We make predictions for the cosmological surveys to be conducted by the future Herschel mission operating in the far-infrared. The far-infrared bands match the peak of the CIRB, the brightest background of astrophysical origin. Therefore, surveys in these bands will provide essential information on the evolutionary properties of Luminous and Ultra-Luminous Infrared Galaxies (LIGs and ULIGs), starburst and normal galaxies. Our predictions are based on a new phenomenological model obtained from the 15-micron luminosity function of galaxies and AGN, fitting all the ISOCAM observables (source counts and redshift distributions) and also the recently published Spitzer source counts in the 24-micron band. We discuss the confusion noise due to extragalactic sources, depending strongly on the shape of the source counts and on the telescope parameters. We derive the fraction of the CIRB expected to be resolved by Herschel in the different wavebands and we discuss extragalactic surveys that could be carried on by Herschel for different scientific puropouses (i.e. ultra-deep, deep and shallow).
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