Absolute Solar Transmittance Interferometer

The University of Denver\u27s Absolute Solar Transmittance Interferometer (ASTI) has been developed to make high-resolution infrared (TR) radiometric measurements of the incident solar radiance and irradiance at the Earth\u27s surface. It is a research instrument that provides spectral data of high scientific interest in the short-wave infrared (SWIR) band covering 0.97 to 5.13 µm. This band contains about 20 percent of the suns incident energy, having a significant impact on global as well as regional climate. ASTI spectra are used to provide significant radiometric information describing the SWlR transmittance and absorption properties of the atmosphere. The ASTl research program and instrumentation are described providing information on the research objectives. and for each of its major subassemblies and performance functions. The analytical techniques used to take the instrument data from the basic interferogram to a radiometrically calibrated spectrum is delineated. A high frequency nonlinearity in ASTI\u27s electronics, uncovered during instrument tests and evaluations, is discussed along with the remedial accomplishments displayed in actual solar spectra. Finally, the use of ASTI solar spectra, obtained over a large atmospheric path difference. to measure broadband absorptions in four SWTR regions are related to the possible influence of the 02 continuum in these regions