A statistical analysis of the parameters of the noise characteristics
of the AVHRR was carried for NOAA 9, 10, 11 and 12, based on high-reso
lution IR-band images (HRPT). It is shown that the main contribution t
o the instrumental noise of the IR channel with wavelength 3.7 mum com
es from harmonic components. The number of harmonic components and the
ir parameters are different for each satellite. An algorithm to suppre
ss the noise harmonics is given.