Thermal Radiation

Description

The Explorer 7 thermal radiation experiment was designed to measure incident and reflected solar UV radiation and terrestrial IR radiation in order to obtain a better understanding of the driving forces of the earth-atmosphere system. The primary instrumentation consisted of five bolometers in the form of hollow silver hemispheres that were thermally insulated from, but in close proximity to specially aluminized mirrors. The hemispheres thereby behaved very much like isolated spheres in space. Two of the hemispheres had black coatings and responded about equally to solar and terrestrial radiation. A third hemisphere, coated white, was more sensitive to terrestrial radiation than to solar radiation. A fourth, which had a gold metal surface, was more sensitive to solar radiation than to terrestrial radiation. The fifth hemisphere, protected from direct sunlight, was used to measure the reflected sunlight. A glass-coated bead thermistor was mounted on the top of each hemisphere to measure the temperature. A complete set of four temperature observations and one reference sample required 30 s. Thus, in each orbit, about 180 temperature measurements could be obtained. The experiment was a success, and usable data were obtained from launch until February 28, 1961.