1 - PSF

The field of view (FOV) is the angular extent on ground that is seen by IASI.

The pixel is used here to describe the elementary spatial unit observed by IASI. For an ideal instrument, the detector output is proportional to the pixel radiance within the footprint, i.e., the geometrical FOV. However, real instruments do not exactly reproduce the spatial radiance field of the pixel essentially because :

a portion of the energy comes from the surrounding areas
non-homogeneity of detector response

The Instrument Point Spread Function (IPSF) is defined for each pixel i as the function PSFi(x,y) such that for a given scene radiance R(x,y), the measured radiance is equal to :

IASI PSF in ascii format "PsF_spatiale_conf_ope.txt"
IASI FOV geometry and PSF format description are available here