The Solar Transmissometer Aerosol Optical Thickness Data Set contains optical thickness data that provide a measure of the effect of aerosols on the attenuation of radiation through the atmosphere at 8 discrete wavelength bands throughout the visible and near IR portion of the electromagnetic spectrum. These data were collected using a ground-based solar transmissometer in June and July of 1987, and July and August of 1989, at two stations in the FIFE study area. These data are used to provide atmospheric correction of remotely sensed data using radiative transfer models and to study aerosol particle size distribution (see Halthore and Markham 1992; King et al. 1978). These data are also used to infer the optical clarity of the atmosphere.