A sky-noise measurement and its implication for ground-based infrared astronomy in the 10μm atmospheric window

A spectral analysis of the fluctuations of the infrared sky radiance at λ ≈ 10μm was made at the ESO-site of La Silla in Northern Chile. The data are compared to literature. The consequences of the results on infrared observing for future large telescopes are discussed: our data suggest that in order to achieve background noise limited performance in the 10μm atmospheric window chopping with frequencies of ≈8 Hz and amplitudes of ≈10 arcsec is mandatory.