NIST Advanced Radiometer (NISTAR)

NISTAR is the NIST Advanced Radiometer on DSCOVR, measuring absolute irradiance from the full sunlit Earth disk from the Sun-Earth L1 vantage point.^[1] It uses three electrical-substitution radiometers and one photodiode channel to monitor reflected and emitted radiation minute by minute.^[1] The four broadband channels are total radiation from 0.2-100 micrometres, reflected solar radiation from 0.2-4 micrometres, near-infrared reflected solar radiation from 0.7-4 micrometres, and a 0.2-1.1 micrometre photodiode channel for filter-stability and EPIC co-alignment checks.^[1] The instrument has a one-degree field of view, a seven-degree field of regard, and alignment with the EPIC boresight to within 0.1 degrees.^[1] The science accuracy goal is total outgoing Earth radiation from 0.2 to 100 micrometres with accuracy of 1.5 percent or better.^[1] NISTAR demonstrates broadband radiometry for daytime Earth-radiation-budget analysis, full-disk reflected and emitted radiation monitoring, and climate energy-balance studies.^[1][2]