Infrared Atmospheric Sounding Interferometer
Independent errors arise from random effects causing errors that manifest independence between any pair of measured values $m'$ and $m$, such that the error in $m'$ is in no degree predictable from knowledge of the error in $m$ (were that knowledge available). In an image, independent errors therefore arise from random effects operating at the image pixel level, the classic example being detector noise. The independent component of uncertainty (or, loosely, independent uncertainty) is the uncertainty contributed by the independent errors.
Intercalibration is the process of cross comparing one satellite with another dataset used as a reference. Often the reference dataset is another satellite whose calibration is better characterised and/or updated relative to the satellite of interest and so can be used to recalibrate and/or provide information on problems/biases in the satellite of interest.