Balloon Measurements of the Far-Infrared Background Radiation

Measurements in five different passbands in the spectral region below 20 cm^-1 have been made with a liquid-helium-cooled radiometer in two flights at approximately 40-km altitude. The equivalent temperatures are 0ex0ex2.7_-0.2+0.4, 2.8±{}0.2, 2.8±{}0.2, {≤}2.7, {≤}3.4^∘{}K in passbands of 1 to 5.4, 7.8, 7.9, 11.1, and 18.5 cm^-1. The results are consistent with a 2.7^∘{}K thermal radiation background. Atmospheric radiation of uncertain magnitude dominates the region above 11 cm^-1.