Credit: Earth as Art

The Remote Sensing Group has two 10-channel, fully automated solar radiometers built by the Atmospheric Remote Sensing Laboratory under the supervision of Dr. John Reagan of the Electrical and Computer Engineering Department at the University of Arizona.

Solar radiometry uses measurements of the sun's energy at the surface of the earth to determine either the absolute output of the sun or to infer properties of the earth's atmosphere. Some of the information we can obtain includes the amount of aerosols (or dust particles), total amount of ozone and water vapor, and the sizes of aerosols. The primary use of solar radiometer data by the Remote Sensing Group is to characterize the atmosphere for use in the vicarious calibrations and atmospheric corrections done by the group.

For vicarious calibration, solar radiometer data are collected around the time of a satellite overpass. These data are first processed to retrieve total optical thickness (related to total amount of absorbers and scatterers along the solar path). The total optical thicknesses are used in an inversion scheme to estimate the aerosol size distribution and columnar amounts of ozone and water vapor. All of these results are used as input to a radiative transfer code to predict the radiance at the top of the atmosphere used in the vicarious calibration.

An identical procedure is followed for the atmospheric correction except the radiances at the top of the atmosphere are predicted for several values of surface reflectance. This table of reflectance versus radiance is then used in the atmospheric correction to predict the surface reflectance.