Infrared Observations Of the Eclipsed Moon from Space


	The MSX 8.3 µm (isophotal wavelength) band had an isophotal bandwidth of  = 3.3 µm, and a system response above 50% from 6.8 to 10.8 µm. Measurements of the eclipsed Moon in this band were saturated during all three DCEs. However, a peculiarity of the read-out electronics for this band was that the response had a soft saturation regime. The detector response would reach a maximum then fold back, or decrease, with increasing flux with a gain decrease of about a factor of four until it went into hard saturation at zero counts. Data from the ground calibration indicates that the soft saturation response for this band spanned a ~150K to 195K dynamic range in brightness temperature. We attempted to correlate this fold back response with brightness temperatures derived from the 4.3 µm observations, but could not do so to our satisfaction as the scatter was too large. However, the 8.3 µm images can be used for qualitative correlation. One such inference in comparing this and the 4.3 µm map is that the mid-infrared brightness temperatures across the Moon is, on the average, roughly 20K cooler than those derived from the near infrared measurements
	About 20% of the Moon is hard saturated in this band. The saturated, black areas are at temperatures above 195K and are mainly warm craters. The concentration of craters in the areas of Mare Tranquilitatus and Serenitatus and the low albedos for these regions result in this area having the most saturation. The coolest temperatures are for the south eastern limb of the Moon and the area northwest of Mare Humorum.