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Space Dynamics Laboratory (SDL), in partnership with GATS, Inc., designed and built an instrument to conduct the
Solar Occultation for Ice Experiment (SOFIE). SOFIE is an infrared sensor in the NASA Aeronomy of Ice in the
Mesosphere (AIM) instrument suite. AIM's mission is to study polar mesospheric clouds (PMCs). SOFIE will make
measurements in 16 separate spectral bands, arranged in 8 pairs between 0.29 and 5.3 μm. Each band pair will provide
differential absorption limb-path transmission profiles for an atmospheric component of interest, by observing the sun
through the limb of the atmsophere during solar occulation as AIM orbits Earth. The AIM mission was launched in
April, 2007.
SOFIE originally completed calibration and was delivered in March 2006. The design originally included a steering
mirror coaligned with the science detectors to track the sun during occultation events. During spacecraft integration, a
test anomaly resulted in damage to the steering mirror mechanism, resulting in the removal of this hardware from the
instrument. Subsequently, additional ground calibration experiments were performed to validate the sensor performance
following the change. Measurements performed in this additional phase of calibration testing included SOFIE end-to-end
relative spectral response, nonlinearity, and spatial characterization. SDL's multifunction infrared calibrator #1
(MIC1) was used to present sources to the instrument for calibration. Relative spectral response (RSR) measurements
were performed using a step-scan Fourier transform spectrometer (FTS). Out-of-band RSR was measured to
approximately 0.01% of in-band peak response using the cascaded filter Fourier transform spectrometer (CFFTS)
method. Linearity calibration was performed using a calcium fluoride attenuator in combination with a 3000K
blackbody. Spatial characterization was accomplished using a point source and the MIC1 pointing mirror. These
techniques are described in detail, and resulting SOFIE performance parameters are presented and compared to original
SOFIE calibration results.
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