Balloon Measurements of the Far-Infrared Background Radiation

Abstract

Measurements in five different passbands in the spectral region below 20 ${\mathrm{cm}}^{\ensuremath{-}1}$ have been made with a liquid-helium-cooled radiometer in two flights at approximately 40-km altitude. The equivalent temperatures are $\phantom{\rule{0ex}{0ex}}{2.7}_{\ensuremath{-}0.2}^{+0.4}$, 2.8\ifmmode\pm\else\textpm\fi{}0.2, 2.8\ifmmode\pm\else\textpm\fi{}0.2, \ensuremath{\le}2.7, \ensuremath{\le}3.4\ifmmode^\circ\else\textdegree\fi{}K in passbands of 1 to 5.4, 7.8, 7.9, 11.1, and 18.5 ${\mathrm{cm}}^{\ensuremath{-}1}$. The results are consistent with a 2.7\ifmmode^\circ\else\textdegree\fi{}K thermal radiation background. Atmospheric radiation of uncertain magnitude dominates the region above 11 ${\mathrm{cm}}^{\ensuremath{-}1}$.