"Irradiance measurements" refers to the process of measuring the amount of radiant energy (such as light or heat) that is received per unit area over a given period of time. In simple terms, it is about measuring the amount of energy coming from a source, like the sun, onto a specific surface.
Full definition
The mfrsrcldod1min value - added product produces cloud optical depth for overcast liquid clouds using
narrowband irradiance measurements from the multifilter rotating shadowband radiometer (MFRSR).
Recently, Shapiro et al. (2010) showed that COSI calculations with the atmosphere model for component C reproduces
spectral irradiance measurements from the last two solar minima with good accuracy.
In scenario 1, the TIM instrument flies on Glory, as planned, in 2009 (continuing the record of total solar irradiance) and NASA builds two additional TSIS (containing TIM and SIM for total and spectrally
resolved irradiance measurements) instruments for NPOESS C2 (2016) and C4 (2022).
Of course, solar
irradiance measurements from just three years of one solar cycle can not be applied to any other period than the one measured by the Spectral Irradiance Monitor on NASA's Solar Radiation and Climate Experiment (SORCE) satellite.
The irradiance measurements were to be an important continuation of the SORCE mission results, and are needed to stably continue the Total Solar Irradiance (TSI) timeseries.