The Spectral Irradiance Monitor (SIM) was a spectrometer aboard NASA's Solar Radiation and Climate Experiment (SORCE) that provided long-duration solar spectral irradiance measurements in visible and near infrared (Vis/NIR) wavelengths. SIM measured how sunlight is distributed among the ultraviolet, visible, and infrared wavelengths. The wavelength coverage was primarily from 300 to 2400 nm, with an additional channel to cover the 200 to 300 nm ultraviolet spectral region. SIM contained two completely independent and identical (mirror-image) spectrometers to provide redundancy and self-calibration capability.