Infrared Observations Of the Eclipsed Moon from Space

The Experiment

•Three data collection events

–50 Minutes apart

•Beginning and end of totality, Moon half sunlit

–10 scans across the Moon

•Lunar maps ~1 and ~3 minutes apart

•4.3 µm narrow band data

–Two bands

•4.22 – 4.36 µm

•4.24 – 4.45 µm

–18.3” square detectors, ~30” resolution


	The sensor was extensively calibrated in a specially built vacuum chamber on the ground and on orbit. A sapphire blocking filter eliminated the out of band spectral response for wavelengths greater than 6.5 µm, resulting in negligible long wavelength contamination (less than 1% for a 200K blackbody). The small out of band response was confirmed by the fact that the in-orbit calibration produced only minor adjustments to the 4.3 µm responsivities derived from the ground calibration. The ground calibration used a flat plate with temperatures similar to the eclipsed Moon while the on orbit calibration sources⁶ were stellar standard with T_eff > 4000K. The effective solid angles in the two near infrared bands were measured by repeated raster scans across stellar point source calibration standards and are estimated to have an uncertainty of < 8%.
	The thermal input from the Moon raises the focal plane temperature by a small amount, which increases the dark offset in a quasi-asymptotic fashion. A dark offset was measured every two minutes, at the end of each scan leg, and linear fits between the measured values for successive offsets for each detector are used to interpolate to the time of observation. The maximum offset bias is estimated from the deviation of the measured offsets from a monotonic trend to be comparable to the rms noise in the measurement. This is equivalent to about a 2K bias at 180K and much smaller at higher brightness temperatures.
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	⁶ Burdick, S.V., and D.C. Morris, “SPIRIT III Calibration Stars: In-Band Irradiance and Uncertainty.” Opt. Eng.36, 2931 – 2931.