A radiometrie fourier transform spectrometer for the measurement of downwelling atmospheric emission

Radiometrically accurate downwelling emission from the atmosphere has been measured using a ground-based ambient temperature Michelson interferometer with a liquid-helium-cooled SiAs detector. Measurements were made under a wide range of atmospheric conditions covering very-cold, very-dry, very-clear sky conditions to heavy overcast with traces of sleet. Spectral resolutions of 0.5 and 0,1 cm^–1 were obtained with a radiometric accuracy of less than 0.5 K and a noise level on the order of 0.25 K rms.Overflights were made with the NASA ER2 high altitude research aircraft carrying a similar instrument [1, 2]. Aircraft and ground based LIDAR, radiosonde and other cloud physics experiments were also made at the same time to provide a data set complete enough to enable a much better understanding of the role of thin high clouds in the Earth's radiation balance.Measurements were made over the period from 10/24/86 to 11/21/86 in support of the NOAA/NASA/NSF project FIRE (First ISCCP Regional Experiment).