Pyrgeometer measurements of the broadband infrared irradiance have hitherto been limited in accuracy because temperature gradients within the instrument produce spurious signals. A new pyrgeometer that has been demonstrated to possess greatly reduced sensitivity to temperature gradients is described. The instrument uses a thermopile evaporated onto a planar substrate with the hot and cold junctions having different adsorption properties. Both laboratory and aircraft flight tests are reported: comparison between the new instrument and an Eppley pyrgeometer is made. Features of the spectral selectivity of the instrument are also presented.