Two-Channel Infrared Radiometer Mars Surface Temperature
The equivalent blackbody temperature of the Martian surface was determined by means of a two-channel infrared radiometer, which measured the infrared energy emitted in the 8- to 12-micrometer and 18- to 25-micrometer bands and had a dynamic range of 120 to 330 deg K. The two channels, located in atmospheric windows, emphasized the upper and lower temperatures of this range, respectively. The experiment package was located on the bottom of the octagonal scan platform of the spacecraft. The radiometer consisted of two refracting telescopes each equipped with an uncooled antimony-bismuth thermopile detector. The experiment used an optical train that included a rotatable plane mirror, which reflected the incident energy into the detector telescopes. The mirror had three orthogonal positions. The first position viewed empty space and obtained a zero energy reference, the second viewed the planet, and the third measured the thermal energy radiated by a temperature calibration plate. After space was viewed for one frame count (4.2 s), 13 observations of the planet were made at 2.1-s intervals in each wavelength channel. Then, following a short look at the temperature reference plate, 14 more planetary observations were made. The cycle, which lasted 63 s (15 frame counts), was then repeated, beginning with a view of space. About 21 min of data were obtained on July 31, 1969, during near encounter, across and beyond the terminator over equatorial regions. The data were used to determine the thermal inertia of the surface material as well as the nature of the varying ground structure. The quality of the data is good. The data have been corrected for the greater than expected response to off-axis radiation.