ACRIM

ACRIM is an acronym used in space science to denote a family of sensors for measuring solar irradiance. It stands for Active Cavity Radiometer Irradiance Monitor. ACRIM instruments were designed to provide accurate, continuous measurements of the Sun's energy received at the top of Earth's atmosphere, supporting studies of solar variability and its role in Earth's climate. Each instrument uses an active cavity radiometer to convert solar energy into electrical signals that can be calibrated against primary radiometric standards, enabling reliable long-term data records. Operational history of the ACRIM program includes deployment on multiple satellites during the late 20th century, allowing cross-calibration with other radiometers and contributing to solar irradiance datasets used in climate research. The program's measurements have helped establish baselines for solar forcing and informed assessments of how solar variability may influence climate on decadal timescales. In contemporary practice, ACRIM-derived data are part of broader solar irradiance records that support uncertainty analyses and model validation.