched on ACRIMSAT on December 20, 1999, see:


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Instrument Owner: NASA