Geomagnetic field and altitude effects on the performance of future IACT arrays

The performance of IACT's arrays is sensitive to the altitud e and geomagnetic field (GF) of the observatory site. Both effects play important role in the re gion of the sub-TeV gamma-ray measurements. We investigate the influence of GF on detection rates and the ene rgy thresholds for five possible locations of the future CTA observatory using the Monte Carlo simulations. We conclude that the detection rates of gamma-rays and the energy thresholds of the arrays can be fitted with line ar functions of the altitude and the component of the GF perpendicular to the shower axis core. These results can be directly extrapolated for any possible localization of the CTA. In this paper we also show the influence of both geop hysical effects on the images of shower and gamma/hadron separation.